Which structures define the boundaries of the triangle of Koch?

Which structures define the boundaries of the triangle of Koch?

• A. Tendon of Todaro; CS ostium; septal leaflet of the tricuspid valve
• B. CS ostium; Eustachian valve; septal leaflet of the tricuspid valve
• C. Tendon of Todaro; fossa ovalis; mitral annulus
• D. Right atrial appendage; tricuspid annulus; aorta

Answer: (A)

Koch's triangle defines the region in the right atrium that houses the AV node. Its boundaries are the tendon of Todaro, the ostium of the coronary sinus, and the septal leaflet of the tricuspid valve. This configuration places the AV node at the triangle’s apex, near the coronary sinus ostium, which is why these specific structures delineate the area most relevant to nodal conduction. The tendon of Todaro marks the superior boundary, the coronary sinus ostium forms the posterior boundary, and the septal leaflet of the tricuspid valve constitutes the inferior boundary. The other structures listed—such as the Eustachian valve, fossa ovalis, mitral annulus, right atrial appendage, the tricuspid annulus away from the septal region, or the aorta—do not form Koch's triangle boundaries and thus are not correct delimiters.

Koch's triangle defines the region in the right atrium that houses the AV node. Its boundaries are the tendon of Todaro, the ostium of the coronary sinus, and the septal leaflet of the tricuspid valve. This configuration places the AV node at the triangle’s apex, near the coronary sinus ostium, which is why these specific structures delineate the area most relevant to nodal conduction.

The tendon of Todaro marks the superior boundary, the coronary sinus ostium forms the posterior boundary, and the septal leaflet of the tricuspid valve constitutes the inferior boundary. The other structures listed—such as the Eustachian valve, fossa ovalis, mitral annulus, right atrial appendage, the tricuspid annulus away from the septal region, or the aorta—do not form Koch's triangle boundaries and thus are not correct delimiters.