Hypertrophic cardiomyopathy (HCM) is the most commonly diagnosed cardiac disease in domestic cats and is characterized by thickened heart muscle in the pumping chamber (left ventricle). As a result, the heart muscle in HCM cannot relax and fill blood efficiently in the pumping chamber that can lead to an increase of pressure and fluid build-up in the body (also known as congestive heart failure).
Signs of congestive heart failure include shortness of breath, difficulty in breathing and weakness and these need to be managed medically (i.e., diuretics). Some area in the thickened heart muscle gets significantly impaired blood flow that can precipitate to developing abnormal heart rhythm and rate, so called arrhythmia. HCM cats with arrhythmia exhibit collapsing episodes or cardiac sudden death.
When applicable, anti-arrhythmic drugs (i.e, atenolol) can be instituted to decrease the number of arrhythmic events and to hopefully prevent sudden death. Although the mechanisms remain further defined, some HCM cats form a blood clot in the heart. Once broken to small enough pieces, these debris travel around the body and lodge onto small branches of blood vessels, particularly either right front leg or both back legs, resulting in cold temperature in affected legs, pale foot pads, extreme pain, inability to walk and often paralysis.
Medical or surgical management for this condition is very limited and unsuccessful. These devastating clinical outcomes from HCM draw attention to the importance of early detection of the heart disease in cats so that it can be detected early, monitored closely and managed appropriately.
Diagnostic methods of HCM consist of 3 major ways. No single test is superior to others and tests suggested are complementary to each other due to the nature of screening tests. 1) Genetic testing: A gene that is mutated in cats (Maine Coon, Ragdoll) with HCM has been identified. The name of gene is called myosin binding protein C (MYPC3). Either blood or buccal swab sample is required and is subject to sequencing analysis. As many other hereditary heart diseases, it is speculated that HCM in cats involve multiple mutated genes in addition to MYPC3. Therefore, the limitation of the genetic testing is that negative result for MYPC3 mutation does not necessarily mean that the cat tested is free of HCM. 2) Biomaker test: This blood test is simply done by measuring proteins such as NT-proBNP or cTnI. The concentrations of both are increased in parallel with severity of heart disease. However, the limitations of this blood test are that negative test results do not mean the absence of heart disease and the rate of false positive results is very high due to the nature of blood tests. 3) Cardiac Ultrasound (aka. Echocardiography): this is the most commonly used diagnostic test for directly visualizing thickened heart muscle, categorizing the severity of HCM and detecting evidence of blood clot in the heart. The limitation of this imaging technique is that negative echocardiographic findings do not predict the future occurrence of HCM at a later age.
The Cardiology Service at Auburn University's College of Veterinary Medicine provides the state-of-the-art facility and equipment for diagnosis and treatment of heart disease in animals. Drs. SeungWoo Jung and Sara Bordelon are dedicated to the enhancement of Auburn's outreach mission in working with referring veterinarians and clients in the area of veterinary cardiology. Please feel free to call us at 334-844-4690 for consultations.