OASIS, the first randomised, controlled, multicentre clinical trial to compare rotor-only ablation with two other ablation strategies in non-paroxysmal atrial fibrillation patients found “poor outcomes in terms of arrhythmia recurrence” with rotor-only ablation, for which enrolment on this treatment arm was terminated prematurely.
Results of the OASIS (Outcome of different ablation strategies in persistent and long-standing persistent atrial fibrillation) trial, presented by Andrea Natale (Texas Cardiac Arrhythmia Institute at St David’s Medical Center, Austin, USA) at HRS 2016, also found rotor ablation in combination with pulmonary vein antrum isolation (PVAI)—which was the second ablation strategy—to incur significantly longer procedure times at a lower rate of efficacy than PVAI with posterior wall and non-pulmonary vein trigger ablation (third strategy). The study was simultaneously published in the Journal of the American College of Cardiology (JACC).
Non-randomised studies have previously reported successful treatment of atrial fibrillation by Focal Impulse and Rotor Modulation (FIRM)-guided ablation. For example, data from the PRECISE (The precise rotor elimination without concomitant pulmonary vein isolation for subsequent elimination of paroxysmal atrial fibrillation) trial, presented by Sanjiv Narayan (Stanford Medicine, Stanford, USA) at HRS in 2013, demonstrated that targeted ablation of stable rotors and focal sources could eliminate paroxysmal atrial fibrillation without the need to isolate the pulmonary veins. This trial reported 82% single-procedure success with FIRM-only treatment in patients with paroxysmal atrial fibrillation. Another study (Multicenter validation of FIRM ablation for atrial fibrillation trial), presented by John Miller (Indiana University School of Medicine, Indianapolis, USA) at the 2013 American Heart Association Scientific Sessions, reported that focal sources with FIRM were localised in 100% of patients.
Noting such and other single-arm trials, Natale and colleagues aimed to investigate freedom from atrial tachycardia and atrial fibrillation after a blanking period following FIRM-only ablation in a randomised, controlled setting. “If rotors/focal sources are mechanisms that sustain atrial fibrillation, then it stands to reason that the ablation of these rotors should be associated with improved clinical outcomes,” the authors write in JACC. The trial’s secondary aim was to measure “acute procedural success, defined as atrial fibrillation termination or ≥10% slowing or organisation into atrial tachycardia.”
Natale reported that 113 non-paroxysmal patients were enrolled at three centres, and randomised 1:1:1 across three treatment groups. Twenty-nine were enrolled in group one, which received FIRM-only treatment. Forty-two participants were enrolled in each of groups two and three, and treated by FIRM plus PVAI and PVAI plus posterior wall plus non-pulmonary vein trigger ablation, respectively. Enrolment in group one was terminated early after the relatively high recurrence of atrial fibrillation “triggered an unplanned interim assessment by the internal safety committee.” The committee thus declared the FIRM-only arm to be futile, halting enrolment due to patient safety concerns, Natale noted.
Baseline characteristics of long-standing persistent atrial fibrillation (group one 31%, group two 29% and group three 31%), left atrium diameter (4.7±0.75, 4.84±0.74, 4.67±0.69) and left ventricle ejection fraction (54±10, 55.4±9.9, 55±10) were used to balance the groups. As in previous studies, focal drivers or rotors were found in all FIRM patients (mean 4±1.2 and 4.2±1.7 in groups one and two, respectively). Non-pulmonary vein triggers were detected in all group three participants.
Participants in groups one and two initially received ablation by FIRM mapping. “A 3D map of the atria was constructed using an electro-anatomic mapping system (CARTO, Biosense Webster or EnSite NavX, St Jude Medical) before advancing the 64-pole basket mapping catheter (FIRMap, Abbott) in the right and then left atria,” Natale explained. Unipolar electrograms recorded for one minute and exported to a dedicated proprietary mapping system (RhythmView, Abbott) were used for FIRM mapping during atrial fibrillation. A 3.5mm irrigated-tip ablation catheter was used to deliver radiofrequency energy with the aim of eliminating atrial fibrillation sources according to the mapping, excluding rotors and focal sources which did not lie in reproducible spatial regions. Persistence of atrial fibrillation was then treated by cardioversion. Following FIRM mapping, participants of group two were treated by PVAI.
Participants in group three underwent PVAI and electrical isolation of the left atrial posterior wall using a 3.5mm irrigated-tip catheter guided by a circular mapping catheter, intracardiac echocardiography (ICE) and a 3D mapping system. Radiofrequency energy was delivered with a maximum temperature setting of 42°C and a power of up to 45W.
Reporting on the results of the study, Natale said that average procedure time was notably longer in groups one and two (222±49, 233±48 minutes, respectively), compared with group three (131±51 minutes) and acute procedural success was achieved in only 12 (41%) of patients in the FIRM-only group, and 11 (26%) in group two.
Office visits, cardiology evaluation, 12-lead electrocardiogram and seven-day holter monitoring were performed at one, three, six and 12 months, while patient event-reporting was required three times a week, and at any occurrence of symptomatic arrhythmia in the first five months. Oral anticoagulants were discontinued at six months in patients who remained arrhythmia-free.
Differences in arrhythmia recurrence were stark between the three groups 12±7 months follow-up. Only four participants remained arrhythmia-free without antiarrhythmic drugs in group one (14%), with 22 (52.4%) remaining arrhythmia-free in group two. Group three reported the highest rate of freedom from recurrence by far at 76% (n=32). Noting the higher success in group two compared to group one, the authors write in JACC, “It is possible that ablation limited to only rotors is not sufficient to maintain sinus rhythm in non-paroxysmal atrial fibrillation.”
They continued, “Our results demonstrated the extensive approach of PVAI plus left atrial posterior wall plus ablation of non-pulmonary vein triggers to be the most effective ablation strategy in the non-paroxysmal atrial fibrillation population… Although more extensive ablation was performed in group three, it took less procedure and fluoroscopic time than the other two strategies while offering comparable safety and better efficacy.”
Considering the differences between this study and earlier studies of FIRM ablation, John D Day (Intermountain Heart Rhythm Specialists, Utah, USA) one of the chairs of the late-breaking session, said, “I think the main difference is that this was a multicentre, randomised study; we have not seen that before.” Speculating on other reasons for the drastically different results of this trial, he commented, “Based on what they have shown, either it does not work in the form that was studied, or they were not using or interpreting the technology right. I have done a number of cases using the FIRM mapping system and, when you look at it, there is a subjective component to interpreting what you see.”
Thomas F Deering (Piedmont Heart Hospital, Atlanta, USA), who co-moderated a press briefing, added, “We are determining more and more what the mechanisms [of atrial fibrillation] are, but I still feel we are in the early stages. We understand a little better what is going on but, especially in persistent patients, our success rates are less than what we would like them to be…I think we have got a lot of work ahead of us.”
When asked to comment on the future of rotor ablation, Day commented, “I believe that there exists a focal driver or rotors in some patients with persistent atrial fibrillation. There are a lot of bright people and a lot of innovative companies trying to solve this, but we are not there yet.”
Noting the high proportion of negative studies presented among this year’s HRS late-breaking clinical trials, Day said, “It just goes to show that atrial fibrillation is a lot more complex of a problem than we realise. Our understanding is not there yet.”