Christopher A.B. Kowalewski

Two Independent Mapping Techniques Identify Rotational Activity Patterns at Sites of Local Termination during Persistent Atrial Fibrillation

The mechanisms for atrial fibrillation (AF) are unclear in part because diverse mapping techniques yield diverse maps, ranging from stable organized sources to highly disordered waves. We hypothesized that AF mechanisms may be clarified if mapping techniques were compared in the same patients, and referenced to a clinical endpoint. We compared two independent AF mapping techniques in patients in whom ablation terminated persistent AF before pulmonary vein isolation (PVI).

Clinical Implications of Ablation of Drivers for Atrial Fibrillation: A Systematic Review and Meta-Analysis

Background: The outcomes from pulmonary vein isolation (PVI) for atrial fibrillation (AF) are suboptimal, but the benefits of additional lesion sets remain unproven. Recent studies propose ablation of AF drivers improves outcomes over PVI, yet with conflicting reports in the literature. We undertook a systematic literature review and meta-analysis to determine outcomes from ablation of AF drivers in addition to PVI or as a stand-alone procedure. Methods: Database search was done using the terms atrial fibrillation and ablation or catheter ablation and driver or rotor or focal impulse or FIRM (Focal Impulse and Rotor Modulation). We pooled data using random effects model and assessed heterogeneity with I2 statistic. Results: Seventeen studies met inclusion criteria, in a cohort size of 3294 patients. Adding AF driver ablation to PVI reported freedom from AF of 72.5% (confidence interval [CI], 62.1%–81.8%; P<0.01) and from all arrhythmias of 57.8% (CI, 47.5%–67.7%; P<0.01). AF driver ablation when added to PVI or as stand-alone procedure compared with controls produced an odds ratio of 3.1 (CI, 1.3–7.7; P=0.02) for freedom from AF and an odds ratio of 1.8 (CI, 1.2–2.7; P<0.01) for freedom from all arrhythmias in 4 controlled studies. AF termination rate was 40.5% (CI, 30.6%–50.9%) and predicted favorable outcome from ablation(P<0.05). Conclusions: In controlled studies, the addition of AF driver ablation to PVI supports the possible benefit of a combined approach of AF driver ablation and PVI in improving single-procedure freedom from all arrhythmias. However, most studies are uncontrolled and are limited by substantial heterogeneity in outcomes. Large multicenter randomized trials are needed to precisely define the benefits of adding driver ablation to PVI.

Identification and Characterization of Sites Where Persistent Atrial Fibrillation Is Terminated by Localized Ablation

Background: The mechanisms by which persistent atrial fibrillation (AF) terminates via localized ablation are not well understood. To address the hypothesis that sites where localized ablation terminates persistent AF have characteristics identifiable with activation mapping during AF, we systematically examined activation patterns acquired only in cases of unequivocal termination by ablation. Methods and Results: We recruited 57 patients with persistent AF undergoing ablation, in whom localized ablation terminated AF to sinus rhythm or organized tachycardia. For each site, we performed an offline analysis of unprocessed unipolar electrograms collected during AF from multipolar basket catheters using the maximum –dV/dt assignment to construct isochronal activation maps for multiple cycles. Additional computational modeling and phase analysis were used to study mechanisms of map variability. At all sites of AF termination, localized repetitive activation patterns were observed. Partial rotational circuits were observed in 26 of 57 (46%) cases, focal patterns in 19 of 57 (33%), and complete rotational activity in 12 of 57 (21%) cases. In computer simulations, incomplete segments of partial rotations coincided with areas of slow conduction characterized by complex, multicomponent electrograms, and variations in assigning activation times at such sites substantially altered mapped mechanisms. Conclusions Local activation mapping at sites of termination of persistent AF showed repetitive patterns of rotational or focal activity. In computer simulations, complete rotational activation sequence was observed but was sensitive to assignment of activation timing particularly in segments of slow conduction. The observed phenomena of repetitive localized activation and the mechanism by which local ablation terminates putative AF drivers require further investigation.

Multicentre safety of adding Focal Impulse and Rotor Modulation (FIRM) to conventional ablation for atrial fibrillation

Aims Focal Impulse and Rotor Modulation (FIRM) uses 64-electrode basket catheters to identify atrial fibrillation (AF)-sustaining sites for ablation, with promising results in many studies. Accordingly, new basket designs are being tested by several groups. We set out to determine the procedural safety of adding basket mapping and map-guided ablation to conventional pulmonary vein isolation (PVI). Methods and results We collected 30 day procedural safety data in five US centres for consecutive patients undergoing FIRM plus PVI (FIRM-PVI) compared with contemporaneous controls undergoing PVI without FIRM. A total of 625 cases were included in this analysis: 325 FIRM-PVI and 300 PVI-controls. FIRM-PVI patients were more likely than PVI-controls to be male (83% vs. 66%, P < 0.001) and have long-standing persistent AF (26% vs. 13%, P < 0.001) reflecting patients referred for FIRM. Total ablation time was greater for FIRM-PVI (62 ± 22 min) vs. PVI-controls (52 ± 18 min, P = 0.03). The complication rate for FIRM-PVI procedures (4.3%) was similar to controls (4.0%, P = 1) for both major and minor complications; no deaths were reported. The rate of complications potentially attributable to the basket catheter was small and did not differ between basket types (Constellation 2.8% vs. FIRMap 1.8%, P = 0.7) or between cases in which basket catheters were and were not used (P = 0.5). Complication rates did not differ between centres (P = 0.6). Conclusions Procedural complications from the use of the basket catheters for AF mapping are low, and thus procedural safety appears similar between FIRM-PVI and PVI-controls in a large multicentre cohort. Future studies are required to determine the optimal approach to maximize the efficacy of FIRM-guided ablation.

Independent mapping methods reveal rotational activation near pulmonary veins where atrial fibrillation terminates before pulmonary vein isolation

To investigate mechanisms by which atrial fibrillation (AF) may terminate during ablation near the pulmonary veins before the veins are isolated (PVI).

Interaction of Localized Drivers and Disorganized Activation in Persistent Atrial Fibrillation: Reconciling Putative Mechanisms Using Multiple Mapping Techniques

Background: Mechanisms for persistent atrial fibrillation (AF) are unclear. We hypothesized that putative AF drivers and disorganized zones may interact dynamically over short time scales. We studied this interaction over prolonged durations, focusing on regions where ablation terminates persistent AF using 2 mapping methods. Methods: We recruited 55 patients with persistent AF in whom ablation terminated AF prior to pulmonary vein isolation from a multicenter registry. AF was mapped globally using electrograms for 360±45 cycles using (1) a published phase method and (2) a commercial activation/phase method. Results: Patients were 62.2±9.7 years, 76% male. Sites of AF termination showed rotational/focal patterns by methods 1 and 2 (51/55 vs 55/55; P=0.13) in spatially conserved regions, yet fluctuated over time. Time points with no AF driver showed competing drivers elsewhere or disordered waves. Organized regions were detected for 61.6±23.9% and 70.6±20.6% of 1 minute per method (P=nonsignificant), confirmed by automatic phase tracking (P<0.05). To detect AF drivers with >90% sensitivity, 8 to 32 s of AF recordings were required depending on driver definition. Conclusions: Sites at which persistent AF terminated by ablation show organized activation that fluctuate over time, because of collision from concurrent organized zones or fibrillatory waves, yet recur in conserved spatial regions. Results were similar by 2 mapping methods. This network of competing mechanisms should be reconciled with existing disorganized or driver mechanisms for AF, to improve clinical mapping and ablation of persistent AF. Clinical Trial Registration: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02997254.

Mapping Ripples or Waves in Atrial Fibrillation

Mapping Ripples or Waves in Atrial Fibrillation? JUNAID A. B. ZAMAN, M.A., B.M.B.Ch., M.R.C.P.,∗,†,‡ CHRISTOPHER A. B. KOWALEWSKI,∗ and SANJIV M. NARAYAN, M.D., Ph.D.∗ From the ∗Department of Medicine/Division of Cardiology, Stanford University, Stanford; †The Heart Institute, Cedars-Sinai Medical Center, Beverly Hills, California, USA; and ‡National Heart Institute, Imperial College of Technology and Medicine, London, UK

Ablation of Focal Impulses and Rotational Sources: What Can Be Learned from Differing Procedural Outcomes?

IntroductionThere is considerable interest in identifying potential drivers for human atrial fibrillation (AF), in order to improve therapy. Ablation via pulmonary vein isolation (PVI) is broadly used, yet is insufficient in many patients yet its outcomes are unimproved by adding extensive ablation of lines or complex electrogram sites, particularly in patients with persistent AF.NoveltyRotational and focal sources for AF represent novel mechanistic and therapeutic targets, often remote from the PVs and proven to drive AF in many studies. This chapter discusses this issue.Aspects of Clinical RelevanceAF sources can now routinely be identified clinically by many methods, yet discrepant results have been reported. AF drivers identified by Focal Impulse and Rotor Mapping (FIRM), the most widely applied method, are also seen in simultaneous optical maps of human atria and have now been detected by other mapping methods applied to the exact same signals. In proof-of-concept studies, ablation of drivers can terminate persistent AF and, in over a thousand patients reported thus far, yield favorable long-term outcomes versus PVI alone. Nevertheless, some centers show disappointing results. This review focuses on discrepant results, which may reflect challenging patients, operator unfamiliarity with basket catheter use, or the technical ablation of drivers, amongst other factors. We discuss challenges, potential solutions, and future directions for map-guided AF driver ablation including basket-data collection, interpreting AF maps, ablation guidance, and extent.ConclusionsMapping and ablation of AF drivers is a rapidly growing field which, with continued scientific discovery and procedural advances, offers a strong mechanistic foundation to improve patient-tailored ablation for complex arrhythmias.