Prehospital-initiated vs hospital-initiated thrombolytic therapy. The Myocardial Infarction Triage and Intervention Trial

Abstract

OBJECTIVE: To determine the effect of prehospital-initiated vs hospital-initiated treatment of myocardial infarction on clinical outcome. DESIGN: Randomized, controlled clinical trial. SETTING: Multicenter study involving 19 hospitals and all paramedic systems in the Seattle, Wash, metropolitan area. PATIENTS: A total of 360 patients with symptoms for 6 hours or less, no risk factors for serious bleeding, and ST-segment elevation were selected by paramedics and a remote physician for inclusion into the trial. They represented 4% of patients with chest pain who were screened and 21% of those with acute infarction. INTERVENTIONS: Patients were allocated to have aspirin and alteplase treatment initiated before or after hospital arrival. Intravenous sodium heparin was administered to both groups in the hospital. MAIN OUTCOME MEASURE: The primary endpoint was a ranked composite score (combining death, stroke, serious bleeding, and infarct size). The relation between time to treatment and outcome (composite score, infarct size, ejection fraction, and mortality) was also assessed. RESULTS: Initiating treatment before hospital arrival decreased the interval from symptom onset to treatment from 110 to 77 minutes (P < .001). Although more patients whose therapy was initiated before hospital arrival had resolution of pain by admission (23% vs 7%; P < .001), there were no significant differences in the composite score (P = .64), mortality (5.7% vs 8.1%), ejection fraction (53% vs 54%), or infarct size (6.1% vs 6.5%). A secondary analysis of time to treatment and outcome showed that treatment initiated within 70 minutes of symptom onset was associated with better outcome (composite score, P = .009; mortality, 1.2% vs 8.7%, P = .04; infarct size, 4.9% vs 11.2%, P < .001; and ejection fraction, 53% vs 49%, P = .03) than later treatment. Identification of patients eligible for thrombolysis by paramedics reduced the hospital treatment time from 60 minutes (for patients not in the study) to 20 minutes (for study patients allocated to begin treatment in the hospital). CONCLUSION: There was no improvement in outcome associated with initiating treatment before hospital arrival; however, treatment within 70 minutes of symptom onset--whether in the hospital or in the field--minimized the infarct process and its complications.