Background-Despite complete interruption of antegrade coronary artery flow in the setting of a chronic total occlusion (CTO), clinical recognition of myocardial infarction is often challenging. Using cardiac MRI, we investigated the frequency and extent of myocardial infarction in patients with CTO, and assessed their relationship with regional systolic function and the extent of angiographic collateral flow. Methods and Results-We included 170 consecutive patients (median age, 62 years) with angiographically documented CTO. Regional late gadolinium enhancement and wall motion score index were assessed by cardiac MRI with the use of a 17-segment model. Angiographic collateral flow was assessed by the collateral connection grade and the Rentrop score. Evidence of previous myocardial infarction was found in 25% of patients by ECG Q waves, in 69% by regional wall motion abnormality, and in 86% of patients by late gadolinium enhancement. Increased angiographic collateral flow was associated with a lower frequency of Q waves on ECG, and a lower regional wall motion score index, late gadolinium enhancement volume (%), and degree of late gadolinium enhancement transmurality (all P<0.001), as well. Conclusions-The frequency of myocardial infarction in territories subtended

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