Advancing prognostic insights in STEMI patients through microvascular resistance reserve evaluation

Background Coronary microvascular dysfunction (CMD) after ST-Elevation Myocardial Infarction (STEMI) is associated with persistent symptoms and poor outcomes. Microvascular Resistance Reserve (MRR) is an innovative metric for evaluating coronary microvasculature that is unaffected by epicardial stenoses or the hemodynamic impact of vasodilators. While MRR's prognostic ability is recognized in chronic coronary syndrome, its application in ACS remains unestablished. Purpose We sought to investigate the prognostic value of MRR in STEMI patients. Methods This is a prospective study of 210 STEMI patients with multivessel disease who had undergone successful primary percutaneous coronary intervention (PCI). At 3 months follow-up, they returned for complete revascularization and coronary physiology evaluations, including coronary flow reserve (CFR), fractional flow reserve (FFR), and index of microcirculatory resistance (IMR), using bolus thermodilution. MRR was calculated using the formula: MRR = (CFR/FFR) × (Pa rest/Pa hyper), where Pa rest and Pa hyper represent resting and hyperemic aortic pressure, respectively1. We utilized an MRR cutoff of 3.0 based on Boerhour et al. The association between MRR and major adverse cerebrocardiovascular events (MACCE) at 12-month follow-up, defined as the composite of stroke, revascularization, myocardial infarction (MI), heart failure hospitalization, and death, was investigated. Results The median age was 65 years, and 40.48% were female. At a 3-month follow-up, 27% (56 patients) exhibited MRR <3.0, who were predominantly female (62.50% vs 32.47%, p<0.001) with a higher incidence of diabetes (39.29% vs 18.83%, p = 0.004). No significant differences were observed in age, body mass index, or STEMI location (anterior or inferior) when comparing between MRR groups. The MACCE-free survival at 12 months was significantly lower in patients with an MRR < 3.0 (48.2%) compared to those with an MRR ≥ 3.0 (11.0%; log-rank p < 0.001, Fig1A). The MRR < 3.0 group showed higher rates of ischemic stroke (8.93% vs. 1.30%, p = 0.022) and hospitalization for heart failure (21.43% vs. 2.60%, p < 0.001), while the incidence of nonfatal myocardial infarction (MI) and cardiovascular death were similar between the two MRR groups (Figu1B). In multivariable Cox regression analysis, MRR was an independent predictor for 12-month MACCE (Hazard Ratio 0.45 per unit increase, 95% Confidence Interval 0.31-0.67, p<0.001). The areas under the receiver operating characteristic curves for predicting 12-month MACCE using FFR, CFR, IMR, and MRR yielded values of 0.609, 0.762, 0.781, and 0.743, respectively (Fig2). The prognostic performances of CFR, IMR, and MRR were similar and superior to that of FFR. Conclusion This study establishes the novel parameter MRR as a superior prognostic indicator in STEMI patients compared to FFR, and on par with CFR and IMR. MRR is a reliable predictor of MACCE, and various clinical incidents post-STEMI.