Anesthesia for congenital heart disease

Shunting

A shunt is an abnormal communication between the systemic and pulmonary circulations, allowing blood to flow directly from one circulatory system to the other. Shunting is the process whereby venous return into one circulatory system (systemic or pulmonary) is recirculated through the arterial outflow of the same circulatory system. Flow of blood from the systemic venous atrium or right atrium (RA) to the aorta produces recirculation of systemic venous blood. Flow of blood from the pulmonary venous atrium or left atrium (LA) to the pulmonary artery (PA) produces recirculation of pulmonary venous blood. Recirculation of blood produces a physiologic shunt. Recirculation of pulmonary venous blood produces a physiologic left to right (L-R) shunt, whereas recirculation of systemic venous blood produces a physiologic right to left (R-L) shunt.

Effective blood flow is the quantity of venous blood from one circulatory system reaching the arterial system of the other circulatory system. Effective pulmonary blood flow is the volume of systemic venous blood reaching the pulmonary circulation, whereas effective systemic blood flow is the volume of pulmonary venous blood reaching the systemic circulation. Effective pulmonary blood flow and effective systemic blood flow are the flows necessary to maintain life, and they are always equal, no matter how complex the lesions. Effective blood flow is usually the result of the normal pathway through the heart, but it may occur as the result of an anatomic R-L or L-R shunt, as in transposition physiology.

Total pulmonary blood flow ( $\dot{\text{Q}}$ p) is the sum of effective pulmonary blood flow and recirculated pulmonary blood flow. Total systemic blood flow ( $\dot{\text{Q}}$ s) is the sum of effective systemic blood flow and recirculated systemic blood flow. Total pulmonary blood flow and total systemic blood flow do not have to be equal. Therefore it is best to think of recirculated flow (physiologic shunt flow) as the extra, noneffective flow superimposed on the nutritive effective blood flow. These concepts are illustrated in Figs. 30.1 to 30.3 .

Clinically, shunting makes the circulation less efficient and places an increased demand on the ventricles. The severity of symptoms in most patients is determined by the degree (volume) of shunting ( ). Factors influencing the direction and degree of shunting include the size of the shunt orifice, the pressure gradient between the chambers or arteries involved in the shunt (sometimes counterintuitive; e.g., a large ventricular septal defect [VSD] will have a low gradient between the left ventricle [LV] and right ventricle [RV] but a high shunt flow), the relative compliance of the right and left ventricles, the ratio of pulmonary vascular resistance (PVR) to systemic vascular resistance (SVR), and the blood viscosity (hematocrit). L-R shunting results in increased pulmonary blood flow (PBF), increased pulmonary artery pressures (PAP), increased PVR, pulmonary edema, increased left atrial volume and/or pressure, and volume overload of both the right and left ventricles, leading to biventricular failure. Low aortic diastolic pressure accompanying large systemic–to–pulmonary artery shunts can lead to myocardial ischemia as well as organ hypoperfusion (e.g., bowel ischemia). Pulmonary overcirculation is associated with decreased lung compliance, increased airway resistance, and airway compression ( ; ; ). R-L shunting results in decreased oxygen content of the systemic arterial blood, with the decrease in proportion to the volume of deoxygenated systemic venous blood mixing with the oxygenated pulmonary venous blood. Even with normal cardiac output, the decrease in tissue oxygen delivery limits exercise tolerance ( ).

Anesthetic considerations: Important considerations are avoidance of air bubbles in intravenous (IV) catheters to prevent systemic embolization and attention to pulmonary vascular tone and its influence on the PVR-to-SVR ratio. Factors influencing PVR are discussed later in the Pulmonary Hypertension section. In patients with L-R shunts, the major perioperative concerns are threats to already limited systemic blood flow. Routine clinical monitoring tools are unlikely to indicate an evolving problem in this regard until severe hypotension and evidence of myocardial ischemia ensue; with L-R shunt physiology, it is important both to maintain myocardial pump function (i.e., avoid myocardial depression) and to try to limit decreases in PVR. Such decreases (e.g., those that can be produced by hyperventilation or hyperoxia) can lead to a steal phenomenon with increased PBF. The major acute consequence will be decreased $\dot{\text{Q}}$ s with increased risk for significant systemic hypotension and hypoperfusion; in the longer term, the increased $\dot{\text{Q}}$ p that results can increase pulmonary congestion, lung water, and cardiac volume overload.

In patients who have or who are at risk for significant R-L shunting or who are dependent on a narrowed systemic–to–pulmonary artery shunt for pulmonary blood flow (e.g., after stage I repair of hypoplastic left heart syndrome [HLHS] or as the initial palliation for reduced blood flow lesions such as tricuspid atresia), primary management considerations are similarly the maintenance of pump (cardiac) function and blood pressure plus the avoidance of factors that further increase PVR or decrease SVR (or both). It is important to note that the resultant arterial oxygen saturation (Sao ₂ ) in such patients will be affected by both the magnitude of the R-L shunting and the saturation of the shunted (essentially systemic venous return) blood.

Obstructive lesions

Congenital narrowing of the ventricular outflow tracts, semilunar valves, and great arteries may occur as isolated lesions or part of more complex malformations ( ). Ventricular outflow obstruction may be subvalvar, valvar, supravalvar, or a combination thereof, and fixed or dynamic. Residual or recurrent obstruction can occur following repair. Outflow obstruction produces increased afterload on the ventricle (pressure overload), leading to ventricular hypertrophy, a less compliant or “stiff” ventricle (diastolic dysfunction), higher filling pressures, and ultimately systolic and diastolic ventricular dysfunction ( ; ).

Left ventricular outflow obstruction may occur with aortic stenosis, coarctation of the aorta (CoA), interrupted aortic arch (IAA), and variants of HLHS and Shone’s anomaly ( Table 30.1 ) ( ). Right ventricular outflow obstruction is seen with pulmonary stenosis (PS), tetralogy of Fallot (TOF), hypoplastic pulmonary arteries, some forms of double-outlet right ventricle (DORV), and pulmonary hypertension. Right ventricle–to–pulmonary artery (RV-PA) conduits are used in the repair of pulmonary atresia, truncus arteriosus, TGA with left ventricular outflow obstruction (Rastelli procedure), and some DORV defects. Conduits calcify and narrow, and together with the increasing stroke volume that occurs with growth, significant obstruction can develop. The septal shift associated with severe RV pressure overload can compromise LV function via a reduction in LV filling and LV outflow obstruction.

Congenital mitral stenosis (MS) is rare, and in many parts of the world mitral stenosis is the result of rheumatic heart disease ( ). The degree of obstruction depends on the valve area, heart rate, and cardiac output. Pulmonary edema develops when high LA pressure leads to pulmonary venous pressures above 30 to 40 mm Hg.

Anesthetic considerations: Pressure-overloaded ventricles are at significant risk for myocardial ischemia during anesthesia, particularly in association with systemic hypotension and tachycardia. Together with hypertrophy-induced increases in myocardial O ₂ consumption and elevated end-diastolic pressure (EDP), subendocardial ischemia can occur with systemic or suprasystemic RV pressures because systolic coronary blood flow may be markedly diminished or absent. The overall goal of anesthetic induction and maintenance is to optimize and maintain the major determinants of ventricular function, coronary blood flow, and cardiac output in the face of outflow obstruction and often some degree of both diastolic and systolic dysfunction. Hemodynamic goals are sinus rhythm, a normal to slower heart rate, and normal to increased preload to maintain cardiac output (CO). Adequate preoperative hydration in accordance with fasting guidelines or a bolus of intravenous fluid prior to or during induction is recommended. Volume administration in the presence of a stiff LV or MS must be done judiciously because of the potential to cause an excessive increase in left atrial pressure with consequent pulmonary edema. With severe ventricular dysfunction, an intravenous induction with agents that maintain contractility and systemic blood pressure without significant alterations in heart rate is usually indicated. Although the majority of patients can tolerate at least modest concentrations of inhalational agent, for the patient with significant ventricular dysfunction a balanced technique employing a potent opioid such as fentanyl in combination with a lower concentration of inhaled agent may offer greater hemodynamic stability. Relief of severe outflow tract obstruction, which can frequently be performed in the cardiac catheterization laboratory, should be considered and discussed with the patient’s cardiologist prior to elective surgery.

Intercirculatory mixing

Intercirculatory mixing is the unique situation that exists in transposition of the great arteries. In TGA, there are two parallel circulations because of the existence of atrioventricular concordance (right atrium to right ventricle, and left atrium to left ventricle) and ventriculoarterial discordance right ventricle to aorta, and left ventricle to pulmonary artery. This produces a parallel rather than the normal series circulation. In this arrangement, parallel recirculation of pulmonary venous blood in the pulmonary circuit and systemic venous blood in the systemic circuit occurs. Therefore the physiologic shunt or the percentage of venous blood from one system that recirculates in the arterial outflow of the same system is 100% for both circuits. This lesion is incompatible with life unless there are one or more communications (atrial septal defect [ASD], patent foramen ovale [PFO], VSD, patent ductus arteriosus [PDA]) between the parallel circuits to allow intercirculatory mixing. In the presence of mixing, arterial oxygen saturation (Sao ₂ ) is determined by the relative volumes and saturations of the recirculated systemic and effective systemic venous blood flows reaching the aorta (see Fig. 30.2 ).

Single-ventricle physiology

Single-ventricle (SV) physiology describes the situation in which there is complete mixing of pulmonary venous and systemic venous blood at the atrial and/or ventricular level, and the ventricle (or one normal and one hypoplastic ventricle) then distributes output to both the systemic and pulmonary circulations. As a result of this physiology, (1) ventricular output is the sum of $\dot{\text{Q}}$ p and $\dot{\text{Q}}$ s, (2) distribution of systemic and pulmonary blood flow is dependent on the relative resistances to flow (PVR and SVR) into the two parallel circuits, and (3) oxygen saturations are the same in the aorta and the pulmonary artery. In patients with SV physiology, the Sao ₂ is determined by the relative volumes and saturations of pulmonary venous and systemic venous blood flows that have mixed and reach the aorta. Complete obstruction necessitates the presence of two shunt pathways.

In the case of a single anatomic ventricle, there is always obstruction to either pulmonary or systemic blood flow as the result of complete or near-complete obstruction to inflow or outflow (or both) from the hypoplastic ventricle. In this circumstance there must be a source of both systemic and pulmonary blood flow to ensure postnatal survival. In some instances of a single anatomic ventricle, a direct connection between the aorta and the pulmonary artery via a PDA is the sole source of systemic blood flow (e.g., HLHS) or of pulmonary blood flow (e.g., pulmonary atresia with intact ventricular septum [PA/IVS]). This is known as a ductal dependent circulation. In other instances of a single anatomic ventricle, intracardiac pathways provide both systemic and pulmonary blood flow without survival dependent on a PDA. This is the case when tricuspid atresia occurs along with normally related great vessels, a nonrestrictive VSD, and minimal or absent pulmonary stenosis. Patients with SV physiology will ultimately undergo the staged surgeries that comprise the single-ventricle pathway and result in Fontan physiology (described later).

Single-ventricle physiology can also exist in the presence of two well-formed anatomic ventricles: (1) TOF with pulmonary atresia (in which pulmonary blood flow is supplied via a PDA or multiple aortopulmonary collateral arteries), (2) unrepaired truncus arteriosus, and (3) severe neonatal aortic stenosis and interrupted aortic arch (in which a substantial portion of systemic blood flow is supplied via a PDA). Table 30.2 lists a number of single-ventricle physiology lesions. Patients with two well-formed ventricles are usually able to undergo a two-ventricle repair. In some cases, the two-ventricle repair will be complete. In others, significant residual lesions (VSD, aortopulmonary collaterals) will remain.

Fontan physiology

Fontan physiology is a series circulation in which one ventricle has sufficient systolic, diastolic, and atrioventricular valve function to support systemic circulation. This ventricle must in turn be in unobstructed continuity with the aorta and pulmonary venous blood return; there must also be unobstructed delivery of systemic venous blood to the pulmonary circulation (total cavopulmonary continuity). The physiology of the Fontan circulation is described in detail in the section Single-Ventricle Lesions and Hypoplastic Left Heart Syndrome. See Figs. 30.4 and 30.5 .

Anatomic versus physiologic repair

In an anatomic repair, there is both atrioventricular and ventriculoarterial concordance (i.e., normal 4-chamber anatomy), the circulation is in series, and cyanosis is corrected. An anatomic repair may be categorized as either a simple or complex reconstruction. With a simple anatomic repair, the heart is structurally normal, and correction for the most part is “curative” without long-term sequelae. Repair of uncomplicated, nonpulmonary hypertensive PDA, ASD, or VSD, as well as vascular rings or successful balloon dilation of pulmonary valve stenosis, would fall into this category. In a complex anatomic repair, anatomic correction is achieved, but because of the complex nature of the surgical repair there may be significant long-term sequelae. Complex repairs comprise extensive ventricular outflow tract reconstruction (right and/or left), atrioventricular (AV) valve repair, and placement of conduits or baffles. Lesions necessitating a complex anatomic repair include D-TGA, TOF with or without pulmonary atresia, aortic stenosis (AS), some PS, atrioventricular canal (AVC) defects, MS, truncus arteriosus, coarctation of the aorta, interrupted aortic arch, and Ebstein anomaly.

