Boundary of the Koch's triangle is not formed by?

Koch's Triangle is a triangle enclosed by the septal leaflet of the tricuspid valve, the coronary sinus, and the membranous pa of the interatrial septum.Koch's triangle: Walter Karl Koch (1880-1962) was a distinguished German surgeon who discovered a triangular-shaped area in the right atrium of the hea that marks the atrioventricular node (known as Koch's triangle).The three sides of the triangle are defined by the following structures within the right atrium: The ostium of the coronary sinus, posteriorly; The anterior poion of the tricuspid valve annulus; and The tendon of Todaro (a tendinous structure connecting the valve of the inferior vena cava ostium to the central fibrous body), posteriorly.Impoance:Used as an anatomical landmark for location of the atrioventricular node during electrophysiology procedures such as pacing or ablation.