Coronary Sinus Reduction for Refractory Angina Caused by Microvascular Dysfunction—A Systematic Review

<b>Background</b>: Recent observational studies suggest that coronary sinus reducer (CSR) implantation may have a beneficial effect on microcirculatory indices in patients with coronary microvascular dysfunction (CMD). However, to date, there is no comprehensive summary of the evidence regarding the impact of CSR in this population. <b>Methods</b>: This systematic review was conducted in accordance with the PRISMA 2020 Statement. The following databases were searched: PubMed, EMBASE, MEDLINE, and ClinicalTrials.gov. Studies assessing microcirculatory indices or primarily involving patients with CMD undergoing CSR implantation were included. <b>Results</b>: After the selection process, 17 studies or trials were included in this systematic review. Across observational studies and case series, CSR implantation was associated with significant improvements in coronary microvascular function, including reductions in the index of microvascular resistance and an increase in coronary flow reserve. These physiological changes were accompanied by consistent improvements in angina severity (CCS class), exercise capacity, and quality-of-life measures, particularly in patients with more severe baseline CMD. Evidence was derived mainly from non-randomized studies involving small patient cohorts, with low procedural complication rates. Ongoing randomized trials are expected to clarify the magnitude of benefit and its clinical relevance in this population. <b>Conclusions</b>: CSR implantation may offer clinical and physiological benefits in patients with refractory angina due to CMD. However, the lack of randomized evidence and uncertainty regarding long-term effects warrant further adequately powered trials.