Impact of Myocardial Bridging on Hemodynamics Evaluated by Coronary Angiography-Derived Fractional Flow Reserve.

Myocardial bridging (MB) is a kind of congenital coronary abnormality. The functional impact of MB on coronary artery remains a subject of debate. This study aimed to assess the hemodynamic effects of MB using coronary angiography-derived fractional flow reserve (caFFR) and elucidate the relationship between MB anatomical parameters and diastolic caFFR (dcaFFR) in patients with isolated MB (iMB) and MB combined with proximal coronary atherosclerosis (MB+AS). A total of 683 patients diagnosed with MB located on left anterior descending (LAD) via coronary angiography (CAG) were retrospectively enrolled and categorized into two groups: iMB (n = 377) and MB+AS (n = 306). The dcaFFR was calculated to evaluate the hemodynamic impact of MB. Multivariate linear regression and mediation analysis were performed to identify predictors of dcaFFR. In the iMB group, diastolic minimal lumen diameter (MLD) of MB segment was the sole independent predictor of dcaFFR (B = 0.036, β = 0.253, p <0.001). In the group of MB+AS, the severity of proximal stenosis emerged as the only independent predictor of dcaFFR (B = -0.004, β = -0.674, p <0.001), with the hemodynamic effects of MB fully mediated by proximal stenosis. In conclusion, the hemodynamic impact of MB depends on the presence of proximal coronary atherosclerosis. In iMB cases, the diastolic MLD of MB segment directly determines hemodynamic impairment. However, the hemodynamic impact of MB is nonsignificant in cases of MB+AS, as its effect is fully mediated through proximal stenosis severity.