Why does atrial fibrillation cause fainting?

Fainting, also called syncope, is a temporary loss of consciousness caused by reduced blood flow to the brain. In atrial fibrillation, the heart can beat irregularly and at times very quickly. If this disrupts effective pumping, you may feel warning symptoms such as nausea, sweating, dimming vision or lightheadedness before collapsing.

Fainting is a common presentation of Atrial Fibrillation. However, blackouts have several possible causes, including blood-pressure changes, dehydration, seizures and other heart-rhythm problems. A collapse should be assessed rather than assumed to be caused by a known rhythm condition.

If you feel close to fainting, lie down with your legs raised if you can do so safely, or sit with your head lowered. Do not drive or return to hazardous work afterwards until you have been assessed. Tell a clinician about what happened before the event, how long you were unconscious if known, any injury, and how you felt on waking.

Continue prescribed heart medicines unless a clinician tells you otherwise. A current medicine list and any available pulse readings can help the medical team understand the episode.

Call emergency services after a fainting episode, especially when there is chest pain, breathlessness, a sustained racing heartbeat, a head injury, pregnancy, weakness on one side, speech difficulty, confusion, or failure to recover promptly. Emergency assessment is also needed if another person is unconscious, not breathing normally or cannot be woken.

Ask what may have triggered the blackout, whether rhythm monitoring is appropriate, which medicines should be reviewed, and what activity restrictions apply while the cause is being clarified.