Objective: Plasma levels of B-type natriuretic peptide (BNP) are often increased in postcardiac surgery patients. The six-minute walking test (6MWT) is useful to assess functional capacity in postcardiac surgery patients. The aim of this study was to determine whether BNP levels are associated with exercise capacity evaluated by 6MWT in patients after cardiac surgery.
Methods: Plasma BNP was measured in 101 consecutive patients referred to our center 8 ± 5 days after cardiac surgery who underwent echocardiography and 6MWT. We considered age, sex, diabetes, renal insufficiency, anemia, chronic obstructive pulmonary disease, hypertension, atrial fibrillation, beta-blocker therapy, left ventricular ejection fraction (LVEF), E/E', indexed left atrial volume (iLAV), type of surgery, and plasma BNP levels as potential predictors of reduced performance at 6MWT evaluated as percentages of the predicted values calculated according to the regression equation obtained in healthy individuals.
Results: The mean distance walked at 6MWT was 325 ± 100 m corresponding to 65 ± 20% of the predicted values. This was independent of the LVEF, E/E' or iLAV. Female patients or patients with atrial fibrillation had a reduced performance compared with male patients or patients with sinus rhythm (52 ± 19 vs. 70 ± 19%, P < 0.001; 50 ± 19 vs. 66 ± 19%, P = 0.017, respectively). BNP levels were inversely related to the performance at 6MWT (Pearson's correlation coefficient = -0.25, P = 0.010). At multivariate analysis, female sex (P < 0.001), atrial fibrillation (P = 0.031), and BNP levels (P = 0.040) remained the only independent predictive factors for reduced exercise capacity.
Conclusion: The increase in BNP levels in postcardiac surgery patients is associated with reduced exercise capacity.