Complimentary roles for N-terminal pro-B-type natriuretic peptide and spirometry to assess functional capacity in patients with complex mixed heart valve disease

Background: Assessing the effects of valvular heart disease on functional capacity is important for optimal timing of surgery. Aim: To determine whether N-terminal pro-B type natriuretic peptide (NT-proBNP) and lung spirometry predict maximum oxygen consumption (pVO₂) on cardio-pulmonary exercise testing in patients with mixed heart valve disease. Methods: Forty-five clinically stable patients with moderate-severe stenosis and/or regurgitation of the aortic, mitral and/or tricuspid valves were studied. The ability of echocardiography, NT-proBNP, forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) to predict impaired pVO₂ was determined. Results: On univariate analysis the natural logarithm of NT-proBNP explained more of the variation in pVO₂ (r² = 0.40, p < 0.0001) than valve severity score (r² = 0.20, p = 0.002), pulmonary artery pressure (r² = 0.21, p = 0.005), left atrial area index (r ² = 0.25, p = 0.001) or LV ejection fraction (r² = 0.02, p = 0.4). Low lean body weight (r² = 0.21, p = 0.002), FEV1 (r ² = 0.26, p = 0.0003) and FVC (r² = 0.20, p = 0.002) were also associated with pVO2. In multi-variable analysis independent determinants of pVO₂ were NT-proBNP (r² = 0.27, p = 0.001), FVC (r ² = 0.20, p = 0.0002) and lean body weight (r² = 0.23, p = 0.001). NT-proBNP and FVC together were better predictors of pVO₂ < 60% (C statistic = 0.83, 95% CI 0.71, 0.95) than either NT-proBNP (C = 0.80, 95% CI 0.66, 0.94) or FVC (C =0.73, 95% CI 0.57, 0.89) alone. NT-proBNP, FVC and age also predicted excessive ventilation on cardio-pulmonary exercise (combined r² = 0.54, p < 0.0001). Conclusion: In patients with mixed heart valve disease NT-proBNP and spirometry provide a more reliable assessment of functional capacity than assessment by echocardiography and symptoms alone.