Current Concepts of Anatomy, Electrophysiology, and Therapeutic Implications of the Interatrial Septum

The interatrial septum (IAS), a fibromuscular structure separating the right (RA) and left (LA) atrium, plays an important role in both intra- and interatrial conduction. Electropathological changes in the IAS such as discordant activation of the right and left septal layer and conduction disorders may facilitate intraseptal re-entry and promote development of atrial tachyarrhythmias such as atrial fibrillation (AF). Various experimental studies have emphasized the importance of the IAS in AF initiation and perpetuation. Moreover, a thicker IAS has been associated with atrial tachyarrhythmias and a lower success rate of catheter ablation. Therefore, it is assumed that the septal interatrial connections, which may be more pronounced in patients with a thicker IAS, may furnish an anatomic pathway for re-entry and may explain failure of catheter ablation therapy. However, the exact role of the IAS in the treatment of AF still remains an enigma. More profound understanding of the role of the IAS in the pathophysiology of AF and other atrial tachyarrhythmias is necessary to improve success of current therapeutic options and develop new treatment modalities. This review outlines the current knowledge on the relationship between anatomic and electrophysiological properties of the IAS and discusses its involvement in atrial tachyarrhythmias. [Display omitted] •Discordant activation of the right and left septal layer and conduction disorders at the IAS may facilitate intraseptal re-entry and promote development of atrial tachyarrhythmias.•The IAS is involved in different macro–re-entry atrial tachyarrhythmias and IAS ablation was effective in eliminating the atrial tachyarrhythmia.•Conduction disorders at the interatrial septum may result in interatrial block that is associated with development of atrial tachyarrhythmias including AF.•Various experimental studies have emphasized the importance of the IAS in AF initiation and perpetuation. Future mapping studies focusing on the IAS are required to determine its exact role in the treatment of AF.