The Substrate and Intervention Mechanisms for Persistent Atrial Fibrillation Trial

Objectives The main objective of the study is to identify the optimal ablation strategy for suppression of persistent AF.

The secondary objectives of the study are:

• To define the local myocardial image characteristics of slow conduction AF substrates.
• To define the local myocardial structural changes post ablation that associate with AF suppression at 1-year follow-up
• To compare cardiac remodeling and atrial function at 1-year follow-up between PVI only and tailored catheter ablation groups

Background

Atrial fibrillation (AF) is associated with increased risk for mortality, heart failure, and thromboembolic events, and has a worldwide prevalence of >33.5 million. Catheter ablation of AF is evolving as an effective therapy for symptomatic AF. Recurrent AF after ablation, however, remains a problem and has been reported to associate with the baseline extent of left atrial (LA) late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR). Mechanistically, persistent AF appears to be more reliant upon fibroblast proliferation and myocyte-fibroblast coupling than paroxysmal AF, which is primarily dependent upon pulmonary vein triggers. Therefore, the investigators hypothesize that the substrate for persistent AF is detectable on atrial LGE-CMR and variable among patients, and that the substrate predicts patient outcomes after anatomic non-tailored ablation, and is more likely to respond to individually tailored ablation approaches. Two individually tailored approaches will be studied including empiric targeting of dense LGE, confirmed on bipolar mapping to have voltage <0.3 mV, and modeling based targeting of rotor anchor sites.

Study Design

Initially, the investigators propose prospective enrollment of 30 participants with persistent AF. Patients presenting to the institution who meet the inclusion criteria will be asked to participate in the study. All patients will undergo routine clinical care including echocardiography as indicated.

All patients will undergo a LGE-MRI within 30 days prior to the ablation procedure. The clinical purpose of the initial MRI is to define the anatomy of the heart chambers as well as the vessels for procedure planning. For research purposes, the investigators will use this initial clinical MRI to delineate atrial structural remodeling or fibrosis to be used during the procedure in patients randomized to group 2 (pulmonary vein isolation + scar-based ablation) and for later analysis in all patients.

Imaging is done at the institution and will be reviewed for quality by the study staff. LGE-MRI sequences that do not meet quality standards for fibrosis analysis will not be further processed and these patients will be excluded from the study. Subjects for whom images are successfully evaluated will be randomized to the study groups.

This will be followed by block randomization in 1:1:1 format to a) pulmonary vein isolation (PVI) only (current standard of care), b) PVI plus targeting of dense LGE sites, which are confirmed on bipolar mapping to have voltage <0.3 mV, and c) PVI plus targeting of rotor anchor sites predicted by modeling.

At baseline, all patients will be evaluated for their quality of life (QOL) using the Short-form health survey (SF-36) for overall as well as AF-related impact on quality of life. The severity of symptoms will also be tested using the European Heart Rhythm Association (EHRA) score of atrial fibrillation. Clinical data will be stored electronically and linked to a specific research number. Information linking de-identified data to the patients will be stored in the locked research office, in a password-protected file. Only members of the research team, in charge of collecting clinical information, will have access to this file. Individual subject binders containing signed consent forms and clinical source documentation will be labeled using study subject numbers and stored in the locked research office mentioned previously.

A pre-ablation cardiac MRI is clinically indicated to assess baseline cardiac anatomy prior to procedure. Routine and LGE protocols will be used to acquire MR images. All patients will be asked to undergo a repeat LGE-MRI 12 months after the ablation. This is done for research purposes. Renal function is routinely monitored prior to gadolinium-enhanced MRI as a standard of clinical care.

With regards to the ablation procedure, all patients will undergo AF ablation. The procedure consists of circumferential pulmonary vein lesions under electro-anatomical guidance using CARTO (Biosense Webster Inc., Diamond Bar, CA). Operators will use either a 3.5mm irrigated tip radiofrequency ablation catheter (ThermoCool Smart-Touch, Biosense Webster Inc., Diamond Bar, CA) or a cryoballoon catheter (Arctic Front Advance, Medtronic Inc., Minneapolis, MN). This procedure is FDA approved and will be conducted in all treatment arms according to standard of care. However, patients in the second group will undergo additional targeting of dense LGE sites, confirmed on bipolar mapping to have voltage <0.3 mV and patients in the third group will undergo targeting of rotor anchor sites as predicted by computational modeling. A detailed protocol of rotor ablation is described in the literature and shows no added complications compared to the conventional procedure.

To prevent short-term recurrence of AF, patients will be kept on anti-arrhythmic regimen for the first 1 to 3 months after the ablation to be discontinued thereafter in the absence of AF recurrence, at the discretion of the treating physician. In addition, standard protocols for anticoagulation prior to, during, and after the ablation procedure will be applied.

After the ablation, clinical follow-up visits are scheduled at 3, 6 and 12 months. Research follow-up questionnaires and 12-lead ECG recordings will be done at the same day of the visits. All patients will undergo rhythm monitoring to detect AF recurrence using a portable, smart phone operated, AliveCor® Mobile ECG device.This device will be provided to the patients at no cost after enrollment in the study.

After the procedure, follow-up will be done on a weekly basis through trans-telephonic transmissions of ECG recordings. Periodic reminders will be sent to patients (via telephone, email, or mail) regarding follow up transmissions in the event that a weekly transmission is missed. In addition, study participants will be advised to provide recordings if they experience heart-related symptoms (palpitations, shortness of breath, rapid heartbeat, chest pain). This extensive rhythm monitoring protocol is not standard of care and is done for research purposes. Review of the rhythm monitoring data will be performed in accordance with current clinical guidelines. The device software and the investigators will analyze rhythm strips and a report will be available to the research team and to the treating physician upon his/her request. In addition, upon detection of any arrhythmia with important clinical implications, the investigators will notify the electrophysiologist involved in the care of the patient. The research team may contact the patient directly if prompt action is advised, such as reporting to the local emergency room or following up with their electrophysiologist. The rhythm monitoring protocol utilized in this study may result in unscheduled visits to the physician. If a repeat ablation procedure is indicated, it will be scheduled according to standards of clinical care.

Study duration and visits.

The investigators aim to complete the proposed study protocol in two years. After the ablation, patients will be followed at 3, 6 and 12 months via in clinic visit; a 1 month and 9 month follow up will take place via remote ECG transmission. Follow-up research questionnaires and post-ablation MRI will be scheduled to coincide with the routine clinical visits. Hence, no additional visits will be required of research participants unless it was not possible to schedule the MRI on the same day as clinic visits. Only then will the investigators ask participants to present to the institution for the follow-up MRI.

Study Statistics

Based on the variable success rate of 40-80% in AF ablation, the investigators anticipate that the study cohort of 30 patients would produce adequate sample size in all treatment arms and be sufficient to make meaningful statistical comparison.

Comparison variables will be presented as means +/- standard deviation, and categorical variables as numbers and percentages. Differences between treatment groups will be assessed using the Pearson Chi-square test and the Wilcoxon rank-sum test. Survival curves for time to event analysis will be estimated using the Kaplan-Meier method, and the differences between the curves will be tested for significance with the log-rank statistic. Weekly event rates will be calculated by dividing the event rate by the maximum follow-up period in each arm of the Kaplan-Meier analysis. Hazard ratios will be calculated by univariate and multivariate analysis using the Cox proportional-hazards regression model. When comparing MR image characteristics as well as LA function between pre and post-ablation imaging, the Student's t-test will be using for comparison of the means. All statistical testing will be 2-tailed. Results will be considered statistically significant at a level of p<0.05.