Download Ventricular Septal Defect (VSD)

Ventricular Septal Defect (VSD)
Your pet has been diagnosed with a ventricular septal defect (VSD). A VSD is the result of malformation of the
intraventricular septum allowing an abnormal communication between the right and left ventricles.
VSDs are classified based upon whether they are restrictive or non-restrictive. A restrictive VSD is a smaller
diameter VSD that provides resistance of blood flow. These are the most common VSDs that we diagnose in
dogs and cats. Due to normally higher pressures in the left side of the heart compared to the right side of the
heart, most restrictive VSDs have abnormal blood flow through this lesion from left-to-right. The amount of
blood shunted depends on size of the VSD and the pressure difference across the VSD. The shunted blood is
quickly moved to the pulmonary arteries (the blood vessels that go to the lungs). This shunting of blood results
in volume overload to the left side of the heart due to pulmonary vascular overcirculation. The left ventricle
remodels and become larger because of the overcirculation. Ultimately this overcirculation can cause fluid to
exude from the pulmonary vasculature. This fluid in the lungs is evidence of congestive heart failure and can
make your pet cough and breath harder/with more effort. Aortic insufficiency can also occur due to lack of
aortic valve support from the position of the VSD.
With non-restrictive VSDs, a larger diameter defect allows blood to flow freely between the left and right sides
of the heart. Direction of flow is determined by resistance to outflow into the lungs and the systemic
vasculature from the right ventricle and left ventricle respectively. Normally systemic resistance is about five
times that of pulmonary resistance so blood will shunt left-to-right through the large defect. An increase in
pulmonary blood pressure occurs due to massive pulmonary overcirculation. Both ventricles become larger
secondary to volume overload and the right ventricle will get thicker as well due to pressure overload with
time. Rarely, pulmonary hypertension can become severe due to pulmonary arterial vasoconstriction allowing
right ventricular pressures to exceed left pressures, causing shunt reversal. VSD murmurs vary in intensity
based on their size.
Many VSDs are so small that therapy is not indicated. Some VSDs need medical management. Occasionally a
VSD is large enough that placement of an occluder device is indicated. These VSDs need to be in a proper
location for the occluder to be deployed. There are also some palliative surgeries that can be considered if
indicated.
For more information: www.AlpenglowVets.com