Exercise capacity can be estimated from systolic and diastolic echocardiographic indices

Background: Exercise capacity as measured by maximal rate of total oxygen consumption (VO2max) has been shown to be a powerful predictor of mortality in patients with congestive heart failure and is the best single measure of prognosis in this population. VO2max lacks consistent correlation with other prognostic factors such as left ventricular systolic function. This could be due to failure to account for diastolic function due to the parabolic nature of diastolic values. Both, diastolic and systolic functions are important in determining the overall function of the heart. Hypothesis: We hypothesize that VO2max can be predicted from the composite of systolic and linear diastolic parameters. Methods: We enrolled patients with congestive heart failure (NYHA functional class II-IV) without prior history of respiratory disease in our study. VO2max was measured during a modified Naughton exercise protocol. The resting left ventricular systolic function was assessed by measuring left ventricular ejection fraction (LVEF) by echocardiography. Diastolic function was assessed by mitral valve Doppler inflow and tissue Doppler imaging; and was reported as a diastolic class (DC): restrictive, pseudo-normalization, abnormal relaxation, and normal. Diastolic classes were given a numeric value of 1 to 4 consequently. Results: Twenty-four patients were included (4 females and 20 males). The mean LVEF was 31±14 % and the mean VO2max was 16±5 ml/kg/min. Five patients had a DC of 3, 9 patients had a diastolic class of 2, and 10 patients had a DC of 1. The relationship between left ventricular systolic and diastolic function indices with VO2max was analyzed by linear regression through the origin. LVEF and DC combined were strong predictors of VO2max (r = 0.92). The regression equation reflecting the relationship was: VO2max = 0.496 × LVEF + 1.54 × DC. Conclusion: We found a good correlation between VO2max and the composite of systolic and diastolic indices determined by echocardiography. This stresses the importance of both systolic and diastolic function in congestive heart failure etiology, prognosis, and the ability to estimate VO2max and consequently the exercise capacity based on echocardiography data.