Thoracic veins and the mechanisms of non-paroxysmal atrial fibrillation

OBJECTIVE: The purpose of this article is to review the importance of thoracic veins in the maintenance of sustained (non-paroxysmal) atrial fibrillation (AF). METHODS: Thoracic veins, including the pulmonary veins (PVs), vein of Marshall (VOM) and the superior vena cava (SVC), have muscle sleeves that connect to the atria. It is well known that electrical activities can be recorded within these venous structures. In some incidences, these thoracic veins may serve as the trigger and/or the substrate for paroxysmal AF. The importance of thoracic veins in chronic (sustained) AF is less well appreciated. Therefore, we review the literature to determine if thoracic veins are important in the maintenance of sustained AF. RESULTS: Our recent study demonstrated that repetitive rapid electrical activities are present in the PVs and in the VOM during pacing-induced sustained AF in dogs. Because of these repetitive rapid activities, these thoracic veins have shorter activation cycle lengths than that of the left atrium, which, in turn, has shorter cycle lengths than that of the right atrium. Others have demonstrated that PV isolation in humans can result in a cure of sustained human AF in >80% of patients undergoing concomitant surgery. CONCLUSION: These findings suggest that repetitive rapid activities within the thoracic veins may be responsible for the maintenance of non-paroxysmal (sustained) AF.