Hospital Readmission after Myocardial Infarction

March 16, 2012

Tori Socha

In July 2009, the Centers for Medicare & Medicaid Services began reporting 30-day hospital readmission rates for 3 common medical conditions, including acute myocardial infarction (MI). Acute MI with ST-segment elevation accounts for 29% to 38% of all cases of MI. With increased use of primary percutaneous coronary intervention (PCI), survival to hospital discharge has dramatically increased; however, patients who survive to discharge remain at risk for early postdischarge hospital readmission. Variations in 30-day readmission rates are considered indicators of inconsistent quality of care; policymakers focus on those rates as both a quality and economic metric. By identifying clinical predictors of readmission rates associated with acute MI, previous studies have sought to improve 30-day readmission rates. Researchers recently performed a post hoc analysis of the Assessment of Pexelizumab in Acute Myocardial Infarction study to determine predictors of 30-day postdischarge all-cause and nonelective readmission among patients with ST-segment elevation MI (STEMI) who were intended to undergo PCI. In particular, the researchers hypothesized that the country of enrollment would be independently associated with risk of 30-day readmission, among other factors. They reported analysis results in the Journal of the American Medical Association [2012;307(1):66-74]. The primary end point of the analysis was 30-day postdischarge all-cause hospital readmission. The secondary end point was 30-day postdischarge readmission, in which readmissions for elective PCI or coronary artery bypass grafting were excluded from the event definition (a total of 231 events). There were 5745 STEMI patients enrolled in the trial; of those, 97.0% (n=5571) survived to hospital discharge. The 5571 patients represented 17 countries (United States, Canada, Australia, New Zealand, and 13 European countries). Within 30 days of discharge, 11.3% (n=631) (95% confidence interval [CI], 10.5%-12.2%) had been readmitted. Among the 631 readmitted patients, 14.5% (95% CI, 12.9%-16.2%) of patients in the United States and 9.9% (95% CI, 9.0%-10.9%) outside the United States were readmitted. Excluding readmissions for elective revascularization, 8.6% (95% CI, 7.8%-9.3%) of patients in the overall cohort (n=478) were readmitted within 30 days of discharge, accounting for 10.5% (95% CI, 9.0%-11.9%) of patients in the United States and 7.7% (95% CI, 6.9%-8.6%) of patients outside the United States. The analysis of length of stay (LOS) revealed that patients in the United States had the shortest LOS (3 days; interquartile range, 2-4 days) and those in Germany had the longest (8 days; interquartile range, 6-11 days). Multivariable regression found the strongest predictors of 30-day readmission were multivessel disease (odds ratio [OR], 1.97; 95% CI, 1.65-2.35) and US location (OR, 1.68; 95% CI, 1.37-2.07). When readmissions for elective revascularization were excluded, US location remained an independent predictor of 30-day readmission (OR, 1.53; 95% CI, 1.20-1.96). However, following adjustment of the models for country-level medical LOS, US location was not an independent predictor of 30-day all-cause or nonelective readmission. US location was not a predictor of in-hospital death (OR, 0.88; 95% CI, 0.60-1.30) or 30-day postadmission death (OR, 1.0; 95% CI, 0.72-1.39). The researchers cited several limitations to the study. Because it is a retrospective of clinical trial data, there may be unmeasured or residual confounding associated with the data. In addition, the population was a selected clinical trial cohort, which may make the results not generalizable to the general population. Finally, the study compares a small proportion of countries, limiting a true global interpretation of the results. In summary, the researchers noted that “there was variation across countries in 30-day admission rates after STEMI, with readmission rates higher in the United States than in other countries. However, this difference was greatly attenuated after adjustment for length of stay.”