AJP - Heart and Circulatory Physiology, Vol 250, Issue 5 736-H740, Copyright © 1986 by American Physiological Society
Determination of effects of internal countershock by direct cardiac recordings during normal rhythm
P. G. Colavita, P. Wolf, W. M. Smith, F. R. Bartram, M. Hardage and R. E. Ideker
Recording cardiac electrical activity after a countershock has been limited
by amplifier saturation. Modifications to our computer-assisted mapping
system allowed us to record electrical activity from 56 epicardial
electrodes within 5 ms of the end of a countershock. Modifications included
the use of solid-state switches to disconnect the filter section of the
amplifiers during the shock and changing the low-frequency response of the
amplifiers from 0.1 to 10 Hz to filter out large, low-frequency potentials
after the shock. Six-millisecond truncated exponential shocks were
delivered between the superior vena cava and right ventricular apex through
a quadripolar catheter during normal rhythm in seven dogs. As shocks of
increasing voltage were delivered during the T-Q interval, progressively
more of the epicardium was directly depolarized. A shock of 109 +/- 17 (SD)
V directly depolarized the entire epicardium. Shocks of constant voltage
were then delivered with increasing prematurity during diastole. As the
ventricles became more refractory with increasing shock prematurity, the
amount of epicardium depolarized became progressively less. Thus
computer-assisted mapping techniques are capable of measuring the area
depolarized by a shock during normal rhythm and may be useful during
arrhythmias to improve our understanding of defibrillation and
cardioversion.
