Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (53 page)

   Natriuretic peptides may be utilized for both diagnostic and prognostic value. Independent of other clinical factors, BNP quartiles are predictive of in-hospital mortality with risk varying more than three- to fourfold on the basis of the patient’s initial BNP. Values >840 pg/mL conferred a twofold increase in hospital mortality in one large registry.

   Biomarkers of myocardial necrosis are also found in HF patients (in some studies 30%), often without overt ischemia or CAD. Given the close association of CAD and HF, markers of cardiac injury should be assessed in all patients with acute dyspnea and may be deployed in a multimarker strategy for risk stratification (class I recommendation). Elevated concentrations of cardiac troponin (0.5 μg/L) have been shown to be predictive of morbidity and mortality in HF patients at every level of admission BNP. With the use of a BNP >840 pg/mL threshold, the presence of positive troponin I >0.5 μg/L identifies patients at highest risk for in-hospital mortality (up to fivefold risk).

   
Echocardiography
: Remains the gold standard cardiac imaging in HF and should be performed in all patients with new onset heart failure. Diagnosis for systolic dysfunction approaches a specificity of 100% (sensitivity 80%). Echocardiography meets professional society appropriateness criteria when performed for patients with dyspnea due to suspected cardiac etiology or when chest x-ray or serum BNP are concerning for cardiac disease. The diagnosis of CHF can be aided by assessment of ventricular size and function (right- and left-sided systole and diastole). Clues to the etiology of HF such as CAD (focal wall motion abnormalities—nonspecific), valvular disease, pericardial findings (constriction, effusion with tamponade), intracardiac shunts, amyloid, as well as duration of HF (atrial size) may be gleaned from initial images. Furthermore, cardiac output, pulmonary pressures, and hemodynamic status may be derived from tissue Doppler to aid treatment decisions and predictor prognosis.

   
Cardiac magnetic resonance (CMR)
: Expense and lack of portability limit use, but with use of gadolinium can differentiate viability/perfusion, fibrosis, and inflammation. CMR can identify hypertrophic cardiomyopathy (HCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), and cardiac amyloid and may obviate the need for endomyocardial biopsy in some cases of myocarditis.

   
Cardiac CT
: Can establish the likelihood of coronary disease contribution to heart failure either by direct imaging of coronary arteries or through calcium scores via EBCT.

Given the similar clinical presentation of heart failure with preserved or reduced left ventricular ejection fraction, additional testing and differential diagnosis is often driven by echocardiographic (or other imaging modality) findings.

SYSTOLIC DYSFUNCTION/DILATED CARDIOMYOPATHY (DCM)

   In developed countries, systolic dysfunction
with
heart failure is most likely due to coronary disease, hypertension, or valvular disease. These common etiologies are often apparent upon initial history and diagnostic evaluation. Idiopathic cardiomyopathy accounts for approximately 30% of cases of symptomatic cases.

   Patients with DCM by echocardiography
without
signs of heart failure have significantly different distribution of etiologies. Coronary disease and hypertension account for only 10–15% of cases with 50% deemed idiopathic. Myocarditis, infiltrative disease, peripartum cardiomyopathy, HIV infection, Chagas disease, connective tissue disease, substance abuse, doxorubicin exposure, and nutritional abnormalities must be considered.

   If the cause of dilated cardiomyopathy is not apparent after initial evaluation, additional laboratory testing is warranted. These include thyroid function tests (especially elderly with atrial fibrillation), Ferritin and TIBC (hemochromatosis), pheochromocytoma evaluation (see Chapter
7
, Genitourinary System Disorders), thiamine, carnitine and selenium (nutritional deficiency), evaluation for Chagas disease, Lyme disease, HIV serologies, and evaluation for myocarditis or inherited diseases predisposing to DCM.

MYOCARDITIS

   Myocarditis is an inflammatory disease of heart muscle due to infectious and noninfectious etiologies with potential long-term sequela of DCM. Most common etiology in developed countries is viral infection (Coxsackie, echovirus, adenovirus, HIV, CMV, parvovirus B19), with rheumatic carditis,
Trypanosoma Cruzi
(more likely to present as chronic cardiomyopathy), and bacterial infections still contributing substantially to cases in the developing world.

   Who Should Be Suspected?