Does physician specialty affect the survival of elderly patients with myocardial infarction?

Objective. To determine the effect of treatment by a cardiologist on mortal ity of elderly patients with acute myocardial infarction (AMI, heart attack ), accounting for both measured confounding using risk-adjustment technique s and residual unmeasured confounding with instrumental variables (TV) meth ods. Data Sources/Study Setting. Medical chart data and longitudinal administrat ive hospital records and death records were obtained for 161,558 patients a ged greater than or equal to 65 admitted to a nonfederal acute care hospita l with AMI from April 1994 to July 1995. Our principal measure of significa nt cardiologist treatment was whether a patient was admitted by a cardiolog ist. We use supplemental data to explore whether our analysis would differ substantially using alternative definitions of significant cardiologist tre atment. Study Design. This retrospective cohort study compared results using least squares (LS) multivariate regression with results from IV methods that acco unted for additional unmeasured patient characteristics. Primary outcomes w ere 30-day and one-year mortality, and secondary outcomes included treatmen t with medications and revascularization procedures. Data Collection/Extraction Methods. Medical charts for the initial hospital stay of each AMI patient underwent a comprehensive abstraction, including dates of hospitalization, admitting physician, demographic characteristics, comorbid conditions, severity of clinical presentation, electrocardiograph ic and other diagnostic test results, contraindications to therapy, and tre atments before and after AMI. Principal Findings. Patients admitted by cardiologists had fewer comorbid c onditions and less severe AMIs. These patients had a 10 percent (95 percent CI: 9.5-10.8 percent) lower absolute mortality rate at one year. After mul tivariate adjustment with LS regression, the adjusted mortality difference was 2 percent (95 percent CI: 1.4-2.6 percent). Using IV methods to provide additional adjustment for unmeasured differences in risk, we found an even smaller, statistically insignificant association between physician special ty and one-year mortality, relative risk (RR) 0.96 (0.88-1.04). Patients ad mitted by a cardiologist were also significantly more likely to have a card iologist consultation within the first day of admission and during the init ial hospital stay, and also had a significantly larger share of their physi cian bills for inpatient treatment from cardiologists. IV analysis of treat ments showed that patients treated by cardiologists were more likely to und ergo revascularization procedures and to receive thrombolytic therapy, aspi rin, and calcium channel-blockers, but less likely to receive beta-blockers . Conclusions. In a large population of elderly patients with AMI, we found s ignificant treatment differences but no significant incremental mortality b enefit associated with treatment by cardiologists.