Atrial Fibrillation Burden Estimates Derived from Intermittent Rhythm Monitoring are Unreliable Estimates of the True Atrial Fibrillation Burden

Background: Estimates of atrial fibrillation (AF) burden (AFB) derived from intermittent rhythm monitoring (IRM) are increasingly being used as an outcome measure after therapeutic interventions; however, their accuracy has never been validated. The aim of this study was to compare IRM-derived AFB estimates to the true AFB as measured by implantable continuous monitoring (CM) devices. Methods: Rhythm histories from 647 patients (mean AFB: 12 +/- 22%; 687 patient years) with CM devices were analyzed. IRM of various frequencies and durations were simulated and the obtained IRM-derived AF burdens were compared to the true AFB measured by CM. Results: The relative error of the IRM burden estimates was dependent on the IRM length (P < 0.001), frequency of IRM (P < 0.001), the true AFB (P < 0.001), and its temporal aggregation (AF density, P < 0.001). In paroxysmal AF patients, the relative error even with aggressive IRM strategies was >80% of the true AFB. The relative error decreased with higher true AF burdens, lower AF densities, and higher IRM frequency or duration (P < 0.001). However, even in patients with high AF burdens and/or low AF densities, IRM estimates of AFB significantly deviated from the true AFB (relative error >20%, P < 0.001) and resulted in a substantial measurement error. Conclusion: IRM-derived AFB estimates are unreliable estimators of the true AFB. Particularly for paroxysmal AF patients, IRM-derived AFB estimates should not be used to evaluate outcomes after AF interventions.