Structure and Function of the Cardiovascular System in Cats

Structure and Function of the Cardiovascular System in Cats

By: Virginia Wells

What Are the Common Diseases of the Cardiovascular System?

  • Hypertrophic cardiomyopathy (HCM). Cardiomyopathy is a disease of heart muscle. In hypertrophic cardiomyopathy the muscles of the heart become tremendously thickened. This disease most often affects the muscles of the left ventricle and septum of the heart. As the muscular walls increase in size, the size of the heart chambers become smaller, which reduces the amount of blood that can flow through the heart. This form of cardiomyopathy is the most common type of cardiomyopathy seen in cats. It may develop spontaneously due to unknown reasons, or it may arise secondary to hyperthyroidism. Some families of Maine coon cats develop an inherited form of this disease.

  • Dilated cardiomyopathy (DCM). Dilated cardiomyopathy is disease where the heart muscle becomes weak and very flabby.
    As the muscles weaken, the chambers of the heart enlarge in size or become dilated. This disease primarily affects the left side of the heart. Weakening of the muscles decreases the ability of the heart to pump blood to the rest of the body. In cats, this disease has been associated with a deficiency in the amino acid, taurine.

  • Heart failure. This is an inability of the heart to maintain a circulation sufficient to meet the body's needs. Congestive heart failure (CHF) occurs as a result of impaired pumping ability and is associated with water and sodium retention. It may arise with severe forms of cardiomyopathy, from weakening of the valves of the heart, from inflammation of the heart, secondary to pericardial diseases, and tumors.

  • Arrhythmias. Cardiac arrhythmias are disturbances in heart rate or rhythm. The electrical activity of the heart is altered, which may greatly affect the ability of the heart to coordinate the contractions of its different chambers. Arrhythmias can be mild and insignificant, or be serious enough to cause heart failure and sudden death. Arrhythmias may arise in conjunction with almost any form of heart disease, and can also develop with other diseases in the body, such as high potassium levels, low oxygen levels, infections, hormone imbalances, drugs, trauma, and organ failure.

  • Infectious endocarditis. Infectious endocarditis is an inflammation of the heart caused by some sort of infectious agent, such as bacteria, protozoa, and viruses. This condition is uncommon in the cat, but may arise with bacterial infections, or infections with toxoplasmosis.

  • Valvular disease. Various diseases affect the valves and alter the normal function of the valves. Congenital valvular defects are uncommon in the cat, but pulmonic stenosis (narrowing of the pulmonary valve), and malformation of the tricuspid and mitral valves may occur. Acquired diseases of the valves are also sometimes encountered in cats and usually cause the valves to leak. As the chambers of the heart contract, blood may leak backward through an abnormal valve. This greatly increases the workload of the heart.

  • Pericarditis and pericardial effusion. Pericarditis is inflammation of the pericardium, which is the fibrous sac that encloses the heart. Pericardial effusion is the accumulation of fluid within the pericardial sac. As fluid accumulates in this sac, it applies pressure to the heart and decreases the ability of the heart to pump blood. Pericardial diseases in the cat may arise with infections (e.g. feline infectious peritonitis, bacterial and protozoal infections), tumors, cardiomyopathies, trauma, and kidney failure.

  • Heartworm disease. Heartworm infection is uncommon in cats, but may occur in many areas of the United States. It is caused by a parasite (Dirofilaria immitis) that enters the body through the bite of an infected mosquito. The adult worms prefer to live in the pulmonary vessels that lead from the right heart to the lungs. Heartworm disease in the cat may cause chronic coughing, intermittent vomiting or difficulty breathing, lethargy, weight loss and sometimes sudden death. Heartworm disease can be difficult to diagnose in the cat, and is sometimes only found after death during a necropsy (an animal autopsy).

  • Thromboembolism. A thrombus is a blood clot that develops within the heart or a blood vessel. An embolus is a blood clot that arises in one area of the circulatory system and is transported in the bloodstream to a distant site, where it becomes lodged in a blood vessel. The most common form of this disease in cats is the development of a blood clot in the left atrium associated with cardiomyopathy. A small embolus may break free and travel down the aorta to lodge at the point where the aorta divides into the two arteries that go to the legs. An aortic embolism often causes paralysis of one or both hindlegs.

  • Arteritis or vasculitis. This is an inflammation of arteries or veins that may be caused by viruses, bacteria, parasites or immune-mediated diseases. This type of inflammation is rare in the cat.

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