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Hypertrophic cardiomyopathy (HCM) is the most common form of heart disease in cats. With this disease the heart muscle increases in size (hypertrophies); usually either the ventricular free wall or the interventricular septum are affected. As these muscles hypertrophy (get bigger), the lumen of the left ventricle gets smaller (the space that blood can occupy is smaller).

During systole, the ventricular heart muscles contract. During diastole, the ventricular heart muscles relax and the lumen is at its widest. In cats with severe HCM, the lumen is non-existent during systole and can be only 1/8 to ¼ its normal size during diastole, impairing blood flow. This leads to increased left ventricular diastolic pressure and can lead to severe pulmonary edema (fluid in the lungs) and both left and right sided heart failure.

HCM can be an inherited disease in American Short Hairs and Maine Coon cats. A genetic etiology is suspected in other breeds with an increased risk of HCM such as Persians, Himalayans, Birmans and Ragdolls. It can be seen in cats as young as 3 months of age to 19 years (mean age 5-7 years). Males have a higher risk.

Cardiomyopathy can be secondary to the following diseases:

  • Nutritional—taurine deficiency (causes Dilated CM)
  • Metabolic—hyperthyroidism, acromegaly (increased growth hormone)
  • Kidney disease—hypertension
  • Neoplasia (cancer), Amyloidosis
  • Inflammatory—immune disease, infectious agents
  • Toxic—doxyrubricin (a cancer drug), heavy metal ingestion

Clinical signs of HCM range from asymptomatic (no clinical signs) to severe. Common clinical signs are dyspnea (difficulty breathing, panting, open mouth breathing), anorexia (inappetence), exercise intolerance, vomiting, collapse, paralysis of rear legs and sudden death. Coughing is not commonly seen with this disease. A heart murmur or arrhythmia may or may not be heard on physical exam. Because of poor blood circulation, a thrombus (clot) can form, usually in the caudal iliac arteries, which leads to a painful paralysis of the rear legs. Prognosis is guarded to poor when this occurs. High blood pressure can potentially cause blindness.

Radiography is not that helpful in diagnosis of HCM. Occasionally an enlarged, valentine shaped heart may be seen on x-ray films. Radiographs should still be taken to assess involvement of lung disease. HCM is definitively diagnosed with ultrasound. Heart functioning, thrombus (clot) formation, obstruction of blood flow and measurement of the ventricle muscle can all be assessed with ultrasound. A thyroid test and blood pressure should also be performed to rule out hyperthyroidism and hypertension as causes of HCM. So that medications can be safely given, a comprehensive blood chemistry and complete blood cell count (CBC) should be performed to assess liver and kidney function.

The goal of therapy is to slow the heart rate, improve relaxation of the heart muscle, and lessen pulmonary edema. Prognosis varies based upon clinical signs, cause of HCM and response to treatment. Cats that are asymptomatic at the time of diagnosis have lived up to 6 years. Median survival time for cats with aortic thromboembolism is 61 days; cats with heart failure is 92 days; cats with a resting heart rate less than 200 live longer than cats with a resting heart rate of over 200. Some animals have complete resolution and remain normal after medications are withdrawn.

Calcium channel blockers improve relaxation and lessen pulmonary edema formation.

Give your pet __________________ orally _________ times daily.

Beta blockers slow heart rate, decreases oxygen demand of the heart muscle, and lessens obstructive disease.

Give your pet ___________________ orally ________ times daily.

Diuretics help to decrease pulmonary edema (remove fluid from the lungs). Diuretics are not selective by removing fluid from the lungs only. Therefore, all patients on diuretic therapy need to have fresh, clean water available at all times so that they do not get dehydrated and develop kidney problems.

Give your pet __________________ orally ________ times daily or as needed to help with difficulty breathing __________________________________________________.

Other medications: _________________________________________________________________________.

Stress needs to be minimized as much as possible. Your pet also cannot tolerate extremes of heat or cold as easily as he once could.

Some cats are placed on aspirin (NEVER GIVE TYLENOL TO CATS!) to help with thromboembolic disease. Give your pet ___________ orally every _______ days.

Diet: The first step is to make sure that your pet continues to eat well. Most asymptomatic cats do not need sodium (salt) restricted diets. If your pet is showing signs of heart disease, your veterinarian will recommend a special diet. However, if your pet will not eat the special diet, let your veterinarian know right away.

Recommend feeding your pet ______________________________________________.

Be sure that any treats or human food that is given to your pet is low in sodium (salt). We recommend that you discuss these in detail with your Doctor.

Recommend follow up exam/diagnostic tests in ____________days/weeks/months.

Call or come in to see your Doctor immediately if you notice any of the following signs:

  • Open mouth breathing; rapid, shallow panting.
  • Vomiting or Diarrhea
  • Collapse
  • Pale (bluish or white) mucus membranes
  • Inability to use (paralysis of) the rear legs.