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The Legendary Triangle of Koch

Updated: Aug 27, 2022

You have read about it in the EP textbooks and heard it mentioned during EP courses, however, no new learner has ever asked me “WHY” they needed to learn it. Honestly, if I was to take a straw poll, I wonder how many allied EP staff really KNOW why they need to know about the Triangle of Koch.

“The eye cannot see what the mind does not know.”

Let us use “CHART Vision” to bring to life the concepts and anatomy that define the mysterious Triangle of Koch so that in your next EP case, you can see the Triangle of Koch through a clear lens.

It is essential to identify the Triangle of Koch's location and associated anatomy to mark critical landmarks when navigating catheter locations using fluoroscopy, identifying ablation targets, and using it as a reference for transseptal access…to name a few.


ANATOMY – the Triangle of Koch is comprised of superficial structures located in the low right atrium.

Defined by three anatomical borders:

  1. Septal leaflet of the tricuspid annulus

  2. Tendon of Todaro, the apex of the Triangle, anterior structure (His bundle catheter placement)

  3. Ostium of the Coronary Sinus - posterior aspect of the atrial septum, posterior structure (vein entrance for CS catheter)


FLUOROSCOPY – Today, 3D mapping systems have enough precision to project anatomical and electrical structures with a high level of accuracy. However, prior to mapping systems, physician operators relied on fluoroscopy imaging to identify the structures defining the Triangle of Koch.

Fluoroscopy is not an ideal modality for imaging soft tissues… so how exactly does one identify the septal leaflet of the tricuspid valve, or the CS ostium, under fluoroscopy?

  • In the correct position, the His catheter electrodes reveal the apex of the Triangle of Koch, as the His bundle courses along the Tricuspid Valve.

  • When the CS catheter is fully inserted into the Coronary Sinus, the proximal electrode of the CS catheter will estimate the CS ostium.

  • In the RAO fluoroscopy position, the borders of the Triangle of Koch can be defined by triangulating the landmarks associated with correct His and CS catheter positions.

Understanding the anatomy associated with AV junction catheters allows the eyes to see what the mind now knows…CHART Vision!

ABLATION TARGETS – For some ablation procedures, such as AVNRT, specific anatomical structures in the Triangle of Koch are targeted. The slow pathway is the ablation target to disrupt the circuit for AV Nodal Reentry Tachycardia. During ablation of AVNRT, the Triangle of Koch serves as a landmark to identify the slow pathway and AV Node -- where the slow pathway is targeted, and the AV node is avoided, not to disrupt the intrinsic conduction system.


TRANSSEPTAL TARGETING – The Fossa Ovalis is typically the target for transseptal puncture for left atrial access -- the Triangle of Koch is anterior to the transseptal target. Again, identifying the His and CS catheter’s location will define the Triangle of Koch. This is important for transseptal targeting with fluoroscopy. Contemporary labs rely on Intracardiac Echocardiography (ICE) imaging to locate the Fossa Ovalis. However, consider what would happen if the ICE system stops functioning or you are assisting in a lab with limited equipment. Astute EP team members learn to be resourceful when resources are limited.

With that being said, having a solid understanding of the anatomy and electrical structures in and around the Triangle of Koch has great utility.


Now...can you "SEE" it?

If you found this BLOG valuable to your EP learning journey, please take this lesson to teach a fellow EP team member or share via your social media channels. For most of us in EP, it took a tribe of contributors to teach us, so let’s pay it forward to others who share the same passion for learning EP and providing excellent patient care.

...Viva EP!

For more information and a self-paced online course visit the CHART Course Store at!

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