In a physiologic repair, the circulation is in series and the cyanosis is relieved, but the heart is either univentricular (single ventricle) or biventricular, with the morphologic RV connected to the aorta and functioning as the systemic ventricle and the morphologic LV connected to the PA and functioning as the pulmonary ventricle. Single-ventricle repairs result in connection of the systemic venous return directly to the pulmonary artery, thereby excluding the pulmonary (pumping) ventricle. By relieving hypoxemia, single-ventricle repairs are “functionally corrective.” A physiologic biventricular repair is seen with the atrial switch operation (Mustard or Senning) for TGA, effectively resulting in a switch at the atrial level and the RV functioning as the systemic ventricle. Physiologic repairs are characterized over time by progressive dysfunction of the single or systemic right ventricle, progressive insufficiency of the systemic atrioventricular valve, dysrhythmias and conduction defects, and baffle leaks or obstruction.

Anesthetic considerations: Patients with simple anatomic repairs who are asymptomatic and have normal to near-normal hemodynamics and exercise tolerance can generally be anesthetized in the same manner as patients with a structurally normal heart. Patients with complex anatomic repairs are at increased perioperative risk, and although parents and older patients may report few symptoms or limitations to activities of daily living, significant limitations (e.g., reduced exercise or aerobic capacity, decreased heart rate and blood pressure response to exercise, ventilation/perfusion [V/Q] mismatch) may be evident on objective testing. Physiologic repairs are always palliative, and because of potentially significant pathophysiology, the anesthetic management is complex and can be associated with considerable intraoperative difficulties if the underlying physiology is not well understood ( ; ; ).

Ventricular dysfunction

Congenital heart disease with progressive ventricular dysfunction is the commonest cause of heart failure in children and the leading cause of death in adults ( ; ). Beyond infancy, children in general have greater cardiac reserve than adults and can compensate for a longer period of time. However, the transition to acute heart failure can be rapid ( ). Risk factors include type of malformation, advancing age, older age at surgery, and frequency of reoperation. Patients with single ventricles, systemic right ventricles, and TOF are particularly at risk ( ; ; ). The etiology is multifactorial and includes genomic variation and modification, epigenetic modification, environmental triggers, many years of abnormal volume and pressure loading (which cause pathologic remodeling of numerous cardiomyocyte and nonmyocyte functions and processes), chronic hypoxemia, damage during surgical repair (inadequate myocardial preservation, scarring, poor repair, damage to coronary arteries), arrhythmias, and acquired disease ( ; ; ). Ventricular volume overload occurs with intracardiac or extracardiac L-R shunts, valvar regurgitation, and single-ventricle lesions. The time course over which irreversible ventricular dysfunction develops is variable, but if surgical intervention to correct the volume overload is undertaken within the first 2 years of life, residual ventricular dilation and dysfunction are uncommon (except for single ventricle lesions) ( ). Ventricular pressure overload results from residual or recurrent ventricular outflow obstruction or pulmonary hypertension. The time to develop significant ventricular dysfunction is longer compared with a chronic volume load, so symptoms are uncommon unless the obstruction is severe and prolonged or it is combined with a volume load ( ). Chronic hypoxemia and cyanosis decrease ventricular oxygen supply and increase oxygen demand through increased work related to increases in pulmonary and systemic vascular resistance associated with polycythemia. Myocardial ischemia resulting from coronary artery anomalies or kinking or torsion after reimplantation may also cause ventricular dysfunction.

Anesthetic considerations: The chronic presence or potential to develop or exacerbate low systemic cardiac output is the single most important consideration for anesthetizing patients with CHD. Sometimes, the correlation between a patient’s or parent’s report of clinical status and functional myocardial reserve can be unreliable. No single parameter or test is best to assist with this assessment. Rather, one is advised to carefully review historical, physical, and diagnostic test information pertaining to myocardial performance to arrive at an integrated assessment of the degree of ventricular dysfunction, as well as the potential for further decompensation that can occur as a result of anesthetic choices and procedural factors. Although there is no single recipe, key aspects of successful management include selection of anesthetic induction and maintenance techniques most likely to maintain contractile function and hemodynamic stability and appropriate fluid administration, most commonly with maintenance of a normal to modestly increased preload. In patients with significant myocardial dysfunction, inotrope administration before, during, or soon after induction and/or during the procedure may be beneficial. Airway management is crucial, as airway obstruction and/or hypoventilation will increase PVR and RV afterload, and in the presence of shunts will also increase R-L shunting. According to Laplace’s law, positive pressure ventilation is likely to improve the function of a dysfunctional systemic ventricle by decreasing the transmural myocardial pressure and thus ventricular afterload; additional fluid administration may be necessary to counteract the associated decrease in venous return and preload.

Rhythm and conduction abnormalities

Arrhythmias and conduction defects have a major impact on the prognosis and management of patients who have undergone repair or palliation of CHD and are a leading cause of impaired quality of life, morbidity, and mortality ( ; ). Rhythm disturbances that may be well tolerated in a structurally normal heart may be life-threatening in a structurally or functionally abnormal heart. The etiology is multifactorial, and as reviewed by includes abnormal anatomy or congenitally displaced or malformed sinus nodes or AV conduction systems, abnormal hemodynamics, primary myocardial disease, hypoxic tissue injury, residual or postoperative sequelae (damage to the arterial supply or direct injury to the SA and AV nodes and conduction system, atrial or ventricular scarring, suture lines, patches, myocardial ischemia, fibrosis), and genetic influences ( ).

Arrhythmias may occur in the perioperative period or many years after surgery, and tend to vary with age, type of underlying heart disease, and surgical procedures performed ( ; ). Supraventricular tachycardias (atrial flutter/intraatrial reentrant tachycardia, AV node reentrant tachycardia, atrial fibrillation) and sinoatrial node dysfunction (bradycardia, tachy-brady syndrome, exit block, sinus arrest) are more common in lesions that required extensive intraatrial surgery or have residual elevations in right atrial pressure, such as the atrial switch (Mustard or Senning) procedure for TGA, the Fontan procedure, and TOF repair. Although the 20-year risk of developing atrial arrhythmias is 7% for a 20-year-old, the prevalence increases to 50% by age 65 years ( ). Isolated right bundle branch block is frequent after right ventriculotomy ( ). The QRS duration may be an independent predictor of arrhythmia, right ventricular dysfunction, and sudden death in patients after TOF repairs ( ). Electromechanical dyssynchrony can lead to pathologic ventricular remodeling and heart failure ( ). Efficacy of cardiac resynchronization therapy (CRT) can vary with the underlying structural and functional substrate, with the best response observed in patients with a systemic LV who were upgraded from RV pacing to CRT ( ; ). Ventricular arrhythmias include mono- or polymorphic VT and ventricular fibrillation (VF) and are more common in lesions with residual ventricular pressure or volume load, such as aortic stenosis, hypertrophic cardiomyopathy, TOF, following the atrial switch and Fontan procedures, and Eisenmenger syndrome. Tachyarrhythmias and ventricular dysfunction are a dangerous combination and a cause of sudden cardiac death ( ).

Anesthetic considerations: Any new onset of palpitations, dizziness, or syncope should be investigated before elective surgery. Consultation with a pediatric cardiologist (electrophysiologist) can be very helpful in understanding the risk factors and causes for various rhythm disturbances in the CHD population, the need for additional diagnostic or therapeutic procedures, and the preferred pharmacologic and electrical approaches to the rhythm disturbances likely to arise. The electrophysiologist may also be helpful for patient optimization. Examples include whether temporary intravenous pacing is placed in select unpaced patients with bradycardia, or whether catheter ablation of amenable tachyarrhythmias should be performed prior to major procedures. Such discussions help ensure availability and appropriate use of antiarrhythmic agents and cardioversion/defibrillation devices. The availability of similar expert consultation during procedures is also advisable, particularly in situations that fail to resolve with usual therapy. In patients with tachyarrhythmias, there is at least a theoretical reason to avoid agents with vagolytic or sympathetic-stimulating properties. The electrophysiologic impact of most inhaled or intravenous agents, with the possible exception of dexmedetomidine, is probably modest ( ; ; ; ; ).

The American Society of Anesthesiologists (ASA) has published an update to the Practice Advisory for the Perioperative Management of Patients with Cardiac Implantable Electronic Devices (CIED) ( ). It is essential to know the reason for pacemaker placement and hence the likely response should the pacemaker fail; for example, whether there is an escape rate in the setting of AV block (this rate is likely to decrease or become absent under general anesthesia). Existing pacemakers should be checked preoperatively, may require reprogramming to an asynchronous mode if electromagnetic interference will interfere with pacemaker function, and may require antitachyarrhythmia and/or defibrillation functions to be suspended. Temporary (transcutaneous) pacing in the event of pacemaker malfunction and defibrillation equipment should be immediately available. For high-risk patients, the external pacing and defibrillator unit should be in the operating room and pads applied around the time of induction of anesthesia. The need for and use of electrocautery (monopolar vs. bipolar) in pacemaker-dependent patients should be discussed with both the surgeon and cardiologist. Postoperatively, it is essential that implanted pacemakers be interrogated and reprogrammed if there has been electromagnetic interference, and that antitachyarrhythmia and/or defibrillation functions are restored. reviewed the perioperative interrogation and management of CIEDs. The same authors have provided detailed guides for specific devices: Medtronic (Minneapolis, MN), Boston Scientific (Marlborough, MA), Biotronik (Lake Oswego, OR), and St. Jude Medical (St. Paul, MN) ( ; ; ; ).

Although MRI has traditionally been contraindicated in patients with CIEDs, in recent years manufacturers have developed MRI-conditional CIEDs. These devices are not MRI safe, and the Heart Rhythm Society released a consensus statement providing detailed instructions for all healthcare providers on the management of children and adults with these devices undergoing MRI (as well as CT scanning and radiation therapy) ( ).

The introduction of leadless transcatheter-deployed intracardiac pacemakers, subcutaneous implantable cardioverter defibrillators, and wireless endocardial pacing introduce new challenges for perioperative management ( ). Although societal perioperative practice guidelines still have to be developed for these newer devices, many of the principles for the management of transvenous systems can be applied.

Ventricular outflow obstruction

Ventricular outflow obstruction may be subvalvar, valvar, supravalvar, or a combination thereof, isolated or part of more complex malformations, residual or recurrent, and fixed or dynamic. Outflow obstruction results in pressure overload on the ventricle, ventricular hypertrophy, a “stiff” ventricle (noncompliant), and ultimately systolic and diastolic ventricular dysfunction ( ). Left ventricular outflow obstruction may occur with aortic stenosis, CoA, IAA, and variants of HLHS and Shone’s anomaly ( ). Right ventricular outflow obstruction is seen with PS, TOF, hypoplastic pulmonary arteries, RV-PA conduits (performed in repair of pulmonary atresia, truncus arteriosus, D-TGA with pulmonary stenosis (Rastelli procedure), some forms of double-outlet right ventricle [DORV]), and pulmonary hypertension. Conduits calcify and narrow, and together with the increasing stroke volume that occurs with growth, significant obstruction can develop. The septal shift associated with severe RV pressure overload can compromise LV function via a reduction in left ventricular filling and systemic outflow obstruction.

Anesthetic considerations: Pressure-overloaded ventricles are at significant risk for myocardial ischemia during anesthesia, particularly in association with systemic hypotension and tachycardia. Right ventricular subendocardial ischemia is a potential risk in patients with systemic or suprasystemic RV pressures because systolic coronary flow may be markedly diminished or absent. The overall goal of anesthetic induction and management is to optimize and maintain the major determinants of ventricular function in the face of a fixed (sometimes dynamic) outflow obstruction and often some degree of both systolic and diastolic dysfunction. Hemodynamic goals are maintenance of sinus rhythm, normal to slower heart rate, normal to modestly increased preload, and inotropic support if significant ventricular dysfunction is present. Adequate preoperative hydration in accordance with fasting guidelines or a bolus of intravenous fluid prior to or during induction is recommended. Volume infusion or replacement in the presence of a noncompliant LV or MS must be done judiciously, because it has the potential to cause an excessive increase in LA pressure and consequent pulmonary edema. As severity of ventricular dysfunction increases, an intravenous induction with agents that maintain contractility and systemic blood pressure without significant alterations in heart rate is probably indicated. Although the majority of patients can tolerate at least modest concentrations of inhalational agent, a balanced technique employing a potent opioid such as fentanyl in combination with low-concentration inhaled agent and muscle relaxant may offer greater hemodynamic stability. When feasible, relief of severe outflow tract obstruction, which can frequently be performed in the catheterization laboratory, should precede all but emergency surgery.

