Association of TIMI Myocardial Perfusion Grade and ST-segment resolution with cardiovascular magnetic resonance measures of microvascular obstruction and infarct size following ST-segment elevation myocardial infarction

Background Impairment of coronary microvascular perfusion is common among patients with ST-segment elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI). Cardiovascular magnetic resonance imaging (CMR) can identify microvascular obstruction (MO) following reperfusion of STEMI. We hypothesized that myocardial perfusion, as assessed by the Thrombolysis in Myocardial Infarction (TIMI) Myocardial Perfusion Grade (TMPG), would be associated with a CMR metric of MO in this population. Methods Twenty-one STEMI patients who underwent successful primary PCI were evaluated. Contrast-enhanced CMR was performed within 7 days of presentation and repeated at three months. TIMI Flow Grade (TFG), corrected TIMI Frame Count (cTFC), TMPG, MO, infarct size, and left ventricular ejection fraction (EF) were assessed. Results The median peak creatine phosphokinase (CPK) was 1,775 IU/l (interquartile range 838-3,321). TFG 3 was present following PCI in 19 (90%) patients. CMR evidence of MO was present in 52% following PCI. Abnormal post-PCI TMPG (0/1/2) was present in 48% of subjects and was associated with MO on CMR (90% MO with TMPG 0/1/2 vs. 18% MO with TMPG 3, P < 0.01). Abnormal post-PCI TMPG was also associated with a greater peak CK (median 3,623 IU/l vs. 838 IU/l, P < 0.001) and greater relative infarct size (17.3% vs. 5.2%, P < 0.01). Conclusion Among STEMI patients undergoing primary PCI, post-PCI TMPG correlates with CMR measures of MO and infarct size. The combined use of both metrics in a comprehensive assessment of microvascular integrity and infarct size following STEMI may aid in the evaluation of future therapeutic strategies.