Article Abstract

MRI manifestations of persistent microvascular obstruction and acute left ventricular remodeling in an experimental reperfused myocardial infarction

Authors: Yuesong Yang, John J. Graham, Kim Connelly, Warren D. Foltz, Alexander J. Dick, Graham A. Wright

Abstract

Purpose: To investigate varied manifestations of persistent microvascular obstruction (PMO) and acute left ventricular (LV) remodeling in an experimental reperfused myocardial infarction (MI) using MRI.
Methods: In eleven Yorkshire pigs an acute MI was produced through a 90-minute balloon occlusion of the middle left anterior descending coronary artery, followed by reperfusion. All animals underwent MRI examinations on a 1.5T system including a SSFP functional study, first pass myocardial perfusion (FPMP), T1 preparation Look-Locker and delayed contrast-enhanced MRI (DE-MRI). Imaging was performed immediately post-intervention (day 0) and at days 7-9. In four animals a repeat MRI examination was performed at day 2 as well. Upon study completion, animals underwent histological analysis including infarct assessment with triphenyltetrazolium chloride (TTC).
Results: Following reperfusion, Thrombolysis In Myocardial Infarction (TIMI) Flow grade 3 was achieved in all animals, demonstrated by repeat angiography following balloon deflation (day 0). Various MR appearances of PMO were noticed including predominance in the subendocardial region, a central core within the infarcted tissue and also multiple separate clusters. In ten of eleven animals PMO was demonstrated as a persistent hypo-enhanced area in FPMP and DE-MRI, and identified as bright regions in later T1 difference images. In one animal PMO was identified only at day 2. At day 7-9 PMO could be identified on early DE-MRI at 5-15 minutes post Gd injection but not on late DE-MRI and T1 difference images after 45-60 minutes post-contrast. A larger volume of PMO and MI at day 2 was noted in comparison to data from day 0 but the difference was not statistically significant. An increased end-diastolic LV volume (EDV) without changes in end-systolic LV volume (ESV) and LV mass at end-diastolic phase (LVM) was observed at day 7-9 in comparison to data from day 0. There was good correlation between the relative extent of persistent MO in the infarcted myocardium (% MO/MI) and EDV at day 7-9 (r=0.83, n=10, P=0.003). MI was confirmed in all animals by TTC staining and/or histology.
Conclusions: A variable MR appearance of persistent microvascular obstruction is observed during a short time course MRI study of reperfused acute MI. Acute negative LV remodeling was closely related to the relative extent of persistent microvascular obstruction within the infarct myocardium.

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