AJP - Heart and Circulatory Physiology, Vol 267, Issue 2 684-H693, Copyright © 1994 by American Physiological Society
Transmyocardial impedance during single and multiple internal ventricular defibrillation shocks
W. Peters, S. Solingen, Y. Kobayashi, R. Scharf, W. J. Mandel and E. S. Gang
Medizinische Klinik, Universitat Wurzburg, Germany.
Little is known about the transmyocardial impedance during internal
ventricular defibrillation. In a canine model, using high rate on-line
digitization, random shock delivery, and titanium electrodes, we determined
the relationship among voltage, current, and impedance, delivered energy,
and defibrillation success within the individual and within successive
defibrillation shocks. Impedance decreased with repeated defibrillation in
10 of 11 dogs. Impedance always increased during trapezoidal discharges,
whereas voltage decreased. Impedance was lower with high energy-voltage
shocks in all dogs. Visually, voltage and current waveform did not show a
phase shift. There was no difference in the total energy delivered and the
energy converted into heat by the resistive part of the impedance. With a
formula valid only for resistive loads, the capacitance of the
defibrillator was calculated to be within the measurement accuracy and
tolerance of the factory-provided value of 132 microF. Polarization voltage
was consistently observed. Thus the transmyocardial impedance during
defibrillation is primarily resistive, nonlinear voltage dependent, and
declines with successive shocks. Defibrillation success was not influenced
by these phenomena.
