Reassessment of the Location of the Conduction System in Atrioventricular Septal Defect Using Phase-Contrast Computed Tomography

The location of the atrioventricular conduction axis in the setting of atrioventricular septal defect has previously been shown by histology and intraoperative recordings. We have now reassessed the arrangement using phase-contrast computed tomography, aiming to provide precise measurements so as to optimize future surgical repairs. We used the system based on an X-ray Talbot grating interferometer using the beamline BL20B2 in a SPring-8 synchrotron radiation facility available in Japan. We analyzed 18 specimens. The atrioventricular node was found within a nodal triangle 1.7 mm from the coronary sinus, with 95% confidence intervals from 1.45 to 2.0 millimeters. The depth of the node from the right atrial endocardium was 1.0 mm, with 95% confidence intervals from 0.73 to 1.34 mm. The overall length of the scooped-out ventricular septum was 30.8 mm, with 95% confidence intervals from 27.5 to 34.1 millimeters. The length from the inferior atrioventricular junction to the take-off of the right bundle branch was 12.8 mm, with 95% confidence intervals from 11.12 to 14.38 mm, giving a ratio of 0.43 for the extent of the axis along the inferior septum, with 95% confidence intervals of 0.38-0.48. The length of the non-branching bundle was 6.6 mm, with 95% confidence intervals from 5.57 to 7.7 mm. The proportion of septum occupied by the non-branching bundle was 0.22, with 95% confidence intervals from 0.18 to 0.26. Our findings confirm previous histological studies, extending them by providing precise measurements to guide placement of sutures during surgical repair.