Double-Chambered Right Ventricle

Etiology

The etiology of these hypertrophied and obstructive muscle bundles remains unclear. Proposed mechanisms include:[9]

1. Acquired maladaptation to the increased flow velocity across the ventricular septal defect causing hypertrophy of the supraventricular crest that results in an acquired obstruction.
2. Superior displacement of the septomarginal trabecula or moderator band causes it to undergo progressive hypertrophy over time.
3. Extension of a muscular shelf from the septoparietal trabeculations to the trabecular component of the right ventricular apex in conjunction with other acquired factors results in the formation of obstructive muscle bundles.

Epidemiology

DCRV presents in 0.5% to 2% of all patients with congenital heart disease. No genetic pattern has been described.[10] DCRV has a 2:1 male-to-female ratio in infants presenting at birth.[11] 

DCRV might occur in up to 10% of children after correction of a ventricular septal defect, 3.1% of patients who have undergone repair of tetralogy of Fallot, and it can also present in adults with a prevalence of 2.1%.[12] These are considered "de novo" cases of DCRV.[2]

Pathophysiology

The abnormal, hypertrophied muscular tissue creates varying degrees of obstruction to flow within the right ventricular cavity and towards the right ventricular outflow tract. The right ventricular cavity is divided by the hypertrophied muscular tissue into two compartments: a high-pressure inlet portion with the tricuspid valve and a low-pressure outlet portion with the pulmonic valve. This right ventricular outflow tract obstruction type is considered sub-infundibular (ie, below the pulmonary valve), where flow must circumvent the hypertrophied muscle bundles within the right ventricular cavity.[2] 

Intracavitary right ventricular pressure gradients in patients with DCRV are commonly higher than 20 mm Hg, which generally increases over time. Therefore, nonobstructive anomalous muscle bundles may later become obstructive.[13]

History and Physical

Most cases of DCRV are diagnosed in childhood. Patients with isolated DCRV and mild-to-moderate right ventricular outflow tract obstruction can be asymptomatic and mimic the most common clinical presentation of pulmonary valve stenosis; these patients are brought to the cardiologist's attention due to a harsh holosystolic murmur often accompanied by a thrill, that is best heard along the left sternal border.[14][15] Another common physical finding is cyanosis observed in patients with atrial septal defect due to right-to-left shunting, as elevated pressures from the inlet portion of the right ventricle transmit to the right atrium.[16] 

Dyspnea and exertional fatigue are the most common findings in adult patients with DCRV due to the inability of the right ventricles to increase their output in response to exercise. If RVOT is severe, the patient may also experience light-headedness, chest discomfort, palpitations, and syncope.[13] Occasionally, patients with moderate-to-severe obstruction to flow may experience sudden death with strenuous exercise. These ominous symptoms are deemed secondary to right heart failure with inadequate cardiac output that leads to decreased myocardial perfusion. This coronary artery insufficiency generates ischemia, which then triggers ventricular arrhythmias that can precede sudden death.[17]

Evaluation

Electrocardiogram

The electrocardiogram (ECG) usually shows right ventricular hypertrophy and right axis deviation [10] but may also have a right bundle branch block (RBBB) pattern.[13] However, in the absence of right ventricular hypertrophy on the ECG, some patients have described upright T waves in V3R.[18]

Echocardiography

Transthoracic echocardiography is the initial diagnostic modality to demonstrate a DCRV and measure intracardiac gradients, especially in pediatric patients. During systole, the space between these muscle bundles decreases, and obstruction to flow is magnified, which is most frequently and readily quantified noninvasively by echocardiography. These turbulent flow patterns can be seen by color Doppler using transthoracic or transesophageal echocardiography. These imaging modalities use pulsed and continuous wave Doppler to measure the gradient across the hypertrophied muscle bundles and can quantify and compare the obstruction to flow as time passes.[10][19][20]

When transthoracic echocardiography is limited due to body habitus, especially in adult patients, a DCRV can be missed, particularly when presenting concomitantly with other congenital heart defects. Additional imaging methods such as transesophageal echocardiography, cardiac magnetic resonance imaging, or cardiac computed tomography can be very helpful in this instance.[10][20]

Cardiac Magnetic Resonance Imaging

Cardiac magnetic resonance imaging (CMR) is a noninvasive, radiation-free diagnostic modality that can be helpful as an adjunct to transthoracic or transesophageal echocardiography, especially in the adult population in whom noninvasive cardiac imaging can be challenging due to body habitus. CMR can also be used when a DCRVis missed due to additional cardiac lesions, as CMR can help confirm any associated cardiac anomalies. It can also help quantify the pressure gradient in the right ventricle and evaluate the wall thickness of the right ventricle.[5] 

