Atrial and Ventricular Septal Defects

A septal defect is an opening between cardiac chambers. The opening itself is only the starting point; the clinically important questions are where it is, which chamber is exposed to abnormal flow, how much blood is shunted, and whether the pulmonary vascular changes are still reversible. Most isolated ASDs and VSDs initially produce an acyanotic left-to-right shunt. Blood recirculates through the lungs instead of moving directly from the right to the systemic circulation. A small defect may have little haemodynamic effect, while a large or strategically located defect can produce chamber enlargement, heart failure, arrhythmias, pulmonary vascular disease, and eventually shunt reversal. A VSD often becomes symptomatic in early infancy as neonatal pulmonary vascular resistance falls. An ASD may remain clinically quiet until adulthood, when a less compliant left ventricle increases left-to-right atrial flow. A normal newborn examination or a passed Canadian pulse oximetry screen does not exclude either lesion: the screen targets critical cyanotic congenital heart disease, not isolated acyanotic septal defects.