Double Chambered Right Ventricle

Double-chambered right ventricle (DCRV), also known as divided right ventricle or anomalous right ventricular muscle bundle, is a complex and rare congenital heart disease. It is characterized by the division of the right ventricular (RV) cavity into two distinct successive chambers by a hypertrophied muscular bundle. This anomalous muscle bundle traverses the RV, creating an obstruction and leading to a high-pressure proximal (inflow) chamber and a low-pressure distal (outflow) chamber. The muscular bundle may cause obstruction either at the RV apex or at the RV outflow tract (RVOT). The typical morphology of a morphologically right ventricle includes inlet, apical trabecular, and outlet components, with coarse trabeculations. In DCRV, this muscle bundle results in a narrowing of the proximal infundibular os. The infundibulum, which is the outflow tract of both ventricular sinuses, is normally incorporated mostly into the RV. In DCRV, the hypertrophied septal band and deviated conal septum contribute to this two-chambered RV variant.

• • The RV is partitioned into two chambers: a proximal high-pressure chamber and a distal low-pressure chamber.

  • This division is caused by the presence of an abnormal muscular band. This can either be an excessively situated moderator band or another type of completely abnormal muscular band.

  • When these muscular bands are very developed, they can create intraventricular right obstructions and right intraventricular stenoses.

  • This condition, characterized by hypertrophied muscle bundles dividing the right ventricle into high- and low-pressure chambers, results in subinfundibular obstruction and elevated right ventricular pressures into the proximal chamber, which can transmit to the right atrium, and systemic veins. These patients may become blue due to right to left shunting at the proximal chamber VSD (if present), or inter-atrial shunt. They may have hepatomegaly if there is systemic venous congestion.  

Associated Conditions: 

DCRV is frequently associated with a ventricular septal defect (VSD), and sometimes with pulmonary valve stenosis. It can also be seen in the context of other complex congenital heart diseases, such as Tetralogy of Fallot (TOF), where DCRV is sometimes considered a morphological feature. Cases have been reported where DCRV develops after repair of Tetralogy of Fallot. Other associated conditions may include an aneurysm of the ventricular septum, an aneurysm of the sinus of Valsalva, accessory tricuspid valve tissue, cardiac tumours, and RV hypertrophy secondary to subpulmonary stenosis. The distance between the pulmonary valve and the moderator band may also be associated with the development of DCRV.

• • DCRV can arise from an excessively situated moderator band or a totally abnormal muscular band that effectively bisects the ventricle.

  • It is sometimes observed in conjunction with a ventricular septal communication (VSD). In some cases, if a VSD was present, it might have gone unnoticed because it closed spontaneously.

Hemodynamics and Pathophysiology: 

The primary hemodynamic consequence of DCRV is the obstruction to blood flow within the right ventricle, leading to a significant pressure gradient between the two chambers. This high pressure in the proximal RV chamber necessitates surgical resection because the obstruction tends to progress over time. In cases where a VSD is associated, the pressure gradient across this defect and the direction of blood flow are important considerations. The VSD seen in DCRV is typically membranous. However, muscular and malalignment defects are also found. The VSD often communicates with the proximal high-pressure RV sinus chamber. The obstruction caused by the anomalous muscle bundles is progressive, and this progression in DCRV can lead to a decrease in the amount of left-to-right shunting across the VSD. In the most severe cases of DCRV, the shunt across the VSD can even reverse. VSDs in patients with DCRV may also undergo spontaneous closure. It is widely believed that DCRV cases presenting with an intact ventricular septum may have had a VSD that closed spontaneously.

Left Ventricular Outflow Tract (LVOT) Obstruction in DCRV

Left ventricular outflow tract (LVOT) obstruction is a concern in some patients with DCRV, and its presence can have several implications:

• LVOT obstruction can occur before, concomitant with, or even years after surgical repair of DCRV. This highlights the need for follow-up assessment of the LVOT in patients with DCRV.

• DCRV is commonly associated with discrete subvalvar aortic stenosis.

• If a large VSD is present along with LVOT obstruction (e.g., in cases of Interrupted Aortic Arch or Coarctation of the Aorta with VSD), the increased afterload on the left ventricle can lead to a large left-to-right shunt and result in early and severe cardiac failure.

• Severe LVOT obstruction can be profound, potentially mimicking hypertrophic obstructive cardiomyopathy, and may result in ductal-dependent systemic blood flow.