Cardiac Computed Tomography

In those unable to undergo a CMR (such as patients with claustrophobia, those with implants, or certain types of pacemakers and defibrillators), a cardiac computed tomography (CT) can also diagnose a DCRV.[21] 

Cardiac Catheterization

Historically, the diagnosis of DCRV was made by cardiac catheterization, where pressure data showed a low-pressure tracing in the pulmonary artery and the sub-infundibular chamber, in contrast to a much higher pressure (often supra-systemic) in the right ventricular apex. Angiography completed the diagnosis of this malformation.[22]

Treatment / Management

Current guidelines recommend considering surgical closure of the ventricular septal defect with resection of the hypertrophied muscle bundles in patients with moderate or greater right ventricular obstruction who have symptoms of heart failure, exercise limitation, or cyanosis. Guidelines also recommend surgery in asymptomatic patients with severe right ventricular obstruction with a pressure gradient greater than 40 mmHg between the proximal and distal compartments within the right ventricle.[3][9][23](A1)

Management is not as straightforward in asymptomatic patients due to the significant discrepancy between the echocardiographic-derived and invasively measured intracavitary right ventricular gradients, with a marked echocardiographic overestimation of this parameter. This is especially important since echocardiography has largely replaced cardiac catheterization for the diagnosis and hemodynamic evaluation of most congenital cardiac lesions.[10] Others advocate surgical closure of the ventricular septal defect with muscle bundle resection due to the generally progressive nature of the right ventricular obstruction in DCRV.[2](B2)

Beta-blockers have been reported to improve symptoms and exercise capacity in patients with DCRV if they have a dynamic obstruction in the right ventricle; thus, beta-blockers can be helpful as a presurgical adjunct.[24] Some patients with DCRV may also present with ventricular tachycardia, and this subset of patients can benefit from other antiarrhythmics or catheter ablation.[6] Some recommend an implantable cardioverter-defibrillator to reduce the arrhythmia burden for patients with preoperative or postoperative ventricular tachycardia or those unwilling to undergo surgical resection of the anomalous muscle bundles.[25](B3)

Differential Diagnosis

Entities that may accompany and may obscure a DCRV include those where the right ventricle is moderately to markedly hypertrophied, including tetralogy of Fallot, pulmonic valve stenosis, isolated ventricular septal defect, pulmonary valve stenosis with ventricular septal defect, and idiopathic hypertrophic obstructive cardiomyopathy on the right side of the heart.[26]

Prognosis

Children who undergo surgery for a DCRV are expected to have positive long-term outcomes and usually do not require reoperation for a recurrent intracavitary obstruction.[13] On the other hand, many adult patients with DCRV who choose nonoperative management also have low long-term morbidity despite high intraventricular gradients.[13] 

However, because this entity can be progressive [12] and outcomes after surgery are mostly positive with only possible mild sequelae, such as mild tricuspid regurgitation, some advocate surgical closure of the ventricular septal defect with resection of the hypertrophied muscle bundle even in asymptomatic patients.[2]

Complications

Complications after surgery are not commonly observed. However, after surgery, patients may be at risk for death from low cardiac output states or heart failure despite successful resection of the anomalous muscle bundle. They may also experience arrhythmias and right ventricular dysfunction.[27]

Development of a DCRVhas been described as a medium-term complication after tetralogy of Fallot repair in infants, with an incidence of 3.1%. In this instance, a progressive condition occurs when anomalous muscle bundles undergo hypertrophy or fibrosis. Reobstruction can be suspected when a loud systolic murmur is heard at follow-up, secondary to an increase in the gradient across the hypertrophied muscle bundles within the right ventricular cavity. It is attributed to anomalous muscle bundle hypertrophy or fibrosis requiring reoperation. Thus, continued follow-up of these patients is recommended.[28]

Another postsurgical complication is the failure to notice additional ventricular septal defects between the left ventricle and the high-pressure proximal portion of the right ventricle during corrective surgery. This can occur because hypertrophied muscle bundles can visually mask small ventricular septal defects on basic examination. In addition, similar pressures between the left ventricle and the right ventricular high-pressure chamber may not generate a Doppler flow gradient or a color Doppler flow in the preoperative transthoracic echocardiogram or the intraoperative transesophageal echocardiogram which is relieved postsurgical when the RV pressure drops.[29] If the shunt is small, the patient will most likely not require reoperation.[28]