Quantitative tracking of edema, hemorrhage, and microvascular obstruction in subacute myocardial infarction in a porcine model by MRI

Abstract

Pathophysiological responses after acute myocardial infarction include edema, hemorrhage, and microvascular obstruction along with cellular damage. The in vivo evolution of these processes simultaneously throughout infarct healing has not been well characterized. The purpose of our study was to quantitatively monitor the time course of these mechanisms by MRI in a porcine model of myocardial infarction. Ten pigs underwent MRI before coronary occlusion with subgroups studied at day 2 and weeks 1, 2, 4, and 6 post-infarction. Tissue characterization was performed using quantitative T2 and T2* maps to identify edema and hemorrhage, respectively. Contrast-enhanced MRI was used for infarct/ microvascular obstruction delineation. Inflammation was reflected by T2 fluctuations, however at day 2, edema and hemorrhage had counter-acting effects on T2. Hemorrhage (all forms) and mineralization (calcium) could be identified by T2* in the presence of edema. Simultaneous resolution of microvascular obstruction and T2* abnormality suggested that the two phenomenon were closely associated during the healing process. Our study demonstrates that quantitative T2 and T2* mapping techniques allow regional, longitudinal, and cross-subject comparisons and give insights into histological and tissue remodeling processes. Such in vivo characterization will be important in grading severity and evaluating treatment strategies for myocardial infarction, potentially improving clinical outcomes. Magn Reson Med 66:1129-1141, 2011. V C 2011 Wiley-Liss, Inc.

Temporal course of microvascular obstruction after myocardial infarction assessed by MRI

“…So far, most observations on the time course of MO are available from short-term animal studies. Consistent with our data, Ghurge et al (14) found a resolution of MO and T2* abnormality after six weeks in a porcine model of myocardial infarction. Rochitte et al (2) found an increasing extent of MO and infarct size within the first 48 hours after ischemia in a study of seven dogs.…”

Contrast-enhanced Steady-state Free Precession in the Assessment of Hypertrophic Obstructive Cardiomyopathy after Alcohol Septal Ablation

“…MVO is the core of MI induced by ASA. 8,13,19 On LGE imaging, the signal intensity of MVO was higher than that of remote myocardium. This might be explained by the T 1 -shortening effect of some hemoglobin contents or by partial volume effect.…”

“…21 The ceSSFP imaging acquired 3 to 7 min after gadolinium injection may reflect an expanded interstitial space or hyperemia in addition to tissue edema. [11][12][13]16,22 These factors may have contributed to the feasibility of ceSSFP for visualizing both MI and MVO following ASA. On the other hand, we could visualize MI 11, 12 We used no preparation pulse, such as T 2 -preparation or black-blood pulse, 11,12 to improve visualization of myocardial edema on routine cine SSFP.…”

“…SSFP may be useful for identifying MI or MVO because of its sensitivity to edema, coagulation, and hemorrhage in the tissues, [11][12][13] but its usefulness for detecting myocardial injuries led by ASA has not been assessed. Some studies have demonstrated that contrast-enhanced SSFP (ceSSFP) permits evaluation of both myocardial wall motion and acute myocardial injury, such as infarction and myocarditis, in a single scan.…”

Coronary Thermodilution Waveforms After Acute Reperfused ST‐Segment–Elevation Myocardial Infarction: Relation to Microvascular Obstruction and Prognosis

“…Microvascular obstruction was defined as a dark zone on early gadolinium enhancement imaging 1, 3, and 5 minutes postcontrast injection that remained present within an area of late gadolinium enhancement at 15 minutes. On the T2* CMR maps, a region of reduced signal intensity within the infarcted area, with a T2* value of <20 milliseconds17, 18, 19, 20 was considered to confirm the presence of myocardial hemorrhage.…”