title: Superiority of biphasic over monophasic defibrillation shocks is attributable to less intracellular calcium transient heterogeneity.
abstract: OBJECTIVE
  The purpose of this study was to test the hypothesis that superiority of biphasic waveform (BW) over monophasic waveform (MW) defibrillation shocks is attributable to less intracellular calcium (Ca(i)) transient heterogeneity.
  
  
  BACKGROUND
  The mechanism by which BW shocks have a higher defibrillation efficacy than MW shocks remains unclear.
  
  
  METHODS
  We simultaneously mapped epicardial membrane potential (Vm) and Ca(i) during 6-ms MW and 3-ms/3-ms BW shocks in 19 Langendorff-perfused rabbit ventricles. After shock, the percentage of depolarized area was plotted over time. The maximum (peak) post-shock values (VmP and Ca(i)P, respectively) were used to measure heterogeneity. Higher VmP and Ca(i)P imply less heterogeneity.
  
  
  RESULTS
  The defibrillation thresholds for BW and MW shocks were 288 +/- 99 V and 399 +/- 155 V, respectively (p = 0.0005). Successful BW shocks had higher VmP (88 +/- 9%) and Ca(i)P (70 +/- 13%) than unsuccessful MW shocks (VmP 76 +/- 10%, p < 0.001; Ca(i)P 57 +/- 8%, p < 0.001) of the same shock strength. In contrast, for unsuccessful BW and MW shocks of the same shock strengths, the VmP and Ca(i)P were not significantly different. The MW shocks more frequently created regions of low Ca(i) surrounded by regions of high Ca(i) (post-shock Ca(i) sinkholes). The defibrillation threshold for MW and BW shocks became similar after disabling the sarcoplasmic reticulum (SR) with thapsigargin and ryanodine.
  
  
  CONCLUSIONS
  The greater efficacy of BW shocks is directly related to their less heterogeneous effects on shock-induced SR Ca release and Ca(i) transients. Less heterogeneous Ca(i) transients reduces the probability of Ca(i) sinkhole formation, thereby preventing the post-shock reinitiation of ventricular fibrillation.
authors.affiliation: Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, USA.
authors.forename: Gyo-Seung
authors.initials: GS
authors.lastname: Hwang
authors.forename: Liang
authors.initials: L
authors.lastname: Tang
authors.forename: Boyoung
authors.initials: B
authors.lastname: Joung
authors.forename: Norishige
authors.initials: N
authors.lastname: Morita
authors.forename: Hideki
authors.initials: H
authors.lastname: Hayashi
authors.forename: Hrayr S
authors.initials: HS
authors.lastname: Karagueuzian
authors.forename: James N
authors.initials: JN
authors.lastname: Weiss
authors.forename: Shien-Fong
authors.initials: SF
authors.lastname: Lin
authors.forename: Peng-Sheng
authors.initials: PS
authors.lastname: Chen