The triangle of Koch is an important surgical landmark for the atrioventricular node location in the right atrium. Which three structures define its boundaries?

• A Tendon of Todaro, coronary sinus ostium, and tricuspid valve annulus ✓
• B Crista terminalis, Eustachian valve, fossa ovalis
• C Fossa ovalis, coronary sinus, and limbus fossa ovalis
• D Right fibrous trigone, mitral annulus, and coronary sinus

Explanation

The triangle of Koch is delineated by the tendon of Todaro (posteriorly — a fibrous ridge from the Eustachian valve to the central fibrous body), the annulus of the tricuspid valve (anteriorly, specifically the septal leaflet), and the ostium of the coronary sinus (the base). The AV node lies at the apex of this triangle, just anterior to the coronary sinus ostium. Knowledge of this triangle is essential in cardiac electrophysiology ablation procedures to avoid inadvertent AV nodal damage.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.