ACYANOTIC CONGENITAL HEART LESIONS WITH LEFT-TO-RIGHT SHUNT
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ATRIAL SEPTAL DEFECT (ASD)
Most common is ostium secundum ASD, located at mid interatrial septum. Ostium primum ASDs (e.g., typical of Down syndrome) appear at lower atrial septum and are associated with abnormal development of atrioventricular (AV) valves, especially a cleft appearance of the mitral valve. Sinus venosus type defects do not actually involve the atrial septum, but rather represent a defect localized between a right pulmonary vein and the junction of the superior vena cava or inferior vena cava with the right atrium (RA). Physiologically such defects mimic ASDs.
When discovered in adulthood, usually asymptomatic until third or fourth decades, when exercise intolerance, dyspnea, and palpitations may occur. Onset of symptoms may be associated with development of pulmonary hypertension (PHT) (see below).
Wide, fixed splitting of S2, systolic murmur from flow across pulmonic valve, possible diastolic flow rumble across tricuspid valve, prominent jugular venous v wave.
Incomplete RBBB (rSR’ in right precordial leads) common. Left-axis deviation frequently present with ostium primum defect. Ectopic atrial pacemaker or first degree AV block occur in sinus venosus defects.
Increased pulmonary vascular markings, prominence of RA, RV, and main pulmonary artery (LA enlargement not usually present).
RA, RV, and pulmonary artery enlargement; Doppler shows abnormal transatrial flow. Echo contrast (agitated saline injection into peripheral systemic vein) may visualize transatrial shunt.
Treatment: Atrial Septal Defect
In the absence of contraindications an ASD with a significant pulmonary-to-systemic flow (Qp/Qs) ratio (≥1.5:1.0) with right heart enlargement should be considered for surgical or percutaneous transcatheter closure. Closure is usually contraindicated with significant PHT and is not undertaken for small defects with trivial left-to-right shunt flow.