Abstract 5606: Effect of Prehospital Tirofiban Treatment in STEMI on Infarct Size and Ventricular Function - MRI Substudy of the OnTime Trial
Objective: Despite optimal reperfusion strategies acute myocardial infarction frequently deteriorates to ischemic heart failure. Early administration of GPIIBIIIA antagonists has been shown to reduce infarct size. The randomized, double-blind On Time-2 study revealed that high dose prehospital tirofiban improves ST resolution and results in improved outcome. The MRI substudy investigated whether a beneficial effect on infarct size and ventricular function can be demonstrated.
Methods: 30 patients were assigned to the MRI substudy. 15 patients received tirofiban treatment. MRI was performed within 48 hours upon admission and at 4 month follow up. Ejection fraction EF, enddiastolic volume EDV and endystolic volume ESV were computed on 10 contiguous CINE SSFP short axis slices. Infarct size was computed on 3D Lateenhancement sequences. Infarct enhancement was defined as signal intensity of more than two standard deviations from remote myocardium. All measurements are given as mean ± SE. Group differences were computed using ANOVA repeated measures, a p value ≤0.05 was considered significant.
Results: At baseline there was no significant difference between groups with respect to EF (Tirofiban: 49.9 ± 2.4%, Placebo: 51.6 ± 2,4%; p=0.6), EDV (Tirofiban: 150.0 7.7 ml, Placebo: 159.7 ± 7.6 ml; p=0.4) and ESV (Tirofiban: 76.3±6.4 ml, Placebo: 77.9 ± 6.4 ml; p=0.85). At 4 month follow up EF, EDV and ESV had improved in both groups with no significant difference between groups in either parameter. However relative infarct size was significantly smaller among Tirofiban treated patients (Tirofiban: 15,4 ± 3,4%, Placebo: 20,8 ± 3,7%; p=0.05) despite similar areas at risk (Tirofiban: 26,7 ± 4,1%, Placebo: 25,1 ± 4,0%).
Conclusion: Prehospital treatment with tirofiban can significantly reduce infarct size.