Coronary Sinus Reducer Implantation in Patients With Ischaemia and Non-obstructed Coronary Arteries and Coronary Microvascular Dysfunction.

Prior treatment

• 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).
• Previous hospitalisation for decompensated heart failure
• Contraindications to receiving dual antiplatelet therapy
• Current enrolment in another investigational device or drug trial
• Contraindications to CMR or receiving intravenous adenosine

Other illness

• Documented arrhythmia requiring planned implantation of a permanent pacemaker or defibrillator
• Severe chronic obstructive pulmonary disease (FEV1 \<55% predicted)
• Known allergy to nickel or steel

Lab values

• 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.
• Chronic kidney disease (creatinine \>200 micromol/L; established on renal replacement therapy; functioning renal transplant)
• Haemoglobin \<80g/L

Other

• Abnormal coronary sinus anatomy (tortuosity, aberrant branch, persistent left superior vena cava)
• Coronary sinus diameter unsuitable for device implantation at operator discretion
• Mean right atrial pressure \>15mmHg at time of implantation
• Clinically or angiographically diagnosed coronary vasospasm
• Pacemaker or defibrillator electrode in the right atrium, right ventricle or coronary sinus
• Moribund patients with life expectancy \< 1year
• Pregnancy

• Age \>18 years
• 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.
• Patients willing to consider no change in anti-anginal drug treatment for the duration of their participation in the trial.
• Unobstructed coronary arteries with ≤50% epicardial stenoses demonstrated on coronary angiography.
• Stress-induced hypoperfusion on CMR (Global MPR ≤ 2.2).
• Willingness to comply with the specified follow-up evaluation and to be contactable during the period of the trial.
• Understands the nature of the trial procedures and provides written informed consent.