Double-Chambered Right Ventricle

Definition and Morphology

Double-chambered right ventricle (DCRV) is characterized by anomalous or hypertrophied muscle bundles, which cause a form of subvalvar right ventricular outflow tract (RVOT) obstruction, dividing the right ventricle (RV) into a high-pressure proximal chamber and a low-pressure distal chamber. Anatomic descriptions of what was thought to be DCRV date back to at least the 1860s, but it was not until 100 years later, in the 1960s, that the hemodynamic abnormalities and surgical approaches were formalized.

The RV is a tripartite structure consisting of the inlet (sinus portion), the trabecular apex (body), and the outlet (conus or infundibulum). The mechanism of obstruction in DCRV may be due to (1) anomalous muscle bands, (2) hypertrophied endogenous trabecular tissue, or in some cases, (3) an aberrant moderator band. These obstructions may rarely sequester the inlet portion, divide the trabecular apex via accessory septoparietal bands or obstructive muscular bands to the septomarginal complex, or sequester the subpulmonary infundibulum. Regardless of the cause, all forms of RV obstruction in DCRV are subinfundibular, making DCRV distinct from pulmonary stenosis with an intact ventricular septum, where hypertrophied muscle bundles protrude from the walls of the RV infundibulum and tetralogy of Fallot (TOF; see Chapter 43 ), in which there is anterior malalignment of the infundibular septum.

Although the obstructing muscle bundles likely have an underlying congenital anatomic substrate, there may be an acquired component that occurs in patients who have a ventricular septal defect (VSD). The presence of a VSD may cause progressive RVOT obstruction over time through hypertrophy of anomalous muscle bundles. One explanation for the development of DCRV in the setting of a VSD is that, in individuals with a genetic susceptibility to cellular proliferation, certain hemodynamic factors may stimulate progressive anomalous RV muscle bundle hypertrophy, causing insignificant RVOT obstruction earlier in life and ultimately severe obstruction in adulthood. A retrospective study of adolescents and adults with unrepaired DCRV showed, by Doppler echocardiography, that the rate of progression of midventricular obstruction ranged from 3.3 to 11.1 mm Hg per year with a mean of 6.2 mm Hg per year. Postoperative histologic evaluation of the anomalous muscle bundles has shown subendocardial thickening, disarrayed myocardial tissue, heterogeneous staining of myofilaments, vacuolization, nuclei of irregular size, and partial replacement of myocardium with fibrous tissue.

The majority of patients with DCRV have coexisting cardiac lesions: (1) VSD (60% to 90%), with the majority being perimembranous followed by muscular and subarterial; (2) pulmonary valve stenosis (∼40%); (3) atrial septal defect (∼17%); (4) double-outlet RV (∼8%); and (5) TOF. Adult individuals presenting with isolated DCRV may have had a VSD earlier in life that spontaneously closed from mechanisms such as adherence of tricuspid valve tissue, fibromuscular proliferation adjacent to the anomalous muscle bundles, or hypertrophy of the anomalous muscle bundles and/or ventricular septum. In a subset of patients, the combination of DCRV and discrete subaortic stenosis may occur with an incidence of approximately 0.5%, nine times the expected rate, likely due to the hemodynamic disturbances from the commonly associated VSD.

The location of the VSD relative to the obstructing muscle bundles plays a role in the flow profile and clinical features. If the VSD is located proximal to the obstructing muscle bundles (∼60% of cases), pulmonary blood flow is decreased and may lead to right-to-left shunting across the VSD causing cyanosis in the setting of severe obstruction. Echocardiographic data has shown that a shorter distance between the pulmonary valve and moderator band in infants with a VSD may predict development of DCRV later in life.

Although DCRV was only recognized recently as a clinical entity, there are small studies that may provide insight into the natural history. The degree of right ventricular obstruction within the RV often determines the clinical features and presenting symptoms, and may make distinguishing the diagnosis from other entities like TOF or VSD with pulmonary stenosis challenging. A retrospective review of 50 patients followed at two tertiary adult congenital heart disease centers was performed, and a portion of the patients (17) were unoperated. Asymptomatic patients had a median age of 26 years, whereas those with symptoms presented at a median age of 40. Interestingly, the mean intraventricular gradient on the most recent transthoracic echo was not significantly different between symptomatic and asymptomatic patients. In addition, 13 of the 17 unoperated patients also showed no more than mild tricuspid regurgitation on their most recent echocardiographic assessment. There were no cases of sudden death in the unoperated adult subpopulation. Many studies emphasize the progressive nature of DCRV leading to RV impairment if not treated, whether demonstrated on repeat preoperative catheterization or echo.

