How common is fainting in atrial fibrillation?

Atrial fibrillation creates an irregular, sometimes fast heartbeat. During an episode, the heart may not fill and pump efficiently, so the brain can briefly receive less blood. Light-headedness, palpitations, breathlessness, chest discomfort, or unusual tiredness may occur before or after a blackout. Fainting can also have causes unrelated to atrial fibrillation, so the event should not be self-diagnosed.

A clinician may ask what you were doing, whether you felt warning symptoms, how long recovery took, and whether anyone saw shaking or injury. An examination and heart-rhythm testing can help distinguish fainting from other events.

If you feel faint, lie down and raise your legs if possible. Do not drive, climb, or swim until a clinician has assessed the cause. Arrange prompt medical review, particularly if you have known atrial fibrillation, take heart medicines, or the episode happened during exertion. Record palpitations, medication changes, illness, fluid intake, and the circumstances around the event.

Call emergency services after fainting with chest pain, severe breathlessness, a sustained racing or irregular heartbeat, new weakness, trouble speaking, confusion, a serious injury, or failure to recover normally. Urgent help is also needed if the blackout occurred during exercise or while lying down. Until help arrives, keep the person safe from further injury and check that they are breathing normally.

Ask whether your rhythm, blood pressure, medicines, or another condition could explain the episode; whether you need an electrocardiogram or longer rhythm monitoring; and which symptoms should trigger emergency help.