BOSTON – The standard definition of an episode of atrial fibrillation is a fibrillation event that lasts at least 30 seconds, but a new analysis of monitoring data collected from 615 patients showed that this threshold can label many patients as having atrial fibrillation despite an extremely low disease burden.
A more clinically relevant definition of atrial fibrillation (AF) might be a patient with at least one episode that persists for at least 3.8 hours, because this threshold identified people with a median AF burden of just under 10%,, said while presenting a at the annual scientific sessions of the Heart Rhythm Society.
The 30-second threshold for defining an AF episode dates from the early days of atrial ablation treatment, when researchers tracked ablated patients for signs of AF recurrence. But this definition that clinicians devised for a very select subgroup of AF patients subsequently “metastasized” to define AF in all settings, he noted. As one recent example, the 2017 consensus document on screening for AF in asymptomatic people defined asymptomatic patients as having AF if they had at least one 30-second event picked up on an ECG recording (EP Europace. 2017 Oct 1;).
“How we define AF is very important as we look for it in asymptomatic people,” Dr. Steinberg said in an interview.
A better definition of AF might depend on total AF burden, which is the percentage of time the patient’s atrium spends fibrillating. But it’s impossible to directly measure AF burden over a reasonably representative period of time without having an implanted device. If AF is monitored with an external device, the sampling time will be relatively brief, and so the AF assessment needs to rely on a surrogate for AF burden: the longest duration of any measured AF episode.
“No prior AF database has been analyzed like we have,” to correlate AF burden with the duration of the longest AF episode, Dr. Steinberg said.