Myocardial infarction, thrombolytic therapy, and stroke. A community-based study. The MITI Project Group

Thrombolytic therapy used in patients with acute myocardial infarction may increase the risk of stroke. Scant information is available from community-based studies.

Among 5,635 consecutive patients admitted with acute myocardial infarction to hospitals in Seattle and surrounding suburban King County, Washington, 116 (2.1%) experienced strokes during hospitalization. Of these strokes, 82 (71%) were ischemic and 34 (29%) were hemorrhagic, defined by a patient's having had a computed tomographic scan of the head that showed blood. Thrombolytic therapy was given to 1,413 of these patients (25%) and was associated with increased risk of hemorrhagic stroke but reduced risk of ischemic stroke. The relative risk of stroke with thrombolytic therapy was estimate using multiple logistic regression to adjust for potential confounding factors. The adjusted relative risk for hemorrhagic stroke was 3.6 (95% confidence interval [CI], 1.7-8.0); for ischemic stroke, 0.4 (95% CI, 0.2-0.9); and for overall stroke, 1.0 (95% CI, 0.6-1.7). The adjusted risk for death from any cause following stroke was 3.0 (95% CI, 1.4-6.4).

Although thrombolytic therapy had little effect on the overall occurrence of stroke, thrombolytic therapy increased the risk of stroke death because more patients with hemorrhagic than ischemic strokes died during their hospitalization. The rates of hemorrhagic stroke with thrombolytic therapy reported in the present study are higher than those reported in clinical trials in which treatment is given to select patients under strict protocols.