Genetics and Epidemiology

DCRV is an uncommon cardiac anomaly with an incidence of approximately 0.5% to 2% of all congenital heart disease. It has not been associated with any particular genetic abnormality, although sporadic cases have been associated with Noonan syndrome and Down syndrome. There is no known pattern of inheritance, association with teratogen exposure, epidemiologic pattern of occurrence, gender predilection (45% to 75% males ), ethnic or racial background, or geographic origin. Various series have shown an association of DCRV with VSD and TOF. The development of DCRV occurs in approximately 3% to 10% of patients with VSD and in approximately 3% of patients with TOF.

Presentation and Diagnosis

The majority of DCRV cases with significant RVOT obstruction are identified and treated during childhood or adolescence. The initial clinical presentation varies, with the degree of intraventricular RV obstruction often determining the clinical features and presenting symptoms, and potentially complicating the distinction between DCRV and other entities like TOF or VSD with pulmonary stenosis. Most patients present with an asymptomatic systolic murmur. The diagnosis of DCRV may be missed if the loud systolic murmur at the left sternal border is attributed to a restrictive VSD. Symptoms may include cyanosis, dyspnea, failure to thrive, excessive sweating, and congestive heart failure. Symptoms are also dependent on any associated VSD (presence, location, and size) and the degree of RVOT obstruction, as well as other associated cardiac anomalies. The primary murmur heard is a grade 2 to 3/6 harsh systolic ejection murmur at the left sternal border in the second intercostal space. Approximately 25% of patients have an associated thrill. Almost all patients with significant obstruction have an RV heave. The first heart sound is single. The second heart sound is physiologically split with normal intensity of the pulmonary component. Other right heart failure physical findings such as the murmur of tricuspid regurgitation, increased jugular venous “V” wave, a right-sided gallop, and hepatomegaly are dependent on the severity and duration of the RVOT obstruction. If the right-sided failure is long-standing, there may lower extremity edema. Other physical findings depend on the presence of associated cardiac abnormalities.

Electrocardiogram (ECG) findings include right ventricular hypertrophy in the majority of patients, incomplete right bundle branch block in approximately 25% of patients, and right axis deviation in a few patients. There is typically a prominent R wave in lead V ₃ R and V1 with an absence of prominent S waves in the left precordial leads. It is suggested that the ECG findings are related to the absence of distal right ventricular chamber hypertrophy. Some patients may have a normal ECG. In 40% of patients in one series, the only ECG finding suggestive of right ventricular hypertrophy was an upright T wave in V ₃ R. Because this is typically not seen in patients with an isolated VSD or TOF, it may be a valuable distinguishing feature if present. A diagnosis of DCRV should be considered when right ventricular hypertrophy is apparent without signs of infundibular hypertrophy or valvular pulmonary stenosis.

Even though there may be clinical, physical, and ECG findings in patients with DCRV, the only reliable methods for confirming the diagnosis are noninvasive imaging, cardiac catheterization with hemodynamic assessment and angiography, and direct inspection during surgery or autopsy. In younger patients with adequate echocardiographic windows, transthoracic echocardiography (TTE) is the primary method of diagnosing DCRV ( Fig. 46.1 ). Cross-sectional and Doppler echocardiographic evaluation using a subcostal window can delineate the anatomy of DCRV in very young patients, but adequate imaging may be difficult to obtain in older patients. If TTE windows are suboptimal, transesophageal echocardiography (TEE) is diagnostic in most cases ( Fig. 46.2A ), and allows calculation of the interventricular pressure gradient by Doppler analysis. Cardiac magnetic resonance imaging (cMRI) provides excellent images to define the RV anatomy and the functional characteristics of DCRV ( Fig. 46.3 ). Its use is becoming more common, especially in patients with suboptimal echocardiographic windows. Cardiac catheterization with hemodynamic assessment and angiography ( Fig. 46.4 ) may be necessary if the diagnosis remains in question, or other information, such as coronary anatomy, is needed before proceeding to surgical repair.

Management

Surgical intervention is generally recommended in patients with DCRV and significant RVOT obstruction, regardless of the age at diagnosis. The associated cardiac defects that are often present will usually require repair as well. Definitive surgical repair is required given that the obstruction is a fixed anatomic structure. Delaying surgical repair is not indicated from a cardiovascular standpoint, unless the degree of RVOT obstruction is mild, since DCRV is frequently a progressive condition resulting in more prominent hypertrophy of the anomalous muscle bundles and proximal RV chamber, which leads to progressive obstruction. Repair becomes more complicated as symptoms, hypertrophy, and fibrosis progress.

