Atrial Fibrillation Burden

AFib burden estimates how much of the monitored time showed signs of atrial fibrillation. It is a percentage over a reporting period, not beats per minute, an ECG tracing or a count of episodes. A heart-rate graph alone cannot establish AFib burden.

Apple’s HealthKit documentation describes a read-only discrete quantity generated after AFib History collects enough rhythm information. Third-party apps can request read access but cannot write new AFib burden samples.

Apple calculates the estimate weekly, with analysis normally beginning on Monday morning when the iPhone can complete it. This reporting cadence differs from the watch’s underlying periodic rhythm checks. A missing weekly estimate can reflect insufficient data or delayed analysis; it does not establish an AFib-free week.

Apple’s setup guidance requires a physician diagnosis of AFib, is intended for ages 22 and older, and calls for at least 12 hours of wear per day on five days a week for consistent estimates. Availability and supported devices depend on the feature and region.

HealthKit percent units represent a 0–1 ratio. PulsHealth preserves that raw quantity under the canonical % unit label: a raw value of 0.05 would display as 5%, after multiplying by 100. This is a unit example, not an observed AFib value in this study. Keep stored values unchanged and avoid applying the display conversion twice.

There is no universal “healthy AFib burden” bracket or treatment threshold for this Apple estimate. Do not infer persistent AFib, stroke risk or ablation success from an isolated percentage. Clinical assessment combines rhythm evidence and the patient’s wider situation.

The October 2025–September 2026 inventory found no AFib burden observations, aggregates or workout-series points, including the July–September focus. No measured percentage range, outlier, weekly-gap distribution or seasonal change can be reported here. The absence does not establish whether AFib History was enabled, whether the person was eligible or whether AFib occurred.

Apple Health offers comparisons with life factors, including exercise, sleep, weight, alcohol and mindfulness. These are observational comparisons. A multi-day burden record overlapping a workout or sleep interval does not tell you that AFib occurred during that interval.

With suitable data, compare verified reporting periods, available watch wear and source provenance before exploring weekly relationships. Do not sum percentages. Unequal or overlapping periods cannot be combined into monitored-time burden without an appropriate denominator. None of these relationships could be measured in this snapshot.

Sleep Analysis, Exercise Time and Body Mass provide context. ECG recordings answer a different, moment-specific rhythm question.

Apple Watch checks periodically and may miss episodes. AFib History does not provide a real-time alert for each episode or detect heart attacks or strokes. Share trends with the treating clinician and do not adjust medication based on the estimate alone. Symptoms needing urgent attention should not wait for a weekly report.