Hypoxemia and cyanosis

Hypoxemia and cyanosis usually result from decreased PBF and/or intracardiac mixing lesions but can also occur in lesions with increased PBF causing pulmonary edema with V/Q mismatch and shunt. Prior to repair, cyanotic lesions include tetralogy of Fallot, tricuspid atresia, pulmonary atresia, HLHS and other single ventricles, transposition of the great arteries, truncus arteriosus, and heterotaxy. Unrepaired TOF, tricuspid atresia, and pulmonary atresia are all lesions that typically have reduced PBF, while truncus arteriosus is associated with increased PBF. In lesions with intracardiac mixing (e.g., TGA, HLHS, SV, heterotaxy), hypoxemia can occur with decreased or increased PBF, depending on whether there is obstruction to PBF. Cyanosis may also be found in the setting of very low cardiac output, increased systemic oxygen consumption, and respiratory pathology. With the advent of early infant repair, chronic hypoxemia is now most frequently encountered in the young child undergoing staged repair, children from resource poor settings, and in the adult with unrepaired or palliated CHD. Indeed, one stimulus for early, definitive repair is to eliminate hypoxemia and the compensatory polycythemia with its rheologic, hemostatic, neurologic, renal, hepatic, and metabolic consequences. Secondary erythrocytosis is one adaptive physiologic response to compensate for the low blood oxygen tension, but does result in increased blood viscosity ( ). As blood viscosity increases, systemic (including coronary) and pulmonary vascular resistances increase markedly, resulting in decreased tissue perfusion and somewhat offsetting the benefits of increased O ₂ carrying capacity. The duration and degree of hypoxemia and polycythemia are important historical factors in the evaluation of possible long-term residual cardiac muscle blood flow abnormalities. Hemostatic abnormalities associated with cyanotic CHD include thrombocytopenia; platelet dysfunction; shortened platelet survival; decreased production of coagulation factors II, V, VII, IX, and X; fibrinogen dysfunction; and accelerated fibrinolysis ( ; ). Although low-grade disseminated intravascular coagulation (DIC) has been proposed as a mechanism, other data do not substantiate this ( ; ). Although sludging of red blood cells increases the risk for thromboembolism and stroke, phlebotomy regimens are used less frequently because of the paradoxical risk of stroke, iron depletion, and reduced oxygen-carrying capacity ( ). Guidelines from the American Heart Association/American College of Cardiology (AHA/ACC) recommend therapeutic phlebotomy for hemoglobin greater than 20 g/dL and hematocrit greater than 65% associated with headache, increasing fatigue, or other symptoms of hyperviscosity in the absence of dehydration or anemia ( ; ). Prenatal hypoxemia, pre- and postoperative hypoxemia, and chronic hypoxemia during infancy and early childhood are significant risk factors for reduced cognitive performance ( ; ; ; ).

Anesthetic considerations: It is important to maintain adequate preoperative hydration by encouraging liberal clear fluid intake in accordance with fasting guidelines or placement of an intravenous catheter and administration of maintenance fluids. Although the data are scant, preoperative hydration may be especially important as the hemoglobin concentration approaches 20 g/dL. There is an increased risk of bleeding in association with the increased tissue vascularity, hemostatic abnormalities, and anticoagulant medications. The risks of regional anesthesia in the presence of a hemostatic abnormality should be carefully considered. The effect of anemia on oxygen-carrying capacity is exaggerated because hemoglobin values “within the normal range” in cyanotic patients may represent a significant deficit. reviewed the general approach to cyanotic CHD and hypoxemia, and other aspects of anesthetic management should be based on the underlying pathophysiology.

Pulmonary arterial hypertension

Pediatric pulmonary arterial hypertension (PAH) is a vascular disease characterized by remodeling of the pulmonary vasculature resulting in elevated PAP; RV dysfunction (systolic and diastolic); compression of the LV resulting in decreased LV diastolic and systolic function, which causes further decrements in RV function; heart failure; and ultimately death ( ). The definition of pulmonary arterial hypertension (precapillary pulmonary hypertension) for biventricular circulations has been redefined as a mean pulmonary artery pressure >20 mm Hg and a pulmonary vascular resistance index (PVRI) ≥3.0 Wood units with a pulmonary artery wedge pressure ≤15 mm Hg ( ; ). Following a cavopulmonary anastomosis, PAH is defined as a PVRI >3.0 Wood units/m ² or a transpulmonary gradient >6 mm Hg (mean PAP minus mean left/common atrial pressure). The etiology of pediatric pulmonary hypertension is multifactorial, but the most frequent causes are hereditable, idiopathic, or associated with CHD ( ). Survival is closely related to RV function ( ). Treatment for PAH includes supportive therapy (diuretics, O ₂ , digoxin, anticoagulants), targeted drug therapy (Ca-channel blockers, endothelin receptor antagonists, phosphodiesterase-5 inhibitors, prostacyclins (epoprostenol, treprostinil, iloprost), and surgical interventions (atrial septostomy, “reverse” Potts shunt, and lung ± heart transplantation) ( ; ). Guidelines on the diagnosis and treatment of pediatric PAH have been published by the American Heart Association/American Thoracic Society (AHA/ATS) and the European Pediatric Pulmonary Vascular Disease Network (EPPVDN) ( ; ).

In the child with unrepaired CHD, unrestricted L-R shunting with increased PBF produces a volume load on the heart ( $\dot{\text{Q}}$ p: $\dot{\text{Q}}$ s >1) and structural changes in the pulmonary vascular bed (muscularization of peripheral arteries, medial hypertrophy of large pulmonary arteries, loss of small precapillary arteries, progressive intimal hyperplasia, and progression to necrotizing arteritis), leading to vessel occlusion and PAH ( ; ). The time course for developing pulmonary vasoocclusive disease (PVOD) depends on the size and site of the shunt and the age at corrective surgery. Progression is more rapid when both the volume and the pressure load on the pulmonary circulation are increased, such as with a large VSD. For the majority of infants with an unrestrictive shunt, repair of the defect in the first year of life is usually associated with regression of the pulmonary vascular changes. Pulmonary arterial hypertension develops more slowly with increased pulmonary blood flow in the absence of elevated pulmonary artery pressures, as with an ASD, where the absence of PAH into the third decade or beyond is not uncommon. Eisenmenger syndrome is characterized by irreversible PVOD and cyanosis related to reversal of the L-R shunt ( ).

The increased PVR can be reactive, fixed, or a combination thereof. The reactivity of the pulmonary vascular bed is determined during cardiac catheterization by the changes in PAP and PVR in response to vasodilators, most commonly oxygen and nitric oxide (NO) ( ; ). A positive response to acute vasoreactivity testing is a ≥20% decrease in both the PVRi and PVRi/SVR ratios, with final values <6 and <0.3 Wood units/m ² , respectively ( ). The major pathophysiologic consequences of a pulmonary hypertensive crisis are acute RV dysfunction with resultant low systemic cardiac output. The cycle is increased RV afterload, causing RV dilation with increased wall stress/RV EDP, decreased RV stroke volume, decreased left heart return, decreased cardiac output with decreased coronary perfusion pressure, and myocardial ischemia. Additionally, RV dilation can cause a leftward shift of the interventricular septum, impairing LV filling and function, and further decreasing cardiac output. The compensatory increase in heart rate can aggravate myocardial ischemia, potentially leading to bradycardia and cardiac arrest. If an intracardiac communication (PFO, ASD, VSD) is present, increases in PAP lead to R-L shunting and desaturation, albeit with better maintenance of LV filling and systemic cardiac output. If the patient has a Potts shunt (side-to-side anastomosis of the left pulmonary artery to the descending artery), the systemic circulation may be maintained but with desaturation.

Anesthetic considerations: reviewed the evaluation and perioperative management of pediatric PAH. Severe PAH imparts major anesthetic risk for both children and adults, even for minor procedures and in the current era with disease-modifying treatments ( ; ; ; ). Important risk factors for complications are younger age (<1 year), severity of PAH (systemic or suprasystemic PAP), and RV dysfunction ( ; ). Of note, many perioperative deaths occur in the postoperative period because of hypovolemia (bleeding, fluid shifts, vomiting), excessive pain with a stress response, atelectasis and/or pneumonia worsening hypoxemia, or other end organ dysfunction ( ; ). In older patients with Eisenmenger syndrome, most deaths appear to occur as a result of the nature of the surgical procedure rather than from anesthesia ( ).

The goals of anesthesia are to prevent increases in PVR and to support the RV. Preoperative knowledge of the degree of PAH, pulmonary vascular reactivity, RV function, and the presence of an intra- or extracardiac communication is imperative ( ). Factors that increase PVR include hypoxemia, hypercarbia, acidosis, extremes of lung volume, sympathetic stimulation associated with stress or light anesthesia, and hypothermia. It is not possible to recommend a specific anesthetic technique because all anesthetic techniques have been used successfully. Excellent airway management is crucial, as is the provision of adequate sedation/depth of anesthesia and analgesia without compromising ventricular function. Hemodynamic goals are avoidance of excessive tachycardia, maintenance of sinus rhythm, normal to increased preload, avoidance of systemic hypotension (risk of RV ischemia), and support of hemodynamics with early use of inotrope and/or vasoactive agent. Although a loading dose of dexmedetomidine over 10 minutes did not produce significant pulmonary vasoconstriction in children without (or with treated) PAH, it has been reported to cause a severe increase in PVR in patients with brittle or severe PAH ( ; ). Ketamine has been used safely, provided that airway control and ventilation is satisfactory ( ; ). The use of invasive monitoring (i.e., arterial catheter, central venous catheter) is usually determined by the nature of the surgical procedure. Endotracheal intubation as a potential mechanical trigger of pulmonary vasoreactivity should be recognized; this also applies to extubation on emergence from anesthesia. In addition to adequate anesthetic depth, lidocaine spray to the vocal cords and trachea may offer some degree of protection during intubation. Noninvasive ventilation may be an attractive alternative to support adequate gas exchange during anesthesia and surgery under some conditions. Although allowing better control of oxygenation and ventilation, positive pressure ventilation increases RV afterload and decreases RV filling, so that excessive inspiratory pressures and volumes, high positive end-expiratory pressure (PEEP), and short expiratory times (reduces venous return) should be avoided.

It is critical that pulmonary vasodilator therapy not be interrupted perioperatively, particularly epoprostenol or treprostinil infusions, the discontinuation of which can result in severe rebound PAH. Epoprostenol has an elimination half-life of 6 minutes, so rebound PAH can occur in as little as 10 to 15 minutes; the elimination half-life of treprostinil is approximately 4 hours. Higher Fio ₂ is generally recommended. With severe pulmonary hypertension and known responsiveness of the pulmonary vasculature to NO, it is advisable to have NO available for immediate or even prophylactic administration. Because of the significant morbidity and mortality of surgery and anesthesia for the patient with severe PAH, a risk-benefit analysis involving the cardiologist, surgeon, and anesthesiologist is essential before performing elective procedures.

Myocardial ischemia

Coronary artery anomalies (e.g., intramural coronary, anomalous origin from the other sinus or pulmonary artery), and early and late coronary artery obstruction associated with the arterial switch operation (ASO) or supravalvar aortic stenosis (SVAS), can result in myocardial ischemia ( ; ; ; ; ; ). In many patients with congenital defects and normal coronary arteries, ischemia is more commonly secondary to imbalances in myocardial oxygen supply and demand. There is some evidence that in lesions associated with abnormal load, including those where the RV is the systemic ventricle, coronary angiogenesis and capillary supply may not keep pace with increased muscle mass. Subendocardial perfusion is largely determined by coronary perfusion pressure (aortic diastolic pressure minus the ventricular end-diastolic pressure) and the time interval available for perfusion (predominately diastole). As a result, the relationship between diastolic blood pressure, ventricular end-diastolic pressure, and heart rate determines whether subendocardial ischemia occurs. These three factors place patients with CHD at risk for ischemia in the following situations: (1) the systolic pressure in the ventricles is abnormally elevated; a frequently forgotten condition is systemic or suprasystemic pressures in the RV; (2) the aortic diastolic pressure is compromised by diastolic runoff of aortic blood into the lower-resistance pulmonary circuit in ductal-dependent circulations and systemic-to-pulmonary artery shunts (coronary perfusion is further compromised if the coronary ostia are perfused with desaturated blood, as in patients with HLHS or unrepaired D-TGA); (3) elevated ventricular end-diastolic pressure or volume, which may be the result of impaired systolic and/or diastolic function (reduced ventricular compliance and relaxation); and (4) increases in heart rate, which geometrically reduce the duration of diastole (the duration of systole stays relatively constant) so the time available for coronary perfusion falls and consequently a higher diastolic pressure is necessary to maintain the same degree of subendocardial perfusion. The combination of a high heart rate and low diastolic blood pressure can, in some situations, produce significant ischemia.

