Cardiopulmonary exercise testing and NT-proBNP before major vascular surgery: do they correlate?

Introduction

The counter-regulatory neurohormone N-terminal proB type natriuretic peptide (NT-proBNP) is predominantly released from the left ventricle in response to increasing wall tension and is a useful prognostic marker in patients with cardiac failure [1]. Cardiopulmonary exercise (CPX) testing is an objective method of assessing functional cardiac status. The anaerobic threshold (AT), the point at which anaerobic metabolism supplements aerobic metabolism, correlates with the severity of cardiac failure [2].

Objective and methods

An ongoing, prospective, observational study, to determine the correlation between preoperative CPX testing and measurement of NT-proBNP (Roche) in patients undergoing elective abdominal aortic aneurysm (AAA) repair (open or endovascular [EVAR]). All patients were preassessed by a consultant vascular anaesthetist with particular emphasis on cardiac risk factors and functional capacity (metabolic equivalents [METs]). CPX testing was performed preoperatively, by a blinded investigator, in a standardised manner [3] with calculation of AT made by the V-slope method. NT-proBNP levels were also measured preoperatively, a level >150 pg/ml considered elevated.

Results

Forty-three patients were recruited, mean (SD) age 71.8 ± 8.9 years. The mean (SD) AT was 10.7 ± 3.2 ml/min/kg. There was no significant correlation between age and AT (r = -0.12, P = 0.45). The median level (range) of NT-proBNP was 322.8 (52–5085) pg/ml. Over 85% of patients had an NT-proBNP level >150 pg/ml. There was a weak negative association between NT-proBNP and AT (r = -0.24, P = 0.18). Results between open repair and EVAR are summarised in Table 1. There was a positive correlation between AT and METs (r = 0.41, P < 0.01).

Table 1 (abstract P195)

Conclusion

There is no correlation between anaerobic threshold and NT-proBNP levels in patients undergoing elective abdominal aortic aneurysm repair but there was a definite positive correlation between AT and functional capacity (METs). Whether CPX or cardiac biomarkers influences outcome requires further study.