Emerging Evidence: Refractory Angina and Coronary Sinus Reducers

Quick Takes The coronary sinus reducer (CSR) is a novel therapy for refractory angina, providing symptom relief when medical and revascularization options are exhausted. CSR reduces angina and improves quality of life with high procedural success and good safety. Emerging evidence suggests CSR may benefit patients with coronary microvascular dysfunction and angina with nonobstructive coronary artery disease/ischemia with nonobstructive coronary arteries, with ongoing trials defining its future role.

Refractory angina (RA) is an increasing global cardiovascular challenge, affecting approximately 10-15% of patients with coronary artery disease (CAD). RA is defined as persistent anginal symptoms (≥3 months) due to myocardial ischemia despite guideline-directed medical therapy, when further revascularization or mechanism-specific therapies are not feasible or have failed.

RA encompasses patients with obstructive CAD, angina with nonobstructive coronary artery disease/ischemia with nonobstructive coronary arteries (ANOCA/INOCA), and coronary microvascular dysfunction (CMD). 1 These patients often experience marked reductions in functional capacity, frequent health care utilization, and impaired quality of life (QoL).

Among emerging device-based therapies, the coronary sinus reducer (CSR) has generated considerable interest because it offers a novel physiological approach to symptom relief without requiring arterial access. The CSR is a stainless-steel, hourglass-shaped expandable mesh that is implanted percutaneously within the coronary sinus (CS) to create controlled narrowing and raise coronary venous pressure, potentially improving subendocardial perfusion.

Findings from recent studies have demonstrated improvements in coronary flow reserve (CFR) and microvascular function following CSR implantation. 2,3 The INROAD (Index of Microcirculatory Resistance Evaluation in Patients With Coronary Sinus Reducer Implantation for the Treatment of Chronic Refractory Angina Pectoris) trial findings further supported CSR therapy, demonstrating improved coronary microvascular function and reduced angina symptoms 4 months after implantation in patients with obstructive CAD and prior revascularization, highlighting its potential role in CMD.

4 Beyond the currently approved balloon-expandable stainless-steel CSR, next-generation devices are under evaluation. The SERRA-I (Self-Expanding Coronary Sinus Reducer for Treatment of Symptomatic Coronary Microvascular Dysfunction) study is assessing a self-expanding nitinol CSR designed to improve conformability, simplify implantation, and accommodate diverse CS anatomies.

Together with the ongoing COSIRA-II (Efficacy of the COronary SInus Reducer in Patients With Refractory Angina II) trial, including a dedicated CMD cohort, these studies are expected to further define the efficacy, safety, and mechanistic effects of CS reduction across a broader spectrum of ischemic heart disease.

The device is implanted through a transvenous approach, typically via the right internal jugular vein. Following CS cannulation and venographic assessment, the CSR is positioned within the midportion of the CS and expanded using balloon inflation. Endothelialization occurs over the subsequent weeks, creating a permanent narrowing that generates the desired pressure gradient.

5 Current clinical practice reserves CSR therapy for patients with severe RA (Canadian Cardiovascular Society [CCS] class III and IV) despite optimal medical therapy and no remaining revascularization options, with documented reversible myocardial ischemia prior to implantation. 6 Although initially developed for left coronary artery ischemia, CSR has demonstrated comparable symptomatic benefits in patients with right coronary artery (RCA) ischemia, including those with RCA chronic total occlusions (CTOs).

A prominent thebesian valve, CS ostial stenosis, tortuosity, extreme CS size, venous anomalies, or prior CS leads may complicate CSR implantation. Careful preprocedural venography and anatomical assessment are essential for safe device deployment. The ORBITA-COSMIC (Coronary Sinus Reducer Objective Impact on Symptoms, MRI Ischaemia and Microvascular Resistance) trial findings provide the strongest sham-controlled evidence for CSR in RA, demonstrating reduced angina frequency and improved QoL.

Although global stress myocardial blood flow was unchanged, exploratory CMR findings suggested enhanced subendocardial perfusion as a potential mechanism. 7 Real-world data from the RESOURCE (Registry of Coronary Sinus Reducer for Refractory Angina) registry and REDUCER-1 (An Observational Study of the Neovasc Reducer System) study demonstrated high procedural success (>95%), low complication rates, and durable symptomatic benefit, with most patients achieving meaningful improvements in angina severity, functional status, and QoL.

8,9 In patients with nonrevascularized CTOs, CSR implantation provides significant angina relief and QoL improvements, particularly when revascularization is not feasible. Emerging evidence also suggests benefits in exercise capacity, reflected by increased peak oxygen consumption after implantation.

CSR may reduce health care utilization and improve quality-adjusted life-years, supporting potential cost-effectiveness in carefully selected patients ( Figure 1 ). 6 CSR therapy is expanding beyond obstructive CAD, with emerging evidence in CMD and ANOCA/INOCA. Preliminary studies suggest improved CFR, microvascular function, symptoms, and QoL.

