Tendon of Todaro

Tendon of Todaro – Anatomy & Details

The tendon of Todaro is a small, collagenous band of connective tissue in the right atrium of the heart, named after the Italian anatomist Francesco Todaro. It is primarily known as an anatomical landmark because it forms one of the boundaries of the triangle of Koch. 

Anatomy and location

• The tendon is a continuation of the Eustachian valve of the inferior vena cava and the Thebesian valve of the coronary sinus.
• It originates from the central fibrous body of the heart and runs toward the inferomedial part of the inferior vena cava valve.
• Its location and relationship with other structures in the right atrium define the triangle of Koch, which is an important landmark for locating the atrioventricular (AV) node, a critical component of the heart’s electrical conduction system.
• It has also been referred to as the “tendon of the inferior pyramidal space”. 

Clinical relevance and limitations

The tendon of Todaro is significant in invasive cardiology and cardiac surgery because of its role in defining the triangle of Koch. The boundaries of this triangle are: 

• Anteriorly: The septal leaflet of the tricuspid valve.
• Posteriorly: The tendon of Todaro.
• Basally: The ostium (opening) of the coronary sinus. 

🔹 Definition

• The Tendon of Todaro is a fibrous band in the right atrium of the heart.
• It runs from the Eustachian valve of the inferior vena cava (IVC) and the Thebesian valve of the coronary sinus toward the central fibrous body.

🔹 Location & Course

• Lies in the subendocardium of the interatrial septum.
• Extends posteriorly and superiorly, forming the posterior boundary of the Triangle of Todaro.
• Invisible to the naked eye in many cases, but electrophysiologists use it as a conceptual line.

🔹 Embryological Origin

• Thought to represent the fibrous continuation of the right venous valve of the sinus venosus, which in development gives rise to:
  • Eustachian valve
  • Thebesian valve

🔹 Clinical Importance

• Forms part of the Triangle of Todaro, which is an essential landmark for locating the atrioventricular (AV) node.
• Guides catheter ablation procedures for arrhythmias like AV nodal re-entrant tachycardia (AVNRT).
• Prevents unintentional damage to the AV node during interventions.

🔹 Boundaries Recap of Triangle of Koch

1. Tendon of Todaro (posterior border)
2. Coronary sinus ostium (base)
3. Septal leaflet of tricuspid valve (lateral border)

👉 Apex contains the AV node.

✅ Mnemonic for Tendon of Todaro:
Think “ET” = Eustachian + Thebesian → Tendon of Todaro

cardiology mcqs

Anatomy and Location

• Origin: The tendon originates from the central fibrous body of the heart. 
• Course: It travels as a collagenous band in the right atrium, extending inferiorly and to the right. 
• Termination: It ends at the eustachian valve (or valve of the inferior vena cava). 

Clinical Significance

• Landmark for the Triangle of Koch: The tendon forms the antero-superior boundary of the Triangle of Koch. 
• Locating the AV Node: The apex of this triangle, near the AV node, is crucial for electrophysiologists. 
• Cardiac Procedures: The tendon serves as an anatomical guide for cardiac surgery and invasive cardiology procedures, such as catheter ablation. 

Triangle of Koch – Anatomy & Key Points

Definition:
The Triangle of Koch is an anatomical area in the right atrium of the heart that is critically important in cardiac electrophysiology because it contains the atrioventricular (AV) node.