Inductors, initiators or triggers for atrial fibrillation are premature heart beats.  These heart beats also termed atrial extra-systoles or atrial premature contractions ("APCs") are the ignitors for an episode of atrial fibrillation.  Without these triggers, atrial fibrillation will not occur.

APCs in atrial fibrillation can occur from anywhere in the heart but most patients originate in the pulmonary veins.  If the cells causing these premature contractions in the heart can be found and either destroyed or isolated, then the patient will no longer have these triggers and will remain in normal sinus rhythm.

APCs inside an isolated pulmonary vein unable to initiate atrial fibrillation following a successful pulmonary vein isolation procedure

In the above illustration, electrical signals are being recorded from inside the left atria and specifically also inside a pulmonary vein after a pulmonary vein isolation procedure.  This patient was having multiple daily episodes of atrial fibrillation prior to this ablation.  As you can see, two closely spaced electrical signals are seen to fire and are recorded from the electrodes in the middle of the page.  These are atrial premature contractions ("APCs") from the left upper pulmonary vein.  Prior to the ablation procedure, every time these extra heart beats occurred, the patient would enter atrial fibrillation.  In this particular patient, we were able to isolate the pulmonary vein that was the trigger for this patients atrial fibrillation episodes.  A series of ablations was performed along the electrical junctions connecting the left atria to the pulmonary vein.  Following these ablations, premature beats originating in the vein cannot get into the atria with the atrial remaining in persistent normal sinus rhythm.  The top two ECG channels on this strip show normal sinus rhythm continuing despite the APCs which are now jailed in the offending pulmonary vein.  Following this patients atrial fibrillation ablation procedure the triggering pulmonary vein for atrial fibrillation is now a lot like Las Vegas; What happens in the pulmonary vein now stays in the pulmonary vein - while the happy and now cured patient stays in persistent normal sinus rhythm off of all previously ineffective medications.