The association between hospital volume and survival after acute myocardial infarction in elderly patients

Background Patients with chest pain thought to be due to acute coronary isc hemia are typically taken by ambulance to the nearest hospital. The potenti al benefit of field triage directly to a hospital that treats a large numbe r of patients with myocardial infarction is unknown. Methods We conducted a retrospective cohort study of the relation between t he number of Medicare patients with myocardial infarction that each hospita l in the study treated (hospital volume) and longterm survival among 98,898 Medicare patients 65 years of age or older. We used proportional-hazards m ethods to adjust for clinical, demographic, and health-system-related varia bles, including the availability of invasive procedures, the specialty of t he attending physician, and the area of residence of the patient (rural, ur ban, or metropolitan). Results The patients in the quartile admitted to hospitals with the lowest volume were 17 percent more likely to die within 30 days after admission th an patients in the quartile admitted to hospitals with the highest volume ( hazard ratio, 1.17; 95 percent confidence interval, 1.09 to 1.26; P<0.001), which resulted in 2.3 more deaths per 100 patients. The crude mortality ra te at one year was 29.8 percent among the patients admitted to the lowest-v olume hospitals, as compared with 27.0 percent among those admitted to the highest-volume hospitals. There was a continuous inverse dose-response rela tion between hospital volume and the risk of death. In an analysis of subgr oups defined according to age, history of cardiac disease, Killip class of infarction, presence or absence of contraindications to thrombolytic therap y, and time from the onset of symptoms, survival at high-volume hospitals w as consistently better than at low-volume hospitals. The availability of te chnology for angioplasty and bypass surgery was not independently associate d with overall mortality. Conclusions Patients with acute myocardial infarction who are admitted dire ctly to hospitals that have more experience treating myocardial infarction, as reflected by their case volume, are more likely to survive than are pat ients admitted to low-volume hospitals. (N Engl J Med 1999;340:1640-8.) (C) 1999. Massachusetts Medical Society.