The prognostic role of microvascular resistance reserve: A systematic review and meta-analysis

Microvascular resistance reserve (MRR) is a novel indice for coronary microcirculation assessment, addressing limitations of coronary flow reserve (CFR) and index of microcirculatory resistance (IMR). Given its promising role in the future of coronary microvascular dysfunction assessment, we aimed to systematically review and meta-analyze available studies reporting its prognostic significance.

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.

Our analysis, including 5 studies and a total of 1605 (453 abnormal MRR; 1152 normal MRR) patients, shows that patients with abnormal MRR are at significantly higher risk for cardiovascular death [Risk Ratio (RR): 4.88 95 % Confidence Interval (CI): 3.49-6.83], major adverse cardiovascular events (RR: 2.37; 95%CI: 1.52-3.70), 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 the normal MRR cohort. As expected, abnormal MRR was not associated with a significantly higher risk of future revascularizations, compared to normal controls (RR: 1.29; 95%CI: 0.52-3.19).

This study shows the significant microcirculation-specific prognostic effect of MRR in both survival and adverse outcomes. Further data from large randomized studies, will delineate the clinical utility and prognostic effect of MRR in coronary microvascular dysfunction.