Impact of left anterior descending myocardial bridges on coronary artery diameters and collateral vessel development: a retrospective coronary computed tomography angiography analysis.

BACKGROUND: A myocardial bridge (MB) is a congenital coronary anomaly most commonly located in the mid-segment of the left anterior descending coronary artery (LAD). This study aimed to evaluate the impact of mid-LAD myocardial bridges on coronary artery segment diameters and the development of supportive collateral circulation using coronary computed tomography angiography (CCTA). MATERIALS AND METHODS: In this retrospective cross-sectional study, CCTA scans of patients with mid-LAD MB and frequency-matched control subjects without coronary anomalies were evaluated. Luminal diameters of all epicardial coronary artery segments were measured during mid-diastole. The presence of deep MBs (depth ≥ 2 mm) and associated supportive collateral channels was systematically recorded. RESULTS: A significant reduction in luminal diameter was identified exclusively in the middle segment of the LAD underlying the bridged segment in the MB cohort compared with controls. Across all other epicardial coronary segments, luminal diameters did not differ significantly between groups. Subgroup analyses demonstrated that female patients had consistently smaller coronary luminal diameters than male patients across both cohorts. Notably, a prominent parallel diagonal vessel supporting post-bridge circulation was identified in a substantial proportion of patients with deep MBs, whereas no such supportive vascular structures were observed in the control cohort. CONCLUSIONS: Myocardial bridges, particularly deep variants, are associated with localized compensatory collateral vessel development without inducing generalized anatomical changes in other epicardial coronary segments. This adaptive vascular remodeling may play a protective role in maintaining perfusion distal to the bridged segment.