Abstract
Objective: Acute myocardial infarction is triggered by plaque disruption and thrombus formation, therefore, it is important to detect high thrombotic risk plaque non-invasively. Coronary high signal intensity plaque (HIP) on T1 weighted magnetic resonance imaging (T1WI) was associated with future coronary events. The aim of this study is to identify pathological findings reflecting HIPs using hearts obtained from autopsy cases and blood samples. Approach and Results: Formalin-fixed hearts (n=7) were imaged with non-contrast T1WI with a 1.5 T magnetic resonance system. We defined HIPs (n=11) or non-HIPs (n=25) as a coronary plaque to myocardial signal intensity ratio (PMR) of √ 1.4 or √ 1.4, respectively. The corresponding histological sections were histologically and immunohistochemically analyzed. Plaque and necrotic core areas or frequency of intraplaque hemorrhage in HIPs were significantly larger or higher than those in non-HIPs. The high intensity portion in large coronary plaque was immunopositive for CD68, CD163, glycophorin A, and fibrin. Glycophorin A-, matrix metalloprotease (MMP) 9-, tissue factor-immunopositive areas were larger in HIPs than those in non-HIPs. Glycophorin A-, fibrin-, MMP9-, and tissue factor-immunopositive areas were positively correlated with PMR. We calculated T1 relaxation time of venous blood, plasma, and erythrocyte-rich blood in vitro. Blood coagulation shortened T1 relaxation time of the blood and plasma, and T1 relaxation times in coagulated whole blood and erythrocyte-rich blood were significantly shorter than those in plasma. Conclusions: Majority of coronary HIPs may reflect intraplaque hemorrhage-derived erythrocyte content, and may be a novel marker for plaque instability and thrombogenic potential.
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