In this observational cohort study, the authors attempted to estimate the incidence of ischemic stroke within 1 year of a Myocardial Infarction (MI) and the predictors of occurrence of a stroke. Additionally, they aimed to identify if advances in modern medicine with regards to medications and procedures have impacted this rate of ischemic stroke. The authors utilized the Register of Information and Knowledge about Swedish Heart Intensive Care Admissions (RIKS-HIA) database that includes all patients treated for acute coronary syndromes (ACS) in coronary care units (CCUs) in Sweden and studied all admissions between 1998 and 2008. The RIKS HIA database records a large number of variables including demographics, diagnosis, medications and procedures. It was merged with the National Patient Register that includes ICD 9 codes for Ischemic stroke in order to identify patients that experienced an ischemic stroke within one year of their Myocardial Infarction.
The entire study period was divided into 5 two year periods and Kaplan-Meier curves were calculated for the occurrence of ischemic stroke within 1 year after AMI during the five different time intervals and compared between groups using the log-rank test. Independent predictors of ischemic stroke following MI were identified using a Cox proportional hazards regression model. A total of 173 233 subjects were studied between 1998 and 2008 and of these, 7185 (4.1%) sustained an ischemic stroke within 1 year [95% confidence interval (CI) 4.01% – 4.19%]. Patients who experienced an ischemic stroke within 1 year after AMI were older (76.5 vs. 70.9 years), female, and had a history of previous MI, Stroke, heart failure, Diabetes and peripheral arterial disease. During the hospitalization for ischemic stroke following MI these patients had twice the incidence of atrial fibrillation when compared to those without stroke. Age, female sex, ST elevation MI, prior stroke, prior diabetes mellitus, heart failure at admission, atrial fibrillation, and ACEi treatment at discharge were independent predictors associated with an increased risk of ischemic stroke whereas Reperfusion therapy, treatment with aspirin or other antiplatelets and statins were associated with a reduced risk of stroke.
The rates of ischemic stroke within 1 year of a MI, over the 5 two year time periods decreased from 4.5% in 1998-2000 to 3.8% in 2007-2008. This drop resulted in 20% relative risk reduction and was likely accounted for improved treatment with statins and antiplatelets as well ACE inhibitors. Additionally rapid Percutaneous coronary intervention has gained popularity in the cardiology world and with decreased door to needle times the morbidity and mortality associated with a MI has considerably reduced.
So we would deduce that the Swedes have done well with regards to their cardiac care and as a result decreased rates of ischemic stroke following a MI. There are some questions that come to mind though – Did the database capture all patients that have MI’s? And how does this data compare to the US data? It is a retrospective cohort of patients where everyone had an MI and even though a small percent of patients developed a stroke their risk profile was distinctly different from the rest of the group. Did having a MI change their baseline risk of stroke? A fair number of variables were recorded in this database however there are likely several confounders due to interaction between vascular risks.