The Physiological Effects of Pacing on Catheter Ablation Procedures to Treat Atrial Fibrillation

Patients will be randomized and proceed to one of two study arms:

1. Pacing during first half of lesions: During each of the 15 pre-specified lesions, pacing
will be initiated at a 500ms cycle length from a catheter in the coronary sinus or right
ventricle prior to the start of the lesion. Pacing will be stopped at the halfway point
(e.g. after 10 seconds for a 20-second lesion and after 15 seconds for a 30-second
lesion). In the event that Wenckebach behavior is noted, pacing will be adjusted to a
550ms cycle length. In the event that Wenckebach behavior persists, the cycle length
will be adjusted to 600ms. In the event that Weckebach behavior continues, the pacing
catheter will be moved to the right ventricle, which and pacing will be performed at a
500ms cycle length. If Wenckebach behavior still persists, the patient will be withdrawn
from the study.

2. Pacing during second half of lesions: During each of the 15 pre-specified lesions,
pacing will be stopped at the halfway point (e.g. after 10 seconds for a 20-second
lesion and after 15 seconds for a 30-second lesion). In the event that Wenckebach
behavior is noted, pacing will be adjusted to a 550ms cycle length. In the event that
Wenckebach behavior persists, the cycle length will be adjusted to 600ms. In the event
that Wenckebach behavior persists, the pacing catheter will be moved to the right
ventricle and pacing will be performed at a 500ms cycle length. If Wenckebach behavior
still persists, the patient will be withdrawn from the study.

Inclusion Criteria:

- Patients with AF scheduled for AF ablation with planned pulmonary vein isolation

- Presenting in normal sinus rhythm (NSR) prior to lesion delivery

Exclusion Criteria:

- Previous radiofrequency ablation

- Previous thoracotomy-type AF ablation (MAZE or similar technique)

- In AF prior to lesion delivery

- Evidence of left atrial scarring on voltage map

- Resting heart rate > 90 bpm