Long term MI outcomes at hospitals with or without on-site revascularization

Context Many studies have found that patients with acute myocardial infarct ion (AMI) who are admitted to hospitals with on-site revascularization faci lities have higher rates of invasive cardiac procedures and better outcomes than patients in hospitals without such facilities. Whether such differenc es are due to invasive procedure rates alone or to other patient, physician , and hospital characteristics is unknown. Objective To determine whether invasive procedural rate Variations alone ac count for outcome differences in patients with AMI admitted to hospitals wi th or without on-site revascularization facilities. Design Retrospective, observational cohort study using linked population-ba sed administrative data from a universal health insurance system. Setting One hundred ninety acute care hospitals in Ontario, 9 of which offe red invasive procedures. Patients A total of 25697 patients hospitalized wi th AMI between April 1, 1992, and December 31, 1993, of whom 2832 (11%) wer e in invasive hospitals. Main Outcome Measures Mortality, recurrent cardiac hospitalizations, and em ergency department Visits in the 5 years following the index admission, adj usted for patient age, sex, socioeconomic status, illness severity, and ind ex revascularization procedures; attending physician specialty; and hospita l volume, teaching status, and geographical proximity to invasive-procedure centers and compared by hospital type. Results Patients admitted to invasive-procedure hospitals were much more li kely to undergo revascularization (11.4% vs 3.2% at other hospitals; P<.001 ). However, many other clinical and process-related factors differed betwee n the 2 groups. Although mortality rates were similar between the 2 institu tion types, the nonfatal composite 5-year event rate tie, recurrent cardiac hospitalization and emergency department visits) was lower for patients in itially admitted to invasive-procedure hospitals (71.3% vs 80.4%; unadjuste d odds ratio [OR], 0.65; 95% confidence interval [CI], 0.52-0.82; P<.001). This advantage persisted after adjustment for sociodemographic and clinical factors and procedure utilization (adjusted OR, 0.68; 95% CI, 0.53-0.89; P <.001). However, the nonfatal outcome advantages of invasive-procedure hosp itals were explained by their teaching status (adjusted OR, 0.98; 95% CI, 0 .73-1.30; P=.87). Conclusions In this sample of patients admitted with AMI, the differing out comes of apparently similar patients treated in 2 different practice settin gs were explained by multiple competing factors. Researchers conducting obs ervational studies should be cautious about attributing patient outcome dif ferences to any single factor.