Early studies in adults with cyanotic CHD reported a lower burden of atherosclerosis with dilated epicardial coronary arteries and mural attenuation caused by medial abnormalities ( ; ; ). The paucity of atheroma was believed to be the result of hypocholesterolemia, hypoxemia, upregulated nitric oxide, thrombocytopenia, and hyperbilirubinemia. However, this concept was later challenged. In a study comparing young adults (median age 50 years) with cyanotic CHD to age-, sex-, smoking status-, and body mass index matched controls, no significant differences in lipoprotein profile, cardiovascular risk score, and prevalence of carotid and coronary subclinical atherosclerosis were found ( ).

Anesthetic considerations: Standard principles are followed to ensure that myocardial oxygen supply exceeds demand. In particular, maintaining aortic perfusion pressures, in combination with avoiding excessive tachycardia, frequently appears to be critical. With cyanotic lesions, a hemoglobin level above the normal range may be necessary.

Infective endocarditis

Infective endocarditis (IE) is a devastating disease with a high incidence of morbidity (heart failure, stroke, cardiac surgery) and overall mortality (pediatric 6.6%, adult 24% to 28.6%) ( ; ). Recommendations for IE prophylaxis are based on expert consensus rather than randomized controlled trials (RCTs), and prevention remains an empirical practice with uncertainty and controversy ( ). Guidelines have been published by the AHA, European Society of Cardiology (ESC), and UK National Institute for Healthcare and Excellence (NICE) ( www.nice.org.uk/CG064 ) ( ; ; ). In 2007 the American Heart Association concluded that only an extremely small number of cases of IE could be prevented by antibiotic prophylaxis for dental procedures ( ). Accordingly, prophylaxis for dental procedures was recommended only for patients with underlying cardiac conditions ( Box 30.2 ) associated with the highest occurrence and risk for adverse outcome from IE. Prophylaxis in this group was recommended for all dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa. The antibiotic is administered in a single dose before the procedure ( Table 30.4 ). Administration of antibiotics solely to prevent endocarditis was not recommended for patients with the same conditions listed in Box 30.2 who undergo a genitourinary or gastrointestinal tract procedure. Although there is some overlap between the various guidelines, they are not identical. The AHA and ESC favor antibiotic administration in select cardiac patients, while the NICE recommended that antibiotic prophylaxis be abandoned in any patient for any procedure ( ). Furthermore, clinicians frequently vary in their interpretation of the same guidelines.

Congenital heart disease is a significant risk factor for IE and its complications. A pediatric population-based study in Quebec found that cyanotic CHD, left-sided lesions, endocardial cushion defects, the 6-month postoperative period of cardiac surgery, and age <3 years were associated with an elevated risk of developing IE ( ). An accompanying editorial commented that although cyanotic lesions and cardiac surgery in the previous 6 months are in line with current guidelines for IE prophylaxis, further research is necessary before extending prophylaxis to other congenital lesions ( ). A more recent retrospective cross-sectional study of the Kids’ Inpatient Database (KID) found that the incidence of IE was stable in the 2000 to 2012 period, but that mortality following implementation of the 2007 AHA IE prophylaxis guidelines was higher for CHD patients than non-CHD patients (11.1% vs. 2.4%, respectively; p <0.001) ( ).

In contrast to high-income countries, rheumatic heart disease accounts for up to 50% of IE cases in low- and middle-income countries, and the rate of access to surgery is dismal ( ).

Rarely, patients scheduled for sedation or anesthesia have IE, in which case the clinical status and results of blood cultures should guide antibiotic therapy and perioperative management.

End organ dysfunction and injury

Unrestricted L-R shunting, in addition to increasing PAP and PVR, produces alterations in lung mechanics and airway compression. The primary effects are a decrease in lung compliance and an increase in airway resistance ( ; ). Decreased compliance will necessitate higher-than-expected airway pressures, with care being taken not to insufflate the stomach during mask ventilation. Even patients with decreased PBF, such as TOF, can have pathologic lung function parameters (functional residual capacity [FRC], ventilation homogeneity) because of the effects of pulmonary hemodynamics on the alveolar architecture ( ; ). Children and adults with reduced lung flow prior to repair of cyanotic CHD have decreased lung volumes as a result of the lower density of intrapulmonary vessels and fewer alveoli ( ). Airway compression can result from dilated pulmonary arteries, left (or right) atrial dilation, massive cardiomegaly, or intraluminal bronchial obstruction ( ) (see Fig. 30.e1 ). The pulmonary lymphatics are also compressed in these circumstances, perhaps explaining an increased incidence of pulmonary infectious symptoms in patients with large L-R shunts.

Neurologic injury and adverse neurodevelopmental outcome in patients with CHD is very common, particularly with moderate and severe disease ( ; ). Children undergoing surgery in infancy have been found to have impairment in executive function, cognition, language skills, learning, fine and gross motor skills, visual-spatial skills, attention, memory, academic achievement, and social skills ( ; ). Less commonly seen in the current era are clinical seizures, major stroke, and choreoathetosis. The etiology is multifactorial and includes innate patient factors (genetic, epigenetic, maternal education and IQ, socioeconomic status); abnormal brain growth and development; and acquired intrauterine, pre-, intra-, and postoperative brain injury ( ; ; ; ; ; ; ; ; ). Smaller total brain volume, delayed maturation, brain injury, and structural and metabolic abnormalities have been found with MRI both antenatally and before any intervention, as well as after surgery or balloon atrial septostomy (BAS). Acquired cardiovascular comorbidities in adulthood make the risk factors for brain injury in the CHD population cumulative and synergistic ( ). Complex CHD may have anywhere from a mild to a profound impact on a child’s psychosocial development ( ; ; ; ). These issues necessitate additional sensitivity with the patient and family, altering the amount of detail discussed in front of the child when obtaining informed consent, and can preclude certain sedation or regional anesthetic techniques.

Renal and hepatic dysfunction frequently develop in response to chronic hypoxemia and cyanosis, low systemic cardiac output, and/or congestion with high central venous pressures ( ; ; ). This may not be evident on routine biochemical testing (e.g., serum creatinine or liver enzymes) but may predispose to perioperative dysfunction in response to relatively minor changes in organ perfusion and oxygen delivery or to otherwise relatively mild toxic stresses (e.g., NSAIDs). Renal dysfunction is associated with higher mortality, and may be present in 50% of young adults (36.0 ± 14.2 years) with CHD ( ). Severe renal dysfunction develops in 3% to 10% of heart transplant recipients within the first 10 postoperative years ( ). Contrast-induced nephropathy (CIN) associated with cardiac angiography increases the risk for perioperative renal dysfunction. Although preprocedural hydration with sodium bicarbonate reduced the incidence of CIN in adults with preexisting renal insufficiency, sodium bicarbonate did not lower the risk for dialysis and mortality ( ). Apart from good hydration, the best strategy to prevent CIN has yet to be defined ( ).

Liver dysfunction associated with single-ventricle physiology and the Fontan circulation appears to begin with chronic congestion, inflammation, and sinusoidal fibrosis, which progresses to centrilobular fibrosis, bridging fibrosis, and portal hypertension ( ; ; ). Fibrosis may begin before the Fontan operation and is associated with pre-Fontan morbidity ( ). Other factors contributing to Fontan-associated liver disease include perioperative liver injury (hypotension, hypoxia), genetic/metabolic factors, and hepatotoxins ( ).

Extracardiac anomalies

Extracardiac anomalies are very common in patients with CHD and, depending on the case series, may be present in up to 50% of patients ( ; ). The anomalies are often multiple and may result from chromosomal, genetic, teratogenic, or unknown causes. Abnormalities are most frequently found in the central nervous system, gastrointestinal tract, kidneys and urinary tract, lung, craniofacial structures, musculoskeletal system, and spleen. In patients with TOF, the risk of 1-year mortality was associated with the number of extracardiac birth defects ( ).

Anesthetic considerations: A focused airway examination and thorough assessment of all organ systems is essential.

The transplanted heart

The worldwide annual transplant rate in children as reported to the International Society for Heart and Lung Transplantation (ISHLT) for the period July 1, 2017, to June 30, 2018, was 620, comprising 14.2% of cardiac transplants ( ). The primary indication varies by age, with CHD being the commonest indication in infants (age <1 year at transplant) and cardiomyopathy in older children (1 to 17 years). Factors to consider in this population are cardiac physiology and functional status, cardiac allograft vasculopathy, rejection, the side effects of immunosuppressive agents, and the development of renal dysfunction, hypertension, and malignancy. The physiology of the transplanted heart involves efferent denervation resulting in resting tachycardia (withdrawal of vagal tone), impaired chronotropic response to stress (slower increase in heart rate, lower peak heart rate, and delayed return to resting rate), and greater dependence on preload and endogenous circulating catecholamines to maintain cardiac output ( ). Cardiac physiology is restrictive, with mildly elevated filling pressures, a low-normal ejection fraction, and increased afterload. There can be a shift from β ₁ to β ₂ receptors, and sinus node dysfunction can occur in the early postoperative period. Afferent denervation results in silent ischemia and alterations in cardiac baro- and mechanoreceptors (less stress-induced increase in systemic vascular resistance). Cardiac reinnervation is complex and has been reviewed in detail ( ). Reinnervation may occur months to years following heart transplant, is partial and regionally heterogeneous, and does not appear in all recipients.

Anesthetic considerations: Anesthesia for the patient with a transplanted heart has been reviewed ( ). Briefly, it is important to maintain adequate preload as the heart rate response is limited. The restrictive physiology, particularly with rejection, increases the risk for pulmonary edema when fluid administration is excessive. Hypotension and/or decreased cardiac output should be treated with direct-acting sympathomimetic agents. Sensitivity is increased to direct-acting catecholamines, β-blockers, adenosine, and verapamil, and it is decreased to digoxin and indirect-acting sympathomimetic agents. Myocardial ischemia is an ever-present threat from coronary artery vasculopathy. A new onset of dysrhythmias or heart block is ominous, suggesting rejection and/or myocardial ischemia. Immunosuppression requires strict aseptic technique, and the hypertension and nephrotoxicity associated with some agents and possible need for stress-dose corticosteroids need to be addressed.

Preoperative evaluation

The preoperative evaluation should be complete enough to provide a clear understanding of the anatomy and pathophysiology of the “original” cardiac defect, and if applicable that following any surgical or catheterization procedures, current medications, involvement of other organ systems, and the likely acute physiologic consequences of the planned surgical procedure.

Intraoperative management

Preoperative evaluation

Broadly speaking, there are three categories of patients with CHD: those who have undergone a reparative (corrective) procedure, those who have undergone a palliative procedure, and those who have not undergone any procedure. The goal of the preoperative evaluation is to understand the current anatomy, physiology, and functional status and how this will interact with the planned procedure. As a general rule, patients with CHD who are doing well clinically (i.e., have good functional status, few or no medications, and only routine cardiology visits) tend to do well with anesthesia and surgery. Not surprisingly, the unrepaired or palliated patient presents a greater risk, as does the more complex and stressful surgical procedure.

Intraoperative management

Standard principles of anesthetic management apply to patients with CHD who present for noncardiac procedures. The choice of anesthetic technique (local, regional, or general anesthesia), selection of pharmacologic agents, and requirement for invasive monitoring are determined by the physical (functional) status of the patient and the nature of the planned procedure. As for cardiac surgery, there is no one-size-fits-all approach. The perioperative administration and holding of cardiac medications are discussed in the preceding section. The patient’s cardiologist should discuss with the surgeon the withholding of aspirin, other antiplatelet agents, and Coumadin. Depending on the circumstances, institution of an appropriate perioperative anticoagulation strategy may be necessary. In general, patients with prosthetic valves or a history of stroke and other thromboembolic events mandate the greatest degree of concern. Approaches to anticoagulation vary and depend to some extent on both the specific indication and the degree of concern regarding the relative risks. Management strategies vary from temporarily discontinuing Coumadin (and usually following the prothrombin time and international normalized ratio [INR] and performing the surgery in the ensuing 24 to 48 hours) or discontinuing Coumadin and instituting low-molecular-weight heparin or IV heparin prior to surgery.

Postoperative management

The preoperative clinical status, nature of the surgical procedure, and perioperative course determine whether postoperative admission will be to a general ward, a cardiology ward, an intensive care unit, or the patient discharged to home. Hemorrhage, hypoxia, hypoventilation, fever, uncontrolled pain, or myocardial ischemia may convert a well-tolerated surgical procedure into a crisis. Day surgery is possible for those patients whose cardiac status is well controlled, who have undergone a minor surgical procedure, and who have attained their baseline status prior to discharge. Higher-risk patients, particularly those undergoing major surgical procedures, are usually best managed in an intensive care setting or on a cardiology ward rather than a general (surgical) ward if changes in cardiac physiology pose a greater risk than complications from the surgical procedure. The healthier cardiac patient with a more complex surgical procedure is usually admitted to the appropriate surgical ward with cardiology consultation and follow-up. Standard fluid replacement guidelines are employed, and postoperative laboratory testing is guided by intraoperative blood loss, fluid shifts, and the child’s preoperative status. Effective pain management is important and can be especially difficult if the patient is tolerant to sedatives and narcotics or has recently been discharged after prolonged hospitalization and is still on a withdrawal regimen. Involvement of colleagues with pediatric pain management expertise is recommended. Despite the best possible anesthetic and procedure, complications could still develop in the postoperative period. Patients with PAH, Eisenmenger syndrome, or preexisting end organ dysfunction are especially prone to complications ( ).

Atrial septal defects

An atrial septal defect is a communication between the left and right atria, and it may be single or multiple, vary widely in size, be located within or external to the atrial septum, and be isolated or associated with other congenital heart defects (50%). ASDs are classified by their location ( Fig. 30.6 ). The four morphologic types are the secundum ASD ( Video 30.3 ), primum ASD ( Fig. 30.7 , Video 30.4A – B ), sinus venosus ASD, and coronary sinus ASD. Strictly speaking, only secundum and primum ASDs are defects in the interatrial septum. A secundum ASD lies within the fossa ovalis and is due to single or multiple defects in the septum primum ( ). Isolated ostium primum ASDs, also known as partial atrioventricular canal defects, extend from the anterior-inferior margin of the fossa ovalis to the atrioventricular valves, and are discussed later (see Atrioventricular Canal Defects). In a sinus venosus ASD, there is a communication between the right pulmonary vein(s) and the cardiac end of the superior vena cava (over 80%) or the posterior-inferior atrial wall just above the inferior vena cava-right atrial junction; there is no direct communication between the RA and LA ( ). A coronary sinus ASD comprises partial or complete unroofing of the tissue between the coronary sinus and the left atrium. Patent foramen ovale (PFO) is a normal interatrial communication during fetal life and is seen in almost all newborns. A probe-patent foramen ovale, present in up to 25% of adults, is not a true defect in the atrial septum but results from incomplete fusion of the septum primum and the superior limbic band of the fossa ovalis (septum secundum). Paradoxical embolism is a major anesthetic consideration in these patients.

ASDs are shunts, and the amount of blood that passes through the defect is determined by the size of the defect and the relative compliance of the right and left ventricles. Early in infancy, because the right ventricle is less compliant, L-R shunting is minimal. With declines in pulmonary artery pressure and remodeling (increased compliance) of the right ventricle, shunting increases as the right atrial pressure becomes lower than the left atrial pressure. The normally decreasing left ventricular compliance with age further increases L-R shunting ( ). ASDs result in increased pulmonary blood flow and place a volume load on the right atrium, right ventricle, and left atrium. Isolated ASDs are generally asymptomatic in infancy and childhood. Although CHF is more common after 40 years of age, a few infants develop CHF as a result of pathophysiology that is incompletely understood ( ). Symptoms and the incidence of atrial fibrillation (and risk of thromboembolism) increases with advancing age ( ). The murmur of an ASD is related to increased flow through the tricuspid and/or pulmonic valve. The second heart sound is widely split and does not change with respiration.

Spontaneous closure of secundum defects is related to defect diameter. The closure rate is 100% for defects <3 mm in diameter, 87% if 3 to 5 mm, and 80% if 5 to 8 mm; defects >8 mm are unlikely to close ( ). Indications for closure are a hemodynamically significant shunt ( $\dot{\text{Q}}$ p: $\dot{\text{Q}}$ s ≥1.5:1) with enlargement of the right heart structures ( ; ). Closure is generally done before starting school; closure beyond 25 years is associated with reduced survival ( ; ). Normal ventricular function after early repair is the rule, but ventricular dysfunction and atrial arrhythmias can occur with late repair. Pulmonary hypertension is uncommon in children with an isolated ASD ( ; ). Pulmonary vascular occlusive disease will develop in approximately 5% to 10% of unrepaired ASDs, most commonly in the second decade or thereafter, and can result in shunt reversal and Eisenmenger syndrome ( ; ). Secundum ASDs can be closed surgically or percutaneously with a device in the cardiac catheterization laboratory ( ). Primum, sinus venosus, and coronary sinus ASDs require surgical closure. Residua and sequelae are more commonly seen after repair of sinus venosus defects (loss of sinus node function, atrial fibrillation, pulmonary venous obstruction, and residual shunt) and ostium primum defects (see Atrioventricular Canal Defects) ( ).

Ventricular septal defects

A ventricular septal defect is the most common congenital cardiac defect (2.5 per 1000 live births) and is an opening in the ventricular septum permitting communication between the left and right ventricles ( ; ; ). VSDs may occur in isolation, but in nearly 50% will have an additional cardiac anomaly ( ). VSDs are classified by their location in the septum, with multiple classifications existing. The physiologic effects are determined by the degree of shunting, which is influenced by the size of the defect and the relative pulmonary and systemic vascular resistances. Smaller (restrictive) defects limit shunting and have a large pressure gradient across the defect. Large (nonrestrictive) defects have less pressure difference between the ventricles, so the magnitude and direction of shunting are more dependent on the relative pulmonary and systemic vascular resistances. The high PVR at birth limits L-R shunting, but the magnitude of the shunt increases over the first few months of life because of the normal postnatal decline in PVR; there is also a contribution from physiologic anemia of the infant (hematocrit has a disproportionately greater effect on PVR than SVR) ( ). Excessive L-R shunting with increased pulmonary blood flow leads to pulmonary vascular congestion, abnormal pulmonary mechanics (decreased compliance, increased airway resistance, airway compression), increased myocardial work, and pulmonary hypertension ( ; ). Congestive symptoms appear with a $\dot{\text{Q}}$ p: $\dot{\text{Q}}$ s ≥1.5. Pulmonary hypertension is reversible initially but becomes increasingly fixed as PVOD develops. Although the timing can be variable, irreversible pulmonary vascular disease is uncommon in infancy ( ).

Most VSDs are small, and many will decrease in size or close spontaneously ( ). Indications for surgical repair in infancy are heart failure refractory to medical management (poor growth), pulmonary artery pressure that fails to fall below 60% of LV pressure by 6 months of age, and aortic regurgitation associated with heart failure ( ). Although patients with irreversible or severe PVOD (PVR 6 to 9 Wood units/m ² ) and pulmonary hypertension (Eisenmenger complex) are generally not candidates for VSD closure, these criteria are not rigid ( ). Over the long term, myocardial and pulmonary function are likely to be normal if complete repair is done within the first year or two of life ( ). Potential sequelae following repair include residual defects, heart block, subaortic obstruction, and aortic regurgitation ( ). Device closure of muscular VSDs, particularly difficult-to-reach apical and anterior septal defects, is possible in the catheterization laboratory provided the device will not impinge on the atrioventricular or semilunar valves or cause heart block ( ). Perventricular VSD device closure is a hybrid approach combining surgical and percutaneous techniques without CPB ( ). The hybrid technique is an option for very small patients, difficult-to-reach defects, or those with limited vascular access ( ). Although early studies of device closure for perimembranous defects found a significant risk of heart block and aortic regurgitation, results with new devices are more encouraging ( ; ; ; ).

Atrioventricular canal defects

Atrioventricular canal defects (AVCDs), also referred to as atrioventricular septal defects or endocardial cushion defects, result from abnormal endocardial cushion development. Embryologically, four endocardial cushions develop in the atrioventricular canal and contribute to the development of the lower atrial septum; the upper, posterior inlet portion of the ventricular septum; and the mitral and tricuspid valves. AVCDs may be complete (common AV valve with ostium primum ASD, moderate to large inlet VSD, and varying chordal attachments to the crest of the ventricular septum) ( Fig. 30.8 , Video 30.5A – B ); partial (two distinct AV valves with ostium primum ASD and usually a cleft in the anterior leaflet of the mitral valve; no VSD is present); or transitional (ostium primum ASD, restrictive VSD, common AV valve orifice with fused anterior and posterior bridging leaflets dividing the common AV valve into distinct mitral and tricuspid components). AVCDs are commonly associated with extracardiac defects and are present in approximately 45% of children with Down syndrome ( ; ). Abnormalities in alveolar and lung vascular development predispose children with Down syndrome to early pulmonary hypertensive arterial changes ( ; ).

The physiology resembles that of atrial and ventricular septal defects, with the possible added feature of AV valve regurgitation. There is an L-R shunt with increased pulmonary blood flow and volume overloading of the right and left ventricles, with the magnitude of shunting largely determined by the size of the VSD component. Large ventricular level shunts, although predominantly left to right, usually have a bidirectional component. Surgery for complete AV canal defects is usually undertaken in the first 2 to 3 months of life because of the risk for accelerated pulmonary vascular disease. Surgery is usually done later in infancy for partial and transitional AV canals because the pulmonary vasculature is protected and the normal AV valve tissue is thin and fragile ( ). The repair typically involves dividing the common AV valve and closing the ASD and VSD with either one or two patches, approximation and suspension of the valve apparatus, and suturing any cleft in the mitral valve.

Patent ductus arteriosus

The ductus arteriosus normally connects the origin of the left main pulmonary artery to the aorta and is a critical component of the fetal circulation ( Fig. 30.9 A). In utero, the high pulmonary vascular resistance results in most (∼90% to 95%) of the blood from the RV bypassing the lungs via flow through the ductus arteriosus to the descending aorta ( ). In most newborns, the ductus closes in two phases. Within 24 to 48 hours of birth, the smooth muscle contracts in response to an increase in Pao ₂ and decreases in PGE ₂ and PGI ₂ as a result of placental removal and pulmonary metabolism. A zone of hypoxia in the media causes smooth muscle cell death and production of hypoxia-inducible growth factors, leading to endothelial proliferation, subintimal disruption, fibrosis, and permanent closure by 2 to 3 weeks of age. If not fully obliterated, a connection remains between the systemic and pulmonary circulations. The PDA may be isolated ( Fig. 30.9 ) or associated with almost any other congenital cardiac anomaly, in many instances of which it is lifesaving (ductal-dependent lesions). Isolated PDA is associated with increasing L-R shunting as the pulmonary vascular resistance falls.

A tiny or small PDA is asymptomatic and associated with normal life expectancy, but in children and young adults closure is generally recommended because of the risk of infective endarteritis ( ; ). With a hemodynamically significant ductus, excessive blood flow to the lungs results in left heart and aortic enlargement, and CHF with very large shunts. Elevation of left atrial pressure may cause enlargement of a PFO with additional L-R shunting. In premature infants with respiratory distress, hypoxia promotes continued patency of the ductus, with the need for more aggressive ventilation. Runoff from the aorta into the pulmonary circulation during diastole reduces aortic diastolic pressure with decreased coronary, cerebral, and abdominal organ perfusion. Necrotizing enterocolitis and intracerebral and intraventricular hemorrhages are potential complications. See Chapter 27 : Neonatology for Anesthesiologists. Other cardiac anomalies determine the direction of shunting across a PDA. For example, with severe aortic coarctation or hypoplastic left heart syndrome, the shunting is predominantly right to left, and in fact is necessary to support systemic perfusion until more definitive interventions are undertaken.

In neonates and preterm infants, there is still no consensus on which PDAs to treat, as well as when and how to treat ( ; ). Closure of a PDA can be accomplished pharmacologically in preterm infants with indomethacin, ibuprofen, or acetaminophen ( ). Surgical management is typically via a small left posterolateral thoracotomy. For older infants and children with a small- to moderate-sized ductus, video-assisted thoracoscopic surgery (VATS) is an option ( Video 30.6A – B ). Percutaneous closure using interventional catheterization techniques is an established procedure with a 97% to 99% success rate, and is frequently employed as an alternative to surgical ligation ( ). Transcatheter techniques can also be used for preterm and term neonates ( Fig. 30.9 B–C; Video 30.7A – B ) ( ; ). Advantages include the ability to perform the procedure on an outpatient basis, reduced surgical scarring, less pain, faster recovery, and avoidance of late thoracotomy complications (cosmetic defects, rib fusion, scoliosis, chronic pain). Percutaneous closure, however, has its own set of risks beyond the usual risks of cardiac catheterization. Adverse events are more frequent in infants younger than 6 months and are mostly related to device or coil placement itself; these include embolization and malposition (more frequent with coils) ( ). Transcatheter techniques are best suited for a restrictive ductus with some length and an ampulla at the aortic end ( ). Understanding the genetics of development of the ductus arteriosus may lead to new strategies of management ( ).

