Abstract Background Abnormal coronary microcirculation is linked to poor patient prognosis. However, the prognostic value of basal microvascular resistance (b-IMR) remains unclear. This study aimed to assess the prognostic relevance of reduced b-IMR in patients without functional coronary stenosis. Methods and results Analyses of 226 patients who underwent intracoronary physiological assessment of the left anterior descending artery were performed. The study population consisted of 159 males (70.0%) with a mean age of 70.3±10.4 years. The median values of FFR, CFR, b-IMR and IMR were 0.88 (interquartile range IQR: 0.85–0.91), 3.06 (IQR: 1.93–4.50), 68.6 (IQR: 45.1–98.0), and 17.1 (IQR: 12.4–24.4), respectively. The primary endpoints were death and heart failure. The secondary endpoints were cardiovascular death and atherosclerotic vascular events. During a median follow-up period of two years, 12 (5.3%) primary and 21 (9.3 %) secondary endpoints occurred. The optimal b-IMR cutoff for the primary endpoints was 47.1U. Kaplan-Meier curve analysis demonstrated worse event-free survival of the primary endpoints in patients with a b-IMR below the cutoff (χ2=21.178, P0.001). b-IMR was not significantly associated with the secondary endpoints (P=0.35). A low coronary flow reserve (CFR) (2.5) had prognostic values for both endpoints (the primary endpoints: χ2=11.401, P=0.001; the secondary endpoints: (χ2=6.015; P=0.014), while high hyperemic microvascular resistance (≥25) was associated only with the secondary endpoints (χ2=4.420; P=0.036). Incorporating b-IMR into the clinical model, which includes CFR, improved the Net Reclassification Index and Integrated Discrimination Improvement for predicting primary endpoints (P0.001 and P=0.034, respectively). Multivariate analysis identified low b-IMR as an independent predictor of the primary endpoints (hazard ratio, 17.700; p=0.001). Conclusions b-IMR may be a specific marker for evaluating risk of death and heart failure in patients without functional coronary stenosis.
Saito et al. (Sat,) studied this question.