Subgroup analyses of the major clinical endpoints in the program on the surgical control of the hyperlipidemias (POSCH): Overall mortality, atherosclerotic coronary heart disease (ACHD) mortality, and ACHD mortality or myocardial infarction

Abstract

The Program on the Surgical Control of the Hyperlipidemias (POSCH) was a secondary atherosclerosis intervention trial employing partial ileal bypass surgery as the intervention modality. For this report, we analyzed 105 subgroups in 35 variables in POSCH, chosen predominantly for their potential relationship to the risk of atherosclerotic coronary heart disease (ACHD). We defined potential differential effects as those with: (1) an absolute z-value ⩾2.0 for the subgroup, if the absolute z-value for the overall effect was <2.0; and (2) an absolute z-value ⩾3.0 for the subgroup and a relative risk ⩽0.5, if the absolute z-value for the overall effect was ⩾2.0. For each of three major POSCH endpoints of overall mortality, ACHD mortality and ACHD mortality or confirmed nonfatal myocardial infarction, we found seven subgroups with a differential risk reduction in the surgery group as compared to the control group. Allowing for identical subgroups for more than one endpoint, there were 13 individual subgroups with differential effects. Of these, seven demonstrated internal consistency across endpoints, and five of these seven displayed external consistency with known ACHD risk factors and for biological plausibility: triglyceride concentration ⩾200 mg/dl; cigarette smoking; overt or borderline diabetes mellitus; a Minnesota ECG Q-QS code of 1-1; and obesity. A greater risk reduction, in comparison to the overall treatment effect, by the reduction of a single risk factor, hypercholesterolemia, in patients with at least two major ACHD risk factors was a provocative and an hypothesis-generating outcome of this analysis. The clinical implications of this finding may lead to more aggressive cholesterol intervention in patients with multiple ACHD risk factors.