Coronary Sinus Reducer in Refractory Angina: A Targeted Approach to Microvascular Ischemia and Symptom Relief

Refractory angina remains a therapeutic challenge in patients with advanced coronary artery disease who are not amenable to further revascularization and remain symptomatic despite optimal medical therapy. The coronary sinus reducer (CSR) is a novel, device-based therapy that aims to alleviate angina by increasing coronary sinus pressure and redistributing blood flow toward ischemic myocardial territories, particularly in the subendocardial region. This article reviews current evidence on the comparative effectiveness of CSR relative to established pharmacologic and interventional therapies, with a focus on its potential role in patients with microvascular versus macrovascular ischemia. Data from randomized trials and real-world registries demonstrate significant symptomatic improvement and favorable safety outcomes in the majority of CSR-treated patients, though nonresponder rates remain between 15% and 30%. Emerging evidence suggests CSR may be particularly effective in patients with microvascular dysfunction, such as those with angina and no obstructive coronary artery disease. However, long-term efficacy, ideal patient selection criteria, and mechanistic underpinnings remain areas of ongoing investigation. Current and upcoming trials such as COSIRA-II (CSR for Treatment of RA) and REMEDY-PILOT (Reducing microvascular dysfunction in patients with angina, ischaemia, and unobstructed coronary arteries- a pilot study) aim to address these uncertainties. CSR represents a promising addition to the therapeutic landscape for refractory angina, particularly in complex or no-option cases, pending further clinical validation.