Systolic pressure gradient across myocardial bridge mediates the effect of bridge depth on clinical symptoms

OBJECTIVE: The relationship between myocardial bridging (MB) morphology and function and the pathways to clinical symptoms remained unclear. This study investigated the association between delta coronary computed tomographic angiography-derived fractional flow reserve (ΔCT-FFR) and angina-equivalent symptoms in left anterior descending MB without coronary atherosclerosis using photon-counting detector CT (PCD-CT). MATERIALS AND METHODS: This retrospective cohort included 180 patients with deep MB (depth > 2 mm) and no plaques. All underwent PCD-CT angiography. CT-FFR was computed by machine learning; systolic (ΔCT-FFRsys) and diastolic (ΔCT-FFRdia) trans-bridge pressure gradients were derived. MB depth and length were measured. Associations with symptoms were assessed by logistic regression and mediation analysis. RESULTS: Symptomatic patients (n = 81) had greater depth (median 3.30 mm vs. 2.45 mm), longer length (mean 36.06 mm vs. 26.10 mm), higher ΔCT-FFRsys (3.81% vs. 1.62%) and ΔCT-FFRdia (3.45% vs. 2.15%) than asymptomatic patients (n = 99) (all p < 0.001). Multivariable analysis identified depth (OR = 1.77, 95% CI: 1.27-2.46, p = 0.001) and ΔCT-FFRsys (OR = 1.16, 95% CI: 1.05-1.27, p = 0.002) as independent predictors. Mediation analysis indicated that ΔCT-FFRsys significantly mediated the effect of depth on symptoms (indirect effect = 0.1881, 95% CI: 0.1023-0.2897). CONCLUSIONS: MB depth and ΔCT-FFRsys were independent risk factors for symptoms, and ΔCT-FFRsys appeared to mediate the morphological-clinical symptoms link. These findings suggested that integrated assessment, particularly ΔCT-FFRsys, might be a new non-invasive imaging biomarker for clinically identify symptomatic MB and understand its potential pathogenic mechanisms. KEY POINTS: Question The precise relationship between myocardial bridging morphological and functional features and clinical symptoms, and whether underlying key mediating factors exist, remains currently incompletely determined. Findings Depth, length, and systolic trans-bridge pressure gradient of myocardial bridging independently predicted symptoms, with the gradient significantly mediating the relationship between morphology and clinical presentation. Clinical relevance Noninvasive assessment of depth and systolic trans-bridge pressure gradient can assist in identifying patients with symptomatic myocardial bridging, serving as potential imaging biomarkers and providing insights into the underlying pathophysiology of symptom presentation.