HCM (Hypertrophic Cardiomyopathy or HKM) is a heart condition characterized by the thickening of the heart muscle. It is the most common heart disease in cats. Most affected cats are already advanced in age, but very young cats can also be affected. Learn more about recognizing symptoms of HCM in cats and treatment options.
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One of the most common heart diseases in cats is Hypertrophic Cardiomyopathy, or HCM for short.
Hypertrophic Cardiomyopathy is a continually progressing condition. If detected early, the vet can slow its progression with medications.
HCM is particularly dangerous for cats if it is not detected because they show very few symptoms. The consequences can be severe, including cardiac arrhythmia (blood clots) and sudden heart failure.
Unfortunately, cats react differently to heart medications. Even patients optimally managed with medications can suddenly experience severe episodes.
In the early stages of Cardiomyopathy, cats usually show no symptoms. The disease can only be identified through a heart ultrasound. Even in advanced stages, symptoms are often non-specific, making it hard to recognize.
The severity of symptoms depends on how pronounced the changes to the heart muscle are. The most common signs of HCM in cats include:
Paralysis of one or more limbs (especially the hind legs) with noticeable pain can indicate a thromboembolism. Here, a blood clot forms in the heart’s atrium and, when dislodged, blocks major arteries, usually in the legs.
A thrombosis is an emergency. See a vet immediately if such symptoms occur.
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Most cats show no symptoms indicating heart failure for a long time. When symptoms appear, the disease is often already advanced. In the following cases, please see a vet immediately:
Every specialised diagnostic method begins with a thorough general examination by your vet, including auscultation (listening) of the heart and lungs.
Heart murmurs or cardiac arrhythmia hint at heart disease. Harmless murmurs can only be distinguished from pathological ones via a heart ultrasound. Many cats with Hypertrophic Cardiomyopathy do not have a heart murmur.
Every heart examination includes an X-ray. In advanced heart disease, X-rays can reveal fluid backlog in the lungs (lung edema) or chest (pleural effusion). They can also show if the heart is enlarged.
The most definitive method for diagnosing HCM is echocardiography (ultrasound examination) of the heart by an experienced cardiologist. This measures the heart muscle thickness at different points.
The cardiologist also checks the heart’s contractility (ability to contract) and possible valve changes, helping to evaluate the severity of heart failure and decide on treatment and prognosis.
Examining for existing blood clots is crucial for selecting appropriate therapy and predicting outcomes. These clots form due to turbulent blood flow returning to the atria.
A comprehensive heart examination always includes blood pressure measurement. It helps distinguish between primary and secondary HCM, aiding in medication choices. High blood pressure worsens and accelerates hypertrophic Cardiomyopathy.
To rule out underlying conditions like hyperthyroidism or renal failure, blood tests and hormone screenings are necessary.
Measuring NT-proBNP in blood is another helpful test. This hormone increases when the heart muscle is stretched due to heart disease. It serves as a screening for early detection of heart disease in asymptomatic cats. If NT-proBNP levels are high, further ultrasound examination is recommended.
If cardiac irregularities are detected during auscultation, an ECG (electrocardiogram) should be performed. It records heart rate and the type and frequency of arrhythmias.
Based on the findings, the vet/cardiologist decides if medication is needed at the current stage. Cats are challenging heart patients, so therapy must be tailored to each cat and its disease stage. Other influencing factors include the cat’s acceptance of medications and its living conditions (outdoor or indoor cat).
In early stages, therapy is often unnecessary. If heart rate is significantly increased with valve changes, beta-blockers or calcium channel blockers can reduce the heart rate. Antiarrhythmics treat arrhythmias.
In advanced stages with lung edema or pleural effusion, immediate treatment is essential. Diuretics (drugs to remove excess fluid) help manage lung edema. The veterinary also uses circulatory support medications (usually ACE inhibitors).
Depending on ultrasound findings, medications enhancing pumping power (e.g., Pimobendan) may be beneficial.
If the vet detects an enlarged atrium or blood clot, anticoagulants (e.g., Clopidogrel) are administered to prevent thromboembolism.
In severe cases, fluid accumulations in the chest or abdomen may need draining.
Treating HCM in cats with aortic thrombosis is challenging. The treatment depends on the duration of symptoms, the extent of affected areas, and the location of the clot. Early intervention offers the best prognosis.
Pain relief, anticoagulants, and heart support medications are used to dissolve clots and restore blood flow to the limbs. However, toxins from poorly perfused areas can cause severe complications, necessitating treatment under strict veterinary supervision.
Besides medical treatment, annual heart ultrasounds help adjust ongoing therapy.
In advanced cases, refraining from treatment for the cat’s well-being and animal welfare reasons is advised.
Hypertrophic Cardiomyopathy does not always lead to clinical symptoms or health issues. Regular heart examinations are needed to assess the disease’s severity. Cats with early-detected and regularly monitored HCM can live many years with the condition.
The prognosis is better when thickening is minimal. However, existing lung water impair the outlook. Thromboembolisms also worsen the prognosis.
Medication response, cooperation between vet and pet owner, and the appearance of complications significantly impact the course of HCM in cats.
There is no single cause for Hypertrophic Cardiomyopathy. Various underlying issues can cause or contribute to HCM in cats.
Primary HCM often has a genetic basis, with affected cats typically between three-quarters of a year and five years old, more commonly male. Breeds often affected include Maine Coon, Ragdoll, British Shorthair, and Persian. Many other breeds and non-pedigree cats can also develop primary HCM.
Secondary Hypertrophic Cardiomyopathy results from other pre-existing conditions, mainly affecting older cats. Hyperthyroidism can lead to HCM in various ways. Diseases causing or associated with high blood pressure (e.g., chronic kidney failure) can also lead to Cardiomyopathy.
Regardless of the underlying cause, HCM results in variable heart muscle thickening. This muscle growth reduces the heart chambers’ internal space, diminishing the blood being pumped into the lungs and body.
This leads to a drop in blood pressure. The cat’s body tries to compensate by increasing heart rate, which exacerbates heart muscle changes, further reducing heart volume. This eventually causes blood to back up in the atria, leading to their dilation. The resulting turbulence promotes blood clot formation.
With the left heart side more commonly affected, fluid accumulates in the lungs (lung edema) or chest (pleural effusion). If the right side is affected, fluid accumulates in the abdomen.
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For frequently affected breeds like Maine Coon, regular heart ultrasounds are recommended. Specific genetic tests can detect inherited HCM predispositions.
Breeders of affected breeds should have their cats undergo cardiac ultrasounds before breeding. This is recommended from age two years for males and three to four years for females.
Despite preventive measures, HCM cannot be completely prevented. Early detection and regular disease monitoring can slow its progression and reduce severe consequences.
To monitor the health of an already affected cat, you can count its breathing rate at home. Breathing difficulties and increased respiration can indicate lung fluid.
A normal resting breathing rate is about 40 breaths per minute. Count chest movements and document them regularly. See a vet for abnormalities and consider a heart ultrasound.
During my studies of veterinary medicine and my doctorate at the Ludwigs-Maximilians-University in Munich, I was able to gain numerous insights into the diverse fields of veterinary medicine. Since 2011, I have been in practice as a veterinarian with a wide variety of animals and their diseases. My passion belongs to the task of helping my patients in the best possible way and ensuring their well-being. I also like to share my knowledge as a veterinarian and as a long-time dog owner and dog athlete as an author.
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