Hypertrophic Cardiomyopathy (HCM) in Cats - Symptoms & Management
Manage feline HCM with cardiac medications and regular veterinary monitoring.
What is Feline HCM?
Feline Hypertrophic Cardiomyopathy (HCM) is abnormal thickening of the heart muscle, particularly the left ventricular wall. As the wall thickens, ventricular volume decreases, reducing the heart's ability to fill with blood and pump effectively. It is the most common feline heart disease, detected in roughly 15% of adult cats in some studies. Maine Coon, Ragdoll, Sphynx, and British Shorthair breeds have known genetic predispositions.
Hypertrophic Cardiomyopathy
Causes and High-Risk Breeds
- Genetic mutation: MYBPC3 variants confirmed in Maine Coon (A31P) and Ragdoll (R820W)
- Increasing prevalence with age: more common in cats over 5 years
- Male cats are more commonly affected than females
- Secondary HCM: hypertension and hyperthyroidism can cause secondary hypertrophy
Symptoms
HCM often progresses without symptoms in the early stages. Many cats are first diagnosed when a heart murmur is detected during a routine exam. When symptoms appear, pulmonary edema or pleural effusion is often already present.
- Rapid breathing (>30 breaths/min) or labored breathing: fluid in lungs makes breathing difficult
- Open-mouth breathing: always an emergency sign in cats
- Exercise intolerance or lethargy: tires easily or avoids activity
- Heart murmur: abnormal sound detected on auscultation
- Rear limb paralysis (thromboembolism emergency): sudden paralysis and severe pain from aortic clot
- Reduced appetite and weight loss: as heart failure progresses
Diagnosis
Echocardiography (cardiac ultrasound) is the diagnostic standard for HCM. It measures ventricular wall thickness, atrial size, and blood flow velocity. A left ventricular wall >5.5 mm confirms HCM. Chest X-rays assess heart size and fluid accumulation. NT-proBNP blood tests measure cardiac stress. Thyroid testing and blood pressure measurement rule out secondary causes.
Medical Treatment
- Diuretics (furosemide): rapidly relieves pulmonary edema and pleural effusion by removing excess fluid
- Anticoagulants (clopidogrel, aspirin): prevent thromboembolism, used when left atrial enlargement is confirmed
- Atenolol (beta blocker): reduces heart rate and improves myocardial relaxation
- Diltiazem (calcium channel blocker): improves myocardial relaxation and rate control in select cases
- Pimobendan: strengthens myocardial contractility, used when systolic function is impaired
| Stage | Cardiac Changes | Symptoms | Treatment |
|---|---|---|---|
| Subclinical | Early hypertrophy, murmur | No symptoms | Regular echocardiogram monitoring |
| Early heart failure | Atrial enlargement, clot risk | Exercise intolerance, occasional cough | Anticoagulants, diuretics |
| Moderate heart failure | Pulmonary edema or pleural effusion | Breathing difficulty, lethargy | Diuretics, fluid drainage |
| Thromboembolism (emergency) | Clot blocking aorta | Rear limb paralysis, severe pain | Immediate emergency care |
Home Monitoring for HCM Cats
- Resting respiratory rate: count breaths per minute while sleeping. Over 30/min = contact vet
- Track appetite and weight weekly. Rapid weight loss signals worsening heart failure
- Activity changes: less movement or easy fatigue may indicate cardiac deterioration
- Regular echocardiogram: even asymptomatic cats should have echo every 6–12 months
Sources & References
- Cornell Feline Health Center - Feline Heart Disease
- ACVIM - Feline Cardiomyopathy Guidelines
※ This article is for informational purposes only. Consult a veterinarian for diagnosis and treatment.