Which structure is NOT a component of the triangle of Koch?

Which structure is NOT a component of the triangle of Koch?

• A. Crista terminalis
• B. Coronary sinus ostium
• C. Tendon of Todaro
• D. Septal leaflet of tricuspid valve

Answer: (A)

The triangle of Koch is the region in the right atrium that contains the AV nodal tissue. Its boundaries are the tendon of Todaro at the top, the coronary sinus ostium at the back, and the septal leaflet of the tricuspid valve forming the lower boundary near the interatrial septum. The crista terminalis, a muscular ridge that separates the smooth posterior wall from the rough anterior wall of the right atrium, does not define this triangle. Because it lies outside those boundaries, the crista terminalis is not a component of Koch’s triangle. This distinction matters because the AV node sits within Koch’s triangle, making the triangle a key landmark during studies and procedures targeting AV nodal conduction. The other structures listed—tendon of Todaro, coronary sinus ostium, and septal leaflet of the tricuspid valve—are the actual boundaries of Koch’s triangle.

The triangle of Koch is the region in the right atrium that contains the AV nodal tissue. Its boundaries are the tendon of Todaro at the top, the coronary sinus ostium at the back, and the septal leaflet of the tricuspid valve forming the lower boundary near the interatrial septum. The crista terminalis, a muscular ridge that separates the smooth posterior wall from the rough anterior wall of the right atrium, does not define this triangle. Because it lies outside those boundaries, the crista terminalis is not a component of Koch’s triangle. This distinction matters because the AV node sits within Koch’s triangle, making the triangle a key landmark during studies and procedures targeting AV nodal conduction. The other structures listed—tendon of Todaro, coronary sinus ostium, and septal leaflet of the tricuspid valve—are the actual boundaries of Koch’s triangle.