Hypertrophic cardiomyopathy is the most common heart disease in cats, causing thickening of the heart muscle that can lead to heart failure, blood clots, and sudden death, often with little warning.
HCM creates welfare challenges at multiple levels. The sudden onset of aortic thromboembolism is one of the most acutely painful events documented in cats - owners describe their cat's sudden screaming, paralysis, and extreme distress as profoundly traumatic. The decision whether to attempt treatment or euthanize must often be made in minutes, in a state of shock. Even without this complication, heart failure causes breathlessness and the distress of air hunger. Many cats with HCM live comfortable lives for years, but the risk of catastrophic complications means that quality-of-life can deteriorate rapidly and unpredictably. Genetic testing in predisposed breeds provides some warning but not all HCM-causing mutations are identified.