Left ventricular function and exercise capacity

Abstract

Context: Limited information exists regarding the role of left ventricular function in predicting exercise capacity and impact on age- and sex-related differences.

Objectives: To determine the impact of measures of cardiac function assessed by echocardiography on exercise capacity and to determine if these associations are modified by sex or advancing age.

Design: Cross-sectional study of patients undergoing exercise echocardiography with routine measurements of left ventricular systolic and diastolic function by 2-dimensional and Doppler techniques. Analyses were conducted to determine the strongest correlates of exercise capacity and the age and sex interactions of these variables with exercise capacity.

Setting: Large tertiary referral center in Rochester, Minnesota, in 2006.

Participants: Patients undergoing exercise echocardiography using the Bruce protocol (N = 2867). Patients with echocardiographic evidence of exercise-induced ischemia, ejection fractions lower than 50%, or significant valvular heart disease were excluded.

Main outcome measure: Exercise capacity in metabolic equivalents (METs).

Results: Diastolic dysfunction was strongly and inversely associated with exercise capacity. Compared with normal function, after multivariate adjustment, those with moderate/severe resting diastolic dysfunction (-1.30 METs; 95% confidence interval [CI], -1.52 to -0.99; P < .001) and mild resting diastolic dysfunction (-0.70 METs; 95% CI, -0.88 to -0.46; P < .001) had substantially lower exercise capacity. Variation of left ventricular systolic function within the normal range was not associated with exercise capacity. Left ventricular filling pressures measured by resting E/e' of 15 or greater (-0.41 METs; 95% CI, -0.70 to -0.11; P = .007) or postexercise E/e' of 15 or greater (-0.41 METs; 95% CI, -0.71 to -0.11; P = .007) were similarly associated with a reduction in exercise capacity, each in separate multivariate analyses. Individuals with impaired relaxation (mild dysfunction) or resting E/e' of 15 or greater had a progressive increase in the magnitude of reduction in exercise capacity with advancing age (P < .001 and P = .02, respectively). Other independent correlates of exercise capacity were age (unstandardized beta coefficient, -0.85 METs; 95% CI, -0.92 to -0.77, per 10-year increment; P < .001), female sex (-1.98 METs; 95% CI, -2.15 to -1.84; P < .001), and body mass index greater than 30 (-1.24 METs; 95% CI, -1.41 to -1.10; P < .001).

Conclusion: In this large cross-sectional study of those referred for exercise echocardiography and not limited by ischemia, abnormalities of left ventricular diastolic function were independently associated with exercise capacity.

Figure 1. Effects of Diastolic Parameters on Exercise Capacity with Aging

Figure 1A. Plot of exercise capacity by age for all patients with normal and mild diastolic dysfunction. The curves were fit to the data by group (normal and mild diastolic dysfunction/impaired relaxation) using linear regression analysis with 95% confidence intervals shown. Exercise capacity was reduced in the group with mild diastolic dysfunction vs. normal. However, the magnitude of this reduction progressively increased with advancing age as shown by the steeper slope in the mild diastolic dysfunction group. The p value, derived from age interaction analysis, shows that the slopes of the two lines are statistically different. Figure 1B. Plot of exercise capacity by increasing age for all patients with post-exercise E/e'≥15 and < 15. The curves were fit to the data by group using linear regression analysis with 95% confidence intervals shown. Exercise capacity was reduced in the group with a post-exercise E/e’ ≥15 vs < 15. However, the magnitude of this reduction increased with advancing age as shown by the steeper slope in the E/e’ ≥15 group. The p value, derived from age/diastolic function interaction analysis, shows that the slopes of the two lines are statistically different.

Figure 2. Effects of Diastolic Function Grade on Exercise Capacity by Sex

Box and whisker plot of exercise capacity by diastolic function grade grouped by sex. Compared to men, women had a lower exercise capacity within each diastolic function grade. However, the p value derived from gender/diastolic function interaction analysis (p=0.36) was nonsignificant, suggesting that the magnitude of reduction in exercise capacity within each diastolic function grade is similar between the sexes.