The tendons of Todaro and the "triangle of Koch": lessons from eponymous hagiolatry

Abstract

Introduction: There is growing use of the Todaro tendon and triangle of Koch as anatomic icons for invasive cardiac electrophysiologists. Reasons exist to doubt this validity.

Methods and results: Histologic sections were prepared from 96 anatomically normal human hearts. The study area extended from the crista supraventricularis to the eustachian valve and included the AV node and His bundle. This encompasses any tendon of Todaro. Because the purported triangle of Koch includes the tendon of Todaro, all of Koch's available publications were examined. The tendon of Todaro is absent in only one fourth of infant hearts, but in two thirds of adult hearts. Tendons present were less often single than double or more, rarely exceeded 4 mm in length, and were seldom > 1 mm in diameter. Tendons usually originated from the central fibrous body and ended in the eustachian valve. Their origin most often was over the His bundle or its junction with the AV node, rather than the AV node. Tendons were primarily composed of collagen. Koch never described any triangle or acknowledged existence of tendons of Todaro.

Conclusion: Todaro tendons are too often absent (or multiple) to warrant use as anatomic landmarks. Without this side of the supposed triangle of Koch, the entire tendon and triangle concept collapses and should be abandoned. There are numerous far more constant anatomic landmarks available to orient one to the human AV node and His bundle; these are briefly reviewed.