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. Sinus venosus type ASD involves the high atrial septum and may be associated with anomalous pulmonary venous connection to the right heart. Ostium primum ASDs (e.g., typical of Down syndrome) appear at lower atrial septum, adjacent to atrioventricular (AV) valves.
Usually asymptomatic until third or fourth decades, when exertional dyspnea, fatigue, and palpitations may occur. Onset of symptoms may be associated with development of pulmonary hypertension (see below).
Prominent right ventricular (RV) impulse, wide fixed splitting of S2, systolic murmur from flow across pulmonic valve, 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 right atrium (RA), RV, and main pulmonary artery (LA enlargement not usually present).
RA, RV, and pulmonary artery enlargement; Doppler shows abnormal turbulent transatrial flow. Echo contrast (agitated saline injection into peripheral systemic vein) may visualize transatrial shunt. Transesophageal echo usually diagnostic if transthoracic echo is ambiguous.
In the absence of contraindications an ASD with a significant pulmonary-to-systemic flow (PF:SF) ratio (≥1.5:1.0) should be considered for surgical or percutaneous transcatheter closure. Closure is usually contraindicated with significant pulmonary hypertension and is not undertaken for small defects with trivial left-to-right shunt flow.