The Building of the Triangular Locus of the Atrioventricular Node from Todaro to Tandler

What is known today as the triangle of Koch (the triangular locus of the atrioventricular node, TLAVN) is bordered by the fibrous attachment of the septal cusp of tricuspid valve, the opening of the coronary sinus and tendon of valve of inferior vena cava (TIVCV). This is a concept developed cumulatively by several exceptional anatomists. The literature was reviewed with a focus on the discovery of the atrioventricular node by Sunao Tawara (January 1906), its previous announcement by Tawara’s mentor Ludwig Aschoff (1905), and the contributions of the authors who described the other components of the triangular locus. Francesco Todaro discovered the TIVCV (1865); Tawara described the atrioventricular node and its relationship with the fibrous attachment of the septal cusp of tricuspid valve and the opening of the coronary sinus. The first description of assembling all components was provided by Arthur Keith (March 1906). Keith was also the first to consider the triangular locus as a useful landmark for identifying the atrial structures of the conduction system discovered by Tawara and Wilhelm His Jr. (1893). Julius Tandler named the TLAVN as Koch’s triangle (1913). Keith’s contributions to this topic have been particularly overlooked. The “triangular locus of the atrioventricular node” or “triangle of the atrioventricular node” are more instructive and impartial names.