Hypertrophic cardiomyopathy is the most common feline acquired heart disease. This disease is characterized by thickening of the muscular wall of the left ventricle. The left ventricle pumps blood from the heart to all parts of the body except the lungs, and the thick walls decrease the filling of the ventricle with blood. Blood backing up into the left atrium (top chamber of the heart) causes it to dilate, and over time can result in congestive heart failure and blood clot formation.
The cause of hypertrophic cardiomyopathy is unknown (idiopathic) in most cases. A genetic mutation has been identified in Maine Coon, American Shorthair, and Ragdoll breeds. We suspect genetic mutations in a number of other feline breeds. A large percentage of cats with hypertrophic cardiomyopathy have a heart murmur, and therefore the disease can be identified prior to clinical signs of congestive heart failure. Gallop rhythms or arrhythmias can also be early indicators that the disease is present. Unfortunately not every cat with hypertrophic cardiomyopathy has a heart murmur, and in these cases the first clinical signs noted are increased breathing rate and effort. The best test to determine if hypertrophic cardiomyopathy is present is an echocardiogram, an ultrasound examination of the heart.
Dilated cardiomyopathy is a disease of the heart muscle. The muscle weakens and is unable to pump effectively. With time the heart begins to dilate to compensate for its poor function. This causes the chambers within the heart to become markedly enlarged and fluid can begin to accumulate in the lungs, around the lungs, or within the abdomen (congestive heart failure). Most cases of dilated cardiomyopathy are idiopathic (unknown cause), but we will often look for nutritional deficiencies, infectious causes, hormonal imbalances, and previous drug toxicities. This disease is genetic in certain families of Boxers and Doberman Pinschers. The most important diagnostic test used to diagnose dilated cardiomyopathy is an echocardiogram.