What Is AFib Burden, and Why Does It Matter?

Atrial fibrillation (AFib) is an irregular, often fast heart rhythm in which the upper chambers of the heart quiver instead of beating in step. Many people with it don’t have it all the time: it comes and goes. AFib burden is the share of time someone spends in AFib over a period, such as a week. For people already diagnosed, it turns “do I have AFib?” into “how much, and is it changing?”.

This article is general information, not medical advice. AFib burden is for people with a diagnosis, to discuss with their doctor.

Why Burden Matters

An American Heart Association scientific statement in 2018, led by Chen, argued that AFib should be thought of as a quantity rather than a yes-or-no diagnosis, since more time in AFib appears to carry more risk. The evidence is still developing:

• Stroke. In a study of 1,965 adults with intermittent AFib wearing a two-week monitor, Go and colleagues found a median burden of 4.4%. Those in the highest third, with a burden of 11.4% or more, had more than three times the rate of stroke and other clots in the following years, after accounting for their stroke risk scores, among people not taking blood thinners.
• Symptoms and heart function. Higher burden is linked to more symptoms and, over time, to weakening of the heart muscle in some people.

The 2023 ACC/AHA/ACCP/HRS guideline for AFib discusses burden too, but treatment decisions, such as whether to take a blood thinner, are still based mainly on a person’s stroke risk factors rather than on burden alone.

How a Watch Estimates It

Apple Watch’s AFib History, for people with an AFib diagnosis, periodically checks your pulse rhythm in the background with its optical sensor and gives a weekly estimate of the percentage of time it showed signs of AFib. Apple’s guidance notes:

• The watch must be worn at least 12 hours a day, 5 days a week, for estimates to be consistent.
• A week with little or none is shown as “2% or less”, never as 0%.
• Because it only checks periodically, it can miss episodes, and it won’t alert you during an episode.

A clinical monitor, such as a patch or an implanted loop recorder, records continuously and measures burden more completely.

How to Use It

• Follow the weekly trend, not a single week.
• Note what changed in the weeks when burden rose, such as alcohol, poor sleep, illness, or a change of medicine, to discuss with your doctor.
• Bring the history to appointments. A rising burden is worth raising with your doctor, and so are new or worse symptoms such as palpitations, breathlessness, dizziness, or tiredness.

Get emergency help for signs of a stroke (sudden face drooping, arm weakness, or difficulty speaking) or chest pain, whatever a watch shows.

Following It in Kaizora

Atrial Fibrillation Burden comes in with your Apple Health export, on the Vitals page, one value for each week it covers. On Correlations, putting it beside Dietary Alcohol or Total Sleep Time by week shows whether they move together. Your ECG recordings sit beside it on Vitals; see What Can a Smartwatch ECG Tell You?

The Short Version

• AFib burden is the share of time spent in AFib, for people diagnosed with it.
• Higher burden is linked to a higher risk of stroke, though treatment still depends mainly on other risk factors.
• A watch’s weekly estimate can miss episodes; follow the trend and share it with your doctor.

Sources

• Chen LY et al., “Atrial fibrillation burden: moving beyond atrial fibrillation as a binary entity: a scientific statement from the American Heart Association,” Circulation 137, no. 20 (2018). doi:10.1161/CIR.0000000000000568
• Go AS et al., “Association of burden of atrial fibrillation with risk of ischemic stroke in adults with paroxysmal atrial fibrillation: the KP-RHYTHM study,” JAMA Cardiology 3, no. 7 (2018): 601. doi:10.1001/jamacardio.2018.1176
• Joglar JA et al., “2023 ACC/AHA/ACCP/HRS guideline for the diagnosis and management of atrial fibrillation,” Circulation 149, no. 1 (2024). doi:10.1161/CIR.0000000000001193
• Apple, Track your AFib History with Apple Watch.