2003 Volume 44 Issue 2 Pages 187-199
This study was undertaken in acute myocardial infarction (AMI) patients with non-insulin-dependent diabetes mellitus (type 2 DM) to investigate their impaired chronotropic response to exercise. Seventy-one AMI subjects entered the study, 30 with type 2 DM and 41 age- and body mass index-matched non-DM (control) patients. One month after the onset of AMI, these patients underwent cardiopulmonary exercise testing on a treadmill under a ramp protocol. Anaerobic threshold (AT) and peak oxygen uptake (peak VO2) were determined as indicators of exercise capacity. Plasma norepinephrine (NE) concentration was measured in blood samples obtained at 2 time points: during pre-exercise rest and immediately after peak exercise. The change in NE concentration during exercise, as an index of sympathetic nervous activity, was calculated as a percentage: ΔNE = [(NE during exercise) - (resting value)]/(resting value) × 100. The change in heart rate (HR) during exercise was calculated as a simple difference: ΔHR = [(peak HR) - (rest HR)]. Index of chronotropic response to exercise was then quantified as the ΔHR/ ΔNE during exercise. No significant intergroup differences in ejection fraction at rest or HR at peak exercise were observed. However, VO2 at AT, peak VO2, ΔHR, and ΔHR/ΔNE were significantly lower in the type 2 DM group than in the non-DM group. ΔHR correlated with VO2 at AT (r = 0.49, P < 0.001) and with peak VO2 (r = 0.53, P < 0.001) in all subjects. Also, ΔHR/ ΔNE correlated with VO2 at AT (r = 0.42, P < 0.001) and with peak VO2 (r = 0.44, P < 0.001) in all subjects. AMI patients with type 2 DM had impaired cardiopulmonary responses to maximal and submaximal exercise testing and impaired chronotropic response to exercise, even though their cardiac function at rest was similar to that of non-DM AMI patients. The data suggest that one mechanism of impaired cardiopulmonary response to exercise in AMI patients with type 2 DM groups is an impaired chronotropic response.
