title: Influence of phase duration of biphasic waveforms on defibrillation energy requirements with a 70-microF capacitance.
abstract: BACKGROUND
  Phase duration of biphasic shocks may be an important determinant of defibrillation success. The purpose of this study was to investigate the effect of changing phase duration of biphasic pulses delivered by 70-microF capacitors on defibrillation energy requirements. This may be clinically relevant for the optimization of implantable cardioverter-defibrillator design and programming.
  
  
  RESULTS
  Defibrillation thresholds (DFTs) were determined for 13 waveforms in 13 pigs by application of a 70-microF capacitance and a transvenous/submuscular lead system. In part I, phase-1 duration varied, preserving a phase-1/phase-2 duration ratio of 60%/40%. The phase-1 durations were 1, 2, 3, 4, 5, and 6 ms. The DFT was lowest (22.9+/-7 J) for phase 1=3 ms compared with phase 1=1 ms (36.4+/-7.5 J), 2 ms (25+/-6.5 J), 4 ms (25+/-7.6 J), 5 ms (30.7+/-7.3 J), or 6 ms (32.9+/-8.1 J) (P<.001). In part II, phase-1 duration was 3 ms but phase-2 duration varied: 0.7, 1.3, 2, 2.7, 3.3, 4, and 6 ms. Significant DFT minima were found at phase 2=2 ms (22.5+/-4.2 J) and phase 2=4 ms (22.5+/-4.2 J) compared with phase 2=0.7 ms (31.7+/-9.3 J), phase 2=3.3 ms (26.7+/-6.1 J), or phase 2=6 ms (28.3+/-6.8 J) (P<.05).
  
  
  CONCLUSIONS
  The strength-duration curve of biphasic defibrillation shocks demonstrates a single optimum for phase-1 duration. In contrast, two optima with minimal energy requirements were found for phase-2 duration. Optimization of both phases of low-capacitance biphasic shocks may reduce energy requirements for defibrillation.
authors.affiliation: Department of Cardiology, University Hospital-RWTH Aachen, Germany. psch@pcserver.mk1.rwth-aachen.de
authors.forename: P
authors.initials: P
authors.lastname: Schauerte
authors.forename: F A
authors.initