Pacemaker and Implantable Cardioverter-Defibrillator Management in Children and Congenital Heart Disease

Pediatric Indications for Pacing

Sinus node dysfunction and atrioventricular (AV) nodal dysfunction are the predominant pediatric indications for pacing. Other indications such as cardiac resynchronization, prevention of atrial arrhythmias, rapid antitachycardia pacing, and pacing in channelopathies represent a minority of procedures. Consensus recommendations for pacing in pediatric patients were published in 2008. An update of the guidelines in 2012 did not significantly change pediatric-specific pacing recommendations.

Sinus Node Dysfunction

The definition of bradycardia differs by age, and published tables tabulate age-related peak, mean, and minimum heart rates ( Table 27-1 ). Symptoms are the most important indication for pacing in children and young adults with sinus bradycardia. Typical symptoms of dizziness, fatigue, and syncope may be present. However, symptoms of sinus node dysfunction are often gradual in their presentation. It may be challenging to separate normal developmental changes in children from symptoms secondary to bradycardia. Clinicians should assess for subtle alterations in behavior and activity, even in the absence of overt complaints. In some cases, a child who has previously been active and physical may begin to focus on sedentary activities. Physical and social discomfort are both strong modifiers of behavior. If exertion produces symptoms or if the social stigma of decreased exercise tolerance is uncomfortable, a child may simply adjust his or her behavior to avoid the activities which provoke symptoms or ridicule. Periodic exercise stress testing, indexed to normal values for age, can be helpful to quantitatively evaluate whether the change in behavior is related to chronotropic incompetence. Growth may be impaired as well, and a longitudinal growth chart can be a helpful tool. Unfortunately, the benefits of reestablishing chronotropic competence can be more obvious in retrospect than at the time of decision making. Children often report feeling “just fine,” but recognize an improvement after pacing without realizing that they were subconsciously limiting their physical activities.

In adult medicine, single-chamber atrial therapy has become less common, prompting editorials that explicitly marginalize the practice of implanting single-chamber atrial lead systems (“We believe that single chamber atrial pacing use (AAI/R) has become an anachronism that should generally be abandoned.”). DANPACE, a large prospective study of AAIR/DDDR pacing in an elderly population, found that AAIR pacing is associated with a higher incidence of paroxysmal atrial fibrillation, without affecting mortality. However, the patient population and pretest probability of atrial fibrillation are markedly different in pediatric patients than in the elderly. In addition, the considerations of lead burden and maintenance of intravascular patency are likely more clinically relevant in younger patients. Finally, there are a number of anatomic variants in which a transvenous atrial single-chamber system remains a technically plausible implantation, but where a ventricular lead would represent a significant increase in the complexity and risk of the operation. Patients with single-ventricle anatomy and a Fontan anastomosis are the archetype of this physiology. In some pediatric cases, transvenous atrial single-chamber systems may be appropriate and the advantages and disadvantages of backup ventricular pacing capability should be weighed at the time of implantation. As a counterpoint to the argument above, dual-chamber leads should be strongly considered when epicardial leads are placed, even in the absence of an explicit ventricular pacing indication. There are substantial advantages to avoiding a future sternotomy or thoracotomy.

Sinus node dysfunction and symptomatic bradycardia occur frequently after repair of congenital heart disease (CHD). Whether due to underlying abnormalities of rhythm generation, direct vascular or tissue trauma to the sinoatrial node, or subsequent scarring after atrial surgery, sinus node dysfunction remains an important issue in repaired CHD.

Sinus node dysfunction presenting immediately after an operation may resolve spontaneously as inflammation and injury recover, but indications for antibradycardia pacing gradually increase with persistent sinus node dysfunction over long-term follow-up. The prevalence of sinus node dysfunction increases over time, especially following extensive atrial surgery, and may present decades after the operation. A recent multicenter study noted that adult patients with simple and moderately complex CHD receive their first device at a median of 31 years of age, whereas complex congenital adult heart disease patients receive their first device at a median of 23 years of age. This study examined adults only, so it ignored the incidence of neonatal and childhood pacing, but it indicates that some patients with CHD will continue to need pacemaker interventions as they age. According to the most recent guidelines, bradycardia with symptoms in CHD is a class I indication for pacing. Congenital heart disease patients whose resting heart rate is less than 40 beats per minute (bpm) or those who have sinus pauses over 3 seconds have a class IIa indication for pacing, even in the absence of symptoms ( Table 27-2 ).

Sinus node dysfunction may also present secondary to negative chronotropic effects of antiarrhythmic medication treatment or after lines of conduction block are created in catheter-based or surgical maze procedures intended as therapies for atrial tachyarrhythmias. Similar indications of rate and symptoms should be considered in placing a pacemaker in this setting; however, atrial arrhythmias may contribute to long-term morbidity and mortality in CHD. If antiarrhythmic medications are required to suppress atrial tachycardias, pacing is a reasonable trade-off to avoid symptomatic bradycardia. In some cases, pacing may need to be instituted to support sinus node function or to prevent further pause-mediated arrhythmias or “tachy-brady syndrome.” Pacing carries a class IIA indication in this setting.

Atrioventricular Node Dysfunction

AV node dysfunction is the most common cause for pacing in pediatric patients, particularly during the neonatal period, and persists as a common indication for pacing throughout childhood.

Congenital heart block is present in approximately 1 in 20,000 live births. A structurally normal heart is present in 50% of newborns with congenital heart block. Only 15% of fetuses with complete congenital heart block will present with a maternal history of connective tissue disease, but complete congenital heart block secondary to maternal anti-Ro and anti-La antibodies remains the most common identifiable cause of neonatal complete heart block. The stereotypical AV nodal dysfunction which occurs in this setting occurs after 18 weeks of gestation. The indications for pacemaker implantation remain the same whether or not anti-Ro and anti-La antibodies are found.

In many centers, maternal testing for anti-Ro and anti-La antibodies is performed routinely when neonatal heart block is encountered. The greatest immediate utility is for counseling families regarding future pregnancies. The recurrence risk for complete AV block is 16% in subsequent pregnancies, which is two- to three-fold higher than the rate for a mother with anti-Ro or anti-La antibodies who has never had an affected child. Fetal therapy with steroids or other anti-inflammatory medications has been so far disappointing. Maternal antibody testing may be a useful adjunct for patients who present beyond the neonatal period; a positive test provides supportive evidence that no other acquired etiology of complete heart block is likely.

The other 50% of newborns with complete heart block have an underlying structural heart disease. Most commonly, these represent disorders of structural situs. Fifty-nine percent of babies with CHD and heart block will have a variant of heterotaxy syndrome; 24% of these newborns will have AV discordance. Congenitally corrected or {S,L,L} transposition of the great arteries has a high risk of spontaneous and acquired AV block, with particularly increased susceptibility to catheter-induced and surgically induced heart block. Although other lesions have been noted to be associated with AV block, including Ebstein anomaly and ventricular septal defects, preoperative AV block is not typically a hallmark of these diseases. There is a genetic form of congenital heart block associated with atrial septal defects, which is typically inherited in an autosomal-dominant fashion, due to a transcription factor mutation (NKX2.5). Similarly, Holt-Oram syndrome often includes inherited abnormalities of AV conduction, due to a different transcription factor (TBX-5).

Mortality in neonatal complete heart block has been reported as high as 18% to 43%, although with current earlier diagnosis and permanent pacemaker intervention, the mortality in the current era is likely lower. Significant structural heart disease, the presence of a heart rate less than 55 bpm, fetal hydrops, and cardiac fibroelastosis are all markers of decreased likelihood of survival in the neonatal period. Fetal pacing has unfortunately not been successful to date.

All symptomatic patients with complete congenital heart block have a class I indication for pacing. Other definitive indications for permanent pacing include complex ventricular ectopy, ventricular dysfunction, and a wide QRS escape rhythm. Heart rate guidelines for pacemaker implantation in infants include a ventricular rate less than 55 bpm in structurally normal hearts or less than 70 bpm in the neonate with CHD. Although the guidelines are not explicit, most practitioners interpret these thresholds as an average heart rate over 24 hours and not as a momentary minimum heart rate value. In addition, long pauses in the ventricular rate (typically two to three times the base cycle length) are suggestive of junctional exit block and raise the possibility of an unreliable escape rhythm. By 1 year of age, those patients who have not yet been paced have a class IIa indication for a pacemaker once their mean heart rate falls below 50 bpm, suggesting that they can be allowed to drop slightly lower than newborns; however, all of these heart-rate-based guidelines are based predominantly on clinical expert consensus and not on clinical trials or other scientific data. No specific guidelines are available for instituting pacing in the setting of left ventricular dilation and subsequent increased mitral regurgitation and aortic root dilation, but these may be sequelae of chronic low heart rates and their presence may weigh into a decision to institute pacing.

Some patients will continue into school-aged years or young adolescence without requiring pacing, but there is some evidence that there is a risk of syncope or even sudden death in older patients with complete congenital heart block. Prophylactic pacing for this reason is a class IIB recommendation. The recommendation does not specify a particular age, but this decision becomes easier when patients are large enough to receive transvenous leads instead of requiring a sternotomy or thoracotomy for epicardial lead placement. Asymptomatic complete heart block in adolescence is unusual and careful consideration should be given to the presence of subtle, progressive symptoms of bradycardia as mentioned above.

Severe neonatal long QT (LQTS) syndrome produces a form of functional 2:1 AV block. Mild sinus node dysfunction may be present, but the prolonged repolarization phase of the ventricle causes the myocardium to remain refractory when the next atrial depolarization wavefront is presented to the ventricle. Two-to-one AV conduction results. Because the therapy for long QT syndrome differs drastically from complete congenital heart block, early identification of neonatal long QT syndrome is critical. Although permanent pacing and ICDs have both been used in neonatal LQTS, typically the first priority is establishing the diagnosis, achieving a combination of medical and pacing therapy that suppresses arrhythmia and promotes 1:1 AV conduction. Depending on local expertise, transfer to an appropriate care center for specialized management of neonatal channelopathies may be advantageous. Once hemodynamic stability has been achieved, implanting a pacemaker or ICD is a clinically specialized decision, often requiring consideration of size, epicardial access, response to medications and arrhythmia history to date. (See Case Study 27-1 for an example of ICD use in a neonate.) Atrial overdrive pacing can be helpful in suppressing arrhythmias in neonatal long QT syndrome, and in some cases, neonatal pacing is sufficient. Case reports of ICDs for infants with long QT syndrome exist, but they are generally not used as primary prevention in the neonatal age group due to additional implantation risks and complexities.

Case Study 27-1

Infant with Severe Long QT Syndrome and Torsade De Pointes

This case is a baby who was diagnosed prenatally with periodic bradycardia and tachycardia by 20 weeks' gestation. By fetal echocardiography, the bradycardia appeared to be sinus bradycardia with intact atrioventricular (AV) conduction with episodic periods of second degree AV block. Runs of nonsustained tachycardia were also detected prenatally ( Fig. E27-1 ). During tachycardia, ventricular rates were over 300 beats per minute (bpm) and atrial rates were 150 bpm. The baby was delivered full term, and almost immediately had short frequent runs of torsade de pointes with spontaneous conversion to sinus bradycardia. The QTc was markedly prolonged at 600 msec, initially with 1:1 AV conduction on the first day of life, but then became 2:1 conduction at 48 hours of life ( Fig. E27-2 ). She underwent placement of a permanent epicardial pacemaker as a neonate and was treated with multiple antiarrhythmic agents, including high-dose propranolol and mexiletine. However, she continued to have episodic polymorphic ventricular tachycardia (VT) and underwent placement of an implantable cardioverter-defibrillator (ICD) system before 1 year of age. Due to size constraints, a single-coil defibrillator lead was placed in the posterior pericardial space, and the ICD generator was placed in the upper abdomen ( Fig. E27-3 ). The existing epicardial pacing leads were utilized, and the pace/sense port of the defibrillator lead was capped. The system worked appropriately, and over the next few years she subsequently had several appropriate shocks for VT, that were successful in converting her back into sinus rhythm ( Fig. E27-4 ).

Postsurgical complete heart block is a well-known result of reparative or palliative surgery in CHD. Permanent heart block can also occur as a result of direct injury during cardiac catheterization, radiofrequency catheter ablation, and other intracardiac manipulations; however, this is less frequent. Principles for managing heart block after catheterization are the same as those for managing heart block after surgical interventions. Cardiac surgery remains the most frequent etiology of iatrogenic mechanical heart block. Conduction returns spontaneously in as many as two thirds of patients in the first 10 days after surgery. The guidelines specify waiting 7 days after the operation before placing a permanent system as spontaneous recovery of conduction may occur. Most congenital heart centers will wait at least 7 days postoperatively, with temporary pacing in place. The waiting period is important because pacemaker implantation for “transient postoperative AV block with return of normal AV conduction in the otherwise asymptomatic patient” is a class III recommendation and generally should not be performed. Late mortality in patients with high-grade AV block after surgery has been well documented; the mortality due to complete heart block can be avoided by placement of a pacemaker. Two special cases of postsurgical heart block are specifically addressed in the guidelines. As a class IIB indication, “Permanent pacemaker implantation may be considered for transient postoperative third-degree AV block that reverts to sinus rhythm with residual bifascicular block.” However, this is a level of evidence C recommendation and care should be taken to compare the patient's preoperative electrocardiogram (ECG) and postoperative ECG. Many patients do not enter surgery with a normal QRS duration and axis; thus pacemaker decisions should be considered in the light of postsurgical ECG changes, and not simply the absolute appearance of the ECG. If syncope complicates the picture of recovered postoperative heart block with residual bifascicular block, pacemaker implantation becomes a class IIA recommendation once other causes of syncope are excluded.

Some patients with postoperative AV block will have subsequent recovery of AV conduction after a permanent pacemaker is placed. However, late recurrence of heart block has been documented even with early complete recovery of conduction, and recurrence of heart block has been suggested to contribute to late sudden death. Long-term rhythm follow-up is indicated for patients with early postsurgical heart block.

Even in the absence of surgically induced conduction damage, patients with CHD should be evaluated for pacemaker implantation when conduction system disease is found. One class IIA indication requires particular consideration: “Permanent pacemaker implantation is reasonable for patients with congenital heart disease and impaired hemodynamics due to sinus bradycardia or loss of AV synchrony.” Knowledge of the hemodynamic consequences of loss of AV synchrony in each congenital heart lesion and repair is useful in determining if there are long-term consequences of failure to correct a bradyarrhythmia. As an example, over long-term follow-up, patients with single-ventricle physiology and passive pulmonary blood flow may not tolerate elevated mean atrial pressures, volume load from bradycardia and AV valve regurgitation. In cases where instituting pacing may correct these hemodynamic abnormalities, consideration should be given to placement of a pacing system. The timing and effects of chronic pacing and potential hemodynamic improvements should be considered at the time of surgical planning in any case where a surgeon will have access to the myocardium and could potentially place epicardial leads.

Other Pacing Indications

Table 27-3 lists other causes for high-grade or complete heart block. In particular, the question of sustained pauses in the setting of breath-holding spells and vasovagal syncope episodes can be a challenging clinical dilemma. Although there are substantial data that the vasomotor component of the syncopal episode can cause loss of consciousness, even in the absence of a profound bradycardic event, there has been some enthusiasm for providing rate support during the event to delay the onset of the syncopal event long enough for patients to remove themselves from danger or to abort the episode all together. Recommendations have been published for pacing in the setting of neurocardiogenic syncope. In practice, pacemakers tend to be reserved for severe presentations. However, implantation is controversial even in these settings, because a placebo effect of placing the pacemaker has been demonstrated. Pacing for this indication in pediatric patients is rare. In particular, breath-holding spells tend to be a developmental interlude and most resolve with age; thus the morbidity of long-term or even life-long pacemaker therapy should be carefully weighed against the evidence that a life-threatening syncopal event is occurring.

Permanent dual-chamber pacing is rarely indicated any longer for symptomatic relief of subaortic obstruction in hypertrophic cardiomyopathy. Myotonic muscular dystrophy patients may develop progressive conduction block and are at risk of sudden unexpected complete AV block (as well as ventricular tachyarrhythmias). Mitochondrial disorders, such as the Kearns-Sayre syndrome, are also associated with progressive AV block and pacemaker implantation in these neuromuscular diseases should be considered early; the clinical course can be unpredictable and sometimes fatal.

Cardiac Resynchronization

The data on cardiac resynchronization have had towering effects on device implantation in cardiology for adults. It is intuitive that similar improvements in ventricular function should be achievable in pediatric cardiology, but thus far the scarcity of relevant patients has prevented large studies with easily quantifiable results. It is likely that the indications for resynchronization in pediatric patients and patients with CHD will continue to expand as we better understand the principles that underlie cardiac resynchronization therapy (CRT). Meta-analysis of data in adults suggests that a QRS greater than 140 msec and left bundle branch block morphology are important predictors of response to cardiac resynchronization. Although there may be some benefit for resynchronization in QRS durations between 120 and 140 msec, QRS resynchronization with a duration less than 120 msec has been shown to be ineffective and associated with increased morbidity. Because the baseline QRS is shorter in children than in adults, it is not clear whether QRS durations for successful resynchronization should be divided in the same locations for children. Right bundle branch block is far more common than left bundle branch block in patients with CHD than it is in patients with typical adult diseases. A 2013 meta-analysis of resynchronization data in adults failed to demonstrate that outcomes favored resynchronization therapy in right bundle branch block. Limited studies in pediatrics have suggested a role for resynchronization therapy, both in patients with two ventricles and in single-ventricle physiology; however, the number of patients that are considered in these studies is only a fraction of the studies in the literature on adults with resynchronization systems. (See Case Study 27-2 as an example of CRT in an infant.) Use of resynchronization in single-ventricle patients and in complex CHD may be effective, but thus far is still anecdotal. For patients whose ventricular function, QRS duration, and heart failure status are within the adult recommendations and in whom vascular or epicardial access permits a resynchronization system, adult guidelines may be applied. In addition, the Pediatric and Congenital Electrophysiology Society (PACES) published guidelines for device implantation including resynchronization therapy, specifically for adults with CHD.

Case Study 27-2

Congenital Heart Block with Pacing-Induced Cardiomyopathy

This case describes a newborn born to a mother with lupus antibody, but no maternal clinical manifestations of systemic lupus erythematosus (SLE) or other significant family history. She was born full term at 37 weeks' gestation and was determined to be in complete atrioventricular (AV) block with an atrial rate of 160 beats per minute (bpm) and ventricular escape rate of 55 bpm. She had normal intracardiac anatomy and normal ventricular function with a trivial pericardial effusion. The baby underwent placement of permanent unipolar dual-chamber pacemaker leads with a single-chamber VVIR pacemaker at 3 days of life via the epicardial route ( Figs. E27-5 and E27-6 ). The device was programmed VVIR with rate range of 140 to 180 bpm. Over the course of the next 4 months, she developed progressive left ventricular dilation and systolic ventricular dysfunction ( Fig. E27-7 , Video 27-2 ). Medical therapy with digoxin and enalapril was instituted, with no functional improvement. The left ventricular ejection fraction was 22%. She was transferred to our institution for evaluation and consideration of cardiac transplantation. After discussion of possible treatment options, the pacing system was upgraded to a resynchronization pacemaker, using bipolar left ventricular lead and incorporating the abandoned atrial lead into the system ( Figs. E27-8 and E27-9 ). The paced QRS duration shortened from 150 msec to 100 msec ( Figs. E27-10 and E27-11 ) and echocardiography revealed markedly improved ventricular synchrony and systolic ventricular function ( Fig. E27-12 , Video 27-3 ). Along with the immediate improvement, she had continued normalization of ventricular size and function, with normal growth and development over the following 2 years.

Lead Implantation Technique

Pediatric patients and patients with CHD require a higher proportion of epicardial leads and atypical lead configurations than adult cardiology. In particular, epicardial leads are more common. Reasons for epicardial placement include variations in venous and intracardiac anatomy as well as the opportunity for placement of leads at the time of open-chest surgical intervention.

The technique for placement of standard transvenous leads is described in Chapter 26 . As in adult patients, transvenous lead placement in children is typically performed in the right atrium and in the right ventricle with routine access through the subclavian, axillary, cephalic vein, or a similar branch vein of the left upper extremity. The right arm can be used if the patient is left-hand dominant or has another preference for right-sided implantation. A left superior vena cava is present in 0.3% of the population, and its incidence is higher in the presence of CHD. In its most typical form, the left superior vena cava continues to the coronary sinus, draining into the right atrium at the os of the coronary sinus; however, other variations exist. The higher frequency of this finding in CHD prompts most implanters to verify the status of an intact left subclavian vein before creating a pocket for a transvenous system. There are several methods of verifying an intact venous pathway, both invasive and noninvasive. Transthoracic echocardiography can be sufficient without the need for ionizing radiation exposure; however, many implanters prefer to perform peripheral venography at the time of implantation using an ipsilateral arm vein before making an incision. An injection of a small amount of radiopaque contrast allows clear visualization of the venous course under fluoroscopic guidance in order to plan a safe and accurate access approach ( Fig. 27-1 ). Three-dimensional noninvasive imaging (CT or MRI) and/or cardiac catheterization performed before implant can be used to determine vascular size and patency or to delineate an appropriate anatomic course. The absence of an intact left subclavian vein requires adjustments in the implantation technique. Right-sided approaches are typically chosen instead; however, it is possible to implant a lead in the right atrium and/or right ventricle through a persistent left superior vena cava to coronary sinus ( Fig. 27-2 ). This approach adds technical difficulty to both implantation and eventual lead extraction.

The location for optimal deployment in the right atrium is similar to what has been described in adult medicine. In postsurgical patients, the right atrial appendage may have been altered or excised during bypass cannulation and so a discrete appendage may not be available to receive the lead. An alternative position with acceptable pacing and sensing characteristics can usually be found. The literature in adults has been extensive regarding optimal location for right ventricular pacing in order to minimize the concern for pacing induced ventricular dysfunction. This research has been augmented by studies specifically in children and young adults. Right ventricular free wall pacing has been demonstrated to be inferior in several studies. Although in adults, resynchronization systems are superior to right ventricular apical systems, thus far, no clinical difference has been demonstrated in long-term ventricular function between placement of a pacing lead in the right ventricular apex and several locations for pacing in the right ventricular septum.

Size considerations are critical for transvenous leads in the pediatric community. Devices have been implanted in children as small as 2.3 kg. However, the implanter must consider not only whether he or she has the technical skill to access the relevant vessel, deploy the lead, and create a pocket that will not erode, but also the long-term implications of vessel thrombosis, stenosis, and vascular access for the child ( Fig. 27-3 ). In general, pediatric patients will need leads for many years and require additional procedures on their leads and devices at a higher rate than adult patients. Most implanters determine whether a child is appropriate for a transvenous device by considering the size and body habitus, the number of leads required, and whether an ICD system is required. A common lower limit of patient weight for any transvenous system is 10 to 15 kg; however, this lower limit varies substantially from center to center, and transvenous devices have been implanted successfully in infants. Because the alternative is usually an epicardial system, with its more invasive approach and longer recovery time, these decisions remain individualized to the physician and family being considered. The literature has not demonstrated any firm patient size cut-off values.

When placing leads in a young patient, the implanter should consider leaving sufficient slack in the lead to allow it to elongate appropriately as the child achieves linear growth. However, as children grow, even perfectly placed leads may become taut and may eventually fracture from linear strain. Even when dramatically elongated, the chest x-ray appearance of the lead alone should not be sufficient to schedule extraction. Leaving the appropriate amount of slack in the lead at the time of implantation is more art than science and should take into account the likely amount of linear growth left to the patient, but not leave so much lead in the heart to permit complications. Atrial leads with too much slack may prolapse across the tricuspid valve and impair its function ( Video 27-1 ). Ventricular leads with too much slack may prolapse into the pulmonary outflow tract where they may also interfere with valve function, cause ventricular ectopy, or increase the systolic outflow gradient. (See Case Study 27-3 for an example of a prolapsing atrial lead.) Both atrial and ventricular lead prolapse can occur after the patient has left the operating table and, depending on impact on valve function, may require reoperation for repositioning.

Case Study 27-3

Transition From Epicardial to Endocardial Implantable Cardioverter Defibrillator

This case describes a 13-year-old young man with genotype positive, phenotype positive catecholaminergic polymorphic ventricular tachycardia (CPVT). He originally presented at age 3 with syncopal episodes and an epinephrine stress test was positive. He was started on β-blockers, with excellent heart rate control. At age 7, he was playing vigorously. His eyes rolled back and he collapsed in the middle of playing. He was initially nonresponsive, but recovered spontaneously, without CPR.

His weight was 19.9 kg and a dual-chamber epicardial implantable cardioverter-defibrillator (ICD) was placed for primary prevention in the absence of documented arrhythmia. A ventricular coil (Medtronic 6937A) was placed in the transverse sinus and was sewn to the pericardium. The pulse generator was placed in a right subrectus abdominal position. Defibrillation threshold (DFT) testing was successfully performed twice with a 15-J margin. Six months after placement of the epicardial system, he had polymorphic ventricular tachycardia (VT) for which the first shock failed to terminate the arrhythmia. A chest x-ray showed a change in position in the high-voltage coil ( Figs. E27-13 and E27-14 ). A second pericardial high-voltage coil was added on the lateral surface of the left ventricle and DFT testing was performed successfully.

During the next 6 years, he received four shocks. These included shocks for sustained ventricular fibrillation that may have been life-saving ( Fig. E27-15 ) but also included a shock for polymorphic VT where it was less clear that the shock was life-saving ( Figs. E27-16 , E27-17 , E27-18 ). He was eventually maintained on atenolol 3 mg/kg/day and flecainide 160 mg/m ² /day with exercise restriction and no further arrhythmia for several years. At 13 years of age and at 35 kg weight, his ventricular lead fractured and he received a dual chamber ICD (Medtronic 3830 atrial and St. Jude 7122Q ventricular transvenous leads). Additional atrial and ventricular lead length was left in place for growth, complicated by prolapse of the “belly” of the atrial lead through the tricuspid valve and into the right ventricular outflow tract ( Figs. E27-19 and E27-20 ). Echocardiography demonstrated new tricuspid regurgitation since lead placement ( Videos 27-4 and 27-5 ). A follow-up procedure was performed to revise the system. The leads were pulled back to decrease the intracardiac lead length, but neither lead fixation screw was removed and the tips of the leads remained in the same position. Follow-up chest radiographs showed the leads with less intracardiac lead length and tricuspid regurgitation was improved ( Figs. E27-21 and E27-22 ).

Anatomic and surgical history must be considered before planning lead implantation in patients with complex CHD. In these patients, implanters should review prior surgical notes in order to ensure that the planned transvenous path remains open. Three-dimensional imaging can be helpful in complex anatomy. The presence of an intra-atrial baffle in those patients who underwent an atrial switch operation (Mustard or Senning procedures) has dominated atypical transvenous lead implantations in CHD for the last 30 years. In this anatomy, the superior and inferior venae cavae are baffled to one AV valve (typically a mitral valve) and the pulmonary vein efflux is allowed to flow around the baffle to enter in the other AV valve (typically a tricuspid valve). The implanter must guide the lead through the appropriate anatomic landmarks before affixing it in place in the (left) subpulmonary atrium or ventricle. Additional considerations include assessing for obstructions and/or right-to-left shunt across the baffle before implantation, weighing the risks and benefits of baffle leak closure before the procedure, and assessing for preimplantation stenosis in the superior limb of the systemic venous baffle. The frequency of atrial switch operations has plummeted since the development of the arterial switch operation for {S,D,D} transposition of the great arteries. However, so-called “double switches” for congenitally corrected transposition of the great arteries maintain a baseline incidence of potential pacemaker implantations in this anatomy. In addition, the general principle of advanced procedural planning in patients with complex congenital anatomy and a history of complex surgeries remains valuable.

A second major anatomic consideration for transvenous lead implantation is in single-ventricle anatomy. In these patients, the typical endpoint is the connection of the superior and inferior venae cavae to the pulmonary circulation. By age 4 years, most patients have received a superior cavopulmonary connection, which precludes transvenous ventricular lead placement from above. The completion of the Fontan palliation with connection of the inferior vena cava to the pulmonary arteries can occasionally reestablish opportunities for transvenous pacing from a subclavian approach. When transvenous pacing is contemplated, the details of the patient's specific operation usually determine whether atrial tissue is available for transvenous pacing. However, in the majority of single-ventricle cases requiring pacing, an epicardial approach is chosen. In addition, the long-term sequelae of even small thromboembolic events are worth considering in the setting of a passive circulation without a subpulmonary ventricle. Consideration of transvenous pacing in single-ventricle anatomy is often performed with the benefit of expert consultation from an electrophysiologist with relevant experience.

One recent study has suggested that the presence of a patent foramen ovale (PFO) is a risk factor for later stroke in patients with transvenous leads, rapidly contrasted by another study which failed to show any difference. PFOs (and left-to-right shunts in general) are very common in pediatric patients and patients with CHD, and it is unclear whether these may at times reverse and become transient right-to-left shunts. In structurally normal hearts, the rate of a PFO is higher in childhood than in adult life. In addition, in complex CHD, some left-to-right shunt often remains after successful surgical repair. The stroke risk of small left-to-right shunts has not been independently studied in a pediatric population. The baseline rate of stroke in pediatric patients is so much lower than in adult patients that it is not yet clear if the risks of adding a transvenous atrial or ventricular closure device are outweighed by the long-term stroke risk. In addition, it is unclear whether standard echocardiography, contrast echocardiography, or transesophageal echocardiography should be routine in pediatric device implantation, nor whether these small shunts should all be closed if they do exist in children.

In residual surgical shunts, the technique to close a shunt may be more difficult than in a centrally located atrial septal communication. A retrospective multicenter review of adults with CHD and intracardiac shunts concluded that transvenous leads were an independent predictor of systemic thromboembolic events. When these communications exist and are amenable to closure with an occlusion device, a covered stent, or other transvenous approach, the best approach may be to close them. However, when closure is not technically possible or if the closure carries unacceptably high risks, the physician must determine the relative risks of no device, placing a transvenous lead, or an epicardial or hybrid approach. Although chronic systemic anticoagulation seems intuitively likely to decrease stroke risk in the setting of transvenous leads with a right-to-left shunt, this has not been demonstrated in the literature. Antiplatelet therapy with aspirin did not affect the stroke rate in the study cited above.

Fully deployable leadless pacing systems, without transvenous leads, remain in development and have just begun adult human implantation trials. The size of the devices and delivery systems are too large in these first-generation systems for use in pediatric patients yet. Although these are appealing to consider for this population, it is not yet clear what the implications will be for younger patients who require many years of therapy. In particular, device longevity, extraction of chronic devices, and the tolerance for multiple devices in the same anatomic chamber will have to be determined.