Effect of Exposure to Evidence‐Based Pharmacotherapy on Outcomes After Acute Myocardial Infarction in Older Adults

Abstract

To assess the effect of exposure to evidence-based medication after hospital discharge for Medicare beneficiaries with acute myocardial infarction (AMI). A discrete-time hazard model was used to estimate time to outcome associated with exposure to four drug classes (angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin-II receptor blockers (ARBs), beta-blockers (BBs), statins, and clopidogrel) used for post-AMI secondary prevention of cardiovascular events and mortality. Medicare administrative data for a 5% random sample of beneficiaries. Medicare beneficiaries (N=9,538) hospitalized for an AMI between April 1, 2006, and December 31, 2007, who survived for at least 30days after discharge. The cohort was followed until death or December 31, 2008. Time-varying exposure was measured as proportion of days covered (PDC) for each quarter during the follow-up period. PDC was classified into five categories (0-0.2, 0.2-0.4, 0.4-0.6, 0.6-0.8, 0.8-1.0). Outcomes were mortality and a composite outcome of death or post-AMI hospitalization. Over a median follow-up of 18months, mean PDC rates ranged from 0.37 (clopidogrel) to 0.50 (statins). When comparing the highest versus lowest categories of exposure, the hazard of the composite outcome was significantly lower for all drug classes except BBs (statins, adjusted hazard ratio (aHR)=0.71, ACEIs/ARBs, aHR=0.81, clopidogrel, aHR=0.85, BBs, aHR=0.93). All four drug classes were significantly associated with reductions in mortality; the magnitude of effect for the mortality outcome was largest for statins and smallest for BBs. Age modified the effect of statins on mortality. Use of evidence-based medications for secondary prevention after AMI is suboptimal in the Medicare population, and low exposure rates are associated with significantly higher risk for subsequent hospitalization and death.