Surgical repair consists of resection of the obstructing anomalous RV muscle bundles, partial resection of the septal and parietal bands, and resection of any hypertrophied trabecular muscle that may impede RV outflow. When a VSD is present, it is closed with a patch or direct suture, and any other associated defects are repaired. Depending on the presence and type of associated defects, DCRV repair is generally straightforward. It is usually approached through a median sternotomy incision with cardiopulmonary bypass and cardioplegic arrest. The RV is accessed through a right atriotomy or a combination of pulmonary arteriotomy and right atriotomy. A longitudinal right ventriculotomy was used in the past, but is generally avoided to decrease the risk of early and late complications. Intraoperative TEE with Doppler is used after repair and discontinuation of cardiopulmonary bypass to assess the hemodynamic result (see Fig. 46.2B and C ). In most cases, the RVOT gradient can be decreased to less than 10 mm Hg.

Surgical repair should be considered if the estimated peak midventricular gradient by Doppler is greater than 60 mm Hg (Doppler jet velocity of ∼3.87 meters per second) or the mean Doppler gradient is greater than 40 mm Hg, regardless of symptoms. If patients have symptoms attributable to DCRV, surgical repair is recommended due to the progressive nature of the disease, if the estimated peak midventricular gradient by Doppler is greater than 50 mm Hg (Doppler jet velocity of ∼3.53 meters per second) or the estimated mean Doppler gradient is greater than 30 mm Hg. In addition, intervention should be considered in patients who have decreased RV function, arrhythmia, or right-to-left shunting via an atrial septal defect (ASD) or VSD. Any clinically or hemodynamically significant associated cardiac lesions should also be evaluated for potential repair, particularly if such lesions may cause problems postoperatively if left unrepaired. Other noncardiac comorbidities, such as renal, hepatic, and pulmonary dysfunction, need to be taken into account when determining the operative risk, especially in older adult patients with significant noncardiac risk factors. Patients with clinically significant coronary artery disease (CAD) may require concomitant coronary artery bypass grafting and will require special intraoperative attention to protect against right ventricular myocardial ischemia, if the right coronary artery is involved.

Those with coexisting right CAD and those with no evidence of VSD may be more likely to develop right-sided complications such as RV dysfunction and/or significant tricuspid regurgitation. Most adult patients studied in the medical literature after undergoing DCRV repair tend to have good mid- and long-term results with low postoperative morbidity and mortality.

In the current era, immediate postoperative complications are uncommon as are in-hospital and late deaths. The most important postoperative consideration after repair of DCRV is low cardiac output, which is likely related to RV trauma from extensive muscle bundle resection and can usually be managed with inotropic support until the ventricle recovers.

In general, medical management has only limited palliative benefits in symptomatic patients since the obstruction is a fixed anatomic structure, but can be attempted in cases when surgical risk is prohibitive. Medical management with beta-blocker therapy in atypical cases of DCRV with dynamic intraventricular obstruction or diuretics in patients with congestive heart failure are only palliative. Beta-blockade therapy in atypical cases of DCRV with dynamic intraventricular obstruction was shown in one case to improve symptoms and exercise capacity. Diuretics may palliate right-sided congestive heart failure symptoms.

Other options for interventional management are limited, although case reports have described other therapies. There is no routine, effective transcatheter therapy for DCRV. Percutaneous myocardial alcohol ablation of the obstructive muscle bundles has been performed in a similar method to that used in the management of hypertrophic obstructive cardiomyopathy. Percutaneous balloon dilatation of the midventricular obstruction has been attempted with partial relief of the gradient. These approaches are not as effective or definitive as surgical resection, but may be options in high-risk adults precluded from traditional surgical repair.

Although there are insufficient data to determine the true incidence of late reintervention in adults after repair of DCRV, it is likely low in the current era of surgical repair. Reintervention for recurrent RVOT obstruction after adequate surgical repair is rare, as the obstructing muscle bundles do not typically recur except in infant cases associated with TOF. The most common reasons for late reintervention include unrecognized discrete subaortic stenosis prior to the initial repair, aortic regurgitation, and residual VSD, which should be preventable with preoperative recognition of these associated defects.

Reintervention for recurrent DCRV involves resection of the residual obstructing muscle bundles similar to the primary repair. A reoperative sternotomy will require meticulous dissection given the potential for dense adhesions and adherence of the anterior RV wall to the posterior sternal table in patients with significant RV enlargement. The risk of other typical operative complications, such as intraoperative and postoperative bleeding, may increase. The approaches to reintervention for associated cardiac defects (eg, residual VSD, discrete subaortic stenosis, or aortic regurgitation) vary depending on the indication for reintervention, and are discussed in the appropriate chapters.