Patients with atrial fibrillation (AF) episodes limited to less than 24 continuous hours had a significantly lower incidence of arrhythmia recurrence following AF ablation according to a study published in JAMA: Network Open. According to the study’s author Jason Andrade (Montreal Heart Institute, Université de Montréal, Montréal, Canada) and colleagues, the findings suggest that the contemporary definition of paroxysmal AF does not reflect post-AF ablation arrhythmia outcomes.
The findings came from a secondary analysis of the CIRCA-DOSE, multicentre, randomised trial which sought to assess the safety and efficacy of second-generation cryoablation versus contact-force irrigated radiofrequency catheter ablation. The current analysis sought to establish the association between the preablation AF episode duration and arrhythmia recurrence outcomes following AF ablation.
In their introduction to the paper, Andrade and colleagues note that current North American and European guidelines recommend that the clinical pattern of AF be classified based on episode duration and persistence, with AF defined as paroxysmal if episode duration is less than seven days and persistent if the episode is seven days or longer. “These clinically determined patterns of AF have been used to characterize the severity of disease, define patient populations in clinical trials, and form the basis of therapeutic recommendations,” they note. However, despite their central role in clinical practice, the study team writes, the historical derivation of these AF patterns was arbitrarily defined and thus may not reflect pathophysiologic processes or clinical outcomes.
The study team used data from the CIRCA-DOSE study, taken from eight Canadian centres between September 2014 and July 2017, which enrolled 346 patients older than 18 years with symptomatic AF refractory to at least 1 class I or class III antiarrhythmic drug referred for a first catheter ablation procedure. All patients underwent insertion of an implantable cardiac monitor (ICM) a minimum of 30 days before AF ablation. The ICM was used to determine arrhythmia recurrence as well as to accurately quantify AF episode duration and burden (defined as percentage of time in AF).
The study’s primary outcome was defined as time to first symptomatic or asymptomatic atrial tachyarrhythmia (AF, atrial flutter, or atrial tachycardia) documented by 12-lead electrocardiogram, 24-hour ambulatory Holter monitor, or ICM between 91 and 365 days after ablation or a repeated ablation procedure at any time. Post ablation AF burden—the proportion of the monitored interval that a patient was in AF—was a secondary outcome. Patients were stratified based on their longest AF episode duration detected on preablation ICM monitoring and split into groups that included: less than 24 hours, 24 to 48 hours, two to seven days, and more than seven days.
The patient cohort had a mean age of 59 years, 231 (67.7%) men, and 238 (68.8%) receiving antiarrhythmic drugs during the pre-ablation period. Continuous rhythm monitoring via ICM was performed for a median of 73.5 (50.0‒98.3) days before AF ablation. Andrade and colleagues write that patients with AF episodes limited to less than 24 continuous hours on pre-ablation monitoring were significantly more likely to be free from recurrent AF, atrial flutter and atrial tachycardia compared with those with longer AF episode durations (<24 hours: 159 [60.5%]; 24‒48 hours: 9 [36.0%]; 2‒7 days: 11 [27.5%]; >7 days: 5 [27.8%]; p<0.001).
In contrast, they find, there was no significant difference between groups with a baseline AF episode duration of greater than 24 hours. Multivariable analysis identified left atrial enlargement and baseline AF episode durations of longer than 24 continuous hours as independent factors associated with arrhythmia recurrence after ablation. Following ablation, the AF burden decreased significantly in all groups, with a similar magnitude of improvement between groups, however the AF burden remained significantly greater for those with baseline episode durations >48 hours.
Discussing the findings, Andrade and colleagues write that the study re-emphasises the “arbitrary nature of the present classification of AF”. They note: “While the current definitions of AF clearly have some meaning, they are not based on detailed analyses of pathophysiologic processes or on clinically relevant outcomes. In our study we found no significant difference in arrhythmia outcomes in patients with AF episodes limited to 24 to 48 hours and two to seven days compared with those lasting more than seven days. Given the significantly better postablation outcomes among the subset of patients with AF episodes limited to less than 24 continuous hours, consideration should be given to 24 hours of continuous AF as a threshold for defining AF persistence.”
However, the study team does note some limitations of the paper, including that it is a sub analysis of a prospective randomised clinical trial, and that groups were defined based on the longest AF episode duration observed on continuous monitoring before ablations. “While attempts were made to account for baseline differences,” they write, “it is possible that residual cofounders may have influenced the results.”