XVIII. Persistent fetal dispersion of the atrioventricular node and His bundle within the central fibrous body.

In the hearts of two victims of sudden unexpected death (one age 20 years and the other 11 years) there was abnormally delayed persistence of the pattern of fetal dispersion of the A-V (atrioventricular) node and His bundle within the central fibrous body. This pattern is characterized by a splayed or excessively fragmented histological appearance of these structures viewed in cross-section. Some of the fronds of A-V nodal tissue formed loops connecting one portion of the node to another. Other fragments of nodal tissue appeared isolated within the central fibrous body, occasionally connecting directly to the crest of the interventricular septum. A number of the A-V nodal fragments were undergoing resorptive degeneration. Directly adjacent to the A-V node of the 11-year-old subject there was an island of cartilage within the central fibrous body. Since these anatomically separated fragments of A-V nodal tissue were so numerous and varied widely in size and thickness, in length, in histological organization, and in their apparent state of preservation probably extant during life, it is suggested that they form potential routes for abnormal conduction or impulse formation within the A-V junctional region and that some of these electrophysiological disturbances might be quickly lethal.