High-energy defibrillation impairs myocyte contractility and intracellular calcium dynamics.
OBJECTIVE
We examined the effects of energy delivered with electrical defibrillation on myocyte contractility and intracellular Ca2+ dynamics. We hypothesized that increasing the defibrillation energy would produce correspondent reduction in myocyte contractility and intracellular Ca2+ dynamics.


METHODS
Randomized prospective study.


METHODS
University-affiliated research laboratory.


METHODS
Ventricular myocytes from male Sprague-Dawley rat hearts.


METHODS
Ventricular cardiomyocytes loaded with Fura-2/AM were placed in a chamber mounted on an inverted microscope and superfused with a buffer solution at 37 degrees C. The cells were field stimulated to contract and mechanical properties were assessed using a video-based edge-detection system. Intracellular Ca2+ dynamics were evaluated with a dual-excitation fluorescence photomultiplier system. Myocytes were then randomized to receive 1) a single 0.5-J biphasic shock; 2) a single 1-J biphasic shock; 3) a single 2-J biphasic shock; and 4) a control group without shock. After the shock, myocytes were paced for an additional 4 mins.


RESULTS
A single 0.5-J shock did not have effects on contractility and intracellular Ca2+ dynamics. Higher energy shocks, i.e., 1- or 2-J shocks, significantly impaired contractility and intracellular Ca2+ dynamics. The adverse effects were greater after a 2-J shock compared with a 1-J shock.


CONCLUSIONS
Higher defibrillation energy significantly impairs ventricular contractility at the myocyte level. Reductions in cardiomyocyte shortening and intracellular Ca2+ dynamics abnormalities were greater when higher energy shock was used.
Ristagno
Giuseppe
G
Weil Institute of Critical Care Medicine, Rancho Mirage, CA, USA.
Wang
Tong
T
Tang
Wanchun
W
Sun
Shijie
S
Castillo
Carlos
C
Weil
Max Harry
MH
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004554:Electric Countershock; D016257:Fura-2; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism*; D008297:Male; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D002118:Calcium; D016257:Fura-2