Tetralogy of fallot

Tetralogy of Fallot is the most common cyanotic lesion, accounting for approximately 10% of all CHD and with a birth prevalence of 0.34 per 1000 live births ( ; ). The defect is characterized by anterocephalad deviation of the outlet (conal) septum, resulting in right ventricular outflow tract obstruction (RVOTO), a nonrestrictive VSD, aortic override, and right ventricular hypertrophy ( Fig. 30.10 , Video 30.8A – E ). The RVOTO can be present at multiple levels: infundibular or subvalvar, valvar, supravalvar (hypoplasia of the main and branch pulmonary arteries), or a combination thereof. Infundibular obstruction may be fixed or dynamic (varying caliber of the RV infundibulum) and is invariably associated with some degree of pulmonary valve stenosis. Associated cardiac anomalies include a right-sided aortic arch with mirror image branching (25%), a second VSD (5%), and coronary artery anomalies (5%) such as anterior descending coronary artery arising from the right coronary artery and crossing the RV outflow tract, dual left anterior descending (LAD), and single right coronary artery ( ). At the extremes of the TOF spectrum are the “pink Tet” (large VSD with minimal RVOTO and pulmonary overcirculation) and TOF with pulmonary atresia or extreme pulmonary hypoplasia and aortopulmonary collaterals. Other less common variants of TOF include TOF with absent pulmonary valve, TOF with complete atrioventricular canal (CAVC) defect, and TOF with double-outlet RV. Chromosomal abnormalities are present in up to 25% of cases, with DiGeorge/velocardiofacial (22q11.2 microdeletions) and Trisomy 21 the most frequent. Other associations are Alagille, VACTERL, and CHARGE ( ).

Hypercyanotic episodes (“Tet spells”) are a hallmark of unrepaired TOF and can be life-threatening, with increased cyanosis, syncope, and convulsions. Spells occur more frequently as RVOTO gets more severe, with a peak frequency between 2 and 3 months of age. Although the mechanism of Tet spells is incompletely understood, infundibular spasm may play a role, and crying, defecation, feeding, fever, and awakening can be precipitating events. Spells are self-aggravating in that hypoxia induces a decrease in SVR, which further increases the R-L shunt. Paroxysmal hyperpnea increases oxygen consumption through increased work of breathing. Treatment of a Tet spell includes the following:

• 1.

  Administration of 100% oxygen.

• 2.

  Knee-chest position or pressure on the femoral arteries, as is commonly done in the pediatrician’s office.

• 3.

  Sedation with morphine sulfate (0.05 to 0.1 mg/kg IM or IV) to relieve distress and air hunger. Ketamine is a suitable alternative and can also be given IM or IV ( ).

• 4.

  Intravenous crystalloid (15 to 30 mL/kg) or colloid (5 to 10 mL/kg) is used to increase preload, which may increase the diameter of the RVOT.

• 5.

  Phenylephrine 0.5 to 1 mcg/kg IV as a bolus or 2 to 5 mcg/kg per minute as an infusion to increase the SVR and reduce R-L shunting. In the presence of severe RVOTO, phenylephrine-induced increases of PVR have little or no effect in increasing RV outflow resistance.

• 6.

  Sodium bicarbonate (1 to 2 mEq/kg) can be administered to correct the metabolic acidosis, increasing the SVR and lowering the PVR.

• 7.

  Judicious use of propranolol (0.1 mg/kg) or esmolol (0.5 mg/kg followed by an infusion of 50 to 300 mcg/kg per min) slows the heart rate and relaxes the infundibulum. β-Adrenergic agonists are contraindicated.

• 8.

  Failure to respond to the above or for a patient in the operating room or ICU, tracheal intubation and mechanical ventilation with 100% oxygen, low inspiratory pressures, and long expiratory times to promote venous return and antegrade flow across the RV outflow. An inhalation agent may be beneficial to reduce hyperdynamic right ventricular outflow obstruction. Manual compression of the abdominal aorta can be an effective means to temporarily increase SVR and decrease cyanosis in the anesthetized patient.

• 9.

  For the child undergoing cardiac repair, there may be the need to proceed very rapidly to cardiopulmonary bypass (CPB) if the spell is severe and not resolving.

• 10.

  Resuscitation by extracorporeal membrane oxygenation (ECMO) in refractory episodes, when immediate operative intervention is not possible ( ).

Primary complete repair in infancy has largely replaced the traditional two-stage repair sequence of a modified Blalock-Taussig shunt (mBTS) in early infancy followed by later repair ( ). Neonatal or young infant repair, however, carries significant perioperative risk so that in systems unable to provide the required postoperative care, early shunting may be necessary ( ). Because an mBTS also carries significant mortality, postoperative instability, and long-term morbidity, palliation with transcatheter techniques is an alternative approach, particularly with prematurity, low birth weight, and small pulmonary arteries ( ; ; ). Transcatheter techniques include balloon dilation of the RV outflow tract (RVOT) with/without stent placement, stenting of the PDA, and guidewire or radiofrequency perforation with/without stent placement for TOF with plate-like pulmonary valve atresia. In well-developed medical systems it is becoming fairly unusual to encounter an older infant or child with unrepaired or shunted TOF.

Surgical repair includes relief of RVOTO by resection of hypertrophied muscle bundles and enlargement of the outflow tract with a pericardial patch. Although pulmonary valve-sparing techniques are increasingly being employed and entail intraoperative balloon pulmonary valvuloplasty or placement of patches below and above the PV annulus, a very small pulmonic annulus and/or a very stenotic pulmonary valve usually dictates placement of the patch across the annulus (transannular patch), resulting in pulmonary regurgitation (PR) ( ; ). The VSD is closed with a Dacron patch; in neonates this is usually done through the right ventriculotomy created for resection of RVOT obstruction and with placement of the infundibular, pulmonary artery, or transannular patch. In infants and older children, the VSD can be closed via a trans–tricuspid valve approach, thereby avoiding the likely deleterious consequences of a right ventriculotomy. With TOF and long-segment pulmonary atresia, or when a major coronary artery crosses the RVOT, a right ventricle–to–pulmonary artery conduit is placed rather than an annular or periannular patch.

The majority of patients with repaired TOF will have residual hemodynamic and electrophysiologic abnormalities with increasing rates of morbidity and mortality beginning during the third decade of life ( ). In the first two decades after repair, many patients are asymptomatic with normal activity, although right ventricular dysfunction and dysrhythmias may only be evident on objective testing. Common indications for late reoperation or intervention are pulmonary regurgitation, residual or recurrent RVOT obstruction or RV-to-PA conduit stenosis, VSDs, arrhythmias, and ventricular dysfunction with electromechanical dyssynchrony (these problems are also shared by other lesions that require RVOT reconstruction or a RV-PA conduit such as truncus arteriosus, pulmonary atresia, and the Rastelli procedure for TGA) ( ; ). The presence of tricuspid regurgitation is a likely surrogate for substantial RV dysfunction. In adults, LV systolic and diastolic dysfunction may also be present ( ; ). Cardiac MRI is the best diagnostic modality for assessment of RV size and function and timing of pulmonary valve replacement ( ). Atrial reentrant tachycardia and high-grade ventricular arrhythmias develop in about 30% and 10% of patients, respectively ( ). The risk of sudden death is increased and estimated at 0.15%/year of follow-up ( ). Although a QRS duration of 180 milliseconds or greater is a highly sensitive marker for sustained ventricular tachycardia and sudden death, its positive predictive value is low ( ). Pulmonary valve replacement can be performed surgically or by a transcatheter technique (see section on cardiac catheterization). The ideal time is still controversial but should be performed before severe RV dilation and systolic ventricular dysfunction develop ( ; ). The presence of sustained ventricular tachycardia (VT) in a symptomatic patient (syncope, cardiac arrest) or electrophysiologic study is significant and necessitates treatment prior to elective surgery. Risk factors for VT are older age (>20 years), multiple cardiac surgeries, longer QRS duration, and left ventricular dysfunction ( ). Electrophysiologic methods are employed to assess and ablate atrial or ventricular arrhythmias and for deciding on the need for an implantable cardioverter-defibrillator (ICD) or resynchronization with biventricular pacing ( ; ).

Aortic stenosis

Bicuspid aortic valve occurs in 1% to 2% of the population and demonstrates a substantial male predominance ( ). It may be an isolated lesion or associated with other left-sided obstructive defects (e.g., aortic coarctation), and it may be asymptomatic or become progressively obstructive or regurgitant. The pathophysiology depends on the severity and duration of the obstruction and/or regurgitation ( ).

Critical neonatal aortic stenosis (AS) is a ductal-dependent lesion, with a clinical pattern similar to that of severe aortic coarctation. In its most severe forms, critical neonatal AS is poorly tolerated and produces left ventricular failure with poor systemic perfusion and pulmonary overcirculation (PFO, any associated ASD/VSD) with vascular congestion and edema; factors that increase myocardial O ₂ demand even modestly (e.g., mild fever, anemia) can markedly exacerbate the low cardiac output state and potentially precipitate cardiovascular collapse. Supravalvar aortic stenosis (SVAS) is associated with variable-sized deletions in the elastin gene (chromosome 7q11.23) and adjacent segments and comprises a diffuse and variable arteriopathy ( ; ). SVAS is characterized by narrowing at the sinotubular junction, which in itself can cause obstruction of the coronary ostia. Associated lesions include coronary artery stenoses, main and branch pulmonary artery stenoses (37% to 75%), stenosis of the thoracic aorta that can extend into the descending aorta (middle aortic syndrome), renal artery stenosis and hypertension, and stenosis at other vascular sites ( Fig. 30.11 ) ( ). Subaortic stenosis may comprise a discrete fibromuscular ridge or membrane, a long fibromuscular tunnel, or hypertrophy of the interventricular septum (hypertrophic cardiomyopathy). Shone’s anomaly consists of aortic coarctation, subaortic stenosis, and mitral stenosis on the basis of both a parachute mitral valve and supravalvar mitral ring ( ). Although the relief of coarctation is typically straightforward, patients with Shone’s anomaly frequently have prolonged and recurrent left-sided obstruction arising from its other components, leading to reduced LV compliance and dysfunction despite one or more attempts at correction. The mitral stenosis (leading to pulmonary hypertension) and reduced ventricular function can make these patients particularly difficult to manage in the perioperative period, particularly with respect to fluid loads and shifts, anemia, fever, and stress response.

Congenital aortic valve stenosis can be relieved by surgical valvotomy or by percutaneous balloon valvuloplasty ( ; ). Although both strategies are effective in relieving the obstruction and promoting growth of the valve annulus, it is still unclear which is the better option ( ; ; ; ). The Ross operation is an alternative for unrepairable aortic valve disease, but in neonates it carries a high mortality ( ). In children and adolescents, surgical intervention becomes necessary when dilation of the stenosis is no longer effective or aortic regurgitation and consequent LV dilation becomes significant. Aortic valve repair rather than replacement is performed in many centers, obviating the risks of anticoagulation, allowing growth, and postponing aortic valve replacement (AVR).

Subaortic stenosis resulting from a discrete subaortic membrane is repaired by membrane resection. In addition to creating increased pressure within the LV, aortic valve damage and regurgitation caused by a jet arising from flow across the membrane is a common finding and an indication for surgery. Tunnel subaortic stenosis is managed by the modified Konno procedure, in which LV septal tissue is excised and a patch placed to enlarge the LV outflow tract.

Coarctation of the aorta

Coarctation of the aorta (CoA) is an arteriopathy with a focal narrowing of the upper thoracic aorta consistent with a discrete posterior shelf or invagination just opposite the insertion of the ductus arteriosus (juxtaductal) and distal to the left subclavian artery ( Fig. 30.12 , Video 30.9 ). In some instances, this shelf may be circumferential or comprise a long segment. The precise etiology is unknown, but theories include extension of duct-like tissue into the wall of the aorta (ductal tissue theory), abnormal fetal blood flow patterns with lesions that reduce antegrade flow into the ascending aorta (hemodynamic theory), or abnormal cellular migration during arch development ( ). Not surprisingly, associations include aortic valve stenosis or bicuspid aortic valve (22% to 42%), ventricular septal defect (48%), aortic arch hypoplasia, hypoplasia of other left-sided structures (mitral valve, left ventricle, Shone syndrome), as well as intracranial aneurysms (usually of the circle of Willis; up to 10%) ( ). The pathophysiology is varied and depends on the severity of the coarctation, associated lesions, and age of the patient. A PDA is critical to provide systemic perfusion, so presentation is in infancy for all patients except those capable of tolerating ductal closure without overt hemodynamic compromise. In general, presentation beyond infancy is limited to patients with an isolated coarctation of mild to moderate severity. Critical neonatal coarctation with abrupt ductal closure results in profound circulatory collapse within the first days to a month of life, because perfusion to the lower body is dependent on patency of the ductus arteriosus and relatively high PVR. The presence of poor perfusion, acidosis, oliguria, and other signs and symptoms of acute systemic illness often results in these patients being seen emergently to rule out sepsis. Severe presentations typically involve some degree of acute myocardial dysfunction and can also include evidence of lung, liver, and renal injury. When a large VSD is also present, the aggravated degree of L-R shunting and heart failure (with elevated left atrial pressure and additional L-R shunting across the foramen ovale) results in presentation within days of birth. The initial treatment involves hemodynamic stabilization by reopening the ductus arteriosus with a PGE ₁ infusion (0.01 to 0.05 mcg/kg per min). Other resuscitative measures may include intubation and mechanical ventilation, inotropic support, volume expansion, and sodium bicarbonate. Of note, once the duct is reopened, it is possible for blood pressures in the upper and lower limbs to be similar despite severe aortic narrowing. Patients who presented with severe decompensation and evidence of organ injury benefit from one or more days of restored systemic perfusion prior to surgical repair.

