Double-Chambered Right Ventricle

Like many other lesions associated with congenital heart disease (CHD), the terminology that surrounds double-chambered right ventricle (DCRV) has evolved over the past several decades. Double-chambered right ventricle was originally described more than 130 years ago. Clinical series began describing it extensively in the 1960s.

Double-chambered right ventricle is better understood as a form of septated right ventricle (RV) caused by the presence of abnormally located or hypertrophied muscular bands.

The abnormally located or hypertrophied muscle bundles divide the RV cavity into a proximal and a distal chamber. Those muscle bundles run between an area located in the ventricular septum, beneath the level of the septal leaflet of the tricuspid valve, and the anterior wall of the RV. Frequent associated lesions include ventricular septal defect (VSD), pulmonary valve stenosis, and discrete subaortic stenosis.[1]

As outlined by Restivo et al, several subtypes of divided RV are noted.[2] These subtypes include anomalous septoparietal band, anomalous apical shelf, hypertrophy of apical trabeculations, anomalous apical shelf with Ebstein malformation, and sequestration of the outlet portion of the ventricle from a circumferential muscular diaphragm in patients with tetralogy of Fallot. Double-chambered right ventricle, the most common form, is noted by the presence of anomalous muscle bundles (AMB) that divide the RV into two chambers. However, no uniformity is observed in the position of these anomalous muscle bundles or in the manner in which the RV is divided.

See the images below.

Anomalous muscle bundles divide the right ventricle (RV) into a high-pressure proximal chamber and a lower-pressure distal chamber. Evidence suggests that double-chambered right ventricle is an acquired disorder in those patients with appropriate substrate. Obstruction to pulmonary blood flow usually progresses with hypertrophy of the muscle and further obliteration of the RV cavity, although cases without progression of obstruction and even of spontaneous regression have been described.

The origin of anomalous muscle bands has been debated. The embryologic basis for double-chambered right ventricle was attributed to failure to incorporate bulbus cordis into the RV or an elevated hypertrophied moderator band. However, Byrum et al used the pattern of electrical activation to determine that muscle bundles were not the result of a displaced moderator band and suggested that activation of the double-chambered right ventricle is similar to activation of the normal heart.[3] Others, however, concluded that both the presence of bundle branch block in some patients and detection of a portion of the right bundle branch in a pathologic sample of the muscle bundle have proven the hypothesis that the moderator band is, in fact, the obstructing bundle.

A contemporary analysis of the origin of the muscle bundles determined the muscular shelf originates from the body of the septomarginal trabeculation. Two positions of muscle bundles are described as high (or horizontal) position and low (or oblique) position. Either position of the shelf divides the apical trabeculated RV in two. This same analysis determined that the normal moderator band widely varies and that the anomalous muscle bundles do not represent an early takeoff from the moderator band in most cases. In a review of surgical cases, 45% of cases had more than one or nondiscrete muscle bundles.[4]

Muscle bundles and the RV itself are usually lined with thickened endothelium. Other, less common, forms of divided RV include those in which a fibromuscular diaphragm or atrioventricular valve tissue partition the RV. These other forms include the anomalous septoparietal band, anomalous apical shelf, hypertrophy of apical trabeculations, anomalous apical shelf with Ebstein malformation, and sequestration of the outlet portion of the ventricle from a circumferential muscular diaphragm in patients with tetralogy of Fallot. These forms are not discussed in this article.

Associated defects are present in approximately 80-90% of patients; a ventricular septal defect (VSD) that involves the membranous septum is the most common defect described. A VSD may communicate with either the proximal or distal chamber, leading to a greater shunt in the latter situation. Development of RV outflow tract obstruction occurs in 3-7% of patients with membranous VSDs within the first years of life. The mechanism responsible for acquired RV obstruction may be progressive hypertrophy and obstruction from anomalous RV muscle bundles.

