Atrial Septal Defect

Abstract

Atrial septal defect (ASD) is a hole in the atrial septum that allows blood flow to shunt between the left and right atria. These defects are generally characterized as secundum type (hole in the septum primum) and sinus venosus type (hole in the atrial septum that is associated with the superior vena cava/inferior vena cava and accompanying anomalous pulmonary venous return). The “ostium primum ASD” is better termed “partial atrioventricular (AV) canal” because it is generally associated with a cleft or zone of apposition in the anterior left AV valve leaflet (see Chap. 9). Figure 7.1 shows a composite view of the most common types of ASD, including the ostium primum ASD (partial AV canal), but the zone of apposition in the anterior leaflet of the left AV valve is not shown. A single atrium has no remnant of atrial septal tissue and is generally thought to be a partial AV canal with absence of the septum primum and septum secundum. Patients with a patent foramen ovale or a “stretched” patent foramen ovale generally have small interatrial communications. The difference between a patent foramen ovale and a secundum ASD involves the amount of residual septum primum and its relationship to the septum secundum, which is superiorly located. These two septa are situated in different planes, in a flaplike configuration. The septum secundum is superior and slightly lateral in location; the septum primum is inferior and slightly medial. If the planes of the septa are brought together and there is enough tissue in the septum primum to effectively cause closure of the defect, then the hole is a patent foramen ovale. If there is not enough septum primum to effectively close the hole, then the hole is a secundum ASD.