The prognostic significance of microvascular resistance reserve: a systematic review and meta-analysis

Abstract Introduction Coronary microcirculation assessment is most commonly performed with the use of coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR), as they are recommended in societal guidelines. Recently, microvascular resistance reserve (MRR) was develop as novel indice for coronary microcirculation assessment, aiming overcomes CFR and IMR limitations, as it is independent of stenosis severity and accounts for both rest and hyperemia conditions. Therefore, we aimed to systematically review and meta-analyze available studies reporting the prognostic significance of MRR. Methods We performed a systematic search in 3 different databases (MEDLINE/PubMed, Web of Science and Scopus). After selecting all appropriate studies according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a random effect meta-analysis was performed. Results Our analysis included 5 studies and a total of 1,605 patients (453 abnormal MRR; 1152 normal MRR). Patients with abnormal MRR had a significantly higher risk for cardiovascular death Risk Ratio (RR): 2.37; 95% Confidence Interval (CI): 1.52-3.70, as well as major adverse cardiovascular events (RR: 4.88; 95%CI: 3.49-6.83), myocardial infarction (RR: 1.93; 95%CI: 1.53-2.42) and heart failure hospitalizations (RR: 4.83; 95%CI: 1.59-14.70), in comparison to patients with normal MRR. Abnormal MRR was not significantly associated with a higher risk of future revascularization, compared to normal controls (RR: 1.29; 95%CI: 0.52-3.19). Conclusion This systematic review and meta-analysis shows the significant microcirculation-specific prognostic effect of MRR in both survival and adverse outcomes. Further data from large randomized studies are needed in order to determine the clinical utility and prognostic significance of MRR in coronary microvascular dysfunction assessment.