Anomalous Muscle Bundles Causing Double-Chambered Right Ventricle in Adults

Editor's Note: View diagnostic videos accompanying this case report.

ABSTRACT: Double-chambered right ventricle (DCRV) causing right ventricular outflow tract (RVOT) obstruction, is an uncommon cardiac disease especially when first diagnosed in adults. Diagnosis can be challenging when it is asymptomatic. We report a 40-year-old man who was referred to cardiology for work-up of a heart murmur that was found on a routine physical examination prior to obtaining a pilot’s license.

A transesophageal echocardiogram (TEE) revealed a DCRV and a small perimembranous ventricular septal defect (VSD) with left-to-right shunt and severe RVOT obstruction. Right heart catheterization showed an estimated gradient of 135 mm Hg across the two chambers due to sub-pulmonary stenosis. The pressure in the proximal right ventricular chamber was 160/25 mm Hg and 25/17 mm Hg in the distal chamber. Surgical correction was successfully performed. A postoperative TEE showed no residual gradients across the RVOT.

DCRV has been reported as a rare disease in adults. It is difficult to diagnose DCRV using the transthoracic echocardiogram in adults. However, subcostal windows can offer better visualization of sub-pulmonary outflow tract compared to the parasternal and apical windows. TEE remains the main non-invasive modality for diagnosing DCRV in adults. Cardiac magnetic resonance imaging and invasive testing can provide further information to confirm the diagnosis and guide therapeutic decisions.

J INVASIVE CARDIOL 2013;25(12):E212-E213

Key words: double-chambered right ventricle, right ventricular outflow tract obstruction, congenital heart disease in adults

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Double-chambered right ventricle (DCRV) in adults is a challenging diagnosis especially when it presents without symptoms. Currently, there are no clear guidelines for management of this disease in adult patients.

Case Report. A 40-year-old man with history of ventricular septal defect (VSD) since childhood without follow-up as an adult presented to his primary care physician for a physical examination prior to obtaining a pilot’s license. He was asymptomatic from the VSD throughout his entire life. He was found to have a loud murmur and was referred to cardiology for further work-up. Physical examination revealed a grade 4/6 harsh systolic ejection murmur most prominent at the left lower sternal border, and a right ventricular heave. A 12-lead electrocardiogram showed right atrial dilatation, right ventricular hypertrophy, right axis deviation, and diffuse ST-wave changes (Figure 1).

Transthoracic echocardiogram (TTE) showed normal left ventricular function and dimensions, a small perimembranous VSD with left-to-right shunt, moderate right ventricular hypertrophy (RVH), moderate right atrial enlargement (RAE), and mild tricuspid regurgitation (TR). This was followed by a transesophageal echocardiography (TEE) that showed severe RAE, severe RVH, severe right ventricular outflow tract (RVOT) obstruction with excessive hypertrophy of the infundibulum, and right ventricular muscle bundles. There was a small restrictive perimembranous VSD measuring 4 mm and mild TR. There was no evidence of valvular or supravalvular pulmonary stenosis or mitral valve disease (Video 1). Right cardiac catheterization demonstrated suprasystemic right ventricular pressures of 160/25 mm Hg compared to aortic pressure of 123/88 mm Hg. On pullback across the RVOT, the pressure was 160 mm Hg in the proximal chamber and 25 mm Hg in the distal chamber with a 135 mm Hg pressure gradient. There was no pressure gradient between the RVOT and the main pulmonary artery. Qp:Qs was 2.62. A right ventriculogram demonstrated RV subvalvar/infundibular stenosis secondary to RVH (Videos 2 and 3). Left cardiac catheterization was unremarkable.

The patient underwent a repair of the DCRV. Substantial RV muscle bundle resection was done through a right atrial approach with closure of the VSD and patch augmentation of the RVOT. A patent foramen ovale (PFO) was incidentally found intraoperatively and was closed. There were no operative or postoperative complications. A postoperative TEE demonstrated moderate RAE, moderate RVH, no RVOT obstruction, no VSD, and normal biventricular systolic function.

Discussion. DCRV is a rare form of congenital heart disease in which the right ventricle is divided into two chambers, a proximal high-pressure inflow chamber (anatomically lower and usually larger in size) and a distal low-pressure outflow chamber (anatomically higher), by an anomalous muscle bundle (AMB) that protrudes from the right ventricular free wall to the interventricular septum.¹

The incidence of DCRV represents 0.5%-2% of all cases of congenital heart disease.² DCRV is a form of RVOT obstruction that develops over time. Obstruction of the RVOT is generally progressive after infancy, and DCRV is usually diagnosed and repaired in childhood or adolescence.³ Rarely, a patient remains asymptomatic while the obstruction progresses gradually, until it presents in adulthood.4 DCRV is rarely asymptomatic in adults, especially when a high gradient is present between the two chambers, as in our case.

Presenting symptoms are usually due to severe RVOT obstruction leading to a low cardiac output state or due to associated right heart failure.

The origin of the AMB as a cause of RVOT obstruction has been debated. It is hypothesized that the anatomic substrate for DCRV exists before the development of a pressure gradient and that the obstruction progresses with time due to the increased blood flow via VSD. The moderator band was found to be superiorly displaced in patients with VSD who developed DCRV compared to those who did not.^1,5,6

DCRV usually is associated with other anomalies. In 90% of cases, it is associated with a membranous-type VSD.² Other co-existing lesions include subaortic stenosis, pulmonary valve stenosis, tetralogy of Fallot, anomalous pulmonary venous drainage, transposition of the great arteries, and patent foramen ovale.⁷

The diagnosis can be difficult in adult patients, since the RVOT is not always a routine part of the adult echocardiographic examination. It is difficult to delineate the morphology of the RVOT by TTE due to its proximity to the transducer, irregular shape, and other limitations encountered while studying adults, such as obesity and emphysema.^2,3

Subcostal echocardiography windows are useful in visualizing the right ventricle and the RVOT compared to the parasternal and apical windows.⁸ TEE from the gastroesophageal junction provides excellent visualization of the RV.^2,3 Doppler echocardiography can provide estimates of the pressure gradients. Although TTE is widely accepted as a method of demonstrating DCRV in pediatric patients, TEE allows better definition of the lesion in adults.

There are no clear guidelines for the indications of surgical repair in adults; however, generally accepted indications are in symptomatic patients, when associated lesions are present, or with a pressure gradient greater than 40 mm Hg between the anatomically lower RV and the main pulmonary artery.⁴

Surgical correction consists of resection of the AMB and closure of the VSD through a transatrial approach to achieve adequate exposure of the AMB.⁹ Surgery offers complete relief of the obstruction, and a substantial improvement in symptoms and functional status. The long-term results of surgical treatment are excellent.¹⁰

Conclusion. Double-chambered right ventricle is a rare condition in adult patients. Full echocardiographic examination of the right ventricle including the RVOT is essential for the diagnosis of this disease. Invasive diagnostic studies and CMR can further define the anatomy and pressure gradients to confirm diagnosis and guide therapeutic decisions. Surgical correction appears to be a successful strategy for management of this rare condition in adults.

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From ¹the Department of Cardiology, University of Louisville, Louisville, Kentucky, and ²the Department of Medicine, University of Cincinnati, Cincinnati, Ohio.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted April 23, 2013, provisional acceptance given May 2, 2013, final version accepted May 16, 2013.

Address for correspondence: Amr Mohsen, MD, University of Louisville, Department of Cardiology, 550 South Jackson Street, ACB, 3rd floor, Louisville, KY 40202. Email: a0mohs01@louisville.edu