A novel CT score to predict the functional significance of coronary myocardial bridges (MB-CT score)

Myocardial bridging (MB) is the most common congenital coronary anomaly and is usually considered benign. However, previously published data have shown that a significant proportion of MB can cause hemodynamically significant obstruction when assessed by fractional flow reserve (FFR). In addition, data have suggested an association with myocardial ischemia, and adverse cardiac events. With the development of the non-invasive imaging modalities, remarkable progress has been made in our understanding of MB-associated myocardial ischemia.

To identify anatomical features of the MB from CT that are predictive of the functional significance of the structure and to create a multi-parametric score to further increase the predictive yield.

In this observational prospective study, consecutive patients with chronic coronary syndrome undergoing coronary computed tomography angiography (CCTA) were considered eligible. Inclusion ri teria were: 1) patients with an intramyocardial course of a coronary artery; 2) the absence of significant atherosclerotic epicardial coronary stenosis (diameter stenosis [DS]>50% ) on the artery with the MB.; 3) invasive functional assessment with FFR distal to the MB available. CT analysis was performed with measurement of the anatomic features of the MB (figure). Logistic regression was performed to identify anatomical characteristics predictive of functional significance of the MB. Optimal thresholds for quantitative variables were defined by area under the receiver-operating characteristics curve (AUC) analysis. A scoring system was developed in a derivation cohort (70% of the overall study population) and tested in a validation cohort (30% of patients).

A total of 285 patients with MB were assessed with CT and invasive FFR, among which 200 patients (200 vessels) were included in the derivation cohort and 85 patients were used for the validation group. In 283 patients (99%) the MB was located in the left anterior descending artery. Mean length of the intramyocardial course was 32 ± 9 mm. 71% (n=202) of the bridges were defined as long (length > 25 mm). The mean depth of the intramyocardial course was 3.1±0.4 mm and the mean angle of the intramyocardial entrance was 36 ± 9o. The mean measured FFR was 0.82±0.09. In 41% of the cases (n=117) the FFR assessment was positive with a value ≤0.80, whereas in 59% of the cases (n=168) the FFR was >0.80. At multivariable logistic regression analysis, intramyocardial depth, length of the MB, MB angle, and left ventricular mass were found as independent predictors of functional significance of the MB. A score (MB-CT Score) ranging from 0 to 6 was developed. The score revealed excellent predictive value for a functional significance of the MB with an AUC of 0.82 (95%CI 0.78-0.87).

A novel score integrating myocardial bridge anatomy characteristics derived from CCTA may aid in identifying patients with functionally significant MB.