What is HCM and why is screening important?
HCM is the abbreviation for Hypertrophic Cardiomyopathy, a disease of the heart which causes the muscles that make up the walls of the cat’s heart to thicken. In cats, it is usually the left ventricle that thickens. The thickening causes the heart to become less efficient by decreasing the volume of blood that can pass through the chamber and changing the heart’s ability to relax. This causes oxygen starvation in the heart cells and arrhythmia (abnormal heart beat pattern). Additionally, HCM can cause blood clots to form in the heart and leads to congestive heart failure and death in 25-30% of affected cats. Many cats with mild HCM show no symptoms, but cats with more severe HCM will often show signs of distress – panting, rapid breathing, lethargy, and even sudden death. The disease is progressive – usually developing when the cat is a few years old and worsening with time as the thickening of the heart muscles increases.
Diagnosis is made by an echocardiogram by a feline cardiologist – the cardiologist will use an ultrasound machine to view the heart and measure the thickness of the chamber walls. HCM is known to be genetic and more common in some breeds than others – particularly Ragdolls, Maine Coons, and Bengals. In both Ragdolls and Maine Coons, there are genetic tests that can identify genes likely to cause the cat to develop HCM. These genes have not yet been identified in Bengals, so currently the only way to identify Bengals with HCM is by echocardiogram. Occasionally a cat with HCM will have a heart murmur that can be detected by a veterinarian using just a stethoscope, but since there are many other issues that can cause heart murmur, an echocardiogram would still be needed to identify the problem.
Early detection is key in treating HCM – medications can slow the progression of the disease and lessen the symptoms, however there is no cure. HCM is known to be an autosomal dominant trait – cats that develop HCM will have a parent who has at least one copy of the gene that causes it. Because of the genetic cause of the disease, cats with even mild HCM should NOT be bred and since many cats with HCM do not show symptoms (especially at first), the only way to prevent breeding HCM positive cats is the have regular echocardiograms done by a feline cardiologist. Unfortunately, since HCM often develops later in life, a cat that is clear of HCM at 1 year old may very well show signs of HCM at 2 or even later, though the older a cat is when it screens clear, the more likely it is to truly be clear. Continued screening of all breeding cats for several generations is the best way to prevent passing on the genes that cause HCM. Screening retired breeding cats who have offspring in breeding programs is also valuable though not often done since retired breeders are usually sent to pet homes. There are breeders who may say that it is pointless to screen at 1 year old because HCM is so rarely diagnosed at that age, however the 1 year screening is valuable for identifying the few cats that develop HCM at a young age as well as identifying any other heart problems that may be genetic (such as mitral valve prolapse). Additionally, the 1 year screening gives the cardiologist baseline measurements which can be compared to future screenings and identify potential thickening of the ventricle walls even earlier. Breeders who do not screen at all can very well be breeding HCM positive cats without even knowing – because how would they know if the disease is currently mild and not causing symptoms? An HCM positive cat has the genes that cause the disease and is statistically passing those genes to its kittens 50% of the time. HCM screening is not a perfect test, but right now it is the best tool available to diagnose the disease and prevent it in future generations. HCM screening every breeding cat every 12-18 months can be inconvenient and expensive, but it is well worth the time and expense to ensure any cat who has HCM is not bred.
- Hypertrophic Cardiomyopathy – Cornell Feline Health Center: https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/hypertrophic-cardiomyopathy
- Feline Hypertrophic Cardiomyopathy: Advice for Breeders – by Kittl