Hypertrophic Cardiomyopathy (HCM) in Cats

Feline hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats, accounting for over half of all diagnosed cases of feline heart disease. 

While HCM is a common condition, it’s also a frustrating one, because it is difficult to predict how it will affect any individual cat. Some affected cats remain asymptomatic for their entire lives, never requiring any sort of treatment for their HCM, while others have significant effects, including sudden death. 

The unpredictable nature of HCM makes it a challenge and a source of frustration for both pet owners and veterinarians. 

What is Hypertrophic Cardiomyopathy?

Hypertrophic cardiomyopathy is a common heart disease in cats, affecting 10-15 percent of pet cats [1]. This condition causes abnormal thickening of the muscular walls of a cat’s heart. Once the muscular walls of the heart become thickened, they interfere with the heart’s function and prevent the heart from beating efficiently.   

Hypertrophic cardiomyopathy primarily affects middle-aged and older cats. Certain cat breeds are more likely to develop HCM than other breeds. Predisposed breeds include Maine Coons, Ragdolls, British Shorthairs, Sphynx cats, Persians, and Chartreux cats. 

What Causes HCM in Cats?

The fact that some breeds are more likely to develop HCM than others indicates that there is a genetic basis for the condition. The specific mutation responsible for HCM has been identified in Maine Coons and Ragdolls, but the HCM gene in cats has not yet been identified in other breeds.  

Symptoms of Feline Cardiomyopathy

The clinical signs of HCM in cats can vary significantly, with some cats being completely asymptomatic and others experiencing sudden death. 

The two most common manifestations of HCM are congestive heart failure and thromboembolism (blood clots). Cats in congestive heart failure develop fluid buildup in or around the lungs, leading to lethargy and shortness of breath. They may also develop fluid accumulation within the abdomen (belly). Cats with a thromboembolism experience a sudden blockage of blood flow to some part of the body. In many cases, the blood flow to the hindlimbs is disrupted, causing sudden pain, weakness, or paralysis of the hindlimbs. This is referred to as a saddle thrombus. 

Possible symptoms of HCM in cats include: 

• Asymptomatic (no clinical signs)
• Rapid breathing 
• Labored breathing
• Open-mouthed breathing
• Coughing (rare) 
• Fluid distention of the abdomen
• Lethargy
• Sudden hind-limb pain, weakness, or paralysis
• Sudden death

Stages of HCM in Cats

Hypertrophic cardiomyopathy in cats is typically a progressive disease, although it may progress very slowly and it may go undiagnosed until the disease is severe. For other cats, progression is rapid and symptoms arise at a young age.

Echocardiogram (ultrasound of the heart) can show changes before cats become symptomatic and should be part of routine check-ups for high-risk cats. In fact, some affected cats will not experience significant progression and may remain asymptomatic for the remainder of their lives.

Over a period of years, cats with HCM may develop moderate or severe disease. Cats with severe HCM are at risk of heart failure and thromboembolism.

Diagnosing HCM in Cats

If your veterinarian suspects heart disease in your cat, he or she will first perform a thorough physical examination. Findings that are typically associated with HCM include a heart murmur, an abnormally rapid heartbeat, and abnormal lung sounds (which may suggest congestive heart failure). However, in some cats with mild, asymptomatic HCM, there may be no abnormalities apparent on physical examination. 

Initial screening tests for feline heart disease include chest radiographs (X-rays), electrocardiogram (ECG), and a blood test called NTProBNP. An enlarged heart in cats may suggest the presence of HCM and ECG abnormalities may also support this finding. If screening tests suggest the presence of HCM, your veterinarian will recommend more specialized testing. Your veterinarian may also perform tests to rule out hyperthyroidism and elevated blood pressure, both of which can be associated with the development of reversible HCM.  

The most definitive HCM testing in cats is echocardiography. Echocardiography involves the use of an ultrasound to obtain a three-dimensional view of the heart, allowing the veterinarian to assess the thickness of the heart walls and the flow of blood through the heart. 

In Maine Coons, Ragdolls, and Sphynx cats, genetic testing can be used to identify affected cats and cats that carry the mutation responsible for HCM.

How to Treat Feline HCM

There is no cure for HCM and no treatment that prevents the progression of this disease. Instead, the goal of HCM treatment is to manage the clinical signs of heart disease and improve the cat’s quality of life. The goals of treatment include treating congestive heart failure, preventing aortic thromboembolism, and preventing arrhythmias. 

Medications for HCM in Cats

There is no medication that specifically addresses HCM. Instead, medications are prescribed based on the effects of HCM that a particular cat is experiencing or expected to experience. Asymptomatic cats do not typically require treatment, until their condition progresses to a point that they become symptomatic. Research has shown that medicating a non-symptomatic cat does not delay onset of symptoms.

Cats with signs of congestive heart failure are often prescribed a diuretic, such as furosemide (Lasix®), and an ACE-inhibitor, such as enalapril. These medications are intended to remove excess fluid from the chest and abdomen. Pimobendan may also be prescribed to cats in congestive heart failure, to improve heart function. 

Additional medications may be prescribed to reduce the risk of thromboembolism (blood clots). These medications may include clopidogrel (Plavix®) or low molecular weight heparin. 

Beta blockers, such as atenolol and propranolol, and calcium channel blockers, such as diltiazem, may also be prescribed in cats with an elevated heart rate. These medications are intended to decrease the heart rate, allowing the heart to fill more efficiently and function more effectively. 

General Cost to Manage This Condition 

The initial diagnosis of HCM in cats is typically the most expensive part of a pet’s management plan, given the need for referral to a veterinary cardiologist for an echocardiogram. 

The initial workup for a cat with HCM typically costs approximately $1,000-$1,500. Once these initial diagnostics have been completed, however, the ongoing costs associated with monitoring and treatment are often relatively low. 

If a cat requires hospitalization for an acute episode of congestive heart failure or aortic thromboembolism, however, costs may be higher.

How to Prevent HCM in Cats

There is no way to prevent the development of HCM in an individual cat. Breeders, however, can play a significant role in preventing HCM in predisposed breeds. In breeds for which a genetic test is available, such as Maine Coons and Ragdolls, genetic testing should be performed prior to any breeding and cats who carry the gene for HCM should not be bred. If you purchase a pure-bred cat, always ask your breeder for records of this important testing.

In predisposed breeds that do not have an available genetic test, screening echocardiography should be performed routinely in breeding cats. Cats with evidence of HCM should be removed from the breeding program, as should their close relatives.  

Related Conditions

• Systemic Hypertension
• Hyperthyroidism
• Heart Failure