Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed
The endocardial cushions form the lower atrial septum, the upper ventricular septum, the septal leaflet of the tricuspid valve and the anterior leaflet of the mitral valve. An ECD defect is due to abnormal development of these endocardial cushions.
In a complete ECD there is a single confluent atrioventricular orifice between the anterior leaflet of the mitral valve and the septal leaflet of the tricuspid valve with fusion of the valve segments into a common valve across this orifice and a deficient base of the diaphragmatic wall of the ventricle. The ASD is usually large and the left to right shunt is regulated by the diastolic distensibillity of the right ventricle. The right atrium receives blood from the left ventricle through an incomplete mitral valve and ASD while the right ventricle receives blood via an incomplete tricuspid valve. This leads to volume overload of the right heart leading to dilation of the right atrium, right ventricle, and pulmonary artery. The VSD and mitral regurgurgitation lead to left ventricle volume overload.
Partial ECD is more common than complete ECD and has an ostium primum ASD, a cleft anterior leaflet of the mitral valve, separate atrioventricular valves attached to the crest of a defective ventricular septum, and a variable occurrence of cleft septal leaflet of the tricuspid valve. With a large ASD the cleft mitral valve results in right heart dilation with minimal left heart effects. With a small ASD the effects of the cleft mitral valve are borne by the left heart.
The left ventricular outflow tract is narrowed and elongated, a "gooseneck deformity," in both complete and partial ECD. In complete ECD there is pulmonary shunt vascularity and right sided cardiomegaly. In a partial ECD without mitral regurgitation, the appearance is similar to that of a large ASD.
See References Chapter.
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