Signs, Symptoms and Treatment of Hypertrophic Cardiomyopathy (HCM) in Cats
January 20th, 2015 | Posted in Medical Articles
Hypertrophic cardiomyopathy (HCM) is the most common heart disease of the cat. It is believed to be an inherited disorder in most cases. Symptoms of HCM vary considerably from cat to cat but a heart murmur is a common finding. Early detection and treatment generally lead to an improved prognosis for survival. Genetic testing is currently available for Maine Coon cats and Rag Doll cats. A negative genetic test for the currently known mutation does not guarantee that HCM from another mutation yet to be identified will not develop. However, a positive test indicates the individual is either a carrier of or will develop HCM.
Hypertrophic Cardiomyopathy (HCM) is the most common heart disease of the cat. This disorder results in hypertrophy or thickening of the heart muscle (Figure 1B) which, in time, creates increased stiffness of the heart walls (muscle) causing poor cardiac function during the relaxation phase of the cardiac cycle (diastole). As this condition becomes worse, the thickened heart muscle can cause obstruction to blood flow leaving the heart via the aorta increasing the effort needed to pump blood out of the heart during the contraction phase of the cardiac cycle (systole).
The cause of HCM is thought to be a genetic mutation of the genes that control heart muscle growth making HCM an inherited disorder. The genetics of one HCM mutation have been determined in the Maine Coon cat and the Rag Doll cat but the genetic defect has not been identified to date in other pure bred or domestic types of cats. In humans, more than one genetic mutation has been identified as causing HCM and it is likely that this is true for cats as well.
The symptoms of HCM are varied, most likely due to varying degrees of severity and possibly different genetic mutations in individual cats. Most frequently, patients are diagnosed when they have no symptoms but after a veterinarian detects a heart murmur or an irregular heart beat during a physical examination. When symptoms arise, they may include signs of congestive heart failure (increased respiratory rate , labored breathing, shortness of breath, lethargy and appetite loss, or changes in daily behavior such as hiding or seclusion); sudden loss of function of one or more legs due to blood clots obstructing blood flow to the affected leg(s); collapsing spells from an irregular heart rhythm or small blood clots traveling to the circulation of the brain (stroke); and occasionally, acute sudden death may occur without any symptoms being noted.
Patients suspected of having HCM or cats who have an unexplained heart murmur or irregular heart beat should have a thorough physical examination including blood pressure assessment, chest x-rays, an electrocardiogram (EKG), and an ultrasound examination of the heart (echocardiogram). Maine Coon cats and Rag Doll cats being considered for breeding should have a DNA test to determine if they are free of the genetic defect known to cause HCM in their respective breed.
The treatment recommended for patients with HCM vary with the severity of the condition at the time of detection. Current medications include drugs that slow the heart rate and improve relaxation of the heart (beta blockers or calcium channel blockers), drugs that thin the blood to prevent blood clots from forming (platelet inhibitors, anticoagulants), and diuretics to control abnormal fluid buildup. The use of one or more of these medications is determined based on each individual patient’s condition.
The prognosis or expected outcome for patients with HCM varies considerably with those patients having more advanced disease having a poorer prognosis. Some patients with HCM remain free of symptoms for several years while others have a more rapid progression of their disorder and develop symptoms quickly. It is not unusual for patients to become symptomatic without any suspicion of previous heart disease. Once in congestive heart failure, most cats with HCM have a life expectancy of 6 and 18 months.
If your cat is showing symptoms that could be the result of HCM or if your cat is known to have a heart murmur, have your primary care veterinarian perform a complete physical examination and any other tests he/she deems appropriate. These tests will help determine if your cat should be referred to a veterinary cardiologist for further diagnostic tests and/or possible treatment.