Noninvasive MR characterization of structural and functional components of reperfused infarct.

BACKGROUND

left ventricular (LV) remodeling is a highly complex phenomenon that starts soon after infarction and progresses to extensive regional and global architectural changes over time.

PURPOSE

to noninvasively comprehensively characterize transient (edema, hemorrhage, microvascular obstruction (MO)) and persistent structural (infarct size) components of reperfused infarct up to 10 weeks and to determine their relation to LV function.

MATERIAL AND METHODS

farm pigs were used for the study. Under fluoroscopy the left anterior descending (LAD) coronary artery was occluded for 90 min. MR imaging was performed at 3 days (n=14 pigs), 5 weeks (n=10), and 10 weeks (n=6) after reperfusion. The following MR imaging sequences were used: (i) cine; (ii) T2-weighted turbo spin echo; (iii) T2*-weighted turbo spin echo; (iv) tagged; (v) phase-contrast velocity-encoded; (vi) first-pass perfusion; and (vii) delayed contrast-enhanced (DE-MR imaging). After imaging, animals were euthanized at 3 days (n=4), 5 weeks (n=4), and 10 weeks (n=6) and hearts were stained with triphenyltetrazolium chloride to define acute, subacute, and scar infarct and interstitial hemorrhage.

RESULTS

T2, T2*, and DE-MR imaging demonstrated transient interstitial edema, interstitial hemorrhage, and MO, respectively. MO was observed in 85% of animals and 60% of these showed hemorrhages. Cine, tagged, and phase-contrast velocity-encoded images documented the persistent impairment in 3D strain of infarcted segments, which on first-pass perfusion showed persistent perfusion deficit. MR imaging demonstrated the progressive increase in LV volumes and decreased ejection fraction over time. The changes in LV between 5 and 10 weeks were not related to the presence of interstitial edema, interstitial hemorrhage, MO or increase in infarct size.

CONCLUSION

the various MR sequences described in this study allowed the demonstration of transient and persistent components of reperfused infarct. The progressive deterioration of global LV function was not related to the transient reperfusion components (edema, hemorrhage or MO) or change in infarct size. The results imply that MR imaging has the potential to identify progressive deterioration of LV function unrelated to reperfusion injury components or infarct size.