The following are key points to remember about atrial fibrillation (AF) burden, and how it may be associated with clinical outcomes:

1. Current guidelines define presence of AF as electrocardiographic documentation of absolutely irregular RR intervals and no discernible, distinct P waves lasting for at least 30 seconds. There are many ways one can define AF burden, such as the duration of the longest AF episode, number of AF episodes, or the percentage of time a patient is in AF during a certain monitoring period.
2. Most published studies evaluated AF in a binary fashion (present or absent) and have not investigated AF burden.
3. Current guidelines recommend using vascular risk factors (as measured by the CHA₂DS₂-VASc score) and do not consider AF burden when making decisions regarding anticoagulation for stroke prevention in AF. While data are mixed, the strongest contemporary evidence suggests that patients with persistent AF are at higher risk of stroke than those with paroxysmal AF.
4. AF burden may be assessed in patients who have an implanted dual-chamber cardiac implantable electronic device (CIED)–pacemaker or implantable defibrillator–cardioverter (ICD). Implantable loop recorders and single-chamber ICDs rely on R-R intervals for arrhythmia detection, and have lower sensitivity and specificity for AF identification than dual-chamber CIEDs.
5. Data from CIEDs suggest that even relatively short AF episodes (>5 to 6 minutes) are associated with increased risk of stroke. Interestingly, among patients with CIEDs, the majority of ischemic strokes are temporally discordant from AF episodes. It is unknown whether there is a threshold of AF burden that results in an increased risk of stroke.
6. AF is also associated with nonstroke outcomes such as heart failure, cognitive impairment and dementia, myocardial infarction, chronic kidney disease progression to end-stage renal disease, sudden cardiac death, and all-cause death.
7. Physical inactivity, obesity, and hypertension have all been linked to increased incidence of AF; however, the degree to which atherosclerotic and lifestyle factors contribute to AF burden is not well established.
8. Weight loss and maintaining a healthy weight are effective in reducing AF burden. Published data regarding whether intensive blood pressure lowering would reduce AF burden are lacking. Randomized clinical trials are needed to determine whether interventions to manage stress (e.g., yoga, mindfulness, meditation) would reduce AF burden.
9. The concept of temporal AF burden aggregation, or AF density, has been proposed. AF density is defined as the absolute cumulative deviation of the patient’s actual burden development from the hypothetical uniform burden development divided by the minimum time required for development of all AF episodes. Given the same AF burden, a patient with a small number of prolonged episodes of AF has a higher AF density than a patient with many brief episodes of AF.
10. Developments in monitoring technologies will likely allow for better definition of the significance of changes in AF burden over time.

Keywords: Anticoagulants, Arrhythmias, Cardiac, Atrial Fibrillation, Blood Pressure, Brain Ischemia, Death, Sudden, Cardiac, Defibrillators, Implantable, Dementia, Electrocardiography, Heart Failure, Hypertension, Kidney Failure, Chronic, Life Style, Meditation, Mindfulness, Myocardial Infarction, Obesity, Pacemaker, Artificial, Primary Prevention, Renal Insufficiency, Chronic, Risk Factors, Stroke, Vascular Diseases, Weight Loss, Yoga

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