Elevated index of microcirculatory resistance predicts vascular adverse events in high-risk patients

Background Coronary microvascular dysfunction (CMD) has been recognized as a residual risk factor for adverse clinical events in patients with non-flow-limiting coronary stenosis. However, it remains unclear which specific adverse clinical events are associated with an elevated index of microcirculatory resistance (IMR), which is an independent diagnostic criterion for CMD according to the current guidelines for chronic coronary syndrome. Purpose This study aimed to investigate which types of adverse clinical events can be identified by IMR in patients with a fractional flow reserve (FFR) > 0.80. Methods We conducted a retrospective study of patients who underwent coronary angiography with intracoronary physiological assessment, including FFR and IMR, for suspected myocardial ischemia. 351 patients with FFR > 0.80 in the left anterior descending artery were included. Patients were stratified based on an IMR cutoff value of 25. The clinical endpoints were categorized into three groups: (1) all-cause mortality, (2) cardiac adverse events, including cardiovascular death (CVD) and heart failure (HF) requiring hospitalization, and (3) vascular adverse events, including acute coronary syndrome (ACS), stable angina requiring ischemia-driven revascularization, cerebral infarction (CI), and chronic limb-threatening ischemia (CLTI). Results Among the 351 patients (30% female, n = 106; mean age: 70 ± 11 years), 81 (23%) had an abnormal IMR (IMR ≥ 25). During a median follow-up of 23 months, 47 patients experienced adverse clinical outcomes, including 11 cases (3.1%) of all-cause mortality, 12 cases (3.4%) of cardiac adverse events, and 25 cases (7.1%) of vascular adverse events. Kaplan-Meier analysis showed no significant difference between the two groups in terms of all-cause mortality and cardiac adverse events (p = 0.25 and p = 0.96, respectively). However, the incidence of vascular adverse events was significantly higher in the abnormal IMR group. The cumulative vascular adverse event-free survival rates at 2 years were 94.7% in the normal IMR group and 85.0% in the abnormal IMR group (log-rank χ² = 11.6, p < 0.001). Furthermore, receiver operating characteristic curve analysis identified an optimal IMR cutoff of 18.3 for predicting vascular events (area under the curve: 0.69, 95% confidence interval: 0.59–0.78). Patients with IMR ≥ 18.3 had significantly lower survival rates than those with IMR < 18.3 (0.87 vs. 0.96, p = 0.001). Conclusion Patients with elevated IMR are at particularly high risk of vascular adverse events. IMR may provide crucial information for guiding treatment strategies in patients without functional coronary stenosis.Vascular Endpoint ROC curve