Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.
Issue link: http://todaysveterinarypractice.epubxp.com/i/891985
64 ADVANCES IN FELINE CARDIAC DIAGNOSTICS PEER REVIEWED and pulmonary edema or pleural effusion support a diagnosis of CHF ( Figure 4 ). Pulmonary infiltrates in cats with CHF often appear as an unstructured interstitial to alveolar pattern with no typical distribution (in contrast to the appearance in dogs). Thoracic radiography is useful to document response to diuresis and to monitor for recurrent CHF. In most situations, radiography is the initial test to determine the underlying cause of respiratory distress. However, when patient instability precludes radiography, point- of-care, cage-side thoracic ultrasonography can provide important information on the likelihood of CHF. Case notes: Point-of-care ultrasonography is the best choice to initially evaluate Elvis; however, after thoracocentesis and improved clinical stability, thoracic radiography is indicated to continue diagnostic evaluation for CHF. ELECTROCARDIOGRAPHY Electrocardiography is the test of choice for the diagnosis of arrhythmias and conduction disturbances but is relatively insensitive as a screening tool for the detection of heart disease in cats. It is recommended when an arrhythmia is auscultated or suspected (eg, syncope). BIOMARKERS A biomarker is a parameter that can be accurately measured and is an indicator of a normal or pathologic process, or a pharmacologic response to therapeutics. 4 The two most commonly used cardiac biomarkers in veterinary medicine are cardiac troponin I (cTnI) and NT-proBNP. Cardiac troponin I is a regulatory protein that binds actin and myosin in cardiac myocytes. When these cells are damaged, cTnI is released into the bloodstream and can be measured. Because of its exclusivity to cardiac cells, an increase in blood cTnI concentration is relatively specific for cardiac cell damage; however, elevations do not indicate a specific disease process. 5 Cardiac troponin I has been reported to be higher in cats with moderate to severe HCM than in healthy cats, but because of the substantial overlap between groups this test is not considered a good screening tool for feline cardiomyopathy. 6,7 Similarly, cTnI is higher in cats with respiratory distress due to CHF than in cats with a noncardiac cause of respiratory distress; however, values overlap enough that clinical utility of cTnI for this purpose is limited. 7,8 The detection of arrhythmias or abnormal echocardiographic wall motion may prompt evaluation of cTnI as an indicator of acute myocardial damage. B-type natriuretic peptide (BNP) is a hormone released in response to cardiac stretch associated with heart disease. The natriuretic action of BNP helps to control fluid homeostasis in the body by renal sodium excretion and so counteracts the volume-retaining effects of the renin-angiotensin-aldosterone system. The breakdown product of BNP (NT-proBNP) can be measured as an indicator of myocardial stress. 9 Several studies have demonstrated the ability of NT-proBNP to help distinguish between normal cats and cats with preclinical heart disease with good sensitivity and specificity (76% to 92% and 71% to 93%, respectively). 10–12 Because these studies compared the performance of NT-proBNP to that of echocardiography as the gold standard, this test is not additive if echocardiography is performed. Rather, it can be used as a screening test for patients at risk for cardiac disease. Although NT-proBNP is sensitive and specific for the detection of cardiac disease, it cannot be used to determine the type of disease. Additional diagnostics are often required if the value is elevated. The negative predictive value of NT-proBNP is very high (ie, heart disease is unlikely if the NT-proBNP level is normal); however, diseases such as hyperthyroidism, hypertension, or renal disease can elevate NT-proBNP concentrations in the absence of cardiac disease. Thus, results of biomarker testing should be interpreted in conjunction with other clinical information. FIGURE 4. (A) Right lateral and (B) dorsoventral thoracic radiographs from Elvis after thoracocentesis was performed. A small amount of residual pleural effusion is present, obscuring the cardiac silhouette in the dorsoventral view. The cardiac silhouette is enlarged and the pulmonary vasculature is enlarged. A mild interstitial pattern is present in the caudal lung fields, consistent with pulmonary edema. A B