Objective: To determine whether changes in health maintenance organization (HMO) penetration or payer mix affected in-hospital mortality and treatment patterns of patients with acute myocardial infarction (AMI).
Study design: Observational study using patient-level logistic regression analysis and hospital and year fixed effects of data from the Agency for Healthcare Research and Quality's Healthcare Cost and Utilization Project Nationwide Inpatient Sample, a geographically diverse sample of 20% of the hospitalized patients in the United States.
Patients and methods: Discharges of patients (n = 340,064) with a primary diagnosis of acute myocardial infarction who were treated in general medical or surgical hospitals that contributed at least 2 years of data to the HealthCare Cost and Utilization Project Nationwide Inpatient Sample from 1989 to 1996. In-hospital mortality and rates of cardiac catheterization, angioplasty, or coronary artery bypass grafting for Medicare patients or non-Medicare patients were the main outcome measures.
Results: Among Medicare patients, increases in HMO penetration were associated with reduced odds of receiving cardiac catheterization, angioplasty, or coronary artery bypass grafting of 3% to 16%, but were not associated with any change in mortality risk. Increases in the number of HMOs within a metropolitan statistical area, our measure of HMO competition, were associated with small but significant increases in the odds of cardiac catheterization and angioplasty of about 2%. There was no pattern of changes in cardiac procedure rates or in-hospital mortality among non-Medicare patients.
Conclusion: Increases in HMO penetration reduced cardiac procedure rates by statistically significant but small amounts among Medicare patients with AMI, without affecting mortality rates.