AIM To explore the value of a new hemodynamics method for assessing the coronary micro-vascular resistance (cMVR) by combining fractional flow reserve (FFR) and invasive coronary angiography (ICA) images.

METHODS Selected patients who underwent coronary angiography at the Xijing Hospital of Air Force Military Medical University from November 2020 to June 2021 but did not have significant coronary stenosis (FFR>0.8) or had coronary stenosis treated with PCI with FFR>0.8, and underwent SPECT resting myocardial perfusion imaging within one month of coronary angiography. A total of 33 patients with 35 blood vessels were included. Based on the total rest score of target vessel (SRSTV), patients were divided into normal myocardial perfusion group (SRSTV ≤ 1, n=21) and abnormal myocardial perfusion group (SRSTV>1, n=12). Among the 35 blood vessels, SPECT myocardial perfusion at rest was normal in 23 vessels and abnormal in 12 vessels. The three-dimensional model of the target vessel was reconstructed from multi angle angiographic images, and the far and near end pressures in Resting state fMRI and congestive states were measured based on FFR. The corresponding blood flow Q of the target vessel was calculated using hemodynamic methods, and the microvascular resistance R, normalized microcirculation resistance index Rn, coronary flow reserve (CFR) and coronary resistance reserve (RRR) were further calculated. Compare the differences in the aforementioned hemodynamic parameters between the two groups.

RESULTS There was no significant difference between the two groups in age, gender, BMI, systolic blood pressure, diastolic blood pressure, heart rate, hospital stay, smoking history, drinking history, hypertension, diabetes history, arrhythmia history, heart, muscle infarction history, cerebrovascular disease history, PCI history, CABG history, cardiovascular disease family history, LVEF and medication history. Under the condition of congestive state, the normalized microvascular resistance index Rn has statistical difference between the normal and abnormal groups of SPECT resting myocardial perfusion, and the normal group is significantly lower than the abnormal group (P<0.01), but under the condition of Resting state fMRI, Rn has no significant difference between the two groups. There is a numerical difference between the two groups in other items, which is not statistically significant. Spearman correlation analysis showed that there was no significant correlation between microvascular resistance R and SRSTV, but the normalized microvascular resistance index Rn showed a strong correlation with SRSTV in the congestive state (rho=0.602, 95% CI: 0.336～0.779, P<0.01), and a weak correlation with SRSTV in the Resting state fMRI (rho=0.335, 95% CI: 0.002～0.601, P<0.05), while there was no significant correlation between CFR, RRR and SRSTV.

CONCLUSION For patients with normal epicardial coronary vessels, the proposed normalized micro-vascular resistance index (R_n) can reflect myocardial perfusion and it is a promising tool for assessing cMVR.