Hypertrophic Cardiomyopathy (HCM) in Cats

Hypertrophic Cardiomyopathy (HCM) in Cats

Overview of Feline Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is condition characterized by a thickening of the main pumping chamber of the heart (the left ventricle) and not attributed to other medical conditions (such as high blood pressure). It can, in severe cases, cause heart failure when fluid accumulates in the lungs. Blood clots, too, can form in the heart and travel to distant blood vessels obstructing blood flow to one or more limbs (especially the back legs). HCM can be mild to life-threatening.

Below is an overview of Hypertrophic Cardiomyopathy in Cats followed by detailed information on the diagnosis and treatment of this serious disease. 

Males of the Maine coon cat, Persian cat and Ragdoll cat breeds are most likely to be affected along with cats ages 6 months to 4 years, though all ages can be affected.

The main causes of HCM are genetic. Factors that can precipitate difficult breathing and/or heart failure in a cat with HCM include: fever, infection, stress (yes, even a veterinarian visit!), anesthesia and/or sedation and intravenous administration.

What To Watch For

  • Noisy, difficult, open-mouthed breathing
  • Sudden inability to use one or more limbs
  • Odd posture of squatting or lying with chest down, head extended and elbows pointed outward
  • Lack of appetite
  • Weight loss
  • Inactivity

    See your veterinarian immediately if you see these signs.


    Veterinary Care for Hypertrophic Cardiomyopathy in Cats

    Veterinary care should include diagnostic tests to determine the underlying cause and help guide subsequent treatment recommendations.

    Diagnosis of Hypertrophic Cardiomyopathy in Cats

    Diagnostic tests are needed to recognize HCM, and exclude other diseases, including:

  • Complete medical history and physical examination, including observation of the heart and lungs using a stethoscope
  • Chest X-rays
  • Echocardiogram (ultrasound exam of the heart) -a painless procedure in which a probe is held against the chest after clipping the hair for initial diagnosis and confirmation.
  • Electrocardiogram (EKG) -a tracing representing the heart’s electrical action derived by amplification of the minutely small electrical impulses normally generated by the heart.
  • Blood tests to evaluate your cat and/or to monitor treatment.
  • Treatment of Hypertrophic Cardiomyopathy in Cats

    There is no recommended treatment for very mild cases with no symptoms, but regular follow-up visits to your vet are vital. There may be an initial hospital admission and possible stay for severe cases. Severe cases of hypertrophic cardiomyopathy are life-threatening.

    Home Care

    Give medications as directed and regularly observe your cat’s relaxed breathing rate. Learn to take the heart rate, record results and relay this information to your veterinarian regularly.

    Minimize stressful situations. Many cats may be best kept as indoor only pets.

    Preventive Care

    This disease is thought to be genetic; therefore, there is no preventative care. Cats affected with this condition should not be bred.

    In-depth Information on Hypertrophic Cardiomyopathy in Cats

    Cardiomyopathy is a general word used to indicate heart muscle disease. Some cardiomyopathies have well defined causes, while the reason for other cardiomyopathies is unknown. Symptoms of cardiomyopathy are not specific, and many heart and lung diseases produce symptoms and clinical findings similar to HCM. The diagnostic tests recommended will help differentiate HCM from the following:

  • Hyperthyroid heart disease (caused by excessive functional activity of the thyroid gland)
  • Hypertensive heart disease (caused by high blood pressure)
  • Feline restrictive cardiomyopathy
  • Feline dilated cardiomyopathy
  • Congenital heart disease
  • Moderate to severe anemia (low red blood cell count; anemia can cause heart enlargement and/or failure in cats with heart disease)
  • Fluid over-infusion (fluid therapy can cause heart failure in cats with heart disease)
  • Primary pericardial diseases (diseases of the sac enclosing the heart and roots of the greater blood vessels)
  • Growth hormone excess
  • Mediastinal mass (a mass in the space between the membrane encasing the lung and lining the thoracic cavity).
  • Veterinary care should include diagnostic tests and subsequent treatment recommendations.

