Ablation of atrial fibrillation.

Recognition that the initiation of atrial fibrillation often is dependent on arrhythmogenic foci within the pulmonary veins1 opened a new chapter in our understanding of the mechanisms of atrial fibrillation, which in turn has led to dramatic improvements in our ability to ablate atrial fibrillation. Based on experimental studies and clinical studies that used a variety of catheter and surgical ablation techniques, it is possible to postulate two major mechanisms for the initiation and perpetuation of atrial fibrillation. 1. Primary drivers. Some types of atrial fibrillation, particularly paroxysmal atrial fibrillation, may be primarily dependent on tachycardias that initiate and drive the atrial fibrillation.2 Although often located in the pulmonary veins, the drivers also may originate from within other thoracic veins,3 such as the superior vena cava, vein of Marshall, or coronary sinus, or within the left or right atrium. Furthermore, secondary tachycardias that also may function as drivers may develop in any of these arrhythmogenic sites, particularly the pulmonary veins,2 in response to the primary driver. Once the primary driver induces secondary drivers, the perpetuation of atrial fibrillation may become more likely because even if the primary driver is extinguished, the other drivers may still function. Elegant studies by Jalife4 demonstrated that rotors with a very short cycle length exist during atrial fibrillation and can play a critical role in the perpetuation of atrial fibrillation. It appears that these rotors may have anchor points within the left atrium, near the pulmonary veins. In another experimental model, atrial fibrillation was found to be caused by an atrial flutter with a very short cycle length that resulted in fibrillatory conduction throughout the atria.4 Based on this mechanism, successful ablation of atrial fibrillation requires elimination of the primary and secondary drivers with strategies such as pulmonary vein isolation, isolation of the coronary sinus from the left atrium, or elimination of the rotors. 2. Multiple wavelet reentry. As described by Moe,5 the multiple wavelet hypothesis proposes that a critical number