Can an Hourglass-Shaped device relieve chest pain when arteries Aren't blocked?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Age \>18 years 2. Ongoing symptomatic angina, CCS Class II-IV, for ≥3 months despite background treatment with at least two anti-anginal drugs at the maximal tolerated dose. 3. Patients willing to consider no change in anti-anginal drug treatment for the duration of their participation in the trial. 4. Unobstructed coronary arteries with ≤50% epicardial stenoses demonstrated on coronary angiography. 5. Stress-induced hypoperfusion on CMR (Global MPR ≤ 2.2). 6. Willingness to comply with the specified follow-up evaluation and to be contactable during the period of the trial. 7. Understands the nature of the trial procedures and provides written informed consent. Exclusion Criteria: 1. Epicardial CAD in a main coronary artery (stenoses \>50%, RFR≤0.92 or FFR≤0.80), percutaneous coronary intervention (PCI; within previous 6 months, stent insertion for acute Type 1 MI or chronic total occlusion (CTO)), coronary artery bypass grafting, or confirmed Type 1 myocardial infarction (MI). 2. Abnormal coronary sinus anatomy (tortuosity, aberrant branch, persistent left superior vena cava) 3. Coronary sinus diameter unsuitable for device implantation at operator discretion 4. Mean right atrial pressure \>15mmHg at time of implantation 5. Structural heart disease including left ventricular hypertrophy with raised LV mass index; cardiomyopathy; severe valvular heart disease; previous valve replacement; significant myocardial bridge on angiography; LVEF\<45% by CMR. 6. Clinically or angiographically diagnosed coronary vasospasm 7. Previous hospitalisation for decompensated heart failure 8. Pacemaker or defibrillator electrode in the right atrium, right ventricle or coronary sinus 9. Documented arrhythmia requiring planned implantation of a permanent pacemaker or defibrillator 10. Chronic kidney disease (creatinine \>200 micromol/L; established on renal replacement therapy; functioning renal transplant) 11. Haemoglobin \<80g/L 12. Contraindications to receiving dual antiplatelet therapy 13. Severe chronic obstructive pulmonary disease (FEV1 \<55% predicted) 14. Moribund patients with life expectancy \< 1year 15. Known allergy to nickel or steel 16. Current enrolment in another investigational device or drug trial 17. Contraindications to CMR or receiving intravenous adenosine 18. Pregnancy