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TITLE Myocardial ischemia lowers precordial thump efficacy: An inquiry into mechanisms using 3D simulations
AUTHORS Weihui Li, Peter Kohl, and Natalia Trayanova
ABSTRACT Precordial thump (PT) is the first International Liaison Committee on Resuscitation prescribed procedure of advanced life support in witnessed cardiac arrest. Reported success rates vary greatly and, according to experimental and clinical evidence, are significantly reduced under ischemic conditions. Objective: The goal of this study is, employing a 3D realistic model of rabbit ventricular geometry and fiber orientation, to elucidate the electrophysiological mechanisms involved in termination of ventricular tachycardia (VT) following PT. Methods: The electrophysiological effect of PT is represented via the involvement of mechano-sensitive channels in the ventricular regions affected by PT. In the normal ventricles, PT recruits cation non-selective stretch-activated channels (SAC-NS, reversal potential of -20mV). In the ischemic myocardium, PT is assumed to additionally activate K-ATP channels (reversal potential -95mV). Ten randomly-selected cases of VT were used, and the impact of PT on VT was examined under both normoxic and ischemic conditions of varying severity. Results: PT was found to have success rate of 60% in normoxia and around 30% in ischemia. Conclusion: The simulation results demonstrate that PT-induced opening of SAC-NS in normoxia reduces the overall heterogeneity in transmembrane potential by partially repolarizing excited tissue and depolarizing resting myocardium, potentially causing foci of excitation that eradicate the excitable gap, thus facilitating VT termination. Decreased PT efficacy in ischemia is caused by additional recruitment of K-ATP channels, which diminishes the depolarizing effect of SAC-NS on resting tissue and causes pronounced shortening of action potentials, thus facilitating the establishment of reentry.
MOVIES

© CCEL 2005
Johns Hopkins University

 < < Click on the image to play the video!
This movie presents an example of termination of ventricular tachycardia with a precordial thump in the normal normal ventricles. The thump lasts for 5ms and is assumed to recruit non-selective stretch-activated channels. The thump suceeds following one extra beat.

© CCEL 2005
Johns Hopkins University

 < < Click on the image to play the video!

 

 This movie illustrates precordial thump that fails to terminate ventricular tachycardia under the conditions of myocardial ischemia. The thump only alters the reentrant pattern. Pre-thump arrhythmia is the same for both movies. Precordial thump is assumed to additionally activate ATP-dependent K channels.