Cardiovascular Imaging

Atrioventricular septal defect

(AVSD), (also called endocardial cushion defect), defect which derives from abnormal embryonic development of the endocardial cushions of the heart causing varying deficits of the primum atrial septum, inlet ventricular septum and medial portions of the mitral and tricuspid valves. The full expression of this defect is a common atrioventricular valve, primum atrial septal defect and inlet ventricular septal defect. The common atrioventricular valve consists of five leaflets with two of the leaflets spanning and opening into both ventricles. An isthmus of tissue may connect the anterior and posterior leaflet and attach to the crest of the ventricular septum. This anatomical arrangement produces an incomplete AVSD by obliterating the interventricular communication and effectively separating the valve into right- and left-sided components. The most frequent incomplete ASVD is a primum atrial septal defect with or without a cleft in the mitral valve.

Plain radiography usually depicts pulmonary arterial overcirculation and enlargement of right-sided cardiac chambers and the pulmonary artery. Cardioangiography demonstrates a left to right shunt across the lower portion of the atrial septum; sometimes left to right shunting across an inlet ventricular septal defect; and regurgitation of the left-sided component of the atrioventricular valve. A defect of the atrioventricular septum may be evident by direct left ventricular to right atrial shunting. Left ventriculography typically shows shortening of the inlet ventricular septum, gooseneck deformity contour of the left ventricle in diastole, and "cleft" of the large anterior leaflet of the mitral valve.

Echocardiography can precisely define the morphology of the atrioventricular valve and the portion of the common atrioventricular valve overlying each ventricle. Commitment of the atrioventricular valve to one or the other ventricle resulting in disparity in sizes of the ventricles is demonstrated by echocardiography. Doppler colour flow mapping can demonstrate the left to right shunt and atrioventricular valve regurgitation. MRI demonstrates the site and size of the primum atrial septal defect, the deficit in the inlet portion of the ventricular septum, and relationships of the large atrioventricular valve to the two ventricles (Fig.1). Cine MRI can display the atrioventricular valve regurgitation.

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Fig.1

ECG-gated spin- echo transaxial MR image demonstrates a common atrioventricular valve spanning both ventricles and an inlet ventricular septal defect.
Atrioventricular septal defect, Fig.1