Hypertrophic Cardiomyopathy (HCM) in Cats
Hypertrophic cardiomyopathy (HCM) in cats is a heart disease caused by the thickening of the left ventricular wall. This thickening reduces the available space for blood within the heart.
As a result, blood accumulates in the left atrium, causing it to enlarge. Eventually, blood builds up in the lungs, decreasing blood flow out of the left ventricle and leading to left-sided heart failure.
The blood remaining in the left atrium may form clots, which can break off and travel to other parts of the body. Additionally, the blood flow out of the left ventricle can become obstructed—a condition known as obstructive HCM—making it even harder to pump blood to the rest of the body.
Causes of Hypertrophic Cardiomyopathy (HCM) in Cats
Hypertrophic cardiomyopathy (HCM) is a common heart disease in cats with diverse origins. In many cases, the exact cause remains unknown, classified as idiopathic.
For certain breeds such as Maine Coon, American Shorthair, and Ragdoll, HCM is recognized as a genetic disease. Additionally, breeds like the Norwegian Forest Cat, Turkish Van, Scottish Fold, British Shorthair, and Devon Rex may also inherit this condition genetically.
Besides genetic causes, HCM can also be secondary to other health issues such as hyperthyroidism, hypertension (high blood pressure), or aortic valve stenosis, which is a congenital heart defect.
Moreover, male cats appear to be more susceptible to developing HCM compared to females.
Clinical Symptoms of Hypertrophic Cardiomyopathy (HCM) in Cats
Hypertrophic Cardiomyopathy (HCM) in cats is often detected before the onset of heart failure because about 80% of affected cats have a heart murmur that is heard during routine physical exams. Abnormal heart rhythms (arrhythmias) or extra heart sounds (such as a gallop rhythm) can also be detected by auscultation.
The severity of HCM varies widely. Mild cases may either progress and worsen over time or remain stable for many years. Early signs, such as lethargy and exercise intolerance, are frequently overlooked.
Common early symptoms that may be noticed include increased respiratory rate (over 50 breaths per minute) and labored breathing. If a blood clot lodges in the arteries supplying a front or hind limb, the affected limb can become paralyzed, cold to the touch, and show bluish discoloration of the paw pads. This condition is also quite painful, especially at the onset.
In summary, the clinical signs of hypertrophic cardiomyopathy in cats include:
- Heart murmur or abnormal heart sounds such as a gallop rhythm
- Arrhythmias (irregular heartbeats)
- Increased respiratory rate and labored breathing
- Lethargy and reduced exercise tolerance
- Sudden paralysis of limbs with cold, blue paw pads caused by blood clots blocking blood flow
- Pain associated with thromboembolism
Because cats are adept at hiding illness, these signs may be subtle and only recognized upon veterinary examination. Regular check-ups are essential for early detection and management of this common cardiac disease in cats.
Recommended Tests After Detection of Heart Murmurs in Cats
When a diagnostic test detects a heart murmur, several follow-up examinations are recommended to better assess the cat's cardiovascular health:
- Chest X-Ray: To evaluate the size and structure of the heart and lungs.
- Echocardiography (Heart Ultrasound): Provides detailed images of the heart's function and structure.
- Blood Pressure Measurement: To check for hypertension, which may contribute to heart conditions.
- Thyroid Hormone Levels: Especially recommended for cats over 5 years old, as thyroid issues can affect heart function.
Additional Laboratory Tests
For cats with heart failure or blood clots, further laboratory tests may be performed to evaluate kidney and other organ function.
Electrocardiogram (ECG)
If an abnormal heart rhythm (arrhythmia) is suspected, an electrocardiogram (ECG) can be used to detect and analyze these irregularities.
Genetic Testing in Breeds Predisposed to HCM
For Maine Coon and Ragdoll cats, blood tests can be performed to identify genetic mutations responsible for hypertrophic cardiomyopathy (HCM).
Treatment Plan for Hypertrophic Cardiomyopathy (HCM) in Cats
Currently, there are no medications available to prevent the progression of hypertrophic cardiomyopathy (HCM). Therefore, asymptomatic cats typically do not receive treatment unless they exhibit significant blood flow obstruction, marked ventricular hypertrophy, atrial enlargement, or an increased heart rate compared to normal. These cats may be treated with atenolol or diltiazem.
For cats who develop secondary HCM due to hypertension or hyperthyroidism but remain asymptomatic, successful treatment of the primary disease generally eliminates the need for further medication.
Cats suffering from heart failure usually require hospitalization to stabilize their condition. Treatment usually involves oxygen therapy, injectable diuretics such as furosemide, and nitroglycerin ointment. If there is significant fluid accumulation in the chest, it can be manually removed.
Once heart failure stabilizes, cats are commonly transitioned to oral furosemide combined with either atenolol (a beta-blocker) or diltiazem (a calcium channel blocker). These two drugs help keep the heart rate low, allowing sufficient time for the left side of the heart to fill with blood.
If the left atrium is enlarged, medications to prevent blood clot formation may be initiated. Infant aspirin has been used for many years, and clopidogrel (Plavix) has also shown benefit.
Angiotensin-converting enzyme (ACE) inhibitors—such as enalapril, benazepril, or ramipril—are also recommended to reduce fluid retention in the body, especially in animals with left-sided heart failure.
Follow-up Care for Cats with Hypertrophic Cardiomyopathy (HCM)
Cats with asymptomatic HCM and no left atrial enlargement are typically re-evaluated every 4 to 6 months at the initial stage, mainly through repeated echocardiography. If their condition remains stable, annual check-ups are recommended.
Cats with mild disease generally require more frequent monitoring, depending on the medications they are receiving.
Cats suffering from left-sided heart failure need regular chest X-rays and laboratory tests. The frequency of these tests depends on how the cat responds to treatment.
After addressing any underlying issues, cats with secondary HCM usually undergo echocardiographic evaluation every 4 to 6 months to assess whether the HCM is regressing.
Finally, cats that have heart murmurs but normal echocardiograms can be monitored with annual echocardiography.
Prognosis of Cats with Heart Conditions
Prognosis: Cats suffering from left-sided heart failure can survive for one year or longer if they respond well to initial treatment. Cats with advanced hypertrophic cardiomyopathy (HCM) usually die due to heart and kidney failure. Cats with thromboembolism have a poorer prognosis. As for asymptomatic cats whose condition remains stable, they can live for many years.
