Effects of exogenous metabolic substrate modulation on exercise-induced myocardial ischemia

BackgroundThe aim of the study is to compare the impact of intravenous glucose versus lipid versus saline on exercise-induced myocardial ischemia in patients with stable angina.MethodsTwelve men with coronary artery disease and positive exercise tests performed a symptom-limited, modified Bruce electrocardiogram (ECG) exercise test at 3 sessions, 3 weeks apart. They randomly received, in double-blind design, at each session equal intravenous volumes of 10% glucose/insulin or Intralipid plus heparin or saline. We assessed the effects on (1) ischemic threshold (heart rate × systolic pressure at 1-mm ST-segment depression [STD]) and (2) maximum ST-depression (Max STD) corresponding to the highest heart rate × systolic pressure common to the 3 tests.ResultsDuring glucose infusion, glycemia increased from 5.7 ± 0.4 to 9.4 ± 3.0 mmol/L but did not change during lipid or saline infusion. During lipid infusion, free fatty acids increased from 0.32 ± 0.19 to 1.44 ± 0.46 mmol/L but decreased during glucose infusion from 0.39 ± 0.21 to 0.04 ± 0.03 mmol/L and did not change during saline. Exercise times were 10.0 ± 3.4, 9.8 ± 3.4, and 10.3 ± 3.5 minutes, during glucose, lipid, and saline infusions, respectively. Ischemic thresholds (×10−3) were 16.5 ± 2.8, 16.8 ± 2.7, and 16.6 ± 2.6, respectively. MaxSTD was 2.5 ± 1.4, 2.5 ± 1.0, and 2.5 ± 1.0 mm, respectively.ConclusionNeither glucose-insulin nor lipid infusion modified exercise ischemic parameters compared with saline control, suggesting that marked and acute changes in exogenous energy substrate are unlikely to affect exercise-induced myocardial ischemia.