Variations in patterns of care and outcomes after acute myocardial infarction for Medicare beneficiaries in fee-for-service and HMO settings

OBJECTIVE: To assess revascularization and mortality after acute myocardial infarction (AMI) for all Medicare patients in fee-for-service (FFS) and health maintenance organization (HMO) settings in California. DATA SOURCES/STUDY SETTING: Hospital discharge abstract and death certificate data linked with Medicare enrollment files for patients aged 65 and over with Medicare coverage (69,040) discharged from a California-licensed hospital in 1994-1996. STUDY DESIGN: Risk-adjusted results were assessed for HMOs and FFS, as well as for FFS beneficiaries from areas served by each plan. DATA COLLECTION/EXTRACTION METHODS: Risk models were based on all sampled patients. The HMO patients were aggregated into 17 pseudoplans: 5 individual plans, 4 large plans split geographically (10 observations), and 2 "pseudoplans" of small HMOs. Observed versus expected 30-day mortality rates, lengths-of-stay (LOS) during the index hospitalization and any transfers, revascularization (coronary artery bypass graft CABG] surgery and/or percutaneous transluminal coronary angioplasty PTCA]) during the index hospitalization or 30 days after admission, were calculated for each pseudoplan. PRINCIPAL FINDINGS: Risk-adjusted death rate was slightly higher in FFS than in HMO settings (p < .01 with one risk adjustment model, n.s. with another). Three pseudoplans had significantly (p < .01) better than expected mortality rates. One pseudoplan was significantly worse (p < .05) with one risk adjustment model but not the other. The LOS and revascularization rates varied widely, but were not associated with outcomes. Plans with among the best results had the lowest LOS and revascularization rates. These pseudoplans were less likely to have their patients initially admitted to a hospital with revascularization capability, but the hospitals they used had higher CABG volumes. Even if CABG facilities were available during the index admission, in these plans with better than expected mortality rates, revascularization was often postponed or carried out elsewhere. CONCLUSIONS: For Medicare patients having an AMI in the mid-1990s in California, risk-adjusted outcomes were no different, or slightly better on average, for those in HMOs than in FFS. Not all plans performed equally well, so understanding what leads to differences in quality is more important than simple comparisons of HMOs versus FFS.