Coronary heart disease and stroke share multiple vascular risk factors and are leading causes of disability and death. Advances in secondary prevention for patients who have had a myocardial infarction (MI) have improved survival by reducing the incidence of recurrent MI and congestive heart failure. However, little is known about the risk of stroke after MI and whether this risk also has declined. Witt and colleagues followed a cohort of patients post-MI in a geographically defined community to determine the incidence of stroke and its subsequent impact on survival.
The community-based cohort study included 2,160 adults with diagnostic codes compatible with MI who were discharged from hospitals in Olmsted County, Minn., from 1979 to 1998. The average age was 67 years, and 57 percent of participants were men. Participants were followed as part of the Rochester Epidemiology Project, a comprehensive inpatient and outpatient medical record linkage system. Physicians identified the incidence of subsequent stroke by reviewing diagnoses in medical records. Stroke, defined as the acute onset of a focal neurologic deficit persisting for more than 24 hours, was classified as cerebral infarction (ischemic), intracerebral hemorrhage, or sub-arachnoid hemorrhage, based on clinical and imaging findings. To avoid reporting changes in stroke incidence related to changing imaging technology during the study, clinically silent strokes identified only on computed tomography or magnetic resonance imaging of the head or at autopsy were excluded.
The incidence of stroke in patients after MI was compared with the incidence of stroke in the general population using data from the Rochester Stroke Registry. In the study cohort, 273 strokes occurred; 259 (95 percent) were classified as ischemic. Factors associated with increased stroke risk included older age (hazard ratio [HR] = 1.04), history of stroke (HR = 2.07), and diabetes (HR = 1.68). The highest rate of first and recurrent stroke (23.9 per 1,000 person-months) occurred in the first 30 days after MI. This stroke rate was 44 times that of the general population. The stroke rate fell sharply to 2.3 per 1,000 person-months after the first 30 days and declined gradually thereafter until year 4, when it equaled the rate of the general population. Patients who had an MI in the late 1990s had the same stroke risk as those who had an MI nearly two decades earlier. After adjusting for baseline differences, patients who had strokes were two to three times more likely to die during the study than those who did not.
The authors conclude that the risk of stroke is dramatically increased during the first 30 days after MI, and unlike the risk of recurrent MI, was unaffected by new medical therapies for secondary prevention. They further conclude that available therapies do not prevent stroke after MI or its associated mortality.