Toward a More Clinically Useful Definition of Paroxysmal AF

Megan Brooks

July 16, 2020

Patients with episodes of atrial fibrillation (AF) lasting less than 24 hours are significantly more likely to be free from recurrent AF after catheter ablation than patients with preablation AF that lasts longer, new research suggests.

"What we have demonstrated in our analysis is that there is a clear threshold for ablation efficacy, whereby outcomes were better if the AF episodes were less than 24 hours compared to greater than 24 hours," JasonG. Andrade, MD, University of British Columbia, Vancouver, Canada, told theheart.org | Medscape Cardiology.

The findings, along with previous research, "suggest that there is something different about AF patients with paroxysmal episodes lasting less than 24 hours, relative to longer durations," said Andrade, who is lead author on the analysis, published July 2 in JAMA Network Open.

The results are also consistent with the view that the conventional definition of paroxysmal AF, "pragmatically but arbitrarily" said to be AF that lasts from 2 minutes to 7 days, the report notes, may not reflect the arrhythmia's pathophysiologic underpinnings in the most clinically useful way.

Perhaps a revision to the definition of paroxysmal AF is in order, the researchers propose.

The current study "supports the concept that ablating earlier in the course of AF progression is associated with better outcomes. Most clinicians who perform these procedures have long observed this in their own practices," Peter Noseworthy, MD, told theheart.org | Medscape Cardiology.

"Although there have been other studies that have also demonstrated this, it is good to see more definitive evidence emerge in the literature," added Noseworthy, from the Mayo Clinic, Rochester, Minnesota, who wasn't involved in the study.

Andrade and colleagues assessed the association between preablation duration AF episodes and time to arrhythmia recurrence after ablation in a prespecified secondary analysis of the Cryoballoon vs Irrigated Radiofrequency Catheter Ablation: Double Short vs Standard Exposure Duration (CIRCA-DOSE) study.

The trial, conducted at eight centers in Canada, entered 346 patients (mean age, 59 years), two-thirds of whom were men, with symptomatic AF refractory to medical therapy who had been referred for a first catheter ablation procedure. All patients received an implantable cardiac monitor at least 30 days prior to ablation and were stratified by duration of their longest AF episode during that month.

Overall, 263 patients (76.0%) experienced preablation AF episodes lasting less than 24 hours, 25 (7.2%) had AF episodes lasting 24 to 48 hours, 40 (11.7%) had episodes lasting 2 to 7 days, and 18 (5.2%) had episodes lasting for more than 7 days.

Recurrence of any atrial tachyarrhythmia after ablation was significantly lower in patients with baseline AF episodes less than 24 continuous hours than in those with longer AF episodes.

Patients with preablation AF lasting less than 24 hours showed about a 60% to 75% reduction in postablation risk for recurrence of any atrial tachyarrhythmia, in an unadjusted analysis, compared with patients with any of the three other AF-duration categories.

Such patients also had a significantly lower median postablation AF burden (0%) than those with AF preablation episodes lasting 2 to 7 days (0.1%; P = .003) and more than 7 days (1.0%; P = .008), the report notes.

There was no significant difference in arrhythmia recurrence rate or AF burden between the three groups with a preablation AF episode duration of longer than 24 hours.

Left atrial enlargement and baseline AF episode duration longer than 24 hours were significant predictors of postablation arrhythmia recurrence in multivariate analysis, with odds ratios of 1.92 (95% CI, 1.11 - 3.34) and 3.36 (95% CI, 1.79 - 6.53), respectively, report Andrade and colleagues.

"Given the significantly better post-ablation 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," they write.

"The current definitions of AF — paroxysmal (less than 7 days), persistent (greater than 7 days), and long-standing persistent (greater than 1 year) — have been used to characterize the severity of disease, define patient populations in clinical trials, and form the basis of therapeutic recommendations regarding pharmacological and invasive arrhythmia management," Andrade told theheart.org | Medscape Cardiology. "However, they are not based on clinically meaningful events."

But the current findings, he said, are "in agreement with antiarrhythmic drug studies that show greater restoration of sinus rhythm efficacy if cardioversion is performed for episodes of less than 24 hours, pacemaker studies that show greater stroke risk in patients with AF episodes lasting more than 24 hours, and cardioversion studies that demonstrate that the periprocedural risk of stroke is increased if cardioversion is performed for AF episodes more than 24 hours."

The results, therefore, mean there may be a "pathophysiological rationale" to revisit the definition of paroxysmal AF and consider shortening the maximum duration of its episodes from 7 days to 24 hours, Andrade proposed.

But Noseworthy said he's "not sure there is enough in this study to suggest we should redefine the term 'paroxysmal AF.'

Usually, "clinicians who take care of patients with AF are most concerned with stroke prevention, not ablation outcomes. We know that AF burden is associated with stroke risk, but we do not really know the cut point at which the risk really begins to increase," Noseworthy said.

"I think creating AF definitions around stroke risk would be most clinically useful, more so than framing atrial fibrillation definitions in terms of ablation efficacy."

The CIRCA-DOSE study was partially funded by Medtronic and Bristol-Myers Squibb. Andrade reports receiving grants and personal fees from Medtronic and personal fees from Biosense Webster; disclosures for the other authors are in the report. Noseworthy had no relevant disclosures.

JAMA Netw Open. 2020;3:e208748. Full text

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