title: Double pulse transthoracic defibrillation in the calf using percent fibrillation cycle length as spacing determinate.
abstract: Recent studies have found that when multiple pulses of energy are used for defibrillation with implantable electrodes, the spacing between these pulses is better determined as a percentage of the fibrillation cycle length (CL), rather than as a fixed function of time. Here, this concept is further tested in the transthoracic defibrillation of calves, which are approximately the size of heavy humans. Eleven 90-110 kg calves (101 +/- 6 kg) were used in evaluating the effectiveness in achieving transthoracic ventricular defibrillation of ten double pulse waveforms (two 50 A 4-ms rectangular monopulses) having leading edge-to-edge spacings of 4 ms (a 50 A 8-ms rectangular monopulse) and 50, 60, 70, 80, 90, 100, 110, 120, 130 percent fibrillation CL, respectively. In each of these waveforms, the total time when 50 A current was flowing (on time) was 8 ms. Our results show an unequivocal adverse interaction between the pulses, when the spacing is around 60%-70% fibrillation CL; but that the two pulses combined to defibrillate as effectively as a single 8-ms pulse when the spacing is around 110%-130% fibrillation CL. Electrocardiographic analysis suggests that the adverse interaction is due to a refibrillation phenomenon. This study confirms that double pulses can interact and have a negative effect on defibrillation efficacy. Our data suggests that the mechanism of this interaction involves the second pulse reinitiating fibrillation when the pulse separation is in a critical range of values. Our results are also compatible with the hypothesis that the spacing of multiple pulses is better determined as a percentage of the fibrillation CL than as absolute time, although more study is necessary to fully test this hypothesis.
authors.affiliation: Department of Surgery, University of Missouri, Columbia, Missouri, USA.
authors.forename: W C
authors.initials: WC
authors.lastname: McDaniel
authors.forename: J C
authors.initials: JC
authors.lastname: Schuder
authors.forename: R J
authors.initials: RJ
authors.lastname: Sweeney
authors.forename: H
authors.initials: H
authors.lastname: Stoeckle
authors.forename: Q
authors.initials: Q
authors.lastname: Zhang
authors.forename: M
authors.initials: M
authors.lastname: Sullivan
authors.forename: M C
authors.initials: MC
authors.lastname: Hogan
mesh_terms: D000818:Animals; D002417:Cattle; D017147:Defibrillators, Implantable; D004195:Disease Models, Animal; D004554:Electric Countershock / Q000295:instrumentation / Q000379:methods*; D004562:Electrocardiography; D006321:Heart / Q000503:physiopathology; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*