A well-known relationship is described among patients with RV outflow tract obstruction, membranous VSD, and subaortic stenosis. Vogel et al described 36 patients with membranous VSD and double-chambered right ventricle, 88% of whom had echocardiographic evidence of subaortic stenosis, with evidence of progressive left ventricular outflow tract obstruction.[5] Progression of subaortic stenosis may occur before or after VSD closure and/or muscle bundles are resected.

The next most common associated lesion is pulmonary valve stenosis. Various other associations have been reported, including double outlet RV, tetralogy of Fallot, anomalous pulmonary venous drainage, complete or corrected transposition of great arteries, pulmonary atresia with intact ventricular septum, and Ebstein anomaly. Double-chambered right ventricle has also been reported in patients with Down syndrome and Noonan syndrome, although differentiation from hypertrophic cardiomyopathy in the latter group is not straightforward.

Although Rowland et al considered patients in 4 groups, based on predominant physiology (pulmonary stenosis, tetralogy of Fallot, large VSD with left-to-right shunt, double-chambered right ventricle associated with other more hemodynamically significant lesions), most patients have moderate-to-restrictive VSD.[6] Most of the remaining patients present with tetralogy physiology or have significant associated lesions.

Natural history varies depending on the presence of associated lesions. Progressive obstruction of the RV outflow tract has been observed and can lead to RV failure, especially in the presence of a VSD. Several report diagnosis in asymptomatic adults in whom anomalous muscle bundles and intact ventricular septum may have been associated with a VSD that underwent spontaneous closure.

No inheritance pattern has been described, and no risk factors for developing the disease have been encountered.

Sporadic cases have been described in patients with Down syndrome and Noonan syndrome.

International data

Double-chambered right ventricle is relatively rare as an isolated anomaly; a large pediatric center typically diagnoses fewer than 10 cases per year. The lesion makes up approximately 0.5-2% of congenital heart disease and occurs in as many as 10% of patients with ventricular septal defect.[7]

Sex- and age-related data

Male-to-female ratio is 2:1.[1]

Presentation can be as early as the newborn period; however, mean age at diagnosis is in early childhood. Both fetal and adult cases have been reported.

Most patients with double-chambered right ventricle (DCRV) initially present with no symptoms.

The most common reason for referral is the detection of a murmur.

Clinically, patients with double-chambered right ventricle and no ventricular septal defect (VSD) resemble patients with isolated pulmonary valve stenosis.

When a VSD is present, the clinical picture relates to a VSD. Usually, the patient is diagnosed with a VSD or pulmonary outflow tract obstruction and, subsequently, may show signs of progression of the outflow obstruction, such as cyanosis, fatigue, and decreased exercise tolerance.

Rowland et al describe four physiologic groups (see Pathophysiology) with patients presenting usually with left-to-right shunt or tetralogy of Fallot physiology.[6]

Patients with severe right ventricle (RV) hypertension may present with cyanosis, RV failure, failure to thrive, and fatigue.

Association with other syndromes is well recognized, and double-chambered right ventricle may be found during their workup.

Most patients are nondysmorphic and acyanotic with normal peripheral examination findings. Auscultation reveals a variable intensity of the second heart sound.

A holosystolic ejection murmur, which peaks in intensity near midsystole, with greatest intensity at mid-left and upper-left precordial areas, characterizes double-chambered right ventricle.

An right ventricle (RV) heave, hepatomegaly, and tachypnea indicate RV hypertension.

Chest radiography

Chest radiography may reveal either a left-to-right shunt with increased pulmonary vascular markings or a severe right ventricle (RV) obstruction with diminished pulmonary vascularity. The usual arrangement includes atrial situs solitus, levocardia, and left aortic arch. Cardiomegaly may be seen in some patients.

Echocardiography

Echocardiography currently enables diagnosis on a 2-dimensional Doppler echocardiogram; before its advent, diagnosis of double-chambered right ventricle (DCRV) could not be made noninvasively. In infancy, subxiphoid imaging is optimal; parasternal short-axis views may be more useful in older patients. The cardinal feature is demonstration of muscle bundles that traverse the RV cavity, with an accompanying gradient starting proximal to the infundibulum. See the images below.