    Diagnosis In-depth

    Diagnostic tests are essential in recognizing HCM. Tests may include:

  • Complete physical examination and medical history review. This includes a stethoscope examination of the chest.
  • Chest X-rays to detect heart enlargement, identify fluid in the chest and exclude other causes of difficult breathing (such as pneumonia, asthma or tumors).
  • An electrocardiogram (EKG – a recording of the heart’s electrical action) to screen for irregular heart rhythms and/or assist in identifying heart enlargement.
  • Thyroid test especially in cats older than 7 years of age to detect thyroid tumors.
  • Arterial blood pressure measurement to diagnose hypertension (persistently high blood pressure) as a cause of abnormal heart findings.
  • A complete blood count to diagnose anemia (low red blood cell count).
  • Blood tests that test organ function and blood electrolytes (blood particles capable of conducting an electric current), such as potassium, especially important in severe cases of heart failure, clot formation or complications in other body systems.
  • An echocardiogram (ultrasound of the heart) is the definitive diagnostic test required to establish proper diagnosis of HCM, after excluding other causes of heart enlargement. A veterinarian with skills in this area or specialist in cat heart disease is the best person to administer this test and draw conclusions from it. This is often a referral procedure. 
  • Treatment In-depth

  • No treatment may be recommended for very mild cases with no symptoms, but regular follow-up vet visits are vital.
  • Initial hospital admission and stay is often recommended for severe cases, such as congestive heart failure (fluid accumulation in lung or chest cavity), abnormal heart rhythms, blood clots, kidney failure, and/or low blood pressure or shock.
  • Oxygen, diuretics and/or nitroglycerine ointment may be given for initial treatment of congestive heart failure.
  • Tapping abnormal fluid accumulations(thoracocentesis) from the chest cavity is needed when fluid when present and interferes with breathing.
  • Blood clot complications need treated with additional medications (for pain and clot control). (NOTE: Clot-busting drugs (TPAs) have been effective in cats, but have very serious side effects.).
  • Dietary modifications in cats with obvious heart failure is sometimes recommended (such as a sodium-restricted prescription or medical diet).
  • Beta-blockers to slow heart rate, minimize the impact of stress and reduce obstruction of the heart’s ventricular outlet.
  • Diltiazem (a calcium channel antagonist) if congestive heart failure or abnormal heart muscle relaxation is evident; Dilacor or Cardizem CD (long-acting forms of diltiazem) may be recommended for the convenience of once-daily dosing.
  • Enalapril or benazepril (to reduce blood pressure) can be recommended for cats with heart failure to reduce activity of harmful hormones and reduce sodium retention.
  • Diuretics (to promote urine secretion) for fluid accumulation.
  • Nitrates (topically applied with a gloved hand to a relatively hairless area, such as the inside of the ear) for home use if difficulty in breathing or home medicating is a problem; old dose wiped off before new dose applied.
  • Aspirin or coumadin for high-risk clot-formation cases.
  • Follow-up Care for Cats with Hypertrophic Cardiomyopathy (HCM)

    Optimal treatment for a pet with HCM requires both home and professional veterinary care with follow-up being critical. Administer prescribed medications and alert your veterinarian if you are experiencing problems treating your pet. Follow-up includes:

  • Precise follow-up depends on the severity of your cat’s disease, its response to therapy, your vet’s recommendations and your views. A possible schedule may include follow-up every 6 to 9 months, depending on the natural course of the disease. Recheck examinations are done more frequently initially to monitor therapy.
  • Chest X-rays to monitor response to therapy
  • Blood samples checked periodically to monitor effect of drugs on kidneys and electrolytes (potassium, for example)
  • Blood pressure measurements taken periodically in cats receiving diuretics or ACE inhibitors like enalapril or benazepril (which reduce blood pressure).
  • Echocardiogram done initially and repeated periodically (at 3 to 6 months after diagnosis and again in 9 to 12 months, for example).
  • Disease can change rapidly, and tests to monitor disease progression will influence decisions about therapy and prognosis.
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