Coronary sinus Reducer for the treatment of refractory angina: how much more evidence do we need?

The coronary sinus Reducer (CSR; Shockwave Medical) is an unintuitive antianginal therapy which is currently utilised in patients with severe epicardial coronary artery disease who have no further conventional treatment options. It has been shown to improve symptoms in this patient group in two randomised placebo-controlled trials: COSIRA and ORBITA-COSMIC12. The efficacy of the CSR is far from universally accepted among cardiologists – an unusual position for a cardiac therapy with two separate placebo-controlled trials supporting its use. This may be because the mechanism of action of the device remains incompletely explained, despite recent insights3. Placebo-controlled trials necessarily curtail follow-up to timepoints that balance detection of device efficacy and ethical considerations for patients. There have therefore been questions raised regarding the longer-term safety and efficacy of the CSR in the “real world”.

In this issue of EuroIntervention, Verheye et al report the findings of the REDUCER-I study, the largest observational study to date of patients treated with the CSR4. The 400 enrolled patients were broadly similar to those in the aforementioned randomised trials: a majority were male,...