Prognostic Value of Coronary Angiography–Derived Index of Microcirculatory Resistance in Non–ST-Segment Elevation Myocardial Infarction Patients

The index of microcirculatory resistance is a reliable measure for evaluating coronary microvasculature, but its prognostic value in patients with non–ST-segment elevation myocardial infarction (NSTEMI) remains unclear. This study aimed to evaluate the prognostic impact of post–percutaneous coronary intervention (PCI) angiography-derived index of microcirculatory resistance (angio-IMR) in patients with NSTEMI. The culprit vessel's angio-IMR was measured after PCI in 2,212 NSTEMI patients at 3 sites. The primary endpoint was 2-year major adverse cardiac events (MACEs), defined as a composite of cardiac death, readmission for heart failure, myocardial reinfarction, and target vessel revascularization. The mean post-PCI angio-IMR was 20.63 ± 4.17 in NSTEMI patients. Two hundred six patients were categorized as the high post-PCI angio-IMR group according to maximally selected log-rank statistics. Patients with angio-IMR >25 showed a higher rate of MACEs than those with angio-IMR ≤25 (32.52% vs 9.37%; P < 0.001). Post-PCI angio-IMR >25 was an independent predictor of MACEs (HR: 4.230; 95% CI: 3.151-5.679; P < 0.001) and showed incremental prognostic value compared with conventional risk factors (AUC: 0.774 vs 0.716; P < 0.001; net reclassification index: 0.317; P < 0.001; integrated discrimination improvement: 0.075; P < 0.001). In patients undergoing PCI for NSTEMI, an increased post-PCI angio-IMR is associated with a higher risk of MACEs. The addition of post-PCI angio-IMR into conventional risk factors significantly improves the ability to reclassify patients and estimate the risk of MACEs. (Angiograph-Derived Index of Microcirculatory Resistance in Patients With Acute Myocardial Infarction; NCT05696379)