What is Feline Hypertrophic Cardiomyopathy (HCM)?
Feline Hypertrophic Cardiomyopathy (HCM) is a progressive, incurable heart disease that affects up to 15% of cats. In cats with HCM, the muscular walls of the heart become abnormally thickened. In HCM, this most commonly affects the left ventricle which is the chamber responsible for pumping oxygenated blood to the rest of the body.
As the walls of the left ventricle thicken, the space inside the chamber becomes smaller, reducing the amount of blood the heart can hold and pump with each beat. This limits the delivery of oxygen to the body and to the heart muscle itself. Thickened heart muscle can also create physical obstructions that interfere with blood leaving the heart. This form of the disease is known as obstructive HCM.
Obstruction to blood flow out of the left ventricle can cause blood to back up into the left atrium, the upper chamber of the heart that receives oxygenated blood from the lungs. When pressure builds in the left atrium, fluid can accumulate in the lungs, leading to a serious and potentially life-threatening condition known as congestive heart failure.
What Are the Signs and Symptoms of HCM in Cats?
In some cases, the first indication that a cat has HCM may be a major cardiac event or, rarely, sudden death. Early signs of HCM can be missed or overlooked for several reasons:
Cats instinctively hide signs of illness, which can allow early symptoms to go unnoticed.
Some early abnormalities, such as heart murmurs or arrhythmias, typically require clinical examination to detect.
Many cats do not appear outwardly ill until the disease is advanced, maintaining normal energy levels, appetite, and behavior.
Certain symptoms may be mistakenly attributed to aging or less serious conditions.
Cats with HCM may experience one or more of the following:
Lethargy, which may result from reduced oxygen delivery due to impaired blood flow.
Labored or rapid breathing, which can occur when fluid accumulates in the lungs.
Sudden weakness or paralysis of the hind legs, caused by blood clots that can form as a result of abnormal heart rhythms. These clots can block blood flow to the arteries supplying the back legs. This is a medical emergency requiring immediate veterinary attention.
Abnormal heart rhythms or heart murmurs, which may be detected during a veterinary examination.
Because HCM can progress silently, early detection through veterinary evaluation is critical. Diagnosis and management decisions should always be made in consultation with a licensed veterinarian.
