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Classification of atrial fibrillation (Afib) would be better off using 24-hour episodes as a cutoff for defining Afib persistence after ablation, a study suggested.

People on continuous rhythm monitoring tended to experience less recurrence of any atrial tachyarrhythmia following ablation if their baseline Afib episodes had lasted less than 24 continuous hours as opposed to 24-48 hours (HR 0.41, 95% CI 0.21-0.80), 2-7 days (HR 0.25, 95% CI 0.14-0.45), or more than 7 days (HR 0.23, 95% CI 0.09-0.55).

Such short preablation episodes were also linked to a 0% median postablation Afib burden that was significantly lower than what was seen with episodes lasting 2-7 days (0.1%, P=0.003) and more than 7 days (1.0%, P=0.008), according to researchers led by Jason Andrade, MD, of the University of British Columbia in Vancouver.

The study, published online in , showed no significant difference in arrhythmia recurrence or Afib burden among people with baseline Afib episodes lasting 24-48 hours, 2-7 days, or more than 7 days.

"Historically, paroxysmal Afib has been pragmatically but arbitrarily defined as 'attacks of arrhythmia lasting from 2 minutes to 7 days.' However, more recent evidence suggests that this classification may not reflect the pathophysiologic process underlying Afib or the complications associated with Afib," Andrade and co-authors wrote.

"Important changes in Afib-related electrical and structural remodeling occur during periods as short as 24 hours, achieving a steady state as early as 48 hours after the onset of an Afib episode," they continued.

Ultimately, the guidelines of Afib classification may not reflect clinical outcomes, the researchers said. "Given the significantly better postablation outcomes among the subset of patients with Afib episodes limited to less than 24 continuous hours, consideration should be given to 24 hours of continuous Afib as a threshold for defining ."

The study was a secondary analysis of the from Canada. Included were 346 adults with symptomatic Afib (mean age 59, 67.7% of whom were men) referred for first catheter ablation in 2014-2017.

Participants received an implantable cardiac monitor at least 30 days before ablation and were followed for a year after the procedure.

Preablation Afib episodes were most commonly less than 24 hours (76.0%), with some patients showing longer episodes of 24-48 hours (7.2%), 2-7 days (11.7%), and more than 7 days (5.2%).

Residual confounding is a possible limitation of the analysis, the investigators acknowledged, adding that most study participants were on antiarrhythmic drugs during the preablation monitoring period, which may have influenced the duration of episodes.

"Furthermore, while the relative differences in postablation Afib burden were significant, the differences in absolute postablation were small," the researchers wrote. "As such, the clinical effect is uncertain given that most cases had a low burden of Afib after ablation."

"These observations are consistent with the idea that intervention early in the natural history of Afib, before the onset of the progressive pathophysiologic and anatomic changes associated with the arrhythmia, may improve clinical outcomes," the team said.

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