More than 50% of patients with stable or unstable angina pectoris have no obstructive coronary arteries by angiographic visual estimation, in which coronary microvascular dysfunction (CMD) is one of the causes of myocardial ischemia and chest pain. A coronary angiography-derived index of microcirculatory resistance (caIMR) is proposed for physiological assessment of microvascular diseases in coronary circulation. The aim of the trial is to assess diagnostic performance of caIMR, using wire-derived index of microcirculatory resistance (IMR) as the reference standard.

More than 50% of patients with stable or unstable angina pectoris have no obstructive coronary arteries by angiographic visual estimation, in which coronary microvascular dysfunction (CMD) is one of the causes of myocardial ischemia and chest pain. Presently, the index of microcirculatory resistance (IMR) measured by the pressure wire is recognized as standard for evaluating coronary microcirculatory function. A coronary angiography-derived index of microcirculatory resistance (caIMR) is proposed for physiological assessment of microvascular diseases in coronary circulation without pressure wire, hyperemic agents, or thermodilution method.

This study is a prospective, multi-center clinical trial. In the study, IMR (measured by pressure wire) will be used as a reference standard to evaluate the feasibility, accuracy and safety of caIMR measured by a non-invasive diagnosis system (FM21a) based on angiography images and aortic pressure wave. 116 patients eligible for inclusion criteria will be enrolled in the study. Both IMR and caIMR measurement will be performed in the same patient in a random order after angiography. The definitions of IMR and caIMR for coronary microcirculatory ischemia are IMR≥25 and caIMR≥25. The primary endpoint is the diagnostic accuracy of caIMR. The secondary endpoint is caIMR's sensitivity, specificity, positive predictive value, negative predictive value, ROC curve and AUC of caIMR diagnosis, and the diagnostic characteristics of caIMR at the vascular level.

Inclusion Criteria:

1. Patients aged 18 years and above, 80 years old and below, with no gender limitation;
2. Patients with stable or unstable angina or suspected myocardial ischemia;
3. Patients voluntarily participated in this clinical trial and signed an informed consent form;
4. Target coronary with <50% diameter stenosis (DS%) by visual estimation.

Exclusion Criteria:

1. Patients with suspected acute myocardial infarction;
2. Patients with old myocardial infarction;
3. Patients with primary or secondary cardiomyopathy;
4. Patients with primary or secondary heart valve disease;
5. Patients with severe cardiac insufficiency and LVEF≤35%;
6. Patients with renal insufficiency (eGFR<60ml/min (1.73m^2)) or patients undergoing dialysis;
7. Patients who are allergic to iodine contrast agents, adenosine, and ATP;
8. Patients with severe organ disease or life expectancy less than 24 months;
9. Patients who are participating in other clinical studies of investigational drugs or devices and have not reached their primary endpoint;
10. The patient who has other conditions that are not suitable for clinical trials;
11. Patients with coronary artery involved in coronary fistula and myocardial bridge;
12. The contrast media is not filled, the blood vessels are overlapped, or the target blood vessel is severely distorted, and the lesion location cannot be fully exposed, or the image quality is poor and cannot be recognized;
13. Left main coronary artery disease and right coronary artery orifice disease;
14. After angiography, the investigator believes that the patient cannot tolerate any of the detection methods between caIMR and IMR;
15. The investigator believes that the patient is not suitable for clinical trials after angiography;

Patients with stable or unstable angina, or suspected myocardial ischemia.