Three-dimensional functional anatomy of the human sinoatrial node for epicardial and endocardial mapping and ablation

The sinoatrial node (SAN) is the primary pacemaker of the human fibrotic structure located at the junction of the superior vena cava intercaval region bordering the crista terminalis (CT). SAN activation originates in the intranodal pacemakers and is conducted to the atria through 1 or more discrete sinoatrial conduction pathways. The complexity of the 3D SAN pacemaker structure and intramural conduction are underappreciated during clinical multielectrode mapping and ablation procedures of SAN and atrial arrhythmias. In fact, defining and targeting SAN is extremely challenging because, even during sinus rhythm, surface-only multielectrode mapping may not define the leading pacemaker sites in intramural exit sites through sinoatrial conduction pathways. These SAN exit sites may be distributed up to 50 mm along the CT beyond the w20-mm-long anatomic SAN structure. Moreover, because SAN reentrant tachycardia beats may exit through the same sinoatrial conduction pathway as during sinus rhythm, many SAN arrhythmias are underdiagnosed. Misinterpretation of arrhythmia sources and/ or mechanisms (eg, enhanced automaticity, intranodal vs CT reentry) limits diagnosis and success of catheter ablation treat-ments for poorly understood SAN arrhythmias. The aim of this re-view is to provide a state-of-the-art overview of the 3D structure and function of the human SAN complex, mechanisms of SAN ar-rhythmias and available approaches for electrophysiological map-ping, 3D structural imaging, pharmacologic interventions, and ablation to improve diagnosis and mechanistic treatment of SAN and atrial arrhythmias.

Automated summary

This article introduces the anatomy, activation mechanism, and arrhythmias related to the sinoatrial node (SAN). The complex structure and conduction mechanism of the SAN pose challenges in clinical mapping and ablation procedures, and incorrect diagnosis and treatment may lead to poor outcomes. The aim of the article is to provide a state-of-the-art overview of the 3D structure, function, and treatment approaches of SAN and atrial arrhythmias to improve diagnosis and mechanistic treatment.