Causes of LVOT Obstruction in DCRV:

LVOT obstruction in patients with DCRV or conditions that share similar anatomical/physiological features can arise from several mechanisms:

• Discrete Subvalvar Aortic Stenosis: DCRV, with or without an associated membranous VSD, is frequently linked with discrete subvalvar aortic stenosis. This type of subaortic stenosis can also occur in perimembranous VSDs, especially with aneurysm formation, and may progress or cause aortic valve damage if left unrepaired.

• Muscular Obstruction/Septal Deviation: LVOT obstruction can be caused by the posterior deviation of the infundibular septum and prominent anterolateral muscle, which may result in a circumferential "tunnel" stenosis. This deviation of the conal septum can protrude into the subaortic area.

• Post-Surgical Development: Subaortic obstruction can develop after surgical correction of DCRV. In cases of Double Outlet Right Ventricle (DORV) repair (which shares some characteristics with DCRV and Tetralogy of Fallot), a muscular conus between the mitral and aortic valves, or the length and acutely angulated nature of an intraventricular baffle, are identified as important predictors of postoperative LVOT obstruction.

• Reduced Aortic Flow during Fetal Life: In conditions like Taussig-Bing anomaly (a variant of DORV with subpulmonary VSD), aortic arch obstructions such as coarctation or interrupted aortic arch are common with subaortic stenosis, and are assumed to be related to reduced aortic flow during fetal life.

• Associated Anomalies and Malalignment: Malalignment of the edges of a VSD can lead to outflow tract obstruction upon closure. In some forms of DORV, the conal septum can deviate into the subaortic region, leading to subaortic stenosis.

Clinical Manifestations 

The clinical manifestations of DCRV closely resemble those of pulmonary valvular or infundibular stenosis. Patients typically present with a loud, grade 3 to 5/6 ejection systolic murmur heard along the upper and mid-left sternal border. Two-dimensional echocardiography is crucial for diagnosing DCRV and reliably documenting the hypertrophied anomalous muscle bundle. Key echocardiographic findings and assessment points include:

• Visualization of the hypertrophied anomalous muscle bundle as a horizontal or oblique structure between the right ventricular free wall and the interventricular septum (IVS).

• Subxiphoid left ventricular short-axis view is particularly useful for visualizing the entire RVOT and the anomalous muscle bundle.

• Parasternal short-axis view can also document the prominent anomalous muscle bundle causing narrowing of the proximal os infundibulum.

• Color flow mapping helps in visualizing the level and direction of obstruction.

• Defining the type of subpulmonary stenosis (e.g., discrete fibromuscular obstruction or hypertrophic cardiomyopathy).

• Determining the morphology of the obstruction in relation to the tricuspid and pulmonary valves.

• Assessing the presence, location, flow direction, and pressure gradient of any associated VSD.

• Evaluating the degree of tricuspid regurgitation.

• M-mode echocardiographic features have emphasized the importance of false anterior or septal-aortic overriding.

Management and Treatment 

Surgical resection of the anomalous muscular bundle is typically indicated as soon as the diagnosis is made because the obstruction progresses over time. Any other associated anomalies, such as VSD or pulmonary valve stenosis, are also repaired during the procedure. 

Echocardiographic example

The example demonstrates a bilateral superior caval veins (SVC ) with absence of a bridging vein. The left SVC persists and drains into a dilated coronary sinus. Echocardiography reveals physiologic tricuspid regurgitation with a right ventricle–to–right atrium peak gradient of 57 mmHg. A small restrictive perimembranous ventricular septal defect (VSD) is present, measuring 0.33 × 0.38 cm, with bidirectional shunting and a peak gradient of 71 mmHg. There is a severe double-chambered right ventricle (DCRV) with significant right ventricular outflow tract (RVOT) obstruction, producing a peak systolic gradient of 100 mmHg. Additionally, there is mild left ventricular outflow tract obstruction due to a fibromuscular shelf, with a peak gradient of 15 mmHg. The pulmonary valve is structurally normal, although increased flow velocity is observed in the main pulmonary artery, with a peak gradient of 74 mmHg. 

PLAX outlining that there is a dilated coronary sinus. This particular example has a concomitant bilateral SVC. The increased RA pressure and the presence of a left sided SVC to coronary sinus, combined, will increase significantly the caliber of the coronary sinus. 

In the PLAX, we can appreciate the narrowing within the RV delineating the orifice of the double-chambered RV and where the acceleration/turbulence of flow initiates..

The membranous VSD is observed and is small in size, with some restriction to flow and pressure equalization. 

Apical view outlining the TR, as well as the RV chamber narrowing. 

Pulmonary valve is well developped. The leaflets are thin and open normally. 

Subcostal views outlining the RV chamber narrowing.