title: Ventricular pacing threshold after transthoracic external defibrillation with two different waveforms: an experimental study.
abstract: OBJECTIVE
  Although an increase in the ventricular pacing threshold (VPT) has been observed after administration of transthoracic shock for ventricular defibrillation, few studies have evaluated the phenomenon with respect to the defibrillation waveform energy. Therefore, this study examined the VPT behaviour after transthoracic shock with a monophasic or biphasic energy waveform.
  
  
  RESULTS
  Domestic Landrace male piglets implanted with a permanent pacemaker stimulation system were divided into three groups: no ventricular fibrillation (VF) induction and transthoracic shock with monophasic or biphasic energy (group I); VF induction, 1 min of observation without intervention, 2 min of external cardiac massage, and transthoracic shock with monophasic or biphasic energy (group II); and VF induction, 2 min of observation without intervention, 4 min of external cardiac massage, and transthoracic shock with monophasic or biphasic energy (group III). After external shock, the VPT was evaluated every minute for 10 min. A total of 143 experiments were performed. At the end of the observation period, groups I and II showed steady VPT values. Group III showed an increase in VPT with monophasic or biphasic external energy, with no difference between the external energy sources. The monophasic but not the biphasic waveform was associated with higher VPT values when the VF was longer.
  
  
  CONCLUSIONS
  Defibrillation does not have a significant impact on pacing threshold, but a longer VF period is related to a higher VPT after defibrillation with monophasic waveform.
authors.affiliation: Department of Cardiac Surgery, Faculty of Medical Science,  State University of Campinas-UNICAMP, Campinas, SP,  Brazil.
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Assumpção
authors.forename: Pedro Paulo Martins
authors.initials: PP
authors.lastname: de Oliveira
authors.forename: Karlos Alexandre de Souza
authors.initials: KA
authors.lastname: Vilarinho
authors.forename: Pirooz
authors.initials: P
authors.lastname: Eghtesady
authors.forename: Lindemberg Mota
authors.initials: LM
authors.lastname: Silveira Filho
authors.forename: Carlos Fernando Ramos
authors.initials: CF
authors.lastname: Lavagnoli
authors.forename: Elaine Soraya Barbosa de Oliveira
authors.initials: ES
authors.lastname: Severino
authors.forename: Orlando
authors.initials: O
authors.lastname: Petrucci
mesh_terms: D000818:Animals; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004554:Electric Countershock / Q000379:methods*; D006321:Heart / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology*; D008297:Male; D023421:Models, Animal; D009200:Myocardial Contraction / Q000502:physiology*; D011897:Random Allocation; D034421:Sus scrofa; D014693:Ventricular Fibrillation / Q000503:physiopathology* / Q000628:therapy