Triangle of Koch & AV Node

AV Node in the Triangle of Koch

Here’s a detailed note on the Triangle of Koch, important in cardiology and electrophysiology:

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Triangle of Koch – Overview

The Triangle of Koch is an important anatomical landmark located in the right atrium of the heart. It serves as a guide to locate the atrioventricular (AV) node, which is crucial for the cardiac conduction system. Knowledge of this triangle is essential in electrophysiology procedures such as AV nodal ablation, slow pathway ablation for AV nodal reentrant tachycardia (AVNRT), and in avoiding iatrogenic AV block.

Anatomical Boundaries:

The triangle is defined by three key structures:

1. Tendon of Todaro – a fibrous band running from the Eustachian valve (at the IVC) to the central fibrous body.

2. Ostium of the coronary sinus (CS) – located at the base of the triangle.

3. Septal leaflet of the tricuspid valve – forming the anterior boundary.

Thus, the triangle is bounded:

Posteriorly by the Tendon of Todaro

Inferiorly by the coronary sinus ostium

Anteriorly by the septal tricuspid annulus

Contents:

The AV node lies within the apex of the triangle, near the central fibrous body and the membranous interventricular septum.

The His bundle originates just anterior and superior to the apex.

The slow pathway inputs (used in AVNRT) are usually located at the base of the triangle, near the coronary sinus ostium.

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Clinical Significance

1. Electrophysiology

Used as a landmark for safe ablation of the slow pathway in AVNRT, targeting the lower part of the triangle to avoid damaging the compact AV node at the apex.

Knowledge prevents inadvertent complete heart block during catheter ablation.

2. Cardiac Surgery

Surgeons must be cautious when operating near the interatrial septum or tricuspid valve to avoid injury to the AV node.

3. Imaging & Anatomy

Echocardiography and intracardiac echocardiography can help visualize structures near the triangle.

Key Points for Exams / Quick Recall

Located in right atrium.

Boundaries: Tendon of Todaro, septal tricuspid leaflet, coronary sinus ostium.

Contains AV node (apex).

Clinical importance: EP ablation, AVNRT, avoiding AV block.

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