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

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.

This study was based on 40 normally structured hearts obtained at autopsy from patients without a history of tachyarrhythmia in the following age ranges: < 1 year (n = 19); 1-12 years (n = 11); and 12-20 years (n = 10). In 38 hearts, the AV septal junctional area was removed en bloc and serially sectioned at 10-microm thickness at right angles to the AV annulus. The length of the compact node and the rightward and leftward inferior extensions were calculated. Computer-assisted three-dimensional reconstructions were made of six hearts. The ratio of right extension to compact AVN showed a statistically significant increase with age; the increase in ratio of left extension to compact AVN was not statistically significant. In addition, with increasing age the geometry of the AVN changed from a half-oval to a spindle shape, concomitant with development of a distinct so-called muscular AV septum. The three-dimensional reconstructions showed widening of the transitional cell zone with an increase in fibrofatty tissue related to age.

The AVN, inferior extensions, and transitional cell zone show distinct age-related changes that may be clinically relevant. The increase in length of the inferior extensions may set the scene for AVN reentry and could explain why this condition is more frequent in young adults than in infants.