title: High-energy defibrillation impairs myocyte contractility and intracellular calcium dynamics.
abstract: 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.
authors.affiliation: Weil Institute of Critical Care Medicine, Rancho Mirage, CA, USA.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Ristagno
authors.forename: Tong
authors.initials: T
authors.lastname: Wang
authors.forename: Wanchun
authors.initials: W
authors.lastname: Tang
authors.forename: Shijie
authors.initials: S
authors.lastname: Sun
authors.forename: Carlos
authors.initials: C
authors.lastname: Castillo
authors.forename: Max Harry
authors.initials: MH
authors.lastname: Weil
mesh_terms: 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
chemical_list: D002118:Calcium; D016257:Fura-2