Anatomy Spotlight: Triangle of Koch

The triangle of Koch is an important region in the lower RA.

• It contains, the compact AV node, the “fast pathway”, the “slow pathway” the CS ostium, and part of the tricuspid annulus, all important structures in a variety of EP studies.

 

• It is usually described in the context of AVJRT ablation, since the triangle location contains both the “danger zone to avoid” – i.e the AV node and fast pathway, and the target site – i.e the slow pathway.

 

The illustration below describes the 3 sides of the triangle:

1. The base: CS ostium
2. 1 side: Tendon of Todaro
3. 2nd side: Septal leaflet of the Tricuspid Valve

 

 

 

Anatomical View of the Triangle of Koch

Anatomical Considerations for His Bundle Pacing. Circ Arrhythm Electrophysiol. 2019;12(7):e006897

 

Fluoroscopic Views

• Here we can see the an RAO fluoroscopic view of the triangle of Koch. An RAO view is excellent at displaying the anterior-posterior view of the triangle. It can be a little harder to see, since we can’t see the anatomy.

 

• Under fluro guidance, we use our EP catheters as landmarks of the triangle! Let’s go step by step.

 

 

The method I’ve described is a little crude and serves as a rough guide at a glance. In reality, EGM’s are in fact the only source of truth, and the EGM’s will help to fine tune our triangle. So the “red line” or anterior border will be defined by the location we have “annular signals” and the Apex will be defined by a position just proximal to His signal EGM’s.

Also, neither the LAO nor the RAO view gives us a perfect view of the triangle. So lets look at an LAO view next.

 

LAO View

So lets looks at how 3D mapping relates to a fluoroscopic view, this time in a LAO view which helps you differentiate the “lateral dimension” of the triangle. I.e “septal vs lateral”.

I have tried to draw an approximate outline of the RA over the top of this fluro image, to help you orientate yourself in the atrium  -it’s not perfect, but hopefully it helps.

 

 

3D Electroanatomical Mapping views

 

My Two Cents:

• EGM’s are the ONLY source of truth in understanding the triangle of Koch. Whilst this BeatBox has been focused on the anatomical, fluoroscopic and 3D landmarks, these landmarks are truly defined by the electrograms.

 

• In reality, the heart may be rotated, and anatomical variation may displace structures within the triangle, adding complexity and introducing uncertainty to ablation methodology.

 

• The fluoroscopic & 3D views help us understand the catheter positions relative to one another.

 

• Slow pathway ablation is usually attempted between the CS ostium and the septal leaflet of the Tricuspid valve, as inferiorly as possible whilst staying within the triangle (in order to avoid AV node/fast pathway injury).

 

Thanks for tuning in :)
Cheers
Mitch & CPiP Team

 

References:

Nagarajan VD, Ho SY, Ernst S. Anatomical Considerations for His Bundle Pacing. Circ Arrhythm Electrophysiol. 2019 Jul;12(7):e006897.