Superiority of biphasic over monophasic defibrillation shocks is attributable to less intracellular calcium transient heterogeneity.
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.
Hwang
Gyo-Seung
GS
Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, USA.
Tang
Liang
L
Joung
Boyoung
B
Morita
Norishige
N
Hayashi
Hideki
H
Karagueuzian
Hrayr S
HS
Weiss
James N
JN
Lin
Shien-Fong
SF
Chen
Peng-Sheng
PS