Atrial Fibrillation: Mechanisms and Implications for Ablation

This abstract session featured presenters for studies that focused on the importance of atrial surface area and refractory period in sustaining atrial fibrillation (AF), mechanisms of CFAE formation in the posterior left atrium during induced AF, the left atrial ganlionated plexus, and complex fractionated atrial electrogramm versus liner ablation for persistent AF.

Importance of Atrial Surface Area and Refractory Period in Sustaining Atrial Fibrillation: Testing the Critical Mass Hypothesis in vivoAnson M. Lee, Abdulhameed Aziz, Kal L. Clark, Richard B. Schuessler, and Ralph J. Damiano Jr, Washington University, Saint Louis, MO

Lee explained that this research was conducted in order to "evaluate the effect of tissue area and effective refractory period (ERP) on the probability of sustaining AF," as no studies precisely define "the relationship between atrial surface area and AF in an in vivo model," despite the critical mass hypothesis for AF having been proposed nearly a century ago. Lee and colleagues found that increased tissue area and decreased ERP are associated significantly with sustained AF probability, a finding that Lee explained could "lead to a greater understanding of the mechanism of AF and help to design better interventional procedures."

Mechanisms of CFAE Formation in the Posterior Left Atrium During Induced Atrial Fibrillation in HumansDavid Calvo, Felipe Atienza, Jesus Almendral, Esteban G. Torrecilla, and Francisco Fernandez-Aviles, Hospital General Univrio Gregorio Maranon, Madrid, Spain; Jose Jalife, Jerome Kalifa, and Omer Berenfeld, Center for Arrhythmia Research, Ann Arbor, MI

On behalf of his colleagues, Calvo explained that the team sought to test their hypothesis that complex fractionated atrial electrogram (CFAE) "formation in the posterior left atrium (PLA) during AF is rate-dependent and secondary to fibrillatory conduction of waves emerging from drifting high-frequency sources (rotors)." As Calvo concluded, what they found was that during "induced AF, wavefront acceleration ahead of drifting rotors on the PLA results in intermittent formation of local CFAEs," and that CFAEs may also be the result of "fibrillatory conduction at the periphery of stationary or meandering rotors."

The Left Atrial Ganglionated Plexus - Its Function and Pathways Relative to Atrial Fibrillation SurgeryEmmanuel Moss, Yalin Yin, J. Andrew Armour, Rene Cardinal, and Pierre Page, Hopital Sacre Coeur de Montreal, Quebec, Canada

This research was conducted to "identify circuits responsible for the bradycardiac response to electrical stimulation of the left atrial ganglionated plexus (LAGP)" by performing "antegrade and retrograde sequential ablations of presumed autonomic pathways," said Moss, speaking on behalf of his fellow researchers. The speaker concluded that the data they collected "demonstrates that 1) the LAGP can be identified intraoperatively by the bradycardiac response to direct stimulation in most cases; 2) this response corresponds to neurophysiological repolarization effects on the atria;" and "3) LAGP-sinus node connections do not depend on a central extrathoracic vagal reflex but rather multiple epicardial and intracardiac pathways." Moss noted that these results "may have important clinical implications relating to ablative treatment of atrial fibrillation, particularly if the LAGP were shown to harbor neurons with arrythmogenic potential."

Complex Fractionated Atrial Electrogramm or Linear Ablation in Patients with Persistent Atrial Fibrillation? Results from a Prospective Randomized StudyHeidi L. Estner, Johns Hopkins University, Baltimore, MD; Stefanie Fichtner, Roman Biegler, Gabriele Hessling, and Isabel Deisenhofer, German Heart Center, Munich, Germany

Speaking for her German colleagues, Estner reviewed the key points to their study, which tested the hypothesis that ablation of complex fractionated atrial electrograms (CFAEs) "is not inferior to a linear ablation design." After randomly assigning 116 patients with persistent AF to CFAE ablation plus segmental pulmonary vein isolation (PVI; the spot group) or circumferential PVI plus additional lines (linear group), the team's simple finding was that spot "ablation is not inferior to a linear ablation approach in patients with persistent AF." More specifically, relapses among those in the linear group were from persistent AF most often, "suggesting that the substrate modification is more effective after CFAE ablation," explained Estner, adding that in a contradictory finding, "success after spot ablation was limited by atrial tachycardia during follow up, indicating remaining zones of slow conduction not sufficiently treated by CFAE ablation alone."