Fig. 8. Transthoracic apical four-chamber view (A4C) with color flow Doppler interrogation of the interatrial septum shows left-to-right shunt via a secundum defect.
Primum ASDs result from the incomplete development of the septum primum with the endocardial cushions in the region of the atrioventricular (AV) valves. Also called partial AV canal defects, this lesion results in an atrial communication that is seen inferi-orly, in the lower portion of the atrial septum that normally is fused with the AV valvular apparatus. The AV valves are therefore affected, typically involving the mitral valve, where a cleft may be seen in the anterior leaflet. Mitral regurgitation may also be seen. Interventricular shunts are not generally seen with this abnormality.
The features of this defect can usually been seen with transthoracic imaging. In the four-chamber view (apical or subcostal), the AV valves may appear to lie on the same plane, forming a "T," referring to the alignment of the AV valves with the ventricular septum. An echolucent space can be seen above the AV valves, usually with a nonrestrictive shunt seen by color flow Doppler. The "goose neck" deformity seen angiographically on left ventriculography can occasionally be seen echo-cardiographically as an abnormal appearing left ventricular outflow tract.
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