THE MERCK VETERINARY MANUAL
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Diagnosis of Cardiovascular Disease

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Diagnosis of cardiovascular disease is based on history and signalment, physical examination (eg, inspection, auscultation, palpation), cardiac biomarkers (NT-proBNP, BNP, ANP, troponin I), 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 highly suspected based on the results of physical examination and radiography. Electrocardiography is specific for diagnosis of rhythm disturbances (eg, atrial fibrillation, sick sinus syndrome). Echocardiography is excellent to confirm tentative diagnoses, assess severity of valvular regurgitations and stenotic lesions, evaluate chamber enlargement and quantify systolic and diastolic myocardial function, characterize the form of cardiomyopathy in cats, detect cardiac tumors or pericardial disease, diagnose pulmonary hypertension or heartworm caval syndrome, and identify congenital cardiac defects. Thoracic radiographs are the best diagnostic tool to evaluate the lungs for evidence of active CHF. Heartworm disease is diagnosed best by detecting antigens of mature, female heartworms circulating in the blood (dogs). In cats, diagnosis of heartworm disease may entail heartworm antigen and antibody testing, supplemented by thoracic radiographs and echocardiography.

Many heart diseases have specific breed prevalences. Any older Cavalier King Charles Spaniel with a cough, labored breathing, and exercise intolerance should be suspected to have left-side CHF due to mitral regurgitation; however, chronic obstructive pulmonary disease with fibrosis may produce nearly identical signs and thoracic radiographs; echocardiography and NT-proBNP testing may be needed to differentiate. 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 should be suspected to have arrhythmogenic right ventricular cardiomyopathy; however, Boxers can also develop neurocardiogenic syncope or sick sinus syndrome, and Holter monitoring may be needed to diagnose the underlying cause of syncope and to formulate the best treatment plan. A middle-aged cat with labored breathing and reluctance to lie down probably has myocardial disease (most commonly hypertrophic cardiomyopathy), whereas an older cat with weight loss and behavioral changes is likely to have hyperthyroidism, which can result in systemic hypertension and exacerbate cardiac disease.

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 (this also occurs due to pain, fever, or excitement); 3) more than two 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 (pulse deficits); 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, to detect enlargement of chambers of the heart and great vessels. In general, the degree of chamber enlargement parallels disease severity. The degree of pulmonary infiltrates detected radiographically, or the degree of impairment of left ventricular wall motion or thinning of the left ventricular walls, 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. NT-proBNP testing may also help in the prognostication of heart disease and heart failure.

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

Last full review/revision April 2015 by Suzanne M. Cunningham, DVM, DACVIM (Cardiology); Kursten V. Roderick, DVM

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