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David Pedersen
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University of Iowa Iowa City, IA 52242-1181
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IOWA CITY, Iowa -- When Dr. Richard Kerber helped update the American Heart Association (AHA) guidelines for defibrillation in 1992, he believed then, as he does now, that they specify the best way to achieve success. Yet, he said the recommendation for apex-to-anterior electrode placement with gel only on the electrode paddles was intuitive; there was little actual data to show that successful defibrillation depended upon following theses specific AHA guidelines on electrode placement.
Kerber, a University of Iowa professor of internal medicine, was disturbed by the number of defibrillation failures. He suspected, but couldn't be sure if technique was partially to blame.
"All too often we saw that the electrodes weren't placed properly or gel was smeared between them--which is understandable when working in an emergency situation. And with little data, it was unclear how important it is to follow the AHA recommendations," he said.
Anxious to know if poor electrode and/or gel placement contributed to defibrillation failure, Kerber and colleagues examined interelectrode impedance in healthy subjects. In one condition AHA guidelines for electrode and gel placement were followed, and other conditions were studied in which electrode placement was too close and/ or gel was smeared on the skin between the electrodes.
They found that following AHA recommendations for electrode placement allowed the most current to reach the heart, thus providing the best condition for successful defibrillation. Gel smeared on the skin between the electrodes and/or too close electrode placement produced an alternate pathway that shunted current away from the heart, producing a deleterious effect.
Interelectrode impedance was measured using a validated test-pulse method in five men and five women whose ages ranged from 22 to 48 years.
No high-energy shocks were given to the volunteers.
Impedance was tested in four conditions: 1) electrodes placed in an apex-to-anterior position with gel only on the paddles (AHA recommendation); 2) same position as in 1 with gel smeared between the electrodes; 3) electrodes in a parasternal-to-anterior position with gel only on the paddles; 4) same position as in 3 with gel smeared between the electrodes.
Kerber and his colleagues found that compared to the AHA recommended technique, the percentage of current transversing the heart was significantly lower in the other experimental groups-especially when the electrodes were placed too close with gel smeared on the skin between electrodes.
This study gives strong support to the AHA electrode placement recommendations for defibrillation.
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