New Insights into Atrial Fibrillation Ablation
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco does research for Medtronic, is a consultant for Medtronic, Novartis, and St. Jude, and is a speaker for Boston Scientific.
Source: Narayan SM, et al. Clinical mapping approach to diagnose electrical rotors and focal impulse sources for human atrial fibrillation. J Cardiovasc Electrophysiol 2012;23:447-454.
This interesting study examined a new technique for exploring the mechanism(s) for atrial fibrillation (AF). Patients scheduled for catheter ablation of paroxysmal or persistent AF were recruited for the study. Antiarrhythmic drugs were stopped before the study was performed. Multisite recordings of the left atrium and, in 20 patients the right atrium, were achieved using 64-pole basket electrode catheters. This catheter (Constellation, Boston Scientific) has eight electrodes on each of eight spines, which when deployed in the left atrium span the orifices of the thoracic veins and atrial appendage. Electrophysiologic data were obtained in stable AF and a proprietary, computational mapping algorithm was used to create patient specific three-dimensional spatiotemporal maps of AF. Movies of numerous AF activation cycles were created by analyzing AF electrograms in the context of tissue wavelength, refractory period, and conduction velocity. Movies were constructed by plotting electrogram voltage over time. Monophasic action potential recordings were also used to define action potential duration and restitution and regional conduction restitution in areas of slow conduction. These constitutional maps were then analyzed to examine sources of AF in the form of either focal impulse or rotor maps. Focal beats were identified as a single point of interest with uniform spread. Rotors were defined as rotational activity around a central point.
The study group included 19 patients with paroxysmal AF and 30 patients with persistent AF. Electrical rotors or focal beats were identified in 47 of 49 patients. The rotors identified showed 1:1 activation within a spiral with fibrillatory conduction to the remaining atrial tissue. Most patients had more than one rotor or focal source for AF. The number of sources per patient was 1.5 ± 0.8 in the paroxysmal AF patients and 2.1 ± 1 in the persistent AF patients. Left atrial sources were identified in all patients and right atrial sources were identified in six of eight paroxysmal AF patients and all 12 patients with persistent AF. Of all AF sources identified, 27% lay in the right atrium.
The authors conclude that left atrial or biatrial electrogram data obtained using multipole basket catheters and computational analysis allow electrical rotors and focal beat sources for human AF to be identified in almost all patients. They hypothesize that these mechanistic insights into human AF may provide a foundation for mechanistically targeted AF ablation procedures.
It is generally accepted that ectopic firing from the pulmonary veins is the most common trigger for AF and that pulmonary vein isolation should be the cornerstone of ablation procedures for AF. However, single procedure success rates with pulmonary vein isolation remain suboptimal for paroxysmal and, to an even greater degree, persistent AF. Even with the addition of linear left atrial lesions and mapping and ablation of regions with fractionated electrograms, ablation success is not assured. In this paper, Narayan et al describe a new approach that allows specific areas responsible for the maintenance of AF to be localized. The hope is that ablation directed at these regions, probably in conjunction with pulmonary vein isolation, will improve ablation success rates.
The details of the analysis algorithm are not provided here nor are the results of rotor or focal source targeted ablation presented. Clearly, this approach requires testing and confirmation in a number of laboratories. Such a clinical trial (NCT01248156) is currently underway. If the hypothesis that regions critical for maintaining AF can be successfully identified is confirmed, we may be on the threshold of a new frontier in AF ablation.