Feline Hypertrophic Cardiomyopathy, or HCM, is the most frequently diagnosed cardiac disease in domestic cats. This progressive condition is characterized by the thickening of the heart’s muscular walls, particularly the left ventricle, which is the main chamber that pumps blood to the body. This hypertrophy causes the muscle to become stiff and less flexible, hindering the heart’s ability to relax and fill with blood between beats and reducing its overall efficiency.
Genetic Predisposition and Causes
The primary driver behind HCM is genetic, with specific gene mutations identified in certain breeds. Breeds with a known hereditary link to HCM include:
- Maine Coon
- Ragdoll
- Sphynx
- Persian
- British Shorthair
For Maine Coons and Ragdolls, scientists have pinpointed a specific mutation in a cardiac muscle protein gene as a cause. Genetic testing is available for these breeds to identify cats carrying the responsible mutation.
While genetics play a large role, HCM is also diagnosed in many cats without a clear hereditary link, including domestic shorthairs. In these instances, the cause is considered idiopathic, meaning it arises from an unknown origin. The condition is most often diagnosed in middle-aged to older cats, though a juvenile form can affect young cats. While conditions like high blood pressure or hyperthyroidism can also cause ventricular wall thickening, this is not classified as primary HCM.
Signs and Symptoms of HCM
Many cats with HCM remain asymptomatic for long periods as the disease progresses silently. Because cats are adept at hiding discomfort, initial subtle signs like a gradual decrease in appetite, lethargy, or a reduced interest in social interaction might be the only clues.
As the disease advances, more obvious signs related to congestive heart failure (CHF) may appear. These symptoms develop because the stiff heart muscle leads to a backup of pressure and fluid accumulation in or around the lungs. Owners might observe rapid breathing (tachypnea), labored or open-mouth breathing, or coughing.
One of the most serious complications is feline aortic thromboembolism (ATE), where a blood clot forms in the heart, travels through the aorta, and lodges in an artery, cutting off blood flow to the hind limbs. This results in sudden paralysis, pain, and distress. Other cats may experience sudden collapse or even sudden death with no prior warning signs.
The Diagnostic Process
Diagnosis of HCM often begins during a routine veterinary examination. A veterinarian listening to the cat’s chest with a stethoscope might detect a heart murmur, a gallop rhythm, or an arrhythmia. However, a significant number of cats with HCM do not have a discernible murmur, making diagnosis from a physical exam alone unreliable.
The definitive diagnostic tool is an echocardiogram, an ultrasound of the heart. This non-invasive procedure is the gold standard for diagnosing HCM, allowing a veterinarian to visualize the heart’s chambers, measure wall thickness, and assess function.
Other diagnostic tools may be used to evaluate the cat’s overall health and the severity of the disease. Chest X-rays are valuable for identifying fluid in or around the lungs, which is a sign of congestive heart failure. Blood tests, such as the NT-proBNP assay, can measure a hormone released when the heart muscle is under strain, providing further evidence of cardiac stress.
Managing an HCM Diagnosis
There is no cure for feline HCM, so treatment focuses on managing the condition. The goals are to control clinical signs, slow disease progression, and reduce the risk of complications like congestive heart failure and blood clots. The specific treatment plan is highly individualized and depends on the stage of the disease and whether the cat is showing symptoms.
For cats that have developed CHF, medications are used to manage fluid accumulation and support heart function. Diuretics are prescribed to help the body remove excess fluid from the lungs. Other medications may include beta-blockers to help the heart muscle relax and slow the heart rate, or drugs like clopidogrel to prevent the formation of blood clots.
At-home care is a component of long-term management. Owners are often instructed on how to monitor their cat’s sleeping respiratory rate (SRR), which is the number of breaths the cat takes per minute while at rest. A rising SRR can be an early indicator of fluid building up in the lungs and warrants a call to the veterinarian. Minimizing stress in the cat’s environment is also recommended.
The prognosis for a cat with HCM is highly variable. Some cats with mild disease may live a normal lifespan with few symptoms, while others with more severe forms may have a shorter life expectancy despite medical management. Regular follow-up visits for repeat echocardiograms and medication adjustments are necessary to ensure the best possible quality of life.