Patients with prior myocardial infarction and LVEF <35% had a slower VO2 time constant during constant work rate exercise than those with LVEF ≥35% (58.0 vs 45.8 seconds, P=0.0002).
Observational (n=40)
Does severely impaired left ventricular function (LVEF < 35%) affect the early dynamics of oxygen uptake (VO2) during exercise in patients with prior myocardial infarction?
The time constant of oxygen uptake during submaximal constant work rate exercise is a sensitive measure of impaired cardiac reserve in patients with prior myocardial infarction and reduced ejection fraction.
Absolute Event Rate: 58% vs 45.8%
p-value: p=0.0002
BACKGROUND: Resting cardiac function does not necessarily affect exercise capacity. However, to determine whether it affects early dynamics of oxygen uptake (VO2) during exercise, we measured VO2 during a constant work rate and during incremental exercise testing in patients with a history of myocardial infarction. VO2 kinetics and exercise capacity were compared between patients with relatively high left ventricular ejection fractions (LVEF > or = 35%, group 1) and those with lower ejection fractions (LVEF < 35%, group 2). METHODS AND RESULTS: Forty patients with a history of prior myocardial infarction (age, 57 +/- 10 years) were monitored during 6 minutes of moderate constant work rate testing (40 +/- 8 W) and during symptom-limited incremental exercise testing with a cycle ergometer. VO2 was calculated from respired gas analysis on a breath-by-breath basis. Cardiac output determinations were made with a computerized cadmium telluride detector every 10 seconds during exercise. The VO2 time constant during constant work rate exercise was slower in group 2 (58.0 +/- 7.6 seconds) compared with group 1 (45.8 +/- 10.5 seconds, P = .0002), indicating slower kinetics in group 2. The time constant for the rise in cardiac output during exercise was also slower in patients with lower EFs (63.0 +/- 12.8 versus 50.0 +/- 12.2 seconds). However, there were no differences in exercise capacity parameters, such as the VO2 or cardiac output at peak exercise, obtained during incremental exercise testing among the two groups. CONCLUSIONS: The prolonged time constant of VO2, which is primarily determined during early parts of exercise, reflects delayed cardiac output response in patients with severely impaired LV function. The time constant of VO2 during submaximal constant work rate exercise can be used as a sensitive and discriminant measure of impaired cardiac reserve in these patients.
Koike et al. (Tue,) conducted a observational in Prior myocardial infarction (n=40). LVEF < 35% vs. LVEF ≥ 35% was evaluated on VO2 time constant during constant work rate exercise (p=0.0002). Patients with prior myocardial infarction and LVEF <35% had a slower VO2 time constant during constant work rate exercise than those with LVEF ≥35% (58.0 vs 45.8 seconds, P=0.0002).