Koch's triangle sized up: anatomical landmarks in perspective of catheter ablation procedures.

Koch's triangle contains the compact part of the atrioventricular node and is anatomically delineated by the Eustachian ridge, the membranous septum, and the insertion of the tricuspid valve. Inferiorly, Koch's triangle ends at the site of the os of the coronary sinus and, in part, is continuous with the sub-Eustachian pouch. Catheter ablation procedures for several types of reentrant tachycardias are based on identifying these anatomical landmarks. Variability in the dimensions of Koch's triangle thus may be clinically relevant. We examined 50 hearts. Anatomical landmarks measured were the Eustachian ridge, the tricuspid valve, the overall length between the membranous septum and the coronary sinus, the width of the coronary sinus, the Eustachian ridge in its roof and the distance to the tricuspid valve, and that of the sub-Eustachian pouch. Individual variations were marked. The mean values (+/- SD) were: Eustachian ridge 29.4 +/- 5.3 mm, tricuspid valve 28.9 +/- 4.5 mm, coronary sinus 10.8 +/- 2.2 mm, Eustachian ridge 3.7 +/- 2.3 mm, space underneath coronary sinus 8.6 +/- 3.4 mm, and sub-Eustachian pouch 26.8 +/- 3.3 mm. The overall length varied between 15 and 38 mm, with a mean of 26.3 +/- 4.5. In conclusion, Koch's triangle shows considerable individual variations in size. Given the fact that the absolute figures for the range in size of the compact atrioventricular node is much less than that of Koch's triangle, these variations have implications for catheter ablation procedures.