Hypertrophic Cardiomyopathy (HCM) In Cats

Hypertrophic cardiomyopathy (HCM) in cats is a disease of the heart muscle. A genetic mutation results in the heart muscle becoming thickened. Most cats with hypertrophic cardiomyopathy don't have any symptoms. A murmur or cardiac arrhythmia may be noticed by your veterinarian. The prognosis of cats with HCM varies with some cats living for many years after the diagnosis but some cats can develop heart failure. This article will discuss the clinical symptoms and treatment options for cats that have been diagnosed with HCM.

What causes hypertrophic cardiomyopathy (HCM) in cats?

The main cause of HCM in cats is unknown, with about 60% of all heart cases in cats being caused by this condition. The origin of most cats and cat breeds remains unknown. However, two distinct genetic mutations are responsible for the development of HCM in the Maine coon and ragdoll breeds.

What is hypertrophic cardiomyopathy in cats?

Hypertrophic cardiomyopathy (HCM) in cats is a condition of the heart muscle, and it occurs when the muscles of the heart wall become abnormally thick. This thickening can cause problems by limiting the ability of blood to flow from one chamber to another during ventricular diastole (the period between ventricular contractions), or by obstructing ventricular systole (the period between aortic valve closure and mitral valve opening).

In HCM, the heart muscle wall becomes hypertrophied (thickened) due to an abnormal proliferation of cardiac muscle cells. There is a genetic basis for this disease in cats. According to a study of Maine coon cats, the Ragdoll cat, and Turkish Van breeds, a mutation in a gene has been implicated as the cause of HCM. Diagnosed Maine coons with this genetic mutation had hypertrophy present from birth which increased with age, reached a plateau at around 4 years old, and declined only slightly thereafter.

Signs and symptoms of hypertrophic cardiomyopathy in cats

Most cats with HCM are asymptomatic. Some cats however show clinical symptoms of HCM including congestive heart failure (CHF). These can be present in the form of rapid breathing, coughing or difficulty breathing due to an accumulation of fluid in the lungs. Other signs that may indicate your cat has HCM are lack of appetite, lethargy, collapse, and sudden blindness due to systemic hypertension (increased blood pressure).

A heart murmur can also be present in cats with HCM due to abnormal turbulence of blood flow caused by the obstruction formed by the thickened muscle wall.

Diagnosis of hypertrophic cardiomyopathy in cats

Your veterinarian will do a thorough physical exam on your cat, and take a complete medical history from you. During the physical exam, your veterinarian will listen for a heart murmur that may be present due to impaired and turbulent blood flow across the aortic valve or mitral valve. Your cat's heart rate will also be monitored because cats with HCM often have tachycardia (increased heart rate).

The gold standard for diagnosis of hypertrophic cardiomyopathy in cats is an echocardiogram (heart ultrasound). The ultrasound will be able to measure the thickness of the heart muscle.

If your veterinarian finds a heart murmur with tachycardia, they may recommend performing a blood test called proBNP. This blood test will help identify if the heart muscle is under stress and/or damaged. A high proBNP value does not mean your cat has HCM, nor does a normal value exclude HCM.

Chest X-rays can be valuable but in early cases of HCM, the thickening affects the inside of the heart and the heart may therefore appear normal on routine chest X-rays. If your cat has clinical symptoms of congestive heart failure, however, chest X-rays will identify any fluid accumulation in the lungs, called pulmonary edema.

How is hypertrophic cardiomyopathy treated in cats?

For asymptomatic cats, atenolol is usually administered. Atenolol decreases cardiac contractility and can help delay further thickening of the heart. Research and studies are unclear however as to if atenolol can delay the onset of congestive heart failure in cats with HCM.

For cats that have heart failure as a result of HCM, diuretics (furosemide) are often prescribed to reduce fluid accumulation within the lungs. ACE inhibitors (e.g. Fortekor®) are used to help the heart function properly. Lastly, medications used to prevent blood clots are often prescribed such as Plavix®. Cats with HCM are prone to developing blood clots within their diseased hearts and these blood clots can leave the heart and obstruct organs and tissues.

Are cats with hypertrophic cardiomyopathy (HCM) at risk for sudden death?

Unfortunately, the risk of sudden death in cats with HCM is increased and there is no known way to prevent HCM-related sudden deaths in cats. Atenolol may theoretically be beneficial in treating HCM and reducing occurrences of sudden death and therefore is often prescribed.

Are there genetic tests available to determine if your cat is a carrier of the mutated gene that causes HCM?

Yes, there is. Your veterinarian can send blood to a special genetic laboratory where they can isolate the mutation.

FAQs about HCM in cats

Hypertrophic cardiomyopathy (HCM) is a disease of the heart muscle that can cause congestive heart failure in cats. While most cats with HCM don't show any symptoms, some may exhibit rapid breathing, coughing, lack of appetite, or difficulty breathing. The diagnosis for HCM is typically made through an echocardiogram which will measure the thickness of the heart muscle. Treatment for cats with HCM includes atenolol (to decrease cardiac contractility), diuretics, ACE inhibitors, and medications to prevent blood clots. Unfortunately, there is no known way to prevent sudden death in cats with HCM. Genetic tests are available to determine if your cat carries the mutated gene that causes HCM. As many cats with HCM are asymptomatic but have a heart murmur and tachycardia on physical exam, regular check-ups with your veterinarian are so important.