Outcome following acute myocardial infarction - Are differences among physician specialties the result of quality of care or case mix?

Background: Studies to determine whether care by cardiologists improves the survival of patients with acute myocardial infarction (MI) have produced conflicting results, and it is not known what accounts for differences in patient outcome by physician specialty. Objectives: To evaluate whether cardiologists provide more recommended therapies to elderly patients with acute MI and, if so, to determine whether variations in processes of care account for differences in patient outcome. Design: Retrospective cohort study using medical chart data and administrative data files. Setting: All nonfederal acute care hospitals in California. Patients: A cohort of 7663 Medicare beneficiaries 65 years and older directly admitted to the hospital with a confirmed acute MI from April 1994 to July 1995 with complete data regarding potential contraindications to recommended therapies. Main Outcome Measures: Percentage of "good" and "ideal" candidates for a given acute MI therapy who actually received that therapy, percentage who received exercise stress testing or coronary angiography, percentage who underwent revascularization, and 1-year mortality, stratified by specialty of the attending physician. Results: During hospitalization, good candidates for aspirin were more likely to receive aspirin if they were treated by cardiologists (87%) than by medical subspecialists (73%; P<.001), general internists (84%; P = .003), or family practitioners (81%; P<.001). Cardiologists were also more likely to treat good candidates with thrombolytic therapy (51%) than were medical subspecialists (29%; P<.001), general internists (40%; P<.001), or family practitioners (27%; P<.001). Patients of cardiologists were 2- to 4-fold more likely to undergo a revascularization procedure. Despite these differences in utilization, we found similar 30-day mortality rates across physician specialties. However, 1-year mortality rates were greater for patients treated by medical subspecialists (odds ratio [OR], 1.9; 95% confidence interval [CI], 1.6-2.3), general internists (OR, 1.4; 95% CI, 1.3-1.6), and family practitioners (OR, 1.7; 95% CI, 1.4-1.9) than for those treated by cardiologists. Adjusting for differences in patient and hospital characteristics markedly reduced the ORs for those treated by medical subspecialists (OR, 1.2; 95% CI, 0.9-1.4), general internists (OR, 1.1; 95% CI, 1.0-1.3), and family practitioners (OR, 1.3; 95% CI, 1.1-1.6), whereas further adjustment for medication use and revascularization procedures had little effect. Conclusions: Differences in the use of recommended therapies by physician specialty are generally small and do not explain differences in patient outcome. In comparison, differences among patients treated by physicians of various specialties (case mix) have a large impact on patient outcome and may account for the residual survival advantage of patients treated by cardiologists. With the exception of the in-hospital use of aspirin, recommended MI therapies are markedly underused, regardless of the specialty of the physician.