Morphology of the human atrioventricular node is age dependent: A feature of potential clinical significance

AVN Morphology Related to Age. Introduction: Advances in catheter ablation procedures have created the need to understand better the morphology of the AV node (AVN), particularly as it relates to age. Methods and Results: This study was based on 40 normally structured hearts obtained at autopsy from patients without a history of tachyarrhythmia in t he following age ranges: <1 year (n = 19); 1-12 years (n = 11); and 12-20 y ears (n = 10). In 38 hearts, the AV septal junctional area was removed en b loc and serially sectioned at 10-mu m thickness at right angles to the AV a nnulus, The length of the compact node and the rightward and leftward infer ior extensions were calculated, Computer-assisted three-dimensional reconst ructions were made of six hearts, The ratio of right extension to compact A VN showed a statistically significant increase,vith age; the increase in ra tio of left extension to compact AVN was not statistically significant. In addition, with increasing age the geometry of the AVN changed from a half-o val to a spindle shape, concomitant with development of a distinct so-calle d muscular AV septum, The three-dimensional reconstructions showed widening of the transitional cell zone with an increase in fibrofatty tissue relate d to age. Conclusion: The AVN, inferior extensions, and transitional cell zone show d istinct age-related changes that may be clinically relevant, The increase i n length of the inferior extensions may set the scene for AVN reentry and c ould explain why this condition is more frequent in young adults than in in fants.