Usefulness of Hyperemic Microvascular Resistance Index as a Predictor of Clinical Outcomes in Patients with ST-Segment Elevation Myocardial Infarction

Background and Objectives: Microvascular function is a useful predictor of left ventricular functional changes in patients with ST-segment elevation myocardial infarction (STEMI). We evaluated the usefulness of the hyperemic microvascular resistance index (hMVRI) for predicting long-term major adverse cardiovascular events (MACEs) in patients with STEMI assessed immediately after primary percutaneous coronary intervention (PCI). Subjects and Methods: hMVRI were evaluated in 145 patients with first acute STEMI treated with primary PCI using an intracoronary Doppler wire. hMVRI was defined as the ratio of mean aortic pressure over hyperemic averaged peak velocity of infarct-related artery. Major adverse cardiovascular events (MACEs) included cardiac death and re-hospitalization for congestive heart failure. Results: During the mean follow-up of $85{\pm}43months$, MACEs occurred in 17.2% of patients. Using a receiver-operating characteristics analysis, hMVRI >$2.82mm\;Hg{\cdot}cm-1{\cdot}sec$ (sensitivity: 87%; specificity: 69%; and area under curve: 0.818) was the best cut-off values for predicting future cardiac events. The Cox proportional hazard analysis showed that hMVRI was an independent predictor for long-term MACEs (hazard ratio 1.741, 95% confidence interval 1.348-2.264, p<0.001). The Kaplan-Meier survival analysis showed a higher incidence of MACEs in patients with hMVRI >$2.82mm\;Hg{\cdot}cm-1{\cdot}sec$ (p<0.001). Conclusion: hMVRI was a strong predictor of long-term MACEs in patients with STEMI treated with primary PCI.