Intracellular calcium and vulnerability to fibrillation and defibrillation in Langendorff-perfused rabbit ventricles.
BACKGROUND
The role of intracellular calcium (Ca(i)) in defibrillation and vulnerability is unclear.


RESULTS
We simultaneously mapped epicardial membrane potential and Ca(i) during shock on T-wave episodes (n=104) and attempted defibrillation episodes (n=173) in 17 Langendorff-perfused rabbit ventricles. Unsuccessful and type B successful defibrillation shocks were followed by heterogeneous distribution of Ca(i), including regions of low Ca(i) surrounded by elevated Ca(i) ("Ca(i) sinkholes") 31+/-12 ms after shock. The first postshock activation then originated from the Ca(i) sinkhole 53+/-14 ms after the shock. No sinkholes were present in type A successful defibrillation. A Ca(i) sinkhole also was present 39+/-32 ms after a shock on T that induced ventricular fibrillation, followed 22+/-15 ms later by propagated wave fronts that arose from the same site. This wave propagated to form a spiral wave and initiated ventricular fibrillation. Thapsigargin and ryanodine significantly decreased the upper limit of vulnerability and defibrillation threshold. We studied an additional 7 rabbits after left ventricular endocardial cryoablation, resulting in a thin layer of surviving epicardium. Ca(i) sinkholes occurred 31+/-12 ms after the shock, followed in 19+/-7 ms by first postshock activation in 63 episodes of unsuccessful defibrillation. At the Ca(i) sinkhole, the rise of Ca(i) preceded the rise of epicardial membrane potential in 5 episodes.


CONCLUSIONS
There is a heterogeneous postshock distribution of Ca(i). The first postshock activation always occurs from a Ca(i) sinkhole. The Ca(i) prefluorescence at the first postshock early site suggests that reverse excitation-contraction coupling might be responsible for the initiation of postshock activations that lead to ventricular fibrillation.
Hwang
Gyo-Seung
GS
Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.
Hayashi
Hideki
H
Tang
Liang
L
Ogawa
Masahiro
M
Hernandez
Heidy
H
Tan
Alex Y
AY
Li
Hongmei
H
Karagueuzian
Hrayr S
HS
Weiss
James N
JN
Lin
Shien-Fong
SF
Chen
Peng-Sheng
PS
D000200:Action Potentials; D000818:Animals; D018780:Body Surface Potential Mapping; D002118:Calcium / Q000378:metabolism*; D004554:Electric Countershock; D006352:Heart Ventricles; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D014693:Ventricular Fibrillation / Q000209:etiology* / Q000503:physiopathology
D012433:Ryanodine; D019284:Thapsigargin; D002118:Calcium