The atrioventricular conduction axis and the aortic root—Inferences for transcatheter replacement of the aortic valve

Abstract

Conduction problems still occur following transcatheter aortic valvar replacement.With this in mind, we have assessed the relationship of the conduction axis to the aortic root. We used serial histological sections, made perpendicular to the base of the triangle of Koch in nine hearts, and perpendicular to the aortic root in 11 hearts.We first defined the extent of the fibrous tissues forming the boundaries of an infero-septal recess of the subaortic outflow tract, found in all datasets but one.When the recess was present, the axis penetrated through its rightward wall, giving rise to the left bundle branch prior to entering the outflow tract. The axis itself was usually on the crest of the ventricular septum, but could be deviated leftward or rightward. Its proximity to the virtual basal plane reflected the angulation of the muscular septum. On average, the superior edge of the left bundle was within 3.3 mm of the hinge of the right coronary leaflet, with a range from 0.4 to 10.2 mm. The arrangement was markedly different in the case lacking an infero-septal recess. Our findings necessitated a redefinition of the right fibrous trigone and the central fibrous body. The atrioventricular conduction axis, having entered the aortic root, is usually closest at the hinge of the right coronary leaflet. Knowledge of the depth of the infero-septal recess, and the angulation of the muscular ventricular septal, may help to avoid conduction problems following transcatheter implantation of the aortic valve.

Vulnerability of the ventricular conduction axis during transcatheter aortic valvar implantation: A translational pathologic study

“…Taken overall, therefore, and in keeping with our previous investigation using a 2D approach (Macías et al, 2022), significant variability was found in the location of the conduction axis relative to the aortic root (Tables S2 and S3). When assessing these findings, we considered only the rightward extent of fibrous continuity between the leaflets of the aortic and mitral valves as the right fibrous trigone.…”

“…The findings, achieved using 3D reconstructions of the root, expand our previous findings obtained using more traditional histological techniques (Macías et al, 2022). These showed that, in the variations placing the conduction axis at greatest risk, the component of the axis closest to the aortic root is the superior fascicle of the left bundle branch.…”

“…As has been emphasized in a recent vignette commemorating the sesquicentennial anniversary of the birth of Tawara (Mori et al, 2023), fully to appreciate his findings it is necessary to put the atrioventricular conduction axis back into the heart. Our aim in this study, therefore, was to expand our previous study, in which we confirmed the findings of Tawara (Tawara, 1906), but using a two‐dimensional (2D) approach (Macías et al, 2022). In our current study, we obtained 3D representations of the aortic root from autopsied adult heart specimens, subsequently using histological sections so as to place the ventricular conduction axis back into the structurally normal heart.…”

“…We have previously described variations of the atrioventricular node within the triangle of Koch. (Cabrera et al, 2020; Macías et al, 2022) The study, in accord with the Helsinki Declaration, was approved by the Institutional Review Board at Cincinnati Children's Hospital Medical Center.…”

Anatomy of the conduction tissues 100 years on: what have we learned?

“…On occasion, the relationship can be very close (figure 7). 39 This proximity is likely to determine the risk of conduction damage subsequent to transcatheter replacement of the aortic valve 40. The third septal division unites the fascicles that run towards the papillary muscles.…”