Wong et al described a "displacement index," which is determined by dividing the distance from the pulmonary annulus to the septal insertion of the moderator band by the tricuspid annulus diameter.[8] An index less than 1 may predict that infants with ventricular septal defect (VSD) are at risk of developing an obstruction from a displaced moderator band.

Transesophageal echocardiography has been used to define structures in older patients with poor windows.

Further evidence of double-chambered right ventricle includes the angiographic demonstration of a filling defect dividing the RV, as well as the absence of infundibular hypoplasia. Double-chambered right ventricle should be differentiated from tetralogy of Fallot by the absence of infundibular hypoplasia and pulmonary artery anomalies in double-chambered right ventricle. Entering both components of the RV is important; ideally, perform angiography from the RV apex in the frontal and lateral projections with craniocaudal angulation.

MRI and CT scanning

Magnetic resonance imaging (MRI) and contrast computed tomography (CT) scanning have been used in addition to echocardiography. These modalities may add to the anatomic delineation of the muscle bundles, although echocardiography is typically sufficient.

Electrocardiography (ECG) findings in double-chambered right ventricle were reviewed in one series of 30 patients.[9] Almost 50% of the patients had evidence of right ventricular hypertrophy (RHV), 40% of them demonstrated an upright T wave in V3 R in the absence of other findings of RVH, and the remainder had normal ECG findings. Similar findings are reported in other series.

Cardiac catheterization still has a role in ruling out other lesions that may be difficult to detect and that may influence operative strategy, although the diagnosis can be made accurately based on echocardiography findings. Recording of the pressure gradient (which widely varies in magnitude) within the right ventricle cavity, remote from the infundibulum, strongly suggests a diagnosis of double-chambered right ventricle.

Symptoms of double-chambered right ventricle (DCRV) that require therapy are generally an indication for operative repair.

In the presence of a ventricular septal defect (VSD), a significant left to right shunt can be present, requiring antifailure treatment, particularly if the muscle bundles are not sufficiently obstructive to reduce pulmonary blood flow.

The first successful surgical repair was reported in 1962. The initial approach was through a ventriculotomy; contemporary series describe both transatrial and transventricular approaches.[10, 11]

Time to intervene naturally depends on the associated lesions; the current practice is to address associated lesions (ventricular septal defect [VSD], subaortic stenosis, pulmonary stenosis) at the time of double-chambered right ventricle repair.

In the absence of a significant associated lesion, observation may be appropriate as long as the intracavitary gradient is not greater than 40 mm Hg and the degree of obstruction is not progressive.

Although attempted, balloon dilatation likely has no role in the management of double-chambered right ventricle. Tsuchikane et al reported a patient who underwent a percutaneous myocardial ablation with an alcohol-induced conus branch occlusion for relief of a significant pressure gradient in double-chambered right ventricle.[12]

Before repair, according to the degree of right ventricular outflow tract obstruction and associated lesions, exercise tolerance may be impaired and cyanosis may be present. After surgical repair and without significant residual anatomic lesions, activity tolerance should be normal.

Guidelines for physical activity and recreational sports participation in children with genetic cardiovascular diseases have been established[13] ; efforts are ongoing to refine guideline and establish evidence-based recommendations.[14]

Prior to surgical therapy for double-chambered right ventricle (DCRV), the follow-up is based on the degree of obstruction, associated lesions, and symptoms. Regular evaluation by a cardiologist is recommended.

The residual lesions determine the follow-up of these patients after surgery. The patients are initially frequently evaluated in order to monitor the progress after repair.

Exercise tolerance and quality of life, endocarditis prophylaxis, and recurrence of obstruction comprise the major issues during the long-term follow-up.

Drug therapy is not currently a component of the standard of care for double-chambered right ventricle (DCRV). See Treatment.

In the presence of a ventricular septal defect with a significant left to right shunt, diuretics and other antifailure measures may be required.