Abstract 2627: High Energy Defibrillation Impairs Myocyte Contractility and Intracellular Calcium Dynamics
Introduction. High energy defibrillation is recognized to increase postresuscitation myocardial dysfunction. We examined the effects of defibrillation energies on contractility and intracellular Ca2+ dynamics at the single cardiomyocyte level.
Hypothesis. Increasing the defibrillation energy would produce correspondent reduction in myocyte contractility and impairment of intracellular Ca2+ dynamics.
Methods. Ventricular cardiomyocytes, obtained from adult Sprague-Dawley rat hearts, were loaded with Fura-2/AM. The myocytes were then placed in a chamber mounted on an inverted microscope and superfused with a buffer solution at 37 °C. The cells were field stimulated to contract at 0.5 Hz with a field stimulator (IonOptix Corporation, Milton, MA). Mechanical properties were assessed using a video-based edge-detection system (IonOptix Corporation, Milton, MA) and expressed as cell shortening percentage. Intracellular Ca2+ dynamics were evaluated with a dual-excitation fluorescence photomultiplier system (IonOptix Myocam System) and inferred from the ratio of the fluorescence intensity at the two different wavelengths. Myocytes were randomized into 4 groups of 10 cells each, to receive:
a single 0.5 Joule biphasic shock;
a single 1 Joule biphasic shock;
a single 2 Joule biphasic shock; and
a control group without shock. The myocytes were paced for additional 4 min after the shock.
Results. A 0.5 Joule shock did not have effects on cardiomyocyte contractility and intracellular Ca2+ dynamics. Higher energy shock, i.e. 1 or 2 Joule, significantly impaired cardiomyocyte contractility and intracellular Ca2+ dynamics (p < 0.01). These adverse effects were greater when higher energy was employed (p < 0.01). Table⇓
Conclusions. Higher defibrillation energy significantly impairs myocyte contractility. Reductions in cardiomyocyte shortening and intacellular Ca2+ dynamics abnormalities were greater when higher energy shock was employed.