Answer

A: B-type natriuretic peptide measurement

Educational Objective

Diagnose heart failure in a patient with unexplained dyspnea.

Critique

B-type natriuretic peptide (BNP) measurement (Option A) is the most appropriate test to perform next. In patients presenting with dyspnea of unknown cause, BNP or N-terminal pro-BNP (NT-proBNP) level can help differentiate cardiac from pulmonary and other noncardiac causes. BNP levels are elevated in patients with increased filling pressures and heart failure (typically >400 pg/mL [400 ng/L]), whereas they are low to normal in those with pulmonary disease (typically <100 pg/mL [100 ng/L]). An elevated BNP level (>400 pg/mL [400 ng/L]) has a sensitivity of 95% to 97% for the diagnosis of heart failure, that is 95% to 97% of patients with heart failure have an elevated BNP. In contrast, BNP levels below 100 pg/mL (100 ng/L) have a negative predictive value of 90% to 97%, meaning a low BNP level confers a 90% to 97% chance heart failure is not present. NT-proBNP levels have similar test characteristics. One note of caution is that BNP levels increase with age, worsening renal function, and female sex and decrease with obesity; therefore, the entire patient must always be taken into account when interpreting a level. This patient presents with findings suggestive of cardiac disease, including progressive dyspnea, orthopnea, pleural effusions, and peripheral edema. Checking a BNP level is the next best test to perform.

D-dimer testing (Option B) is helpful in evaluating pulmonary embolism (PE) in patients at low risk because the combination of a low clinical probability and a negative D-dimer test makes PE very unlikely. All the findings in this patient, however, fit the Pulmonary Embolism Rule-out Criteria (PERC; age <50 years, heart rate <100/min, oxygen saturation >95%, no estrogen use, no unilateral leg swelling, no past deep venous thrombosis/PE, no recent surgery/trauma in the past 4 weeks, no hemoptysis). In this patient, the very low clinical probability, in large part driven by the gradual onset of dyspnea over 3 months, and meeting the PERC criteria preclude the need for further testing for PE.

High-resolution CT scan of the chest (Option C) is an appropriate option if parenchymal lung disease is suspected. In this patient, the lack of abnormal breath sounds on examination and clear lung fields on imaging make this significantly less likely, and a focus on cardiac disease as the cause of dyspnea is more appropriate.

Patients with heart failure often have a mildly increased high-sensitivity cardiac troponin level when they present with acute heart failure. This presentation is usually more reflective of myocardial strain than ischemia. Although troponin levels may be elevated, measuring high-sensitivity cardiac troponin (Option D) is not the best test to differentiate between heart failure and other causes of dyspnea.

Key Point

An elevated B-type natriuretic peptide level (>400 pg/mL [400 ng/L]) has a sensitivity of 95% to 97% for the diagnosis of heart failure, whereas levels less than 100 pg/mL (100 ng/L) have a negative predictive value of 90% to 97%.

Bibliography

Alcidi G, Goffredo G, Correale M, et al. Brain natriuretic peptide biomarkers in current clinical and therapeutic scenarios of heart failure. J Clin Med. 2022;11. [PMID: 35683578] doi:10.3390/jcm11113192

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