Sex differences in CT-FFR of myocardial bridging with or without atherosclerosis: an AI-based quantitative study

Background: Myocardial bridging (MB) is a prevalent coronary anomaly with potential links to major adverse cardiac events. While computed tomography-derived fractional flow reserve (FFRCT) offers a non-invasive functional assessment, current evidence predominantly treats MB as a homogeneous entity, overlooking potential sex differences in hemodynamic impact. Existing studies often fail to distinguish between isolated MB and MB with concomitant atherosclerosis, and rarely employ sex-stratified analyses. This study aimed to noninvasively assess sex-specific differences in FFRCT among patients with MB, with or without atherosclerosis, using an artificial intelligence (AI)-based platform to clarify the clinical implications of these differences.

Methods: This retrospective cohort study included 300 left anterior descending artery (LAD)-MB patients, subdivided into an MB group (n=155) and an MB with atherosclerosis (MBLA) group (n=145), along with 104 controls with normal coronary computed tomography angiography (CCTA) findings. Demographic data, clinical symptoms, and risk factors were collected. Morphological parameters of MB were quantitatively analyzed using cardiac function post-processing software, and whole-vessel and local segments (proximal to MB, within MB, and distal to MB) FFRCT values were obtained via an AI-based platform (Shukun-FFRCT). Patients were stratified by FFRCT <0.8, and statistical analyses [t-tests, analysis of variance (ANOVA), Mann-Whitney U tests, and binary logistic regression] were applied to examine sex-based associations with FFRCT abnormalities and influencing factors.

Results: (I) Demographic analysis revealed significantly higher proportions of male patients in the MB (52.9%) and MBLA (57.2%) groups compared to controls (24.0%, both P<0.05). (II) Sex-stratified analysis within pathological subgroups showed that in the MB group, females had significantly lower distal FFRCT values (FFR3: median 0.92 vs. 0.95, P=0.006) and higher trans-bridge pressure drop (ΔFFR: 0.08 vs. 0.05, P=0.004) than males. No significant sex-based differences in FFRCT were observed in the MBLA group (all P>0.05). (III) Intra-group comparisons of FFRCT between systolic and diastolic phases showed no significant differences in either case or control groups (all P>0.05). (IV) Binary logistic regression indicated that MB length was an independent risk factor for FFRCT abnormalities in both sexes. Each 1-mm increase in MB length raised the risk of FFRCT abnormality by 5.3% in males [odds ratio (OR) =1.053, 95% confidence interval (CI): 1.004–1.104, P=0.033] and 11.3% in females (OR =1.113, 95% CI: 1.024–1.209, P=0.011).

Conclusions: This study innovatively demonstrates through CT-AI quantitative analysis that sex significantly influences FFRCT in LAD-MB patients. Females with isolated MB exhibit more pronounced distal hemodynamic alterations, whereas sex differences diminish when atherosclerosis coexists. Notably, MB length is an independent risk factor for FFRCT abnormalities, with a greater impact observed in females. These findings provide preliminary evidence to inform risk stratification of MB.