Association between time of hospitalization with acute myocardial infarction and in-hospital mortality

Aim: To study the association between time of hospitalization and in-hospital mortality for acute myocardial infarction (AMI). Methods and Results: Patients admitted with ST-elevation myocardial infarction (STEMI) and non-STEMI (NSTEMI) across 243 hospitals in England and Wales between 1st January 2004 and 31st March 2013 were included. The outcome measure was in-hospital mortality. Adjusted odds ratios for in-hospital mortality were estimated across six four-hourly time periods over the 24-hour clock using multilevel logistic regression, inverse-probability weighting propensity score and instrumental variable analysis. Among 615,035 patients (median age 70.0 years, IQR 59.0 - 80.0 years; 406,519 (66.0%) men), there were 52,777 (8.8%) in-hospital deaths. At night, patients with NSTEMI were more frequently co-morbid, and for STEMI had longer symptom-onset-to-reperfusion times. For STEMI, unadjusted in-hospital mortality was highest between 20:00 and 23:59 (four-hour period range 8.4% to 9.9%; OR compared with 00:00 to 03:59 reference 1.13, 95% CI 1.07 to 1.20), and for NSTEMI highest between 12:00 to 15:59 (8.0% to 8.8%; OR compared with 00:00 to 03:59 reference 1.07, 95% CI 1.03 to 1.12). However, these differences were only apparent in the earlier years of the study, and were attenuated by adjustment for demographics, co-morbidities and clinical presentation. Differences were not statistically significant after adjustment for acute clinical treatment provided. Conclusions: There is little evidence to support an association between time of hospitalization and in-hospital mortality for acute myocardial infarction; variation in in-hospital mortality may be explained by case mix and the use of treatments.