(P128) ENDOTHELIAL PROGENITOR CELLS ENGINEERED TO OVER-EXPRESS ENDOTHELIAL NO-SYNTHASE AND THEIR EFFECT ON ARRHYTHMIC SUBSTRATE AS ASSESSED BY GRAY ZONE ANALYSIS - A SUB-STUDY OF THE ENACT-AMI TRIAL

Background: Adverse remodeling post myocardial infarction increases heart failure and arrhythmia risk. The ENACT-AMI trial (NCT00936819) recently demonstrated that endothelial progenitor cells (EPCs) over-expressing endothelial nitric oxide synthase (eNOS) may reduce LV infarct mass compared with eNOS-free EPCs, but did not reach its primary endpoint (change in LVEF). In this sub-study of ENACT-AMI, we assessed whether eNOS-EPCs reduced arrhythmic substrate, assessed by gray zone analysis using cardiovascular magnetic resonance (CMR) imaging.

METHODS AND RESULTS: ENACT-AMI was a double-blind placebo-controlled trial in which participants were randomized to receive intracoronary injection post-STEMI with either: 1) saline placebo (Arm A); 2) EPCs (Arm B); or 3) eNOS -transfected EPCs (Arm C). CMR late gadolinium enhancement imaging was performed at baseline (day 4) and 6 months post-STEMI. Blinded gray zone analysis was performed using the signal threshold vs. reference myocardium technique to quantify total scar and gray zone mass using the 5SD method. The primary outcome was change in percent gray zone (gray zone mass divided by scar mass) over six months. We compared all arms using a one-way ANOVA. Secondary outcomes included absolute changes in gray zone mass and scar mass over six months. 32 of 47 ENACT-AMI participants had CMR studies interpretable for gray zone analysis (13, 10, and 9 in Arms A, B and C, respectively). There was no significant difference in change in percent gray zone between the arms. Arm A patients’ percent gray zone increased by 2.1 ± 26.8% (15.4% to 17.5%), while that for Arm B increased by 3.9 ± 21.9% (14.9% to 18.8%) and that for Arm C decreased by -2.3 ± 21.0% (15.9% to 13.6%). There was also no significant difference in the absolute changes of gray zone mass (0.0 ± 4.9 g for Arm A, +0.4 ± 6.5 g for Arm B, and -1.1 ± 7.6 g for Arm C) or scar mass (-3.9 ± 10.6 g for Arm A, -7.5 ± 9.5 g for Arm B, and +1.1 ± 15.6 g for Arm C) between the arms.

Conclusion: Neither eNOS-transfected nor eNOS-free EPCs reduced gray zone area to a statistically significant extent. Notably, eNOS-transfected EPC patients were the only study arm with any reduction in percent gray zone, implying a trend towards gray zone benefit may exist. Further studies with larger sample sizes are required to confirm changes in infarct and peri-infarct size, and whether this impacts ventricular remodeling.