Ventricular septal defects

These defects represent 25% of all congenital heart defects. When considering ventricular septal defects (VSD) with other congenital anomalies, the proportion rises to 50%! The most common are membranous septal defects, with rare defects occurring in the muscular portion. A genetic component has been implicated, as an increased incidence of VSD has been observed in both Asian populations and progeny of patients having a VSD themselves.

Isolated VSD (not associated with other defects, as in the tetralogy of Fallot, for example) have been categorized as follows:

• Type I defects are positioned in the infundibulum of the right ventricle, caudal to the pulmonary valve. These arise from defects in the formation of the bulbus cordis and truncus arteriosus. These are also referred to as supracristal, conal or infundibular VSD.
• Type II defects occur in the membranous portion of the septum, and are the most commonly observed defects. These are also referred to as paramembranous VSD.
• Type III defects are found in close proximity to the tricuspid valve, within the inlet of the right ventricle. These are thought to arise from defects in the partitioning of the AV canal by the endocardial cushions. Also identified as atrioventricular canal defects or inlet defects.
• Type IV defects are present in the muscular portion of the interventricular septum. These can be single or multiple, showing extremely irregular borders (variable in many planes). Type IV defects are not easily visualized or repaired.

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