Mechanisms of Exercise Intolerance

Abstract

Background— A decreased ratio of early to late diastolic mitral inflow velocities (E/A <1.0) reflects slowing of left ventricular (LV) relaxation. This finding is widely believed to indicate significant diastolic dysfunction. However, E/A <1.0 is common during normal aging and often is not associated with symptoms of heart failure. We asked (1) whether slowed LV relaxation is associated with exercise intolerance and (2) whether tissue Doppler imaging of the early diastolic mitral annular velocity (Ea) is helpful in understanding mechanisms of exercise intolerance. Methods and Results— Patients (n=121) underwent echocardiography before maximal exercise testing. Fifty-nine subjects had E/A <1.0, and 36 subjects had E/Ea ≥10. Exercise capacity was similar in the population with a normal mitral inflow pattern and those with a slow relaxation pattern when E/Ea was <10. In contrast, the subjects with slow relaxation and E/Ea ≥10 had reduced exercise tolerance. Of all the echo and clinical parameters assessed, E/Ea had the best correlation with exercise capacity ( r =−0.684, P <0.001) and was the strongest independent predictor of exercise capacity ≤7 METs by multivariate analysis (prevalence-corrected odds ratio=12.6, P <0.001). E/Ea continued to be strongly associated with exercise capacity in all age groups and in those with preserved or reduced systolic function. Conclusions— Of the subjects with slow LV relaxation, only those with E/Ea ≥10 have objective evidence of reduced exercise tolerance. These data suggest that elevated LV filling pressures rather than slow relaxation per se reduce exercise capacity.