Ischemic stroke after acute myocardial infarction. A population-based study.

BACKGROUND AND PURPOSE

Modern treatment may have influenced the risk of stroke after myocardial infarction (MI). The purpose of this study was to examine the incidence of ischemic stroke during the first month after an acute MI in an unselected population, to identify predictors of MI-related stroke, and to investigate the secular trend in MI-related stroke incidence.

METHODS

In this case-control study, from a population of approximately 310000 25- to 74-year-old inhabitants, case subjects with a stroke within 1 month after an MI were prospectively recorded in the population-based Northern Sweden MONICA (Monitoring of Trends and Determinants in Cardiovascular Disease) study from 1985 to 1994. The same number of control subjects with an MI but without a stroke were matched for age, sex, and year when MI occurred.

RESULTS

One hundred twenty-four case subjects were recorded. Fifty-one percent (63/124) of the strokes occurred within 5 days after onset of MI. The odds ratios (ORs) of an MI-related stroke were for a history of hypertension 1.7 (95% confidence interval [CI], 1.0 to 3.2), previous stroke 2.4 (CI, 1.0 to 6.1), chronic atrial fibrillation 3.0 (CI, 1.1 to 9.2), onset of atrial fibrillation during the hospital stay 3.5 (CI, 1.4 to 10.1), ST-segment elevation 2.4 (CI, 1.4 to 4.6), and anterior infarction 1.5 (CI, 0.9 to 2.6). In a conditional multiple logistic regression model, previous stroke (OR, 2.8; CI, 1.1 to 7.6), chronic atrial fibrillation (OR, 3.8; CI, 1.3 to 11.0), new-onset atrial fibrillation (OR, 4.6; CI, 1.6 to 12.8), and ST-segment elevation (OR, 3.4; CI, 1.6 to 7.4) were independent predictors of stroke. MIs preceding stroke were larger and in 51% were located anteriorly. There was a decrease in the incidence and event rate of MI-related stroke during the study period (P < .01 and P < .05, respectively).

CONCLUSIONS

The risk of stroke is highest the first 5 days after MI. Only approximately half of the strokes occurring the first month after an MI are preceded by an anterior MI. The most important predictors of MI-related stroke are atrial fibrillation (chronic or new onset), ST elevation, and a history of a previous stroke. There is a long-term trend toward a lower incidence of MI-related stroke. These findings have important implications concerning both the pathophysiology and prevention of MI-related stroke.