Feline Cardiac Disease
Heart murmurs & gallop sounds
Heart murmurs in cats can be benign or from underlying heart disease. Because cats can have significant heart murmurs and no cardiac disease, or can have no heart murmur and significant cardiac disease present, the use of heart murmurs to screen for heart disease is not very sensitive. An echocardiogram is often needed to determine if a murmur is present secondary to heart disease or not.
A gallop sound is always an abnormal heart sound and any cat with a gallop should have a cardiac evaluation.
Hypertrophic cardiomyopathy (HCM)
Hypertrophic cardiomyopathy is the most common feline acquired heart disease. Several different genetic mutations have been identified in pure bred cats that results in this disease. On an anatomic level, HCM is characterized by a thickening of the ventricular muscle wall. Microscopically this disease appears as abnormally arrayed muscle fibers with inflammatory cells, fibrosis, and thickened coronary arterial walls. Physiologically, the disease causes impaired muscle relaxation so that blood cannot adequately empty into the ventricles. Eventually, this causes left atrial enlargement and eventually can lead to congestive heart failure.
Hypertrophic obstructive cardiomyopathy (HOCM)
Hhypertrophic obstructive cardiomyopathy occurs when there is a thickening of the ventricle wall (HCM) and the presence of some abnormal motion of the mitral valve. The mitral valve can get “sucked” out of position as the heart contracts, and this can cause a leak in the mitral valve with blood moving backwards, as well as a narrowing of the outflow tract to the aorta, causing increased work for the heart to pump blood to the body. This is considered the “obstructive” part of the disease. The obstruction can contribute to the ventricular thickening, as it is causing the heart to have to pump harder and generate more pressure. The fast, turbulent blood flow out the aorta is often associated with a heart murmur.
Restrictive cardiomyopathy (RCM)
Restrictive cardiomyopathy is the term given to cats that have demonstrable cardiac disease as evidenced by enlarged atria, but whose ventricles are normal thickness and appear to have normal contractile function on echocardiogram. Usually large amounts of fibrosis are seen microscopically in this disease. The physiology can be similar to HCM, where the heart muscle does not relax normally, leading to buildup of blood in the left and right atria and eventual atrial enlargement.
Dilated cardiomyopathy (DCM)
Dilated cardiomyopathy in cats has been associated with taurine deficient diets. Since the discovery of the link between taurine deficiency and DCM in the late 1980’s, commercial diets have been supplemented with taurine and DCM is much rarer in cats, although it does still occur. The heart muscle is abnormal and cannot contract normally, thus systolic function is impaired, leading to massive dilation of all the heart chambers and eventual congestive and even sometimes forward heart failure. If the disease is not secondary to taurine deficiency (home cooked diet, etc), then the prognosis is quite grave.
Problems secondary to feline cardiomyopathies
Congestive heart failure (CHF) can occur when blood backs up in the lungs or chest cavity. This usually presents as lethargy, inappetance and difficulty breathing. It is an emergency situation.
Sudden death from arrhythmias can occur in feline cardiomyopathies. As the heart muscle is thickened or excessively fibrotic and markedly abnormal, this can be a substrate for arrhythmias forming and causing irregular electric activity in the heart. Sometimes this results in a fatal arrhythmia.
Feline arteriothroboembolism is a syndrome when a clot forms in the heart, presumably due to altered blood flow in an enlarged chamber, and then the entire clot or a piece of the clot breaks free and is ejected into the aorta and lodges in an artery, typically the femoral arteries. This typically presents as sudden, painful paralyzation of the back legs. It is a true emergency.