Atrial branches of circumflex artery of heart

The atrial branches of the left circumflex artery (LCx) are a group of small to medium-sized arterial vessels that arise from the LCx as it courses through the left atrioventricular (coronary) groove between the left atrium and the left ventricle. These branches ascend to supply the walls of the left atrium and, in some cases, portions of the right atrium and the interatrial septum.

Origin and course

The left circumflex artery originates from the left main coronary artery and travels posteriorly in the atrioventricular groove. Along its course, it gives off several atrial branches that supply the overlying atrial myocardium. The most clinically significant of these atrial branches include:

• Sinus node artery (sinoatrial nodal artery): In approximately 27-42% of individuals, the sinus node artery arises from the proximal left circumflex artery rather than from the right coronary artery. When originating from the LCx, it may follow a characteristic S-shaped course around the neck of the left atrial appendage before reaching the sinoatrial node region. This S-shaped variant was identified in about 18% of left-origin sinoatrial nodal arteries in imaging studies.

• Left atrial circumflex artery (left atrial branch): A branch that courses over the left atrial wall, supplying the posterior and lateral aspects of the left atrium. This vessel has been described as a recognized branch of the circumflex artery territory.

• Kugel's artery (arteria anastomotica auricularis magna): An anastomotic atrial artery that can originate from the circumflex artery and provides a collateral pathway between the anterior and posterior atrial circulations, potentially reaching the atrioventricular node area.

• Left atrioventricular artery: In left-dominant or co-dominant circulations, the distal continuation of the LCx in the posterior atrioventricular groove is termed the left atrioventricular artery, which gives off branches to the adjacent atrial tissue.

Vascular territory and clinical significance

The atrial branches of the circumflex artery supply the left atrial free wall, portions of the interatrial septum, the region around the pulmonary vein ostia, the mitral isthmus, and the left atrial roof. Anatomical studies of 24 heart specimens demonstrated that major atrial arteries (≥1 mm in external diameter) were found in the mitral isthmus in 54% of cases, at the left atrial roof in 54%, and at the left atrial anterior wall in 29%. Around the pulmonary vein ostia, major arteries were present in up to 37% of specimens at the roof and inferior segments.

These vessels are of particular clinical importance in the context of catheter ablation for atrial fibrillation, as their proximity to ablation target sites (pulmonary vein ostia, mitral isthmus, left atrial roof) may impede the creation of transmural lesions, interfere with electrical isolation, or lead to ischemic injury of the sinus node or atrial myocardium. Additionally, the atrial branches are relevant in coronary angiography for identifying the dominance pattern of the coronary circulation and in surgical planning.

Variability

The atrial arterial supply is highly variable. In a study of 60 human hearts, the atria were supplied by the right sinoatrial artery alone in 40%, the left sinoatrial artery alone in 30%, and by both in 30%. The region of the coronary sinus received direct branches from the right coronary artery trunk in 41%, the left coronary artery in 11%, and from both in 48%. Many small atrial vessels are inconsistent and defy strict classification.