AVNRT arises from a micro reentrant circuit present within which structure?

• A. Triangle of Koch
• B. Right atrial appendage
• C. Fossa ovalis
• D. Coronary sinus

Answer: (A)

AVNRT lies in the region of the AV node, where dual AV nodal pathways create a tiny reentrant loop. This area is the triangle of Koch in the right atrium, the anatomical zone that houses the AV node and the lower His-Purkinje conduction tissue. The reentrant circuit uses a slow AV-nodal pathway for antegrade conduction and a faster pathway for retrograde conduction, all within this compact nodal tissue. Because the triangle of Koch contains the AV node, it is the correct site for the micro reentrant circuit. Structures like the right atrial appendage, fossa ovalis, or coronary sinus do not contain the AV node and are not where this reentry typically arises.