Which option correctly lists the three structures that form the triangle of Koch?

Which option correctly lists the three structures that form the triangle of Koch?

• A. Septal leaflet of tricuspid valve; CS os; Tendon of Todaro
• B. Crista terminalis; CS os; Fossa ovalis
• C. Septal leaflet of tricuspid valve; Crista terminalis; Tendon of Todaro
• D. CS os; Fossa ovalis; Mitral valve

Answer: (A)

Koch's triangle in the right atrium marks the region where the AV node resides. It is defined by three landmarks: the septal leaflet of the tricuspid valve, the coronary sinus ostium, and the tendon of Todaro. These three structures together outline the boundaries of the triangle, and the AV nodal tissue sits at the inferior/apical part of that area. That’s why identifying those exact structures is key: they form the anatomical frame that contains the AV node, which is central in electrophysiology procedures like ablation for certain tachycardias. The other structures listed don’t form this boundary—fossa ovalis and mitral valve are in different regions, and the crista terminalis is a prominent muscular ridge not constituting Koch’s triangle.

Koch's triangle in the right atrium marks the region where the AV node resides. It is defined by three landmarks: the septal leaflet of the tricuspid valve, the coronary sinus ostium, and the tendon of Todaro. These three structures together outline the boundaries of the triangle, and the AV nodal tissue sits at the inferior/apical part of that area. That’s why identifying those exact structures is key: they form the anatomical frame that contains the AV node, which is central in electrophysiology procedures like ablation for certain tachycardias. The other structures listed don’t form this boundary—fossa ovalis and mitral valve are in different regions, and the crista terminalis is a prominent muscular ridge not constituting Koch’s triangle.