Atrioventricular nodal branch of circumflex artery of heart

The atrioventricular nodal branch of the circumflex artery of the heart is a small arterial branch that arises from the terminal (distal) portion of the left circumflex artery (LCx) and supplies blood to the atrioventricular (AV) node and adjacent structures within the inferior pyramidal space of the heart. It represents the less common variant of the AV nodal artery origin, occurring when the left circumflex artery is the dominant coronary vessel.

Origin and Prevalence

The AV node artery most commonly originates from the distal right coronary artery (RCA) at the crux of the heart specifically at the apex of the U-turn (or "U-turn of James") in approximately 80-87% of individuals. In the remaining 81-5% of cases, the AV nodal artery arises instead from the terminal portion of the left circumflex artery, and in 2-10% it receives a dual supply from both the RCA and LCx. The origin of the AV nodal artery is closely linked to coronary dominance: when the LCx is the dominant artery (extending to the crux cordis to give rise to the posterior descending artery), it also gives off the AV nodal branch.

Course and Anatomy

Regardless of its origin, the AV nodal artery penetrates into the inferior pyramidal space - the extracardiac fibroadipose tissue wedge located between the atrial and ventricular musculatures at the crux of the heart. It courses through Koch's triangle in close proximity to the ostium of the coronary sinus (mean distance approximately 3.2 ± 1.3 mm) and the attachment of the septal cusp of the tricuspid valve. The artery has a mean length of approximately 22.6 mm and a mean diameter at its origin of approximately 1.4 mm (range 13.5 mm). It typically has no branches or only one branch.

Territory of Supply

The AV nodal branch provides blood supply to:

• The compact AV node and its inferior extensions

• The penetrating bundle of His

• Portions of the posterior interventricular septum

• The interatrial septum in the region of the crux

Histological studies have shown that the artery primarily supplies the proximal part of the AV conduction axis, as it most commonly exits at the level of the distal compact node.

Clinical Significance

Understanding the anatomy of this vessel is important in several clinical contexts:

• Radiofrequency ablation of the slow pathway region near Koch's triangle carries a risk of AV nodal artery injury, as the artery may run just beneath the endocardium (mean distance to endocardial surface approximately 3.5 ± 1.5 mm at the base of Koch's triangle).

• Cardiothoracic surgery, particularly mitral valve procedures and operations near the crux cordis, may place this artery at risk.

• Stenosis or occlusion of the AV nodal artery has been implicated in conduction abnormalities requiring permanent pacemaker implantation and has been associated with cases of sudden cardiac death.