What is a perimembranous VSD? Cardiology Basics

What is a perimembranous VSD? Cardiology Basics

Perimembranous VSD is the commonest type of ventricular septal defect. When there is a ventricular septal defect, blood shunts from the left ventricle to the right ventricle as the pressure in the left ventricle is higher. This leads to increased pulmonary blood flow. VSD usually occurs as a congenital defect, though it can rarely occur in the adult after a myocardial infarction due to rupture of the ventricular septum. If the VSD is large, high pulmonary blood flow increases the amount of blood returning to the left atrium and left ventricle through the pulmonary veins. This volume overloading of the left ventricle can lead to heart failure as the immature left ventricle of the infant has more of mitochondria than contractile elements.

Important locations of VSD are perimembranous, muscular, outlet and inlet. Outlet VSD is near the outlet of the ventricles, near the origin of the great arteries. Perimembranous VSD is in the upper part of the interventricular septum, where it is thin and like a membrane. Muscular VSD is a defect in the thick muscular part of the interventricular septum. Inlet VSD is near the atrioventricular valves which form the inlet of the ventricles. It is often associated with other endocardial cushion defects like a cleft in the anterior mitral leaflet, producing mitral regurgitation and ostium primum atrial septal defect.

VSD can be suspected clinically when there is a pansystolic murmur in the left parasternal region. In small VSD, it is often a loud murmur due to the large pressure difference across the defect. It is usually associated with a thrill. Small VSD is also called “Maladie de Roger”. Murmur is softer in large VSD because the pressure gradient between the two ventricles will be low. Presence of the large defect equalizes the pressures in the two ventricles. Perimembranous VSD can be documented by an echocardiogram, as shown here.

When a perimembranous VSD is detected in an infant, there is a chance that it can close spontaneously over a period of time. Chance for spontaneous closure is more for a small VSD than a large VSD. Even large VSD can decrease in size gradually. If a large VSD decreases in size later, it may even be left alone and followed up with certain precautions like prompt treatment of all infections. Lifetime risk of a small VSD is the occasional occurrence of an infective endocarditis, which can be dangerous.

But it is very rare with meticulous treatment of all infections. Perimembranous VSD which remains large may have to be closed by surgery, early in life. Device closure for perimembranous VSD is evolving and is not as popular as device closure of muscular VSD. This is because device closure of perimembranous VSD can sometimes cause an atrioventricular block. Special asymmetrical VSD closure devices are used to avoid pressure by the device in the region of the conduction system which is near the rim of the VSD.