title: Signal-averaged P wave reflects change in atrial electrophysiological substrate afforded by verapamil following cardioversion from atrial fibrillation.
abstract: BACKGROUND
  Detailed analysis of signal-averaged P waves (SAPW) can provide insights into atrial electrophysiology. Abbreviated dosing of verapamil prior to cardioversion improves outcome at 1 week postcardioversion. The mechanism by which verapamil manifests benefit is uncertain. We hypothesized the SAPW would reflect any change in atrial electrophysiologic substrate afforded by verapamil when compared with controls.
  
  
  METHODS
  We investigated 23 patients attending external cardioversion of persistent atrial fibrillation (AF) (6 female; mean age 68 years). Patients were randomized to verapamil 240 mg daily in three divided doses 3 days before cardioversion and 1 week after, or usual medication. SAPW recordings were performed during sinus rhythm (SR) immediately after cardioversion, at 24 hours and 1 week.
  
  
  RESULTS
  The groups were comparable in terms of age, gender, left atrial size, and duration of AF. Eight of nine patients prescribed verapamil maintained SR at 1 week postcardioversion compared with 6 of 14 controls (P = 0.027). SAPW spectral analysis delivered higher energy for patients prescribed verapamil (median (IQ range)); 40.8 (33.4-95.1) versus 25.7 (19.0-38.0) for energy within 20-150 Hz, P20 (microV(2)x s; P = 0.03). There was no difference in P-wave duration (PWD) or root mean square of the terminal 30 ms between the two groups. Early reinitiation occurred in patients with significantly lower P-wave energy 19.6 (12.9-24.6) versus 39.9 (24.0-47.0) (P = 0.017).
  
  
  CONCLUSIONS
  Verapamil 240 mg daily for 3 days prior to cardioversion and 1 week after reduces early recurrence of AF. The SAPW observations indicate change in atrial electrophysiologic substrate might be responsible for benefit afforded by verapamil.
authors.affiliation: Arrhythmia Service, London Health Sciences Centre, University Campus, 339 Windermere Road, London, Ontario, Canada N6A 5A5. damianredfearn@yahoo.co.uk
authors.forename: Damian P
authors.initials: DP
authors.lastname: Redfearn
authors.forename: Allan C
authors.initials: AC
authors.lastname: Skanes
authors.forename: Joanne
authors.initials: J
authors.lastname: Lane
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Stafford
mesh_terms: D000368:Aged; D000889:Anti-Arrhythmia Agents / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000503:physiopathology* / Q000628:therapy*; D003131:Combined Modality Therapy; D004554:Electric Countershock; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006325:Heart Atria / Q000187:drug effects* / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D014700:Verapamil / Q000627:therapeutic use*
chemical_list: D000889:Anti-Arrhythmia Agents; D014700:Verapamil