Selection Bias in the Use of Thrombolytic Therapy in Acute Myocardial Infarction

Objective.—To determine whether clinical selection for thrombolytic therapy for acute myocardial infarction results in a skewed population for subsequent adverse cardiovascular events. Design.—A comparison of the clinical features of the patients in the Survival and Ventricular Enlargement Study who either had or had not received thrombolytic therapy was conducted in both univariate and multiple logistic regression analyses. Setting.—Hospitalized patients experiencing acute myocardial infarction from 112 broadly representative, private, academic, and government hospitals in the United States and Canada. Patients.—All patients in the Survival and Ventricular Enlargement Study had had a recent myocardial infarction (<16 days) and had a left ventricular ejection fraction of 40% or less. Intervention.—Thrombolytic therapy was administered to 733 patients and was not given to 1498. Main Outcome Measures.—The comparisons with respect to use of thrombolytic therapy were formulated after the completion of enrollment and indicated that the majority of patients did not receive thrombolytic therapy. Results.—The 1498 (67.1%) patients who did not receive thrombolytic therapy were at higher risk (older age, lower functional capacity, greater likelihood of a history of prior myocardial infarction, angina, diabetes, and hypertension) for subsequent cardiovascular events and, as anticipated, were more likely to have concomitant gastrointestinal and neurological diseases. A multiple logistic regression analysis indicated that older age, prior myocardial infarction, impaired functional status, employment status, diabetes, and neurological diseases were predictors of use of thrombolytic therapy. Conclusion.—Although the Survival and Ventricular Enlargement Study population was selected for left ventricular dysfunction, the majority of patients who currently are judged clinically as unsuitable for thrombolytic therapy have a higher risk for adverse cardiovascular events.