Topographic anatomy of the inferior pyramidal space: Relevance to radiofrequency catheter ablation

Inferior Pyramidal Space and Ablation, Introduction: Radiofrequency cathete r ablation carried out in the vicinity of the triangle of Koch risks damagi ng not only the AV conduction tissues but also their arterial supply, The a im of this study was to examine the relationship of the AV nodal artery to the inferior pyramidal space, the triangle of Koch, and the right atrial en docardial surface. Methods and Results: We studied 41 heart specimens, 24 by gross dissections and 17 by histologic sections. The proximity of the AV nodal artery to the surface landmarks of the triangle of Koch was variable, but it was notable that in 75% of specimens the artery passed close to the endocardial surfac e of the right atrium and within 0.5 to 5 mm of the mouth of the coronary s inus. In all specimens, the mean distance of the artery to the endocardial surface was 3.5 +/- 1.5 mm at the base of Koch's triangle. The location of the compact AV node and its inferior extensions varied within the landmarks of the triangle, At the mid-level of Koch's triangle, the compact node was medially situated in 82% of specimens, but it was closer to the hinge of t he tricuspid valve in the remaining 18% of specimens. In 12% of specimens, the inferior parts of the node extended to the level of the mouth of the co ronary sinus. Conclusion: The nodal artery runs close to the orifice of the coronary sinu s, the endocardial surface of the right atrium, the middle cardiac vein, an d the specialized conduction tissues in most hearts. The nodal artery and/o r the AV conduction tissues can be at risk of damage when ablative procedur es are carried out at the base of the triangle of Koch.