Impact of global hemodynamic load on exercise capacity in aortic stenosis.

BACKGROUND: The determinants of maximal exercise capacity (MEC) in aortic stenosis (AS) are, in large part, unknown. We hypothesized that the left ventricular (LV) global hemodynamic load--as assessed by the valvulo-arterial impedance (Zva)--is one of the main determinants of MEC and we sought to evaluate the factors associated with reduced MEC in AS. METHOD AND
RESULTS: Asymptomatic patients with moderate or severe AS (n=62, aortic valve area <1.5 cm(2), 65 ± 13 years, 68% men) and preserved LV systolic function (ejection fraction>50%) were prospectively referred for comprehensive resting echocardiography and cardiopulmonary exercise test. Absolute peak VO2 was 19.5 ± 5.7 mL/kg/min (median 19.6 mL/kg/min; range 7.2-33.1 mL/kg/min). There were significant correlations between peak VO2 and: age, body mass index, LV stroke volumes, cardiac output, mean flow rate, mitral annulus s' and e' wave velocities, E/e' ratio and left atrial diameter (all p<0.05). Indexed mean flow rate and Zva were the strongest univariable echocardiographic determinants of peak VO2 (r=0.44, p<0.001 and r=-0.39, p=0.002, respectively). In addition, patients with reduced MEC (peak VO2<median) had higher Zva than those with preserved MEC (4.24 ± 1.18 vs. 3.71 ± 0.68 mmHg/mL/m(2), p=0.036). In multivariable analysis, age (p<0.001) and Zva (p=0.048) were the only independent predictors (r(2)=0.40) of peak VO2.
CONCLUSION: In asymptomatic patients with moderate to severe AS, MEC varies widely among patients, and is often lower than expected. Global LV hemodynamic load is the main echocardiographic determinant of reduced MEC in these patients, suggesting its usefulness for their clinical evaluation and management.