Hypertrophic cardiomyopathy (HCM) is the most common cause of heart disease in cats. This disease causes thickening of the left ventricular heart muscle. If mild, many cats can go on for years and, sometimes, never suffer any consequences from the left ventricular thickening. However, if the left ventricle becomes severely thickened, it becomes stiff and cannot fill properly. The pressure rises in the left ventricle and is eventually transmitted back to the left atrium and the lungs (see normal cardiac circulation). The end result is congestive heart failure (fluid in or around the lungs). Other possible complications that can occur with this disease are aortic thromboembolism (blood clot to the limbs), and, occasionally, sudden death.
There are certain breeds of cats that are predisposed to this disease including the Maine Coon, Ragdoll, British Shorthair, Sphynx and Bengal. However, the disease is also very common in Domestic Shorthairs. There is a genetic test available in the Maine Coon and Ragdoll.
How do I know if my cat has HCM?
Often the first evidence of heart disease is a heart murmur, which is picked up by your regular veterinarian at the yearly visit. However, not all cats with HCM have a heart murmur. Conversely, it is not uncommon for a cat that is stressed at the vet clinic to develop a murmur but have a perfectly healthy heart. Sometimes an arrhythmia (irregular heart rhythm) is the first sign of cardiac disease.
An echocardiogram (heart ultrasound) is the only real way to diagnose HCM. Under no or mild sedation, an echocardiogram allows full visualization of the ventricular walls and all cardiac chambers in order to evaluate wall thickness, chamber enlargement, cardiac function, clot formation and the cause of the murmur.
Detection of a thickened heart is not possible on chest xrays in cats. However, if your cat is showing any respiratory signs such as coughing, heavy or rapid breathing, chest xrays will be recommended to look for congestive heart failure.
If your cat is diagnosed with HCM, a blood thyroid level and blood pressure measurement will be recommended to look for potentially treatable secondary causes of left ventricular thickening. If the disease progresses to congestive heart failure, a blood kidney profile will be recommended at the start of treatment then periodically in order to monitor kidney function.
There is no known treatment that will reverse or delay the progression of HCM. If your cat has a very large left atrium or evidence of clot formation, Clopidogrel (Plavix) will be recommended to try and reduce further clot formation. Some cats with HCM develop a concurrent condition called ‘systolic anterior motion of the mitral valve’. In this syndrome, abnormal movement of the mitral valve caused by the HCM results in the valve obstructing blood flowing out of the aorta. This obstruction causes a further increase in workload on the left ventricle. If severe, treatment with a drug called Atenolol will be recommended to try and reduce this increased workload. If your cat’s disease progresses onto congestive heart failure (fluid in or around the lungs), frusemide and benazepril will be added to his or her treatment regime (see congestive heart failure).
We will always work closely with your regular vet to make sure you cat remains as comfortable as possible.