Prognostic Significance of Newly Diagnosed Atrial Fibrillation After Acute Myocardial Infarction: A Study of 184,980 Medicare Patients.

We aimed to determine whether newly diagnosed atrial fibrillation (AF) predicted cardiovascular events and death after myocardial infarction (AMI) in a large nationwide cohort of patients. All Medicare beneficiaries aged >65 years who were discharged alive after a diagnosis of AMI between January 1, 2007 and December 31, 2008 were identified. Main exposure was a diagnosis of AF during admission or within 90 days after discharge. Primary outcome was a composite of recurrent AMI, stroke and all-cause mortality. Secondary outcomes were each of recurrent AMI, stroke and all-cause mortality. We used Cox proportional hazards regression to assess the relationship between AF and time-to-event outcomes with follow up ending at 3 years. Of 184,980 patients, 9.1 % had AF; 40.6 % were male; 82.8 % were non-Hispanic whites. Mean age was 79.1 ± 8.1 years. Overall, 15.7 % had subsequent AMI, 5.7 % had stroke and 43.9 % died during a mean follow up of 26.4 months. AF was associated with a significantly increased risk of the primary outcome (Hazard ratio (HR) = 1.10; 95 % confidence interval (CI): 1.07-1.12). AF was also separately associated with significantly increased risk of recurrent AMI (HR = 1.09; 95 % CI: 1.04-1.14), stroke (HR = 1.29; 95 % CI: 1.21-1.37), and death (HR = 1.09; 95 % CI: 1.06-1.12). Neither age, race nor sex modified the effects of AF on primary or secondary outcomes. In conclusion, AF is a significant predictor of adverse cardiovascular outcomes and mortality after AMI. Further studies are needed to understand mechanisms by which AF alters outcomes in survivors of AMI.