If the coarctation is not severe and closure of the ductus has occurred slowly, or if compensatory collaterals develop rapidly, presentation may be later in infancy, with tachypnea and failure to thrive. In such patients, the degree of coarctation commonly becomes more obstructive as the child grows. Blood pressure is elevated in the upper extremities, with an average gradient between upper and lower extremity sites of 30 to 40 mm Hg at rest ( ). Collaterals may originate from the internal thoracic, intercostal, subclavian, or scapular arteries, and with extensive collateral development, patients may be asymptomatic with little difference in blood pressure between the arms and legs. Large collaterals can be a source of an auscultatable bruit over the rib cage or elsewhere, as well as rib notching on a chest x-ray. Coarctation causes left ventricular hypertension and hypertrophy as well as systemic hypertension ( ). Symptoms (exercise intolerance, headache, chest pain, lower extremity claudication) are an absolute indication for surgical repair. For the asymptomatic patient, surgical indications include a blood pressure gradient between the upper and lower limbs of greater than 20 mm Hg, upper body blood pressure greater than two standard deviations above normal, or aortic diameter loss of 50% or greater.

The current strategies for CoA repair include surgical repair or catheter-based techniques (balloon aortic angioplasty, balloon-expandable stent implantation) ( ; ). Recoarctation can occur after both types of repair. Surgery comprises complete excision of the area of coarctation and surrounding ductal tissue with end-to-end anastomosis. With a hypoplastic aortic isthmus, complete excision in conjunction with an extended end-to-end or end-to-side anastomosis is performed ( ). Owing to insufficient studies and long-term follow-up of percutaneous treatment for primary repair, the superiority for the primary repair of a catheter technique over surgery has not been proven ( ; ; ). In some centers balloon angioplasty or stent angioplasty is reserved for children with recurrent coarctation after previous surgical repair or as the first-line treatment for older children and adults with newly diagnosed coarctation ( ). Paraplegia secondary to spinal cord ischemia is the most devastating complication associated with surgical repair. The incidence is relatively low (0.14% to 0.4%), and several factors are associated with an increased risk of developing paraplegia: hyperthermia, prolonged aortic cross-clamp time, elevated cerebrospinal fluid pressures, low proximal and distal aortic blood pressures, and poorly developed collaterals to the descending aorta.

In addition to recoarctation, long-term consequences of CoA increase risk of premature or sudden death resulting from persistent hypertension (over one-third of patients, even in the absence of a residual coarctation gradient), intracranial hemorrhage, heart failure (LV hypertrophy with diastolic dysfunction, premature coronary atherosclerosis), aortic aneurysm and fistula formation, aortic dissections and rupture, and endarteritis at the repair site and increased risk of premature or sudden death ( ; ; ; ; ). The etiology of persistent hypertension is multifactorial and includes reduced pulsatility of the postcoarctation descending aorta, reduced upper-body vascular responses to reactive hyperemia and glyceryl trinitrate (possibly abnormal smooth muscle relaxation or structural abnormalities of the arterial wall), aortic arch geometry, and abnormalities in baroreceptor reflexes and the renin-angiotensin-aldosterone system ( ; ; ; ). There is evidence to suggest that abnormalities in cardiovascular reflexes are already present in neonates with coarctation before repair ( ).

Transposition of the great arteries

Transposition of the great arteries (D-TGA) accounts for 3% to 10% of all CHD and is rarely associated with congenital anomalies and syndromes ( ). Ventriculoarterial discordance results in the aorta arising from the anatomic right ventricle and the pulmonary artery from the left ventricle. In other words, a right-sided RA connects via a right-sided tricuspid valve and RV to a right-sided and anterior aorta, and a left-sided LA connects via a left-sided mitral valve and LV to a left-sided and posterior pulmonary artery ( Fig. 30.13 , Video 30.10 ). TGA can occur with an intact ventricular septum (IVS) or a VSD (40% to 45%), with or without subpulmonic (LVOT) obstruction (25% of those with a VSD), and variability in coronary artery pattern ( ; ). A much less common form of TGA is congenitally (physiologically) “corrected” TGA (ccTGA), in which there is both ventriculoarterial and atrioventricular discordance (i.e., a series circulation in which the RA connects via the mitral valve to the LV and then the PA, and the LA connects via the tricuspid valve to the RV and then the aorta). Congenitally corrected transposition without associated cardiac lesions may go undetected for decades until the RV, which is the systemic ventricle, begins to fail. Patients with ccTGA are at risk of spontaneously developing complete heart block, at a rate of 2% per year, owing to the abnormal location of the atrioventricular node (AVN) and infranodal common bundle. The AVN is anteriorly situated in the right atrium at the lateral junction of pulmonary and mitral valves with the common bundle passing in the subendocardium anterior to the pulmonary valve annulus and inferiorly over the anterosuperior aspect of the membranous septum ( ; ).

D-TGA produces two parallel circulations with recirculation of systemic and pulmonary venous blood. Clinically, these infants may present with severe hypoxemia shortly after birth and/or with pulmonary overcirculation and congestive heart failure. Adequate systemic oxygenation and short-term survival are dependent on one or more communications between the two circuits to allow intercirculatory mixing; these communications can be intracardiac (PFO, ASD, VSD), extracardiac (PDA, bronchopulmonary collaterals), or both. Initially, the infant is maintained on a prostaglandin E ₁ (PGE ₁ ) infusion to provide PBF via the PDA. With adequate mixing and a good-sized PDA, arterial oxygenation is satisfactory, but over time the decline in PVR leads to increased pulmonary blood flow. Patients with increased pulmonary blood flow, particularly those with a large VSD, are at risk of developing pulmonary overcirculation, having a large volume load imposed on the LA and LV, and congestive heart failure. Pulmonary overcirculation (e.g., tachypnea, systemic hypoperfusion, pulmonary congestion on chest x-ray, acidosis), although in the past managed by reduced Fio ₂ via blending of atmospheric air with nitrogen or controlled ventilation with induced hypercarbia via added inspired CO ₂ , is now managed with circulatory support as needed (e.g., dopamine), intubation and mechanical ventilation, and early surgical repair. Conversely, the more severe the LVOT obstruction, the more dependent the effective pulmonary blood flow will be on the presence of a PDA. In patients with reduced pulmonary blood flow or poor intercirculatory mixing despite PGE ₁ and a widely patent atrial communication, hypoxemia can be lessened by increasing the cardiac output (volume loading, inotropic support), red blood cell (RBC) transfusion, and reducing oxygen consumption by sedation, paralysis and ventilation, and avoidance of fever.

If the atrial septum is restrictive (inadequate intracardiac mixing), the neonate will be hypoxemic with left atrial hypertension, and will have pulmonary edema and poor systemic perfusion with metabolic acidosis. A balloon atrial septostomy is then performed in the catheterization laboratory or at the bedside to improve mixing and to reduce left atrial pressure and pulmonary edema. This can be an emergent procedure performed shortly after delivery.

A general rule of thumb aims for arterial saturations in the 75% to 85% range in the nonintubated, spontaneously ventilating patient. Infants with evidence of multiple organ dysfunction resulting from severe hypoxemia and hypoperfusion are generally better managed with a period of stabilization and recovery, facilitated by the aforementioned measures to improve mixing and oxygen delivery, before undergoing corrective surgery. However, ongoing hypoxemia and longer time to surgery has been shown to increase preoperative brain injury ( ; ).

D-TGA/VSD and D-TGA/IVS are currently repaired anatomically by the arterial switch (Jatene) operation (ASO), which is usually performed 2 to 4 days after birth ( Fig. 30.14 , Video 30.11 ) ( ; ). The pulmonary artery and aorta are transected distal to their respective valves. The coronary arteries are excised with a button of surrounding tissue and reimplanted into the proximal pulmonary artery (neoaorta). The great arteries are then switched, with the pulmonary artery brought anterior (Lecompte maneuver) and anastomosed to the proximal aorta (right ventricular outflow) and the aorta anastomosed to the proximal pulmonary artery (left ventricular outflow). Most patients with TGA have coronary anatomy that is suitable for coronary reimplantation. The exact coronary anatomy must be delineated because variants can contribute significantly to operative difficulty and the success of surgical repair. The “late” or two-stage repair for D-TGA with IVS can be used for neonates and infants in whom significant regression of LV mass has occurred ( ). These are generally infants on whom surgery was not performed during the first several weeks of life because of other factors (e.g., delayed diagnosis and referral, other anomalies, sepsis, or prematurity). The ASO is associated with an early hospital mortality of less than 5% in experienced centers ( ; ; ; ). Although the majority of patients reach adulthood with New York Heart Association functional class I, there are significant lifelong concerns. Postoperative sequelae have been reviewed and include neoaortic regurgitation, neoaortic root dilation, supravalvar pulmonary stenosis, supravalvar aortic stenosis, coronary artery disease, sudden cardiac death, and chronotropic incompetence ( ). The most common cause of mortality related to the ASO is coronary artery obstruction (5% to 7% of survivors); the pattern is bimodal, with a high early incidence related to technical difficulties with coronary reimplantation and a slow later incidence ( ). In adults, coronary artery occlusion (2% to 7% of cases) is generally asymptomatic, with the arteries displaying varying degrees of proximal eccentric intimal proliferation and concentric intimal smooth muscle hyperplasia with preserved tunica media, suggesting the potential for the development of early atherosclerosis in the reimplanted coronary arteries ( ; ; ; ). Detection of subclinical myocardial ischemia is still a challenge ( ). Noninvasive tests are not sufficiently sensitive to detect delayed coronary artery stenosis. ECG-gated CT angiography provides excellent spatial resolution and is an alternative to coronary artery angiography or intracoronary ultrasound. Stress echocardiography, cardiac MRI, or positron emission tomography may detect regional wall motion abnormalities and perfusion defects. It is still unclear whether invasive testing should be a mandatory component of surveillance in all patients who have undergone an ASO.

The variant of D-TGA/VSD and severe LVOT obstruction precludes the ASO. In this setting, the Rastelli procedure is performed whereby the VSD is repaired by a patch that directs blood from the left ventricle through the defect into the aorta (and also closes the VSD), and a valved conduit is placed from the right ventricle to the main pulmonary artery. With the Rastelli procedure, the LV functions as the systemic ventricle, but conduit stenosis and valve degeneration are inevitable ( ). The Nikaidoh procedure involves translocation of the root of the aorta posterior to overlie the LV and translocation of the pulmonary artery anteriorly prior to creating RV-to-PA continuity ( ).

The atrial switch procedure (Mustard, Senning), which revolutionized the early management of infants with TGA, is now rarely performed. The sole indication in the current era is for repair of ccTGA ( ). The atrial switch is a physiologic repair in which a baffle in the atrium directs systemic venous blood to the mitral valve (and consequently to the LV and pulmonary artery) and pulmonary venous blood to the tricuspid valve (and consequently to the RV and aorta) ( Fig. 30.15 ). The atrial switch procedures provide excellent midterm results (15-year survival, 77% to 94%; 20-year survival, 80%), with many patients able to lead fairly normal lives into their third and fourth decades ( ). In the long term, there is progressive deterioration in RV function and development of tricuspid regurgitation, with 25% to 67% of patients having CHF by 45 years of age. Even in asymptomatic patients, exercise testing demonstrates chronotropic incompetence and moderate to severe limitations in RV function and maximal aerobic capacity. Sinus node dysfunction and atrial bradyarrhythmias and tachyarrhythmias are common. At 20 years follow-up, sinus rhythm was present in only 40% of patients ( ). Atrial flutter parallels the development of ventricular dysfunction, is experienced in one-third or more of patients 20 years after surgery, and is a probable marker for sudden death ( ; ; ; ). Intraatrial baffle leaks can result in shunting and hypoxemia. Baffle obstruction of the systemic venous return can cause superior vena cava (SVC) syndrome, hepatic congestion, ascites, and peripheral edema, whereas pulmonary venous baffle obstruction can cause pulmonary edema and pulmonary hypertension. Pulmonary hypertension unrelated to baffle obstruction can develop in about 7% of patients who survive to adulthood ( ).

