Sinuatrial nodal branch of circumflex artery of heart

The sinuatrial (sinoatrial) nodal branch of the circumflex artery of the heart is a variant of the sinoatrial nodal artery (SANa) that arises from the left circumflex artery (LCx) rather than from the more common origin, the right coronary artery (RCA). Its primary function is to supply blood to the sinoatrial node (SAN), the heart's primary pacemaker, as well as surrounding atrial myocardium.

Origin and prevalence

The sinoatrial nodal artery most commonly originates from the proximal RCA (approximately 55-68% of cases), but in approximately 22-39% of individuals, it arises from the proximal to middle portion of the left circumflex artery. When originating from the LCx, it typically branches from the posterolateral segment, within the first 19-35 mm from the LCx origin. Dual supply from both the RCA and LCx is observed in roughly 4% of cases.

Course

When arising from the LCx, the artery courses posteriorly and superiorly across the left atrial wall, often traveling in the groove between the left superior pulmonary vein and the left atrial appendage. It then passes either anterior (precaval), posterior (retrocaval), or around (pericaval) the superior vena cava to reach the sinoatrial node at the junction of the SVC and right atrium. A notable variant is the S-shaped sinoatrial nodal artery, which is found in approximately 142-0% of cases and arises almost exclusively from the LCx. This variant follows a characteristic S-shaped course along the posterior left atrial wall.

Territory of supply

Beyond the sinoatrial node itself, this artery supplies variable portions of the atrial myocardium. In some cases particularly the large sinus node artery variants arising from the LCx it can supply the entire left atrium, a large part of the interatrial septum, portions of the right atrium, and even partially supply the atrioventricular node area.

Clinical significance

Knowledge of this artery's origin and course is critical during:

• Catheter ablation procedures involving the left atrium (e.g., for atrial fibrillation or atrial tachycardia), where radiofrequency energy delivery near the artery can cause thermal injury, vasospasm, or occlusion, leading to sinus node dysfunction.

• Mitral valve surgery using the septal approach and the Cox maze procedure, where the artery is at risk of iatrogenic injury.

• Coronary interventions on the LCx, where stenosis of the parent vessel can compromise sinus node perfusion and cause sinus node dysfunction.