Atrioventricular Node: The Heart's Electrical Gatekeeper

The atrioventricular (AV) node is a specialized cluster of cells in the inferior interatrial septum that regulates electrical conduction between atria and ventricles.

Key Functions

1. Delay (~120 ms): Allows atrial contraction to complete ventricular filling before ventricular systole (atrial kick contributes 20–30% of stroke volume).
2. Synchronization: Ensures coordinated atrial-ventricular contraction.
3. Protective filtering: Limits rapid atrial rates (e.g., atrial fibrillation) from driving ventricles 1:1; prevents dangerously fast ventricular rates.
4. Backup pacemaker: Intrinsic rate 40–60 bpm if SA node fails.

Anatomy & Blood Supply

• Located at apex of Koch's triangle (tendon of Todaro, tricuspid annulus, coronary sinus).
• Supplied by AV nodal artery (90% from RCA, 10% from LCx).

Clinical Relevance

• AV block: Delayed/failed conduction (1st, 2nd, 3rd degree).
• AV nodal reentrant tachycardia (AVNRT): Most common paroxysmal SVT; reentry within AV node.
• Ablation target: Slow pathway modification for AVNRT; AV node ablation + pacemaker for rate control in refractory AF.

The AV node is the critical "gatekeeper" ensuring efficient, sequential cardiac pumping.