The Ongoing COSIMA (COronary SInus Reducer for the Treatment of Refractory Microvascular Angina) and REMEDY-PILOT (REducing Microvascular Dysfunction in Patients With Angina by Using a Coronary Sinus Reducer—Pilot Study) trials will define its broader role in CMD. Figure 1: Clinical Impact of CSR Therapy CCS = Canadian Cardiovascular Society; CSR = coronary sinus reducer; CTO = chronic total occlusion; MBF = myocardial blood flow; QALY = quality-adjusted life-year; QoL = quality of life; VO 2 max = maximal oxygen consumption.

The safety profile of CSR therapy has been favorable across randomized controlled trials and registries. Procedural success rates consistently exceed 95% whereas serious complications remain uncommon. Reported adverse events include CS dissection or perforation (~1.1%), device migration (~1.5%), embolization (~0.3%), and access-site complications (~1.8%).

Overall, procedural complications are uncommon, with contemporary pooled data demonstrating high (98.3%) implantation success and no reported periprocedural deaths or strokes. Most complications are manageable with conservative or percutaneous interventional techniques. 10 Despite encouraging results, important questions remain.

Most studies have focused on symptom relief and QoL outcomes rather than hard clinical endpoints such as death, myocardial infarction, or heart failure hospitalization. Furthermore, placebo effects are well recognized in RA, emphasizing the importance of sham-controlled studies when evaluating device-based therapies.

Ongoing investigations, including the larger COSIRA-II trial, are expected to provide more definitive evidence regarding long-term efficacy, durability of benefit, and optimal patient selection. In summary, the CSR represents an important innovation in the treatment of RA. Current evidence supports its ability to reduce angina burden and improve QoL in carefully selected patients who have exhausted conventional therapeutic options.

Emerging data suggest a potentially important role in CMD, an area of growing clinical interest and unmet need. As ongoing randomized trials further clarify its mechanisms, efficacy, and long-term outcomes, the CSR is poised to become an increasingly valuable component of the contemporary management strategy for patients with RA.

References de Silva R, Cheng K, Henry TD, et al. Refractory angina: mechanisms and stratified treatment in obstructive and non-obstructive chronic myocardial ischaemic syndromes. Eur Heart J.

2025;46(38):3738-3757. doi:10.1093/eurheartj/ehaf284 Wang H, Fan L, Choy JS, Kassab GS, Lee LC. Mechanisms of coronary sinus reducer for treatment of myocardial ischemia: in silico study. J Appl Physiol (1985).

2024;136(5):1157-1169. doi:10.1152/japplphysiol.00910.2023 Tryon D, Corban MT, Alkhouli M, et al. Coronary sinus reducer improves angina, quality of life, and coronary flow reserve in microvascular dysfunction. JACC Cardiovasc Interv.

2024;17(24):2893-2904. doi:10.1016/j.jcin.2024.09.018 Tebaldi M, Campo G, Ugo F, et al. Coronary sinus narrowing improves coronary microcirculation function in patients with refractory angina: a multicenter prospective INROAD study. Circ Cardiovasc Interv.

2024;17(1):e013481. doi:10.1161/CIRCINTERVENTIONS.123.013481 Prasad M, Konigstein M, de-Silva R, Lerman A, Banai S. Principles of coronary sinus narrowing to relieve myocardial ischemia and improve angina. Am J Cardiol.

2026;258:128-133. doi:10.1016/j.amjcard.2025.08.066 Dash D, Dash U, Reddy S, Hasanfatta N. Coronary sinus reduction therapy for refractory angina: current evidence and future directions. Cardiovasc Revasc Med.

Published online August 3, 2026. doi:10.1016/j.carrev.2026.07.015 Foley MJ, Rajkumar CA, Ahmed-Jushuf F, et al. Coronary sinus reducer for the treatment of refractory angina (ORBITA-COSMIC): a randomised, placebo-controlled trial. Lancet.

2024;403(10436):1543-1553. doi:10.1016/S0140-6736(24)00256-3 Ponticelli F, Khokhar AA, Leenders G, et al. Safety and efficacy of coronary sinus narrowing in chronic refractory angina: insights from the RESOURCE study. Int J Cardiol.

2021;337:29-37. doi:10.1016/j.ijcard.2021.05.034 Verheye S, van de Hoef TP, de Silva R, et al. Coronary sinus narrowing for treating refractory angina: REDUCER-I multicenter "real-world" observational study primary endpoint analysis. JACC Cardiovasc Interv.

2024;17(24):2908-2918. doi:10.1016/j.jcin.2024.08.047 Ojha U, Mohsin M, Macierzanka K, et al. Safety, efficacy, and effectiveness of coronary sinus reducer implantation in refractory angina: a meta-analysis. JACC Cardiovasc Interv.

2025;18(15):1864-1877. doi:10.1016/j.jcin.2025.06.012 Clinical Topics: Stable Ischemic Heart Disease, Chronic Angina, Invasive Cardiovascular Angiography and Intervention Keywords: Angina, Unstable, Coronary Sinus, Microvascular Angina Want to Learn More? This content is brought to you by the Interventional Member Section .

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