Gerbode defect

Last revised by Bahman Rasuli on 24 Sep 2020

The Gerbode defect describes a rare abnormal left-to-right shunt between the left ventricle and right atrium through a defect in the atrioventricular septum, usually congenital in etiology.

Gerbode defects are rare congenital cardiac anomalies, and are thought to account for less than 1% of all congenital cardiac anomalies, and only 0.08% of intracardiac shunts 1-3.

Additional malformations are seen in approximately one-third of cases, the most common associated lesions being the atrial septal defect and patent foramen ovale 1.

Clinical presentation varies depending on the size and resultant severity of the defect 1,2,4-6. Small lesions with minimal shunting may be asymptomatic, however, large lesions with ample shunting may cause signs of heart failure such as exertional dyspnea, raised jugular venous pressure, hepatomegaly, peripheral edema, or failure to thrive in pediatric patients 1,2,4-6. Cyanosis is generally not seen in patients with Gerbode defects 1,2,4-6. Praecordial auscultation is indistinguishable to that of ventricular septal defects, with a pansystolic murmur heard over the left sternal border 1,2,4-6.

A defect between the left ventricle and right atrium results in a left-to-right shunt 1,4-6. Similar to other left-to-right shunts, significant shunting can result in increased pressure on the right side of the heart, and eventual cardiac compromise (heart failure, etc.) 1,4-6.

Classically, a Gerbode defect is considered to be a congenital lesion whereby there is an abnormal perforation of the septal leaflet of the tricuspid valve, near the edge of the leaflet or its attachment 1,4,7. A perforation in this location, the atrioventricular (membranous) portion of the interventricular septum (just inferior to the posterior and right cusps of the aortic valve), allows for communication between the left ventricle and right atrium 1,4,7.

In addition to having a congenital etiology, Gerbode defects are increasingly being described as acquired 1,4,7. These are most commonly acquired iatrogenically through surgery performed near the atrioventricular (membranous) portion of the interventricular septum, but there are numerous causes 1-7:

Gerbode defects can be classified according to location 1,6:

  • supravalvular (direct): defect is superior to the septal leaflet of the tricuspid valve
  • infravalvular (indirect): defect is inferior to the septal leaflet of the tricuspid valve
  • intermediate: both inferior and superior defects are present in relation to the septal leaflet of the tricuspid valve

Supra- and infravalvular types are the most common 1,6.

The chest radiograph can be normal with a small Gerbode defect, and may only be abnormal with large defects. In these cases, cardiomegaly and pulmonary plethora may be appreciated on the plain radiograph 8.

Transthoracic echocardiography is generally the imaging modality of choice 1-4,7. It allows direct visualization of the Gerbode defect and resultant right atrial dilatation 1-4,7. In particular, color flow Doppler revealing high-velocity systolic flow originating from the upper atrioventricular (membranous) portion and directed into the right atrium, is characteristic 1-4,7.

Electrocardiographically-gated CT and cardiac MRI (CMR) allow for further direct visualization of the defect 1,9. CMR in particular is able to provide detailed shunt anatomy and quantification of shunt severity 1,9.

Although some small Gerbode defects may close spontaneously, most do not 1,6. Treatment may be required for defects causing symptoms, with surgical closure being the management of choice 1,6. However, some authors argue that all Gerbode defects should be surgically-closed due to an inherent risk of infective endocarditis 1.

The defect is named after Frank A Gerbode (1907-1984), an American cardiothoracic surgeon, who described the surgical closure of the defect in a series of patients in 1958 10. However, the first description of the defect was over a century prior to this, in 1838 by John Thurnam (1810-1873), an English physician 11.

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