THE MERCK VETERINARY MANUAL
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Diagnosis of Cardiovascular Disease

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The following procedures are important in the diagnosis of cardiovascular disease: history and signalment, physical examination (eg, inspection, auscultation, palpation), radiography, electrocardiography, and echocardiography. Clear images must be obtained for radiography, electrocardiography, and echocardiography, or accurate, valid interpretation will not be possible. Most cardiovascular diseases (eg, mitral regurgitation, dilated cardiomyopathy) can be diagnosed by physical examination and radiography. Electrocardiography is specific for diagnosis of rhythm disturbances (eg, atrial fibrillation, sick sinus syndrome). Echocardiography is excellent for confirming tentative diagnoses, characterizing the form of cardiomyopathy in cats, detecting cardiac tumors or pericardial disease, or determining the severity of stenotic lesions. Heartworm disease is diagnosed best by detecting antigens of or antibodies to mature, female heartworms that circulate in the blood (dogs) or by thoracic radiography (cats).

Many heart diseases have specific breed prevalences. Any older Cocker Spaniel with a cough, labored breathing, and exercise intolerance, or any Cavalier King Charles Spaniel most likely has mitral regurgitation; however, chronic obstructive pulmonary disease with fibrosis may produce nearly identical signs. Any middle-aged, depressed, coughing, exercise-intolerant Doberman Pinscher with a rapid, irregular heart rate likely has dilated cardiomyopathy. Any middle-aged to older Miniature Schnauzer with fainting likely has sick sinus syndrome. Any Boxer who faints intermittently is likely to have arrhythmogenic right ventricular cardiomyopathy or dilated cardiomyopathy. A middle-aged cat with labored breathing and reluctance to lie down probably has myocardial disease (most commonly hypertrophic cardiomyopathy). An old cat is likely to have hyperthyroidism.

Heart disease should be considered if any of the following are identified on physical examination: 1) the heart rate is rapid, slow, or irregular (and not due to respiratory sinus arrhythmia); 2) respiratory sinus arrhythmia is absent even when the animal is at rest (also occurs due to pain, fever, or excitement); 3) more than 2 heart sounds are heard (eg, producing a “gallop” rhythm) in any animal but a horse (most common in cats with cardiomyopathy); 4) a loud murmur is heard; 5) heart sounds are muffled in the absence of obesity (may indicate pericardial or pleural effusion); 6) arterial pulsations are rapid, feeble, or irregular with more heart beats than arterial pulsations (a pulse deficit); 7) the animal faints or has reduced exercise tolerance in the absence of skeletal muscle disease or obesity; 8) the mucous membranes are acutely cyanotic in the absence of primary pulmonary disease.

Echocardiography is more effective than radiography—which is more effective than electrocardiography—for detecting enlargement of chambers of the heart and great vessels. In general, the degree of chamber enlargement parallels disease severity. The degree of engorgement of pulmonary veins detected radiographically, or the degree of impairment of left ventricular wall motion or thinning of the left ventricular free wall, may predict the severity of heart failure. Unfortunately, the correlation between hemodynamic or echocardiographic measurements and either signs or likelihood of death is not always good. There appears to be a better correlation between increase in heart and respiratory rates, and exercise incapacity to severity of heart disease.

Diagnosis of specific cardiovascular diseases are discussed in their respective chapters.

Last full review/revision March 2012 by Daniel F. Hogan, DVM, DACVIM (Cardiology)

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