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Related Experiment Videos

Transthoracic impedance does not decrease with rapidly repeated countershocks in a swine cardiac arrest model.

James T Niemann1, Daniel Garner, Roger J Lewis

  • 1Department of Emergency Medicine, UCLA School of Medicine, Harbor-UCLA Medical Center, Box 21, 1000 West Carson Street, Torrance, CA 90509, USA. jniemann@ucla.edu

Resuscitation
|December 31, 2002
PubMed
Summary

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Transthoracic impedance remained stable during repeated defibrillation shocks in a swine model of ventricular fibrillation (VF) cardiac arrest. This finding contrasts with previous studies in non-arrest models and has implications for electrical therapy during resuscitation.

Area of Science:

  • Cardiovascular Research
  • Emergency Medicine
  • Biomedical Engineering

Background:

  • Successful defibrillation relies on adequate current delivery to the myocardium.
  • Transthoracic impedance is a key determinant of current flow during defibrillation.
  • Previous research suggested impedance decreases with repeated shocks in sinus rhythm.

Purpose of the Study:

  • To investigate changes in transthoracic impedance during repeated defibrillation shocks.
  • To evaluate impedance variations in an animal model of cardiac arrest due to ventricular fibrillation (VF).

Main Methods:

  • Ventricular fibrillation (VF) was induced in anesthetized swine.
  • Repeated 'stacked shocks' (monophasic or biphasic waveforms) were delivered via adhesive electrodes.

Related Experiment Videos

  • Transthoracic impedance was calculated from measured voltage and current during each shock.

    • Main Results:

    • Transthoracic impedance did not significantly change from the first to the fourth shock (46+/-8 Omega to 46+/-9 Omega) in 13 animals requiring at least four shocks.
    • No significant impedance change was observed in animals receiving more than four shocks.
    • Analysis by defibrillation waveform (monophasic vs. biphasic) also showed no significant impedance change.

    Conclusions:

    • Transthoracic impedance remains stable with repeated defibrillation shocks in a VF cardiac arrest model.
    • This stability is attributed to the absence of reactive hyperemia and edema seen in non-arrest models.
    • Findings suggest impedance management strategies may differ between arrest and non-arrest states.