Natriuretic peptide tests in suspected acute heart failure

Abstract

Heart failure should always be considered in patients with shortness of breath and reduced exercise tolerance, especially older people, and irrespective of comorbidities such as chronic obstructive pulmonary disease. 1 Symptoms and signs are rarely enough for diagnosis, and additional investigations usually follow. 2 Measuring the serum concentration of natriuretic peptides improves diagnostic accuracy in patients with suspected heart failure in the non-acute setting, 3-5 and evidence for these tests also being helpful in patients with suspected acute heart failure is growing. International guidelines now recommend measuring natriuretic peptide concentrations, and set age independent but different exclusionary thresholds for the acute and non-acute setting. 2 Although age independent thresholds are an attractive option in daily practice, their diagnostic accuracy has not yet been established. In a linked diagnostic meta-analysis (doi:10.1136/ bmj.h910), Roberts and colleagues evaluated thresholds for plasma B type natriuretic peptide (BNP, ≤100 ng/L), N terminal probrain natriuretic peptide (NTproBNP, ≤300 ng/L), and mid-regional proatrial natriuretic peptide (MRproANP, ≤120 pmol/L) recommended for excluding heart failure in acute care settings such as emergency departments. 6 Their conclusion that natriuretic peptide concentrations below these thresholds rule out heart failure, with and without reduced ejection fraction, is a major step towards routine use of these tests in emergency departments and the safe but rapid assessment of patients presenting with subacute or acute breathlessness. Natriuretic peptides are a family of vasoactive hormones produced by myocytes in response to stretch or increased wall tension primarily caused by the pressure or volume overload present in decompensated heart failure. 7 In line with Laplace's law (wall tension=pressure×radius/wall thickness), the production of natriuretic peptides will in general be higher in heart failure with reduced ejection fraction (loss of myocytes followed by left ventricular dilation and wall thinning) than in heart failure with preserved ejection fraction (myocardial dysfunction followed by interstitial fibrosis and left ventricular wall thickening). 8