Truncus arteriosus

Truncus arteriosus is a single arterial trunk arising from the base of the heart and giving origin to the aorta, pulmonary arteries, and coronary arteries ( ). Truncus arteriosus is classified based on the origin of the pulmonary arteries ( Fig. 30.16 , Video 30.12A –G). There is a single semilunar valve and VSD in the vast majority of cases. The semilunar valve is sometimes dysplastic, usually tricuspid but can also be uni-, bi-, quadri-, and pentacuspid, and may be regurgitant or stenotic ( ; ). The infundibular septum is virtually absent superiorly so that the VSD is nonrestrictive. Like tetralogy of Fallot, it is frequently associated with 22q11.2 microdeletions, DiGeorge, and velocardiofacial syndromes ( ). Extracardiac anomalies are seen in approximately 30% of patients.

Truncus arteriosus is a single-ventricle-physiology lesion amenable to a two-ventricle repair. It is the quintessential parallel circulation, with the $\dot{\text{Q}}$ p: $\dot{\text{Q}}$ s ratio determined by the ratio of pulmonary to systemic vascular resistance ( ; ). As the pulmonary and systemic circulations are supplied in parallel from a single vessel, for a given ventricular output increases in flow to one circulatory system will produce reductions in flow to the other. Shortly after birth, the balance of PVR and SVR is such that pulmonary blood flow is high and the patient with truncus arteriosus has symptoms of CHF with mild cyanosis. After cardiac reserve has been exhausted, further decreases in PVR increase pulmonary blood flow at the expense of systemic and coronary perfusion. This produces a progressive metabolic acidosis. If truncal valve insufficiency is present, an additional volume load is imposed on the ventricles.

Surgical repair is performed in the neonatal period as delay in repair results in early development of PVOD and myocardial dysfunction. Definitive repair involves patch closure of the VSD and detachment of the pulmonary arteries from the truncus with establishment of right ventricle–to–pulmonary artery continuity with a valved homograft. The RV-to-PA conduit requires placement of the proximal end over a ventriculotomy in the RV free wall. In some instances, truncal valve repair (preferred) or replacement is necessary to address valvular insufficiency or stenosis. Valvuloplasty is preferred over valve replacement, and the RV-to-PA valved conduit requires replacement as the child grows.

Ebstein anomaly

Ebstein anomaly consists of displacement of the septal and posterior leaflets of the tricuspid valve toward the apex of the right ventricle ( Fig. 30.17 , Video 30.13 ) ( ). The right ventricle between the true annulus and the level of attachment of the septal and posterior leaflets to the ventricular septum is thin and dysplastic (“atrialized”). The anterior tricuspid leaflet at the annulus is larger than normal, whereas the other leaflets may be redundant, contracted, or thickened. The tricuspid valve is usually incompetent but can be stenotic and the anterior leaflet can occasionally cause RVOT obstruction. The right ventricular cavity beyond the atrialized portion ranges from small to large, whereas the right atrium is invariably enlarged. There is virtually always an interatrial communication (PFO or ASD), and an accessory AV conduction pathway (e.g., Wolff-Parkinson-White syndrome) is present in 10% to 25% of cases ( ; ).

The clinical spectrum of Ebstein anomaly is extremely variable, ranging from the critically ill neonate with minimal to no anterograde flow out the right ventricle to the pulmonary artery, with severe tricuspid regurgitation and heart failure, to the child with minimal or no symptoms ( ). The severity of cyanosis depends on the magnitude of the atrial R-L shunt. Interventions for significant lesions include tricuspid valve repair (cone procedure) or replacement, closure of interatrial communications, and catheter ablation of accessory pathways ( ; ).

Single-ventricle lesions and hypoplastic left heart syndrome

A single ventricle is defined as the presence of two atrioventricular valves with one ventricular chamber or a large dominant ventricle with a diminutive opposing ventricle ( ). Single-ventricle or univentricular hearts encompass a wide variety of lesions that include hypoplastic left heart syndrome (HLHS) ( Video 30.14A – C ), tricuspid atresia or severe tricuspid stenosis, double-inlet single ventricle (usually left), single ventricle with common atrioventricular valve (unbalanced complete AV canal, heterotaxy variants), and some forms of double-outlet right ventricle and pulmonary atresia with intact ventricular septum. Initial management is aimed at optimization of systemic oxygen delivery and perfusion pressure. In the presence of approximately the right amount of pulmonary obstruction to balance the circulations, no procedure will be required in the neonatal period. Any surgical procedure required varies with the anatomy and may include the Norwood operation, a stage 1 hybrid procedure, pulmonary artery band, or systemic–to–pulmonary artery shunt. Subsequent management is aimed at reducing the volume load on the ventricle (superior cavopulmonary connection or bidirectional Glenn procedure) and finally achieving a series circulation with fully saturated systemic arterial blood (Fontan procedure). This is usually achieved through a staged approach. Although, collectively, single-ventricle defects are relatively rare, they account for a disproportionate share of repeated procedures with increased anesthesia risk, with resultant morbidity and mortality ( ).

As discussed early in this chapter, unoperated single-ventricle physiology is a parallel circulation characterized by complete mixing of systemic and pulmonary venous blood at the atrial level, ventricular level, or both. With some lesions, systemic or pulmonary perfusion is dependent on a PDA. If there is no obstruction to pulmonary or systemic outflow, the amount of flow to each circulation is determined by the relative resistances of the pulmonary and systemic vascular beds. With no obstruction to pulmonary blood flow and the normal postnatal regression in PVR, PBF gradually increases and leads to congestive heart failure. Severe obstruction to PBF will result in progressive cyanosis in the absence of a PDA, while moderate obstruction can be associated with suitable balancing of the systemic and pulmonary blood flows. Systemic outflow obstruction will result in increased PBF, CHF, and systemic hypoperfusion. In single ventricle physiology, the effects of pulmonary and systemic blood flows on aortic and mixed venous oxygen saturations are shown in Table 30.5 . An arterial saturation of 75% to 80% is felt to be indicative of a relatively balanced circulation (maximum systemic O ₂ delivery) with a $\dot{\text{Q}}$ p: $\dot{\text{Q}}$ s at or near 1:1 (assuming pulmonary venous saturation of 95% to 100% and mixed venous saturation of 50% to 55%) ( ). However, even with a “balanced” $\dot{\text{Q}}$ p: $\dot{\text{Q}}$ s of 1:1, the systemic ventricle is essentially pumping double the normal cardiac output. This gives some appreciation for the even greater degrees of systemic ventricular volume overload that is imposed by increased amounts of PBF. The addition of nitrogen to the inspired gas mixture in order to lower Fio ₂ in order to increase PVR is rarely done ( ; ).

Norwood operation

The Norwood operation, also referred to as stage I single-ventricle palliation, is performed for patients with HLHS and its variants or when the pathway to the aorta from the systemic ventricle is obstructed ( ). It is a palliative procedure that eliminates the need for continued patency of the ductus arteriosus. Prior to the stage 1, a nonrestrictive atrial septum is essential for pulmonary venous blood to reach the systemic right ventricle. Creating a nonrestrictive atrial septum can be achieved in the cardiac catheterization laboratory with a Rashkind-Miller balloon atrial septostomy, or a surgical atrial septectomy can be performed at the time of initial palliation. The stage 1 procedure is performed during the first several days to a week of life using CPB in conjunction with 40 to 60 minutes of deep hypothermic circulatory arrest or regional cerebral perfusion during reconstruction of the aortic arch (see later) ( ). The procedures necessary for palliation of HLHS are outlined in Fig. 30.18 . The Norwood operation consists of establishing unimpeded flow of venous return from both the systemic and pulmonary circulations into the right ventricle and then into the (neo)aorta and creating a stable conduit for pulmonary blood flow. In practice, this requires a freely patent atrial septum (an atrial septectomy is often necessary), transection of the main pulmonary artery just proximal to its bifurcation and anastomosis end to side to the ascending aorta (the Damus-Kaye-Stansel procedure) so the combined venous return is ejected by the right ventricle into the aorta, and reconstruction and enlargement of the ascending aorta and aortic arch (using both the proximal pulmonary artery and homograft material). A well-functioning tricuspid (or atrioventricular valve) is very important for the single ventricle circulation. Pulmonary blood flow is established with a systemic-to-pulmonary artery shunt in the form of a modified BT shunt (the proximal insertion typically into the innominate artery) or an RV-PA conduit (the Sano modification) ( ; ). A superior cavopulmonary connection cannot be performed in lieu of a systemic–to–pulmonary artery shunt in neonates and early infancy because the elevated pulmonary artery pressure and PVR necessitates a high perfusion pressure. The Norwood operation still leaves the infant with a single-ventricle parallel circulation.

Hybrid procedure

When the risks of CPB are higher than normal, such as with very low birth weight, intracerebral hemorrhage, and necrotizing enterocolitis, or as a means of resuscitation, the hybrid procedure is an alternative strategy to the Norwood operation ( ). The hybrid procedure is a combined catheter-based and surgical approach that comprises pulmonary artery banding via a median sternotomy and placement of a stent in the PDA. Transcatheter creation of an ASD with stenting is performed when necessary ( ) ( Fig. 30.19 ). The initial hybrid procedure is then followed by a comprehensive stage II, which combines components of both the Norwood and the traditional stage II (cavopulmonary connection) ( ). Although some centers perform the hybrid procedure routinely, there is insufficient evidence as to whether this is superior for the majority of patients ( ). (For a discussion of anesthetic management for the hybrid procedure, see Anesthesia for Cardiac Catheterization.)

The fontan procedure or total cavopulmonary connection

The Fontan procedure was first performed in 1968 and was initially described for patients with tricuspid atresia ( ). The original version included a Glenn shunt, which drained the SVC into the distal right pulmonary artery. The proximal end of the right pulmonary artery was joined to the right atrial appendage via an aortic valve homograft, and a pulmonary valve homograft valve was placed at the IVC-RA junction. The main pulmonary artery was ligated, and the ASD was closed. In subsequent early iterations, creation of the Glenn shunt and placement of homograft valves at the RA-PA and IVC-RA junctions were eliminated, resulting in creation of a direct atriopulmonary connection. Experience with direct atriopulmonary connections has found that elevated systemic venous pressure leads to progressive and severe atrial dilation (volumes as large as 300 to 500 mL) that is believed to contribute to stasis (and thus thromboembolism) and atrial arrhythmias. Since that time, many additional modifications have been described, but the goals of the procedure remain the same: total cavopulmonary connection delivers all systemic venous blood directly to the pulmonary arteries with the presumption that a subpulmonary ventricular pump is not essential for venous return to cross the pulmonary vascular bed ( ).

The Fontan procedure is generally performed at 2 to 3 years of age and is normally the final operation in the staged correction of single-ventricle defects ( Video 30.16A – C ). The Fontan places the systemic and pulmonary circulations in series (thereby correcting cyanosis) and driven by the single ventricle ( ). The principles for success of a Fontan are the same as those discussed for the BDG; that is, total cavopulmonary continuity without obstruction (absolute and relative), a well-functioning AV valve, and a single ventricle in unobstructed continuity with the aorta and sufficient systolic and diastolic function to support the systemic circulation.

The most commonly performed procedures in the current era are the lateral tunnel and extracardiac Fontan procedures (see Figs. 30.4 and 30.5 ). The lateral tunnel Fontan incorporates a small amount of systemic venous atrium in the cavopulmonary pathway, whereas the extracardiac Fontan does not incorporate any atrial tissue. It is still unknown which of these two procedures is superior ( ). In theory, the extracardiac Fontan may offer additional protection from development of atrial arrhythmias because of a lack of suture lines in the atrium. Research using computational fluid dynamics found that an 18 to 20 mm extracardiac conduit leads to lower power loss ( ; ). Fenestration of the Fontan circuit was described in 1990, and although not used routinely in all centers, it has been shown to be associated with reduced morbidity (e.g., low cardiac output, increased pleural effusions, increased volume requirements) and improved outcomes in standard and high-risk patients ( ; ). Fenestration is discussed in more detail after post-CPB management.

Factors that make a patient unsuitable for a Fontan procedure include nonmodifiable conditions such as early infancy, chronic lung disease with pulmonary hypertension, severe ventricular systolic or diastolic dysfunction, and recalcitrant pulmonary vein stenosis ( ; ). Many coexisting lesions previously believed to be at least relative contraindications (AV valve regurgitation or stenosis, significantly narrowed or distorted pulmonary arteries) are now corrected at the time of the BDG and/or Fontan.