Mechanisms of exercise intolerance - Insights from tissue Doppler imaging

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 greater than or equal to 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 greater than or equal to 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.