532 In vivo characterization of microvascular obstruction resolution after reperfused myocardial infarction.

Purpose: Using cardiac imaging techniques it has been demonstrated that, after successful coronary revascularization of acute myocardial infarction (MI), microvascular obstruction (MVO) resolves spontaneously. Data on the course of this process in “in vivo” models are scarce. We aimed to characterize the dynamics of MVO in a swine model of reperfused anterior MI.Methods: Swine were subjected, by means of percutaneous balloon inflation, to a transient 90-min occlusion of mid left anterior descending artery followed by 72-h (acute MI model) or 1-month (chronic MI model) reperfusion. Area at risk (thioflavin-S staining) and the extent of MVO (% of area at risk without thioflavin-S staining) were quantified. Microvessel density (using immunohistochemistry by von Willebrand factor antibody, vessels/field) and the expression of Hypoxia Induced Factor-1α (HIF-1α mRNA) were determined in controls and in the acute and chronic MI models.Results: In the acute MI model, MVO (8.4±4.5%) was detected in all cases. MVO significantly decreased in the chronic MI model (0.14±0.09%, p <0.001 vs. acute MI model, Figure). Microvessel density was significantly reduced in the acute MI model in comparison with the chronic MI model and controls (p <0.001, Figure). The expression of HIF-1α mRNA was significantly increased in the acute MI model in the infarct area (p<0.05 vs. controls) and in the chronic MI model in the infarct, adjacent and remote areas (p <0.01 vs. controls, Figure).Conclusion: In an “in vivo” controlled model of reperfused anterior MI, MVO spontaneously improves one month after reperfusion at macroscopic and microscopic levels. HIF could play a role in the molecular control of this process. [ABSTRACT FROM AUTHOR]