Dilated Cardiomyopathy: Clinical Manifestations

By | 2013-06-07

History Because cats are relatively sedentary, they often hide the signs of their disease until they are in severe distress. Cats most commonly present in acute respiratory distress from pulmonary edema, pleural effusion, or both. Some cats will cough. This is frequently thought to be vomiting by the owner because vomiting and coughing in cats appear very similar. Distinguishing the two may be possible in the exam room by palpating the trachea vigorously enough to produce a cough while the owners witness the event. A thorough diet history should be obtained on any cat with dilated cardiomyopathy.

Physical Examination Many cats are tachypneic and dyspneic upon presentation. They may also be lethargic, dehydrated, or hypothermic (or a combination of these symptoms).

Auscultation often reveals a soft to moderately loud systolic heart murmur (usually heard best over the sternum, just medial to the left apex beat). A gallop sound may also be heard if the disease is severe. Most cats with dilated cardiomyopathy have an elevated heart rate so that atrial systole occurs immediately after rapid ventricular filling, making it impossible to distinguish a third from a fourth heart sound. Auscultation of the lungs is often normal except for increased airway sounds due to hyperpnea. If pleural effusion is present, lung sounds may be absent ventrally when the cat is upright. The ears and feet are commonly cold because of intense peripheral vasoconstriction.

The retinas should be examined in all cats suspected of having feline dilated cardiomyopathy for the presence of feline central retinal degeneration (FCRD). If it is present the cat is most likely taurine deficient. However, many cats with taurine deficiency do not have FCRD.

If the cat is severely dyspneic, pleurocentesis using a butterfly catheter should be part of the examination process to determine if pleural effusion is the cause of the dyspnea. If pleural effusion is the cause, one should be able to remove 150 to 250 mL of fluid from the pleural space.

Radiography Radiographs cannot be used to distinguish feline dilated cardiomyopathy from other forms of feline cardiomyopathy. They should primarily be used initially to determine if a dyspneic cat is in heart failure (cardiomegaly plus pleural effusion, pulmonary edema, or both). Radiographs should not be attempted in a severely dyspneic cat if the process is stressful to the cat because this will often result in death. In cases of severe feline dilated cardiomyopathy, the cardiac silhouette is markedly enlarged, often especially in the area of the left auricle on the dorsoventral (DV) or ventrodorsal (VD) view.

Left atrial enlargement generally cannot be appreciated on the lateral view. If pleural effusion is present, it often becomes impossible to identify pulmonary edema. Pulmonary edema in cats can be caudodorsal in distribution (as in the dog) but is more commonly patchy, is often more ventrally distributed, and may involve the accessory lung lobe.

Echocardiography Echocardiography is the diagnostic test of choice for identifying dilated cardiomyopathy.The striking feature of severe dilated cardiomyopathy is the remarkable lack of left ventricular wall motion. The end-systolic diameter is increased to a value over 10 mm (usually over 12 mm and often in the 15 to 20 mm range when severe), whereas the end-diastolic diameter is also increased but to a lesser degree (usually in the 18 to 23 mm range). In cats with severe dilated cardiomyopathy, the shortening fraction is commonly less than 20%. Both the left ventricular free wall and the inter-ventricular septal motion are reduced, although one may be more reduced than the other. Neither wall is hyperdynamic. Cats that have severely reduced free wa’l motion and a hyperdynamic interventricular septum (IVS) most commonly have primary mitral valve degeneration or dysplasia rather than dilated cardiomyopathy. Rarely a cat will have one region of the left ventricular myocardium that is hypokinetic, akinetic, or even dyskinetic and may also be thinner than the rest of the myocardium. Although this may be due to a primary regional myocardial disease, it may also be due to a thrombus or a thromboembolus that has produced an infarct in that region. This pattern of motion may or may not be categorized as dilated cardiomyopathy, depending on one’s viewpoint.

Color flow Doppler echocardiography often reveals the presence of mild mitral regurgitation. Spontaneous echo contrast due to red cell aggregation may be present, especially in the left atrium.

Elearocardiography Electrocardiography rarely reveals clinically significant information unless an arrhythmia is ausculted. Abnormalities in QRS morphology and an axis deviation may be noted but are nonspecific findings.

Clinical Pathology Any cat with dilated cardiomyopathy should have a plasma and whole blood taurine concentration measured. The sample must be anticoagulated with heparin, placed on ice, and a portion centrifuged within 15 minutes. Platelets contain a large concentration of taurine, which is released upon platelet activation during the clotting process, so any thrombotic activity in the tube will result in a falsely high plasma taurine concentration. Taurine will also leach out of platelets and white cells into plasma if the sample is left standing, especially at room temperature. Taurine is a very stable compound, but plasma and whole blood samples should generally be frozen to prevent bacterial growth because bacteria will destroy taurine. Normal cats have a plasma taurine concentration greater than 60 nmol and mL and a whole blood taurine concentration greater than 250 nmol/mL. Most, but not all, cats with dilated cardiomyopathy due to taurine deficiency have a plasma taurine concentration less than 20 nmol/mL and a whole blood taurine concentration less than 100 nmol/mL. Fasting can lower the plasma taurine concentration in cats. Fasting does not alter whole blood taurine concentration. Thromboembolism of skeletal muscle will cause skeletal muscle necrosis and the release of taurine into the circulation, causing a false elevation in a cat that is taurine deficient.

Prerenal azotemia due to low cardiac output is common in cats with severe dilated cardiomyopathy, cats with dehydration, cats that are not eating or drinking, or cats receiving a high dose of a diuretic. If the azotemia is mild to moderate and the cat feels good enough to eat and drink, the azotemia can safely be ignored. If the azotemia is severe, diuretic therapy must be discontinued and judicious fluid therapy administered. Electrolyte abnormalities occur more frequently in cats on diuretic therapy than in dogs, probably because cats tend to become anorexic more easily when they are dehydrated. Electrolyte levels below the reference range for a laboratory do not mean that this decrease is clinically significant.