Bradycardia is one of the triggers of atrial fibrillation.
  Vagal stimuli such as eating, sleeping, relaxation following stress or exercise and alcohol consumption have been reported as triggers of atrial fibrillation.
  This is called vagally-mediated atrial fibrillation. It is seen in 6 % of patients with paroxysmal atrial fibrillation.
  All cases of nocturnal atrial fibrillation are not due to vagal stimulation. Obstructive sleep apnea (OSA) may also cause nocturnal atrial fibrillation.
  Vagal stimulation shortens atrial effective refractory period. By this way, an atrial premature beat can initate atrial fibrillation.
  Beta blockers, verapamil or diltiazem does not benefit in vagal atrial fibrillation.
ECG 1. The ECG above belongs to a 54 years-old man with systemic arterial hypertension.
Coronary angiography did not show any significant coronary artery stenosis.
His only medication is Ramipril 2.5mg/day.
He is not taking any beta blocker, non-dihydropyridine calcium channel blocker or ivabradine.
His usual heart rate is below 50/minute.
This ECG shows an atrial premature beat initiating a short-lasting episode of atrial fibrillation during bradycardia (vagally-mediated atrial fibrillation).