title: Safety of atrial defibrillation shocks synchronized to narrow and wide QRS complexes during atrial pacing protocols simulating atrial fibrillation in dogs.
abstract: BACKGROUND
  The potential ventricular proarrhythmic effect of atrial defibrillation shocks (ADS) remains a concern with automatic internal atrial defibrillation. Optimal R-wave synchronization alone may not be sufficient to prevent the induction of ventricular fibrillation (VF).
  
  
  RESULTS
  The proarrhythmic effect of ADS synchronized to normally conducted QRS complexes (NQRS) and to supraventricular complexes with left or right bundle-branch block (L/RBBB) was investigated in a canine atrial pacing study. Short-long-short, single premature, and burst pacing protocols from the high right atrium were performed at baseline, during isoproterenol infusion, and after intravenous procainamide. The ADS were delivered between decapolar catheters in the coronary sinus and lateral right atrium. They were initially delivered 20 milliseconds (ms) after the end of the last conducted QRS complex and then scanned decrementally through that complex until VF was induced. For NQRS complexes, VF occurred only when the ADS were delivered at or before the onset of the QRS complex and never during the complex itself. In the presence of LBBB or RBBB, VF was induced by ADS delivered at the onset of or within the first 45 ms of the QRS complex in 16 animals. The longest RR (VV) intervals preceding ADS-induced VF were 345 ms at baseline and 380 ms after procainamide.
  
  
  CONCLUSIONS
  In this study, ADS synchronized to NQRS complexes appeared to be safe regardless of the preceding RR interval. In the presence of LBBB or RBBB, RR intervals preceding the ADS of >345 ms at baseline and >380 ms in the presence of procainamide would have been required to avoid VF. Alternatively, ADS delivered 50 ms after the onset of the RV electrogram appeared to be safe in all circumstances regardless of the preceding RR interval.
authors.affiliation: Electrophysiology Laboratories, University of Wisconsin Medical School-Milwaukee Clinical Campus, Sinai Samaritan and St Luke's Medical Centers, USA.
authors.forename: E T
authors.initials: ET
authors.lastname: Keelan
authors.forename: D
authors.initials: D
authors.lastname: Krum
authors.forename: J
authors.initials: J
authors.lastname: Hare
authors.forename: K
authors.initials: K
authors.lastname: Mughal
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Akhtar
authors.forename: M R
authors.initials: MR
authors.lastname: Jazayeri
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000175:diagnosis / Q000503:physiopathology*; D018880:Atrial Premature Complexes / Q000503:physiopathology; D002037:Bundle-Branch Block / Q000503:physiopathology; D004195:Disease Models, Animal; D004285:Dogs; D004554:Electric Countershock / Q000592:standards*; D004562:Electrocardiography; D006329:Heart Conduction System / Q000502:physiology*; D010138:Pacemaker, Artificial; D012449:Safety