Signs of heart disease and heart failure in dogs and cats

Testing to determine the cause of intermittent weakness or syncope usually includes and electrocardiogram (ECG)(obtained while resting, during exercise, and/or after exercise or a vagal maneuver), a complete blood count (CBC) serum biochemical analysis (including electrolytes and glucose), neurologic examination, thoracic radiographs, heartworm testing, and echocardiography. Other studies to rule out neuromuscular or neurologic disease may also be valuable. Intermittent cardiac arrythmias not apparent on resting ECG may be uncovered by 24-hour ambulatory ECG (Holter monitor), event monitoring, or in-hospital continuous ECG monitoring.

Signs of heart disease in dogs may be present even if the animal is not in a state of heart failure. Objective signs of heart disease include cardiac murmurs, rhythm disturbances, jugular pulsations and cardiac enlargement. Other clinical signs that can result from heart disease include syncope, excessively weak or strong arterial pulses, cough or respiratory difficulty, exercise intolerance and cyanosis. Further evaluation using thoracic radiography, electrocardiography, echocardiography and sometimes other tests is usually indicated when signs suggestive of cardiovascular disease are present.

The clinical signs of heart failure relate to high venous pressure behind the heart (congestive signs) or inadequate blood flow out of the heart (low output signs). Congestive signs secondary to right-sided heart failure stem from systemic venous hypertension and its sequelae; congestion behind the left side of the heart results in pulmonary venous hypertension and edema. Chronic left-sided congestive heart failure may facilitate the development of right-sided heart failure if pulmonary arterial pressure rises secondary to pulmonary venous hypertension. Low output signs from right ventricular failure are similar to the low output signs of left ventricular failure because the left heart can pump only what it receives from the right heart. Biventricular failure develops in some animals.

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