Circulation, Vol 85, 1510-1523, Copyright © 1992 by American Heart Association
JM Wharton, PD Wolf, WM Smith, PS Chen, DW Frazier, S Yabe, N Danieley and RE Ideker
BACKGROUND. Potential gradient field determination may be a helpful means
of describing the effects of defibrillation shocks; however, potential
gradient field requirements for defibrillation with different electrode
configurations have not been established. METHODS AND RESULTS. To evaluate
the field requirements for defibrillation, potential fields during
defibrillation shocks and the following ventricular activations were
recorded with 74 epicardial electrodes in 12 open-chest dogs with the use
of a computerized mapping system. Shock electrodes (2.64 cm2) were attached
to the lateral right atrium (R), lateral left ventricular base (L), and
left ventricular apex (V). Four electrode configurations were tested:
single shocks of 14-msec duration given to two single anode-single cathode
configurations, R:V and L:V, and to one dual anode-single cathode
configuration, (R+L):V; and sequential 7-msec shocks separated by 1 msec
given to R:V and L:V (R:V-- --L:V). Defibrillation threshold (DFT) current
was significantly lower for R:V----L:V than for the other configurations
and markedly higher for L:V. Despite these differences, the minimum
potential gradients measured at DFT were not significantly different
(approximately 6-7 V/cm for each electrode configuration). Potential
gradient fields generated by the electrode configurations were markedly
uneven, with a 15-27-fold change from lowest to highest gradient, with the
greatest decrease in gradient occurring near the shock electrodes. Although
gradient fields varied with the electrode configuration, all configurations
produced weak fields along the right ventricular base. Early sites of
epicardial activation after all unsuccessful shocks occurred in areas in
which the field was weak; 87% occurred at sites with gradients less than 15
V/cm. Ventricular tachycardia originating in high gradient areas near shock
electrodes followed 11 of 67 successful shocks. CONCLUSIONS. These data
suggest that 1) defibrillation fields created by small epicardial
electrodes are very uneven; 2) achievement of a certain minimum potential
gradient over both ventricles is necessary for ventricular defibrillation;
3) the difference in shock strengths required to achieve this minimum
gradient over both ventricles may explain the differences in DFTs for
various electrode configurations; and 4) high gradient areas in the uneven
fields can induce ectopic activation after successful shocks.
ARTICLES
Cardiac potential and potential gradient fields generated by single, combined, and sequential shocks during ventricular defibrillation
Department of Medicine, Duke University Medical Center, Durham, N.C. 27710.
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