Insulin resistance in cardiac syndrome X and variant angina: influence of physical capacity and circulating lipids.

Insulin resistance has been demonstrated in patients with angina pectoris irrespective of detectable atherosclerosis at coronary angiograms. We compared insulin sensitivity, lipid profiles, and exercise capacity in 20 patients with syndrome X, 15 patients with variant angina, and 20 healthy controls to investigate whether the presentation of the insulin resistance syndrome differs between the two patient groups with disparate vascular abnormalities. All patients had angiographically normal coronary arteries. Maximal oxygen uptake (VO2 max) was determined at bicycle exercise testing. Insulin sensitivity (SI) was assessed by the minimal model analysis of the intravenous glucose tolerance test. Patients with variant angina had significantly lower VO2 max than controls (mean +/- SE, 25.6 +/- 1.5 vs 30.6 +/- 1.4 ml x kg-1 x min-1, p < 0.05), whereas VO2 max in patients with syndrome X was intermediate (27.1 +/- 1.3 ml x kg-1 x min-1). Compared with controls, patients with syndrome X and variant angina had reduced insulin sensitivity (controls, 1.47 +/- 0.16 10(-4) x min-1/per pmol/L vs syndrome X, 0.86 +/- 0.11 10(-4) x min-1 per pmol/L and variant angina, 0.96 +/- 0.15 x 10(-4) x min-1 per pmol/L; analysis of variance, p < 0.05). Only patients with syndrome X exhibited fasting hyperinsulinemia. Patients with syndrome X also had higher fasting concentrations of triglycerides and total cholesterol and lower concentrations of high-density lipoprotein cholesterol than controls. When adjusting SI for variances of VO2 max, differences in SI vanished between controls and patients with variant angina but not between controls and patients with syndrome X. Thus syndrome X and variant angina are both associated with insulin resistance, but lipid abnormalities are only prominent in patients with syndrome X. A variable expression in terms of concomitant disturbances of lipid profiles and disparate influences of physical capacity suggests different underlying mechanisms.