Beyond the classical triangle: morphological variations of the Triangle of Koch in human hearts and their clinical implications

BACKGROUND: The Triangle of Koch (TOK) is an important anatomical region located in the right atrium of the heart. It contains the atrioventricular (AV) node and forms a crucial landmark during electrophysiological and cardiac surgical procedures. Variations in its boundaries and morphology may increase the risk of inadvertent injury to the cardiac conduction system. The present study aimed to evaluate the morphology (shape, boundaries, and anatomical variations) of the TOK in thirty donated human hearts and its clinical implications. MATERIALS AND METHODS: Thirty formalin-fixed adult human hearts were studied in the Department of Anatomy. The right atrium was opened carefully to expose the TOK. The boundaries formed by the tendon of Todaro (TT), the septal leaflet of the tricuspid valve, and the ostium of the coronary sinus (CS) were identified. Morphological features, location of the apex, and anatomical variations were documented and photographed. RESULTS: The TOK was identified in all specimens. Considerable variations were observed in shape, prominence of the TT, and position of the CS ostium. In most cases, it was broad and triangular, while in some hearts, the triangle appeared narrow and elongated. The apex corresponding to the AV nodal region showed positional variation relative to the membranous septum. Variability in the septal leaflet attachment and CS morphology was also noted. CONCLUSIONS: The TOK demonstrates significant anatomical variation in its shape and boundaries. Knowledge of these variations is essential for cardiologists, electrophysiologists, and cardiac surgeons during catheter ablation, pacemaker implantation, and valve surgeries to prevent injury to the AV node and associated conduction pathways.