Prehospital thrombolysis: beneficial effects of very early treatment on infarct size and left ventricular function

The purpose of this study was to compare the effects of very early (< or = 1.5 h after symptom onset) and later (> 1.5 up to 4 h) thrombolytic therapy on infarct size, left ventricular function and early mortality in patients with acute myocardial infarction. To start thrombolysis at the earliest possible moment, it was performed in the prehospital setting. A cutoff time of 1.5 h was prospectively stipulated.

Shortening of ischemic time is crucial within the 1st 2 h. Prehospital thrombolysis can reduce time to treatment and enables very early initiation of therapy for many patients.

One hundred seventy patients received 30 mg of anistreplase up to 4 h from symptom onset by a mobile intensive care unit physician. Infarct size was measured from cumulative release of alpha-hydroxybutyrate dehydrogenase, and left ventricular function was assessed by contrast angiograms 10 days after the infarction.

The decision to treat on scene was correct in 98% of patients. There were no bleeding complications or deaths outside the hospital setting. In 28 patients (17%) the ischemic process was interrupted. Findings with thrombolytic therapy initiated < or = 1.5 (96 patients) versus > 1.5 h (74 patients) were the following: initial extent of epicardial injury, 1.6 +/- 0.9 versus 1.4 +/- 0.7 mV, p = NS; infarct size by cardiac enzyme release 646 +/- 634 versus 886 +/- 712 IU/liter, p < 0.05; ejection fraction 57 +/- 14% versus 51 +/- 13%, p < 0.05; regional dyssynergic area 24 +/- 22 versus 33 +/- 24 U, p < 0.05; 21-day mortality 1 of 96 versus 5 of 74 patients (1% vs. 7%, p < 0.05).

The data suggest that in evolving myocardial infarction up to 4 h in duration, the start of thrombolytic therapy at < or = 1.5 h compared with > 1.5 h limits infarct size, preserves left ventricular function and may save lives.