Congenital Heart Disease in Cats- VSD

Ventricular Septal Defect (VSD) in the Cat

Ventricular septal defect (VSD) is a birth defect of the heart. This defect is a hole between the left ventricle and right ventricle. Blood that is supposed to be flowing into the aorta gets pushed through the defect (called left-to-right shunting) because there is less resistance in the low pressure right ventricle. The right ventricle has to pump more blood and dilates in response (called eccentric hypertrophy).

Over time, the right ventricle gets so large and strong that the pressure gradient changes between the left and right sides of the heart. What was once the path of least resistance into the right ventricle through the defect is now reversed (right-to-left shunting). This leads to un-oxygenated blood flowing to the body via the left ventricle. Due to poor oxygen supply to the tissues, the kidneys respond by signaling the bone marrow to produce more red blood cells (called polycythemia). This excess of red blood cells makes the blood more viscous, thereby making the heart work even harder, eventually leading to congestive heart failure. Click here to better understand how a normal cat heart works.

Congenital heart defects make up ¼ of all heart disease. Of congenital defects, VSD is the 3rd most common in dogs at between 12-14% pending which study is read. Non-published data from UC Davis suggests that VSD in cats is seen with only 1/3 of the frequency in dogs.

Tidholm A. Retrospective study of congenital heart defects in 151 dogs. J Small Anim Pract. 1997 Mar;38(3):94-8.

Baumgartner C, Glaus TM. Congenital cardiac diseases in dogs: a retrospective analysis. Schweiz Arch Tierheilkd. 2003 Nov;145(11):527-33, 535-6.

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Dr Roger Johnson and Dr Kyle Marano

Roger K. Johnson, DVM, Diplomate ACVIM (internal medicine) is a board-certified veterinary internal medicine specialist. His professional interests include cardiology as well as using advanced diagnostics to help his patients. His particular favorites include echocardiography, abdominal ultrasonography, and endoscopy. Kyle Marano, DVM is a small animal veterinarian practicing out of Northern Colorado. He has written pieces ranging from sports commentary and analysis to quips on the every day life of veterinary medicine. His furry family includes a chocolate lab mix and an overly nosy cat.

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