Ventricular septal defects (VSD) are openings in the wall, or the ventricular septum, that separates the lower chambers of the heart called the right and left ventricles. Ventricular septal defects allow oxygen-rich (red) blood to pass from the lower left chamber through the opening in the septum into the lower right chamber where it mixes with oxygen-poor (blue) blood.
There are four basic subtypes of ventricular septal defects: (1) membranous ventricular septal defect, which is an opening in the membrane of the upper section of the ventricular septum, (2) muscular ventricular septal defect, which is an opening in the muscle of the lower section of the ventricular septum, (3) atrioventricular canal, which is an opening located near the upper valves and is associated with the atrioventricular canal defect, and (4) the rarest type called a conal septal ventricular septal defect, which is an opening located in the ventricular septum just below the valve that connects the lower right chamber of the heart and the pulmonary artery.
Ventricular septal defects are the most common cardiac malformations, accounting for half of all congenital heart defects. The incidence rate of ventricular septal defects is 3.5 per 1,000 live births.
It can be difficult to accurately diagnose isolated ventricular septal defects using prenatal ultrasound and echocardiography; as a result, the accuracy rate is low. As an isolated diagnosis, ventricular septal are not fatal; however, these defects are often associated with other cardiac malformations such as tetralogy of Fallot as well as chromosomal abnormalities.
The recurrence risk for ventricular septal defects is related to the underlying cause. Most cases are random in occurrence; however, the familiar recurrence risk is 3% if one sibling has a ventricular septal defect, 10% if the defect is present in two siblings, 6-10% if the mother has the defect, and 2% if the father has the defect.