Echocardiogram in apical four chamber view demonstrating a primum atrial septal defect (primum ASD). RV: right ventricle; LV: left ventricle; RA: right atrium; LA: left atrium; Primum ASD is part of the AV canal defect and is sometimes called a partial AV canal defect. In AV canal defects the atrioventricular septum (AV septum) is absent and both AV valves are at the same level. Primum ASD is usually associated with a cleft of the anterior mitral leaflet (AML) which appears like an additional commissure in the parasternal short axis view. Cleft AML produces significant mitral regurgitation, which is an association of ostium primum ASD. A similar defect in the tricuspid valve can cause tricuspid regurgitation. Another association of an ostium primum ASD is the inlet or canal ventricular septal defect (VSD).
This frame with colour flow mapping demonstrates the left to right shunt (L>R Shunt) across the primum ASD. Though the actual direction of the shunt is perpendicular to the direction of the beam, most of the blood moves from the left atrium across the ASD towards the tricuspid valve in a direction which is parallel to the beam and towards the transducer. That is why this flow is encoded red.
Apical four chamber view demonstrating tricuspid regurgitation (TR jet) in a case of primum ASD. The bluish mosaic coloured jet is due to the blood flowing away from the transducer in systole. The mosaic indicates turbulent flow with aliasing since the velocity is above the Nyquist limit of the colour Doppler system. Nyquist limit is the maximum velocity which can be imaged by a particular system and is half of the pulse repetition frequency.