Role of Rotors in the Ablative Therapy of Persistent Atrial Fibrillation

Abstract

Catheter ablation is more effective than pharmacological therapy for the secondary prevention of patients with paroxysmal 1,2 and persistent 3,4 atrial fibrillation (AF) and has an emerging role in the primary prevention of paroxysmal AF. 5,6 Nevertheless, in randomised clinical trials (RCTs) its success in treating patients with paroxysmal AF is 40-60 % for a single procedure and 70 % for multiple procedures at one year, 1,2 and results for persistent AF are lower. 7,8 Thus, there is an urgent unmet need to improve our understanding of mechanistic targets for AF in each patient, to match recent advances in ablation energy delivery and catheter positioning.This report reviews mechanistic data on human AF, mapping technologies that provide the opportunity to reconcile fundamental mechanisms in individual patients and their therapeutic application. Atrial Fibrillation MechanismsAF is initiated by triggers predominantly near the pulmonary veins (PV), 9 with increasingly recognised sites outside the PVs. [10][11][12] To improve success, ablation to eliminate AF triggers should thus also target non-PV triggers, although they are transient and difficult to locate. Another potential ablative target is the mechanistic cascade by which triggers initiate AF, yet this is relatively unstudied. We recently showed -using wide-area mapping during spont aneous and induced AF -that the first cycles of AF after a trigger exhibit a single organised re-entrant spiral wave or focal driver (see Figure 1) that subsequently disorganises. 13 Remarkably, these AF-initiating mechanisms may be relatively spatially fixed for each patient -even for different triggers from both atria -separated by 2.1 ± 1.7 cm from trigger sites (see Figure 1). 13 Thus, AF initiation is likely to be a two-step mechanistic process, in which 1) a trigger initiates an organised spiral wave or focal source at patient-specific anatomical sites that 2) lead rapidly to disorganisation to produce the classical AF phenotype. This begs the question of whether AF maintenance is driven by self-sustaining disorganisation, or whether disorganisation is actually sustained by localised AF drivers (rotors or focal drivers).Self-sustaining disorganisation was traditionally considered the mechanism of AF maintenance. This mechanism is supported by computational models in which multiple wavelets sustain AF if there is enough room in the atrium ('critical mass'), 14 proposals that dissociation between the epicardium and endocardium may be contributory 15 and plaque recordings from the atria of patients in the operating room showing re-entry without apparent organisation. Limitations to these studies are that fibrillatory maps are based upon recordings that poorly represent local activation;16 only small areas of the atria were mapped (<10-20 %) and while these studies show that disorganisation exists they did not test if it self-sustains. The success of widespread ablation or Maze surgery supports the concept of self-sustaining disorganisation, but are also consistent with coinci...

Type and rate of atrial fibrillation termination due to rotational activity ablation combined with pulmonary vein isolation

“…Second, the time period that fibrillatory conduction can sustain AF without driver is still questionable. It may last from seconds to hours . It is still unclear how localized ablation effects on RoAc and what mechanisms lead to the termination of AF.…”

“…In the present study, NavX (St. Jude Medical, St Paul, MN, USA) 3‐D electroanatomic mapping system was used. RoAc was defined as sustained clockwise or counterclockwise activation around a core, or a centrifugal activation from an origin, which were located on the basis of their electrode coordinates . The basket coverage was confirmed in all cases by fluoroscopy and/or ICE, electrograms quality checking and basket visualization on the 3‐D mapping system.…”

“…The power setting was <25 W for the posterior atrial wall and 40 W for the rest of atria, the temperature limit was set to 43 C o . In FIRM‐guided ablation the RF applications were applied directly to center of the RoAc bounded by ≈2 electrodes distance in each axis for around 300 seconds in each side . AF terminated rigorous attempts were used in all patients to re‐induce AF using pacing maneuvers protocol for AF initiation.…”

In silico Comparison of Left Atrial Ablation Techniques That Target the Anatomical, Structural, and Electrical Substrates of Atrial Fibrillation

“…This suggests that not all possible PS hotspots are identified during a single AF episode, motivating the methodology of Boyle et al (2019) that identifies different driver locations through different AF initiation protocols. Narayan et al (2012) demonstrated high success rates by ablating focal and re-entrant drivers identified through phase and activation mapping of basket catheter data (Schricker and Zaman, 2015). Ensuring the correct classification of phase singularities is critical for targeting ablations because wavefront break up does not represent an equal target to a stable rotor.…”