Editor,—Richards et alsuggest that brain natriuretic peptide (BNP) measured 24–96 hours after acute myocardial infarction (AMI) is a powerful, independent prognostic indicator for subsequent development of left ventricular failure and death.1

In their multivariate analysis the site (anteriorv inferior) and type (Q wavev non-Q wave) of infarction do not appear to have been included. The important prognostic value of these indicators has been established.2 ,3 One might expect the anterior infarcts (39% of their study population) to demonstrate greater left ventricular dysfunction, higher BNP concentrations, and a poorer prognosis than the inferior infarcts (51%). A similar relation may exist between type of infarct and outcome, although figures for each type are not given. It would be interesting to see whether BNP is still a powerful prognostic variable if site and type of AMI were included in their analysis.

Two further confounding variables that may have weakened the association between BNP and outcome are the timings of the radionuclide ventriculography and blood sampling (1–4 days after AMI). Assessment of ventricular function in the first 24–48 hours after AMI can lead to an overestimation of damage due to the phenomenon of myocardial stunning.4 The time course of BNP shows a peak at 16 hours followed by a significant decline in the next 48–72 hours.5 A narrower and standardised time window for ventriculography and venesection may have improved the correlations.

It would have been useful to know the area under their receiver operating characteristic (ROC) curve for BNP, which is highly relevant in assessing the true value of a test.6 They demonstrated a negative predictive value of 100% for BNP at a threshold of 20 pmol/l, but they …