Lack of evidence for longitudinal dissociation of the atrioventricular conduction axis.

Longitudinal dissociation of the aggregated specialized cardiomyocytes within the non-branching portion of atrioventricular conduction axis has proved a controversial topic for both morphologists and electrophysiologists. We have now used morphological methods, including three-dimensional assessment, to revisit, in human, canine, and bovine hearts, the presence or absence of interconnections between the aggregated cardiomyocytes making up the non-branching bundle. We analyzed three datasets from human and canine hearts, and two from bovine hearts, using longitudinal and orthogonal serial histological sections. In addition, we assessed three hearts using translucent India ink injected specimens, permitting assessment of the three-dimensional arrangement of the cardiomyocytes. Using the longitudinal sections, we found numerous oblique interconnections between the groups of specialized cardiomyocytes. When assessing orthogonal sections, we noted marked variation in the grouping of the cardiomyocytes. We interpreted this finding as evidence of bifurcation and convergence of the groups seen in the longitudinal sections. The three-dimensional assessment of the bovine material confirmed the presence of the numerous interconnections. The presence of multiple connections between the cardiomyocytes in the non-branching bundle rules out the potential for longitudinal dissociation. This article is protected by copyright. All rights reserved.