Abstract 2803: Index of Microcirculatory Resistance: A Novel Measure for Predicting Myocardial Damage in Patients with Acute Myocardial Infarction
Background: Studies suggest that the status of the coronary microvasculature in patients with acute myocardial infarction (AMI) is important in determining outcomes. Current techniques for evaluating the microvasculature in the cardiac catheterization laboratory have limitations. We compared a novel coronary pressure wire-derived Index of Microcirculatory Resistance (IMR) to standard techniques for evaluating the microvasculature in patients with AMI.
Methods: After 27 patients with ST-elevation AMI underwent primary stenting, the resting mean transit time (Tmn) of injected room temperature saline was measured in the culprit vessel via a validated thermodilution technique using a coronary pressure sensor/thermistor-tipped wire. After inducing maximal hyperemia, the hyperemic Tmn and the mean distal pressure were measured. Because Tmn is inversely proportional to flow, coronary flow reserve (CFR) was defined as resting Tmn / hyperemic Tmn and IMR as distal pressure x Tmn during hyperemia. IMR was compared to CFR, TIMI Myocardial Perfusion Grade (TMPG), corrected TIMI Frame Count (cTFC), ST segment resolution (ST res), peak creatinine kinase (CK), neutrophil %, and 3 month echocardiographic left ventricular ejection fraction (EF) and wall motion score.
Results: At the end of the procedure 23 of the patients had TIMI grade 3 flow. IMR correlated significantly with peak CK (R=0.54, p=0.003), while CFR, TGF, TMPG, cTFC, and ST res did not. IMR correlated significantly with cTFC (R=0.54, p=0.004), TMPG (R=-0.42, p=0.03), TGF (R=−0.44, p=0.02), CFR (R=−0.43, p=0.03), and neutrophil % (R=0.52, p=0.01), but not with ST res. Patients in whom the IMR was above the median level of 35 had a significantly greater peak CK (3387 ± 1531 vs. 1209 ± 966 IU/L, p<0.001), and at 3 month echo, a lower EF (43 ± 8 vs. 52 ± 12%, p=0.03), and more wall motion abnormalities (29.23 ± 7.4 vs 26.9 ± 6.4, p=0.01). None of the other indices were significant predictors of EF or wall motion score at 3 months.
Conclusion: IMR is a relatively simple, wire-based index that can be measured at the time of primary stenting in patients with AMI. IMR is a better indicator of microvascular function and predictor of myocardial damage than current techniques for evaluating the microvasculature.