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For every 30-minute delay to reperfusion, myocardial infarct size should increase by 37%. However, extensive preclinical studies support that mechanically unloading the left ventricle (LV) and delaying reperfusion is cardioprotective and reduces infarct size (IS). The Door-To-Unload STEMI Pilot Trial (DTU-STEMI) was the first study testing the feasibility and safety of LV unloading and delaying reperfusion in ST-elevation myocardial infarction (STEMI) without cardiogenic shock.
In a multicenter, prospective, Phase 1 randomized trial, 50 patients with anterior STEMI referred for primary percutaneous coronary intervention (PCI) within 1-6 hours of symptom onset were assigned to primary unloading with an Impella CP followed by either immediate reperfusion (U-IR) or 30 minutes of unloading prior to reperfusion (U-DR). The safety of delayed reperfusion was assessed by comparing infarct size between groups as measured by cardiac magnetic resonance (CMR). The current study focused on patients who underwent CMR along with the subgroup of patients who presented with an ST elevation (STE) >6mm.
Of the 50 patients enrolled, 41 had CMR within the defined timeframe. Of those, 40 had imaging at both 3-5 days and at 30 days (U-IR=19, U-DR=21). Baseline characteristics were similar between groups. The time from symptom onset to reperfusion (SOR) was 210 minutes in the U-IR group vs. 220 minutes in the U-DR group (p=NS). In the subgroup with STE >6, SOR time was 174 minutes in the U-IR group vs. 227 minutes in the U-DR group (p=0.05). Infarct size as a percent area (IS/AAR) at risk at 3-5 days was 51.6% vs. 44.2% in the U-IR vs. U-DR groups (p=NS). The STE >6 sub-group had an IS/AAR of 59.9% vs. 44.1% in the U-IR vs. U-DR groups (p=0.04).
LV unloading using the Impella CP and delaying reperfusion by 30 minutes in patients with anterior STEMI did not increase infarct size. In the subgroup of patients with STE >6, despite a significantly longer ischemic time, IS/AAR was significantly lower in the U-DR group compared to the U-IR group. These results are fundamental to the development of the DTU-STEMI pivotal trial comparing LV unloading and delayed reperfusion to the current STEMI standard of care.