Stepwise catheter ablation of chronic atrial fibrillation:: Importance of discrete anatomic sites for termination

Background: Chronic atrial fibrillation (CAF) can be acutely terminated using a combination of approaches targeting thoracic veins, left atrial areas showing rapid/heterogeneous electrical activity, and by linear ablation. This observational study emphasizes the crucial role for conventional endocardial mapping to identify discrete anatomical sites, ablation of which is indispensable for the achievement of atrial fibrillation (AF) termination. Methods: Eighty consecutive patients with CAF underwent catheter ablation using the stepwise approach. Pulmonary vein isolation and roof-line ablation were performed as the initial two steps in all patients. In the presence of locally rapid or heterogeneous activity, ablation was then performed at all sites within the left atrium and coronary sinus (CS) region with the endpoint of local organization or slowing. If AF persisted, the mitral isthmus was targeted. Patients in whom AF terminated during one of these five ablation steps were differentiated from those in whom AF was terminated by radiofrequency ablation at a single discrete anatomic site within 1 minute. Electrograms at discrete anatomic sites of termination were classified according to morphology. Results: Termination of AF was achieved in 69 (86%) patients by ablation alone. In 50 patients (72%), this occurred while following the predetermined ablation schema. In the remaining 19 patients (28%), ablation targeting a discrete site (preferentially located at the CS, the base of left atrial appendage, and the interatrial septum) terminated AF. Such sites were identified by (1) continuous electrical activity and fractionation and (2) bursts of short cycle activity (130-160 msec), centrifugal activation or local activation gradients, indicating sources perpetuating AF. Conclusion: In 28% of patients with termination of CAF, the final successful ablation site is anatomically discrete and displays electrophysiological characteristics that can be effectively identified by point and activation mapping. Failure to identify these sites may significantly reduce the likelihood of termination of CAF by catheter ablation.