Preoperative plasma N-terminal pro-brain natriuretic peptide as a marker of cardiac risk in patients undergoing elective non-cardiac surgery (Br J Surg 2005; 92: 1041-1045)

Sir This paper is severely limited by subjective, self-fulfilling end-points. Only four of the 190 patients in the study fulfilled the objective end-point of cardiac death; the remaining events consisted of postoperative congestive heart failure. This diagnosis is notoriously subjective, especially when made retrospectively and without the use of an established tool, such as the Framingham heart failure classification scoring system. It can also be precipitated by non-cardiac causes such as over-transfusion and decreased osmotic pressure. Some authors have found it to be of questionable clinical relevance, since heart failure does not appear to lead to an increase in cardiac ischaemia or mortality at 2 years1. In addition, as brain natriuretic peptide (BNP) is established as a predictor of left-ventricular systolic dysfunction2, it is not surprising that it should predict the occurrence of postoperative heart failure. The retrospective nature of the study and lack of screening for cardiac events may also mean that some complications were missed. The American Society of Anesthesiologists fitness grade was used in the multivariate model, despite the fact that a recent clinical model has been shown to be a more accurate predictor of outcome after non-cardiac surgery3. Nonetheless, the magnitude of the difference in NT-pro BNP levels between those patients who had a cardiac complication and those who were event-free, as well as the numbers analysed, would suggest that natriuretic peptides might play an important role in the pre-operative evaluation of patients. Further prospective studies are required to identify the practical role of the assay.