Novel Adenosine-independent Index of Coronary Artery Stenosis Severity Resting Flow Reserve

This study will enroll patients who are referred for coronary angiography and require physiological assessment to see if the lesion can be treated as per the local standard of care. Approximately 92 participants will be enrolled. There are no follow up visits required so participation in this study will end when subjects are discharged from the hospital.The study will be comparing the resting flow reserve against the instantaneous wave-free ratio (iFR) and fractional flow reserve. All these tests offer a way to image a legion and determine if it is suitable to be treated. FFR measures the pressure differences across (narrowed coronary arteries usually due to atherosclerosis), iFR's are performed during cardiac catheterisation (angiography) using invasive coronary pressure wires which are placed in the arteries of the heart that are to be assessed and the Resting flow reserve looks at the maximum increase in blood flow through the coronary arteries above the normal resting volume.

Fractional flow reserve (FFR) measurement by under hyperemic conditions has become the invasive gold standard for determining the physiologic extent of cardiac ischemia, and which has been validated in several clinical outcomes studies as a way of optimizing case selection for percutaneous coronary intervention (PCI). More recently in two large-scale randomized controlled trials using a non-hyperemic resting measurement, the instantaneous wave free ratio (iFR) showed non-inferiority in major adverse cardiovascular events (MACE) comparing iFR to FFR for physiological assessment of moderate coronary stenosis. FFR is calculated as the ratio of the distal coronary pressure to the aortic pressure (Pd/Pa) during maximal micro-circulatory relaxation. iFR is a diagnostic tool used to assess whether a stenosis is causing a limitation of blood flow in coronary arteries with subsequent ischemia. iFR is performed during cardiac catheterization (angiography) using invasive coronary pressure wires which are placed in the coronary arteries that are to be assessed. The iFR negates the time averaging and administration of vasodilators necessary for FFR by identifying from the resting pressure waveform a period when the native microcirculatory resistance is constant and minimized in diastole. The study is looking at the accuracy and precision of a novel adenosine-independent index of coronary artery stenosis, the resting flow reserve, against the instantaneous wave-free ratio and fractional flow reserve.

Eligibility Criteria:
Inclusion Criteria:

1. Age ≥ 18 years.
2. Patient provides signed written informed consent before any study-specific procedure.
3. Undergoing coronary angiography, for silent ischemia, stable angina, acute coronary syndrome, or other acceptable indication per the local standard of care.
4. Angiographically 40%-90% stenosis present in at least one native coronary artery.
5. Undergoing physiological assessment for standard clinical or diagnostic indications

Exclusion Criteria:

1. Aorto-ostial lesion location within 3 mm of the aorta junction (both right and left).
2. Left main stenosis
3. Vessel(s) and lesion(s) not amenable for percutaneous coronary intervention (PCI) , for example diffuse disease.
4. Saphenous vein graft, chronic total occlusion
5. Haemodynamic instability at the time of intervention (heart rate\<50 beats per minute, systolic blood pressure \<90mmHg), balloon pump
6. Currently participating in another clinical study that interferes with study results.
7. Pregnant or nursing subjects and those who plan pregnancy in the period up to 1 year following index procedure.
8. Any other medical condition that in the opinion of the investigator will interfere with patient safety or study results.
9. High degree A-V block, sinus node disease.
10. Asthma/Chronic obstructive pulmonary disease (COPD) with active wheeze
11. Known hypersensitivity to adenosine
12. ST-Elevation Myocardial Infarction (STEMI) within 48 hours.