What is a ventricular septal defect (VSD)?
A ventricular septal defect is an opening in the ventricular septum, or dividing wall between the two lower chambers of the heart known as the right and left ventricles. VSD is a congenital (present at birth) heart defect. As the fetus is growing, something occurs to affect heart development during the first 8 weeks of pregnancy, resulting in a VSD. Normally, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped into the lungs where it
receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped out to the body through the aorta.
When there is a large opening between the ventricles, a large amount of oxygen-rich (red) blood from the heart's left side is forced through the defect into the right side. Then it's pumped back to the lungs, even though it's already been refreshed with oxygen. This is inefficient, because already-oxygenated blood displaces blood that needs oxygen. This means the heart, which must pump more blood, may enlarge from the added work. High blood pressure may occur in the lungs' blood vessels because more blood is there. Over time, this increased pulmonary hypertension may permanently damage the blood vessel walls. If the opening between the ventricles is small, it doesn't strain the heart. In that case, the only abnormal finding is a loud murmur.
Ventricular septal defects can be further described by size of the defect, location of the defect, whether there is more than one defect present, and 4) the presence or absence of a ventricular septal aneurysm. The size of the defect is usually described as small, moderate, or large. In general, small defects cause no symptoms during infancy or childhood and often close spontaneously. Moderate and large defects are less likely to close spontaneously, may result in congestive heart failure, and more often require surgical closure. Sometimes, the term restrictive or non-restrictive are used to describe the size of the defect. The term restrictive describes small defects that allow little or no blood to flow from the left side of the heart to the right side of the heart. Non-restrictive defects are large defects that allow a significant amount of blood to flow from the left side to the right of the heart. This results in excessive blood flow to the lungs, high pulmonary artery pressures, extra work for the heart, and congestive heart failure.
Different systems for describing the location of ventricular septal defects are used. Some are located in the lower portion of the septum called the muscular septum. Defects in this location are called muscular ventricular septal defects. Perimembranous ventricular septal defects (also called membranous VSD'S) are located in the membranous septum, a relatively small portion of the septum located near the heart valves. Ventricular septal defects may also be described as inlet or outlet VSDs. These terms further describe where the defect is located. Inlet VSDs are located close to where the blood enters the ventricular chamber and outlet VSDs are located close to where the blood exits the ventricular chamber.