title: Defibrillation threshold varies during different stages of ventricular fibrillation in canine hearts.
abstract: BACKGROUND
  Recent studies have shown that short duration ventricular fibrillation (SDVF) and long duration ventricular fibrillation (LDVF) are maintained by different mechanisms. The objective of this study is to evaluate how the defibrillation threshold (DFT) varies over the duration of fibrillation since the mechanism of VF maintenance changes as VF progresses.
  
  
  METHODS
  Twelve canines were randomly divided into two groups (Group A and B, n=6 each). DFTs were measured three times in each group: SDVF (20s), LDVF (3min in Group A and 7min in Group B) and the first episode of refibrillation after successful defibrillation for LDVF. Two 64-electrode baskets used to globally map the endocardium were deployed into the left ventricle and right ventricle, respectively.
  
  
  RESULTS
  LDVF-DFT in Group A was significantly higher than that of Group B (628±98V vs 313±81V, P<0.001). In Group B, the DFT of refibrillation was significantly increased compared with the LDVF-DFT (570±199V vs 313±81V, P=0.035) but did not differ from the DFT of refibrillation in Group A (570±199V vs 638±116V, P=0.39). Highly synchronised activation patterns on the left ventricular endocardium were observed between 3 and 7min of LDVF in Group B but not within 3min-LDVF in Group A or during refibrillation in each group.
  
  
  CONCLUSIONS
  DFT varied during different stages of VF. The highly synchronised activation patterns exhibiting after 3min VF might contribute to the decreased LDVF-DFT.
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Jin
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China.
authors.forename: Changjian
authors.initials: C
authors.lastname: Lin
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Pang
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China.
authors.forename: Yangxun
authors.initials: Y
authors.lastname: Xin
authors.affiliation: Department of Cardiology, Shanghai Luwan Hospital, Shanghai, PR China.
authors.forename: Jiajun
authors.initials: J
authors.lastname: Pan
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China.
authors.forename: Gang
authors.initials: G
authors.lastname: Gu
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China. Electronic address: rjshenweifeng@yahoo.com.cn.
authors.forename: Weifeng
authors.initials: W
authors.lastname: Shen
authors.affiliation: Department of Cardiology, Shanghai Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai, PR China. Electronic address: wuliqun89@yahoo.com.cn.
authors.forename: Liqun
authors.initials: L
authors.lastname: Wu
mesh_terms: D000818:Animals; D004285:Dogs; D004554:Electric Countershock; D004699:Endocardium / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D011897:Random Allocation; D012008:Recurrence; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000503:physiopathology* / Q000628:therapy*