An evaluation of composite indicators of hospital acute myocardial infarction care: a study of 136,392 patients from the Myocardial Ischaemia National Audit Project.

ABSTRACT

BACKGROUND: Hospital acute myocardial infarction (AMI) care is increasingly evaluated using composite quality scores. We investigated the influence of three aggregation methods for an AMI indicator on mortality and hospital rank. METHODS AND RESULTS: We studied 136,392 patients discharged alive from 199 hospitals with AMI recorded in the Myocardial Ischaemia National Audit Project, between 01/01/2008 and 31/12/2009. A composite of prescription of aspirin, thienopyridine inhibitor, ß-blocker, angiotensin converting enzyme inhibitor, HMG CoA reductase enzyme inhibitor and enrolment in cardiac rehabilitation at discharge was aggregated as opportunity based (OBCS), weighted opportunity-based (WOBCS) and all-or-nothing (ANCS) scores. We quantified adjusted 30-day, 6-month and 1-year mortality rates and hospital performance rank. Median (IQR) scores were OBCS 95.0% (3.5), WOBCS 94.7% (0.8) and ANCS 80.9% (11.8). The three methods affected the proportion of hospitals outside 99.8% credible limits of the national median (OBCS 52.2%, WOBCS 64.3% and ANCS 37.7%) and hospital rank. Each 1% increase in composite score was significantly associated with a 1 to 3% and a 4% reduction in 6-month and 1-year mortality, respectively. However, the ANCS had fewer cases and no significant association with 30-day mortality. CONCLUSIONS: A hospital composite score, incorporating 6 aspects of AMI care, was significantly inversely associated with mortality. However, composite aggregation method influenced hospital rank, number of cases available for analysis and size of the association with all-cause mortality, with the ANCS performing least well. The use and choice of composite scores in hospital AMI quality improvement requires careful evaluation.