Abstract 4360: The Relation of the Index of Microcirculatory Resistance to Indices of Microvascular Perfusion and Cardiac Injury Following Primary Angioplasty for ST-Segment Elevation Myocardial Infarction
Background: Despite adequate epicardial artery reperfusion following primary angioplasty for ST-segment elevation myocardial infarction (STEMI), microvascular injury is not an uncommon event and confers a poor clinical outcome. We used the index of microcirculatory resistance (IMR) as a quantitative measure of microvascular function and myocardial injury, correlating it with established indices of myocardial reperfusion and echocardiographic measures of cardiac injury.
Methods: IMR was measured using a pressure sensor/thermistor-tipped guidewire in patients following successful primary angioplasty for STEMI. The TIMI myocardial perfusion grade (TMPG), corrected TIMI frame count (cTFC), peak creatinine kinase (CK), ST-segment resolution, echocardiographic left ventricular ejection fraction (LVEF) and wall motion score (WMS) at index admission, as well as major adverse cardiovascular events (MACE) at 6 months (composite of death, myocardial infarction, stroke, and target vessel revascularization) were evaluated.
Results: Successful primary angioplasty with IMR evaluation was performed in 167 patients. The culprit arteries were: LAD 59.8%, RCA 32.9%, LCX 7.3%. The IMR correlated significantly with TMPG (R=−0.517, P<0.001), cTFC (R=0.413, P<0.001), peak CK (R=0.182, P=0.018) and WMS (R=0.178, P=0.029). It did not correlate with ST-segment resolution (R=−0.125, P=0.158). There was a trend toward negative correlation for LVEF (R=−0.156, P=0.052). There were 76 patients (45.5%) with an IMR>32 (a threshold value previously reported to predict microvascular damage). A lower proportion of patients with IMR>32 had TMPG 3 (70.4% vs 96.5%, P<0.001). The group with IMR>32 had higher peak CK (3175.4±2188.7 mmol/L vs 2439.1±1898.2 mmol/L, P=0.024), lower LVEF (45.0% vs 48.5%, P=0.025) and higher WMS (27.5 vs 24.5, P=0.002). Although cTFC trended higher in the group with IMR>32, this was not statistically significant (37.7 vs 31.3, P=0.154). MACE at 6 months was similar between the 2 groups (9.8% in IMR>32 versus 8.7% in IMR≤32, P=0.835).
Conclusion: IMR measured after primary angioplasty for STEMI correlates with most indices of microvascular perfusion. An elevated IMR also predicts left ventricular dysfunction.