Hypertrophic cardiomyopathy (HCM) in cats: causes, symptoms and prevention

• susceptible breeds, including Maine Coons, Ragdolls, Persians and British Shorthairs
• cats older than 5–7 years
• males, which are affected more often than females
• cats with endocrine or other systemic diseases

HCM can also occur in young cats, so the age in the list is not a minimum age for investigation. Exact prevalence in different breeds and the significance of every underlying factor are incompletely known. An endocrine disease can cause a change resembling HCM and must be distinguished from inherited or otherwise unexplained heart muscle disease.

Diagnosis is confirmed using:

• auscultation, listening to heart sounds and rhythm abnormalities
• heart ultrasound, or echocardiography, the diagnostic gold standard
• an ECG to identify arrhythmias
• chest X-rays to assess the heart and lungs
• blood tests, including thyroid hormone measurement

What do ultrasound and other tests investigate?

As well as ventricular walls, ultrasound assesses areas including the heart chambers, atrial size and blood flow. Left atrial enlargement can help identify cats with increased clot or heart failure risk. Interpretation requires an overall assessment; a single wall measurement does not describe the severity of the whole disease.

A murmur may prompt investigation, but some cats with HCM sound entirely normal on auscultation. Conversely, a murmur alone does not prove HCM. An ECG examines electrical rhythm and does not replace ultrasound for assessing heart muscle structure. X-rays particularly investigate fluid changes in the lungs and chest cavity if the cat's condition allows imaging.

Blood pressure and thyroid values help identify other causes of thickening. Blood markers of cardiac strain can also be measured when needed. Their results do not replace cardiac imaging on their own, particularly when mild disease or disease without symptoms is suspected. A cat with breathing difficulties is stabilised before extensive investigations.

DNA tests for MYBPC3 mutations are available for Maine Coons and Ragdolls and are used in breeding animals. However, a negative test does not exclude HCM, so regular heart ultrasound remains important. Count your cat's breathing while asleep: one breath in and out counts as one breath; count for 30 seconds and multiply by two. A normally sleeping cat breathes fewer than 30 times per minute. If the rate repeatedly exceeds 30, call the vet; if breathing is open-mouthed or laboured, take your cat to a practice immediately.

Interpreting breathing measurements

Count when your cat is sleeping calmly and not purring. Record results and compare them with its previous baseline. A measurement after heat, play or stress does not represent sleeping respiratory rate. The vet may provide an individual threshold for contact. Laboured breathing is an emergency regardless of whether you have counted an exact number.

A genetic test indicates risk associated with the tested mutation, rather than establishing whether or when the cat will become ill. One normal heart ultrasound does not guarantee disease cannot appear later either. Genetic testing for breeding and monitoring of heart structure complement each other.

Nutrition and giving medication

Monitor appetite and preservation of muscle as well as weight. A cat with heart disease may lose muscle even without looking very thin. The diet should be complete and palatable; a substantial appetite reduction may indicate a problem with disease or medication. Supplements, salt restriction and possible dietary changes are assessed individually.

Ask for practical instructions if your cat resists medication. Report missed doses, vomiting of medicine or reduced eating. This helps assess how treatment is being carried out. Mention the HCM diagnosis before anaesthesia or treatment of another illness too, so the heart's condition can be considered.