Local Variation and Age-Related Change in Atrial and Ventricular Myocardial Contiguity at the Atrioventricular Junction in Human Hearts.

Background: We explored the histologic patterns of and age-related changes in atrial and ventricular myocardial contiguity at the left and right atrioventricular (AV) junction that could be a target site for catheter ablation. Methods and Results: Twenty-three structurally normal adult hearts obtained at autopsy were studied. The 2 AV annuli were divided into 13 clinically recognized portions in which we measured distance between the atrial and ventricular myocardium at the AV junction. Overall, measured distance was less on the right than left side (mean [±SD] 0.74±0.59 vs. 1.15±0.78 mm, respectively), and distance increased gradually with age. The gap was smallest at the anterolateral portion on the right side and posterolateral portion on the left side. Three specific features were noted, namely extension of the ventricular myocardium (coarse trabeculae) towards the atrium on the right side of the AV junction, extension of the atrial myocardium onto the AV valve leaflets, and a collection of small myocardial cells, perhaps including specialized cells, in the right anterolateral portion. No concealed AV muscular connections were found. Conclusions: Contiguity and separation of the myocardium at the AV junction have specific patterns, and myocardial proximity is influenced by age. These histologic features of the AV junction may prove to be informative for catheter ablation of tachyarrhythmias related to the AV junction.