B-type Natriuretic Peptide Useful Marker in Diagnosing CHF

Abstract & Commentary

Source: Maisel AS, et al. Rapid measurement of B-type natriuretic peptide in the emergency diagnosis of heart failure. N Engl J Med 2002;347:161-167.

Acute congestive heart failure (CHF) often is difficult to differentiate from other cardiac and non-cardiac causes of dyspnea in patients presenting to the emergency department (ED). B-type natriuretic peptide (BNP) is a neuro-hormone natriuretic polypeptide secreted by cardiac ventricular tissue in response to ventricular volume expansion and pressure overload. Recent studies suggest that serum BNP levels increase with acute CHF exacerbations and may aid in the diagnosis in the emergent setting.

In this study, the authors performed a multi-center, international (five United States and two European sites), prospective study investigating the predictive value of serum BNP levels measured by a fluorescence immunoassay rapid bedside kit (Triage, Biosite) for the diagnosis of acute CHF in patients with acute shortness of breath. Two independent cardiologists (blinded to BNP results) reviewed all ED and hospital records after patient discharge to determine a final diagnosis of either dyspnea due to acute CHF, dyspnea due to non-cardiac causes in patients with left ventricular (LV) dysfunction, or dyspnea not due to CHF.

Of the 1586 patients enrolled in the study, 744 (47%) were diagnosed with acute CHF, 72 (5%) with non-cardiac dyspnea with LV dysfunction, and 770 (49%) with no finding of CHF. Serum BNP levels were significantly higher in the acute CHF group (675 pg/mL ± 450 SD) when compared to either the LV dysfunction group (346 pg/mL ± 390) or no CHF group (110 pg/mL ± 225).

Moreover, among patients with CHF, higher BNP levels correlated with increased severity. Mean BNP levels for acute CHF patients with NYHA class I severity were 244 pg/mL (± 286), but increased to 389 pg/mL (± 374) in those with class II, 640 pg/mL (± 447) in those with class III, and 817 pg/mL (± 435) in those with class IV severity.

The authors conclude that the rapid, bedside measurement of BNP is useful in conjunction with other clinical information in establishing or excluding the diagnosis of CHF in patients presenting with acute dyspnea to the ED.

Commentary by Theodore C. Chan, MD, FACEP

In this industry-sponsored study, a rapid, point-of-care BNP assay demonstrated excellent utility in discriminating CHF from other causes of dyspnea in patients presenting to the ED. Moreover, BNP levels correlated with overall severity in CHF patients.

BNP secretion from cardiac ventricular tissue is part of a cascade of neuro-hormonal responses to LV dysfunction, volume expansion and pressure overload. Other investigators have reported that BNP, in combination with troponin and c-reactive protein (CRP), each may provide important prognostic value and serve as a new "multimarker" approach to cardiac acute coronary syndrome (ACS) patients.1

Natriuretic peptides such as BNP represent a favorable side of neurohormonal activation as their diuretic, natriuretic, and vasodilator properties aim to improve the loading conditions on the failing heart. Indeed, recent research on a therapeutic BNP medication (nesiritide) has shown promise in the treatment of severe CHF.2

In interpreting the results of this study on the utility of the bedside BNP assay, it is important to note that the investigators excluded patients with acute myocardial infarction, as well as renal failure. Moreover, BNP levels demonstrated a large variance in all three groups (acute CHF, LV dysfunction, and no CHF) as demonstrated by the sizeable standard deviations. It is notable that the BNP cutoff level with the highest diagnostic accuracy (100 pg/mL) was actually lower than the mean BNP level in the no CHF group (110 pg/mL). Thus, while BNP levels have clear diagnostic utility, they certainly are not infallible, and must be used in conjunction with other pertinent clinical findings in these patients.

Dr. Chan, Associate Clinical Professor of Medicine, Emergency Medicine, University of California, San Diego, is on the Editorial Board of Emergency Medicine Alert.

References

1. Sabatine MS, et al. Multimarker approach to risk stratification in non-ST elevation acute coronary syndromes: Simultaneous assessment of troponin I, C-reactive protein, and B-type natriuretic peptide. Circulation 2002;105:1760-1763.

2. Poole-Wilson PE. Treatment of acute heart failure: Out with the old, in with the new. JAMA 2002;287:1587.