Ventricular septal defects (VSDs) are very common and account for approximately 20%–30% of congenital heart defects, often as part of complex lesions. From the anatomical point of view, the interventricular septum consists of a small membranous part, from which radiates a larger muscular component. The latter has three portions, an inlet, trabecular, and outlet portion.
VSDs solely affecting the membranous septum are exceedingly rare. In the vast majority of cases, membranous VSDs extend into the surrounding muscular septum and are therefore referred to as perimembranous defects. They form the largest group of VSDs. Due to a close anatomical relationship to the septal leaflet of the tricuspid valve, perimembranous VSD s are often restricted or even closed by accessory septal leaflet tissue. In contrast to a perimembranous outlet VSD, a muscular outlet VSD has muscular margins only. Inlet VSD s are typically associated with defects of the atrio-ventricular septum.
A subarterial VSD (or doubly committed VSD) is characterized by the complete absence of the infundibular septum and commitment of the defect to both semilunar valves. In this type of defect, the leaflets of the aortic and pulmonary valves are in fibrous continuity. In many cases, the right coronary cusp of the aortic valve prolapses into the defect, partially occluding it. This type of defect is common in the Asian population. In a malalignment VSD , there is a lack of alignment between the infundibular (outlet) and the trabecular septum. Muscular VSD s can have a variety of locations, which are summarized in Figure 1 . They can occur in isolation or as multiple defects. In extreme cases, the interventricular septum has a “Swiss cheese” appearance.
Significant left-to-right shunt at the ventricular level leads to left heart volume overload, excessive pulmonary blood flow, and progressive development of pulmonary hypertension. The treatment of VSDs consists of surgical or transcatheter closure. Palliative pulmonary artery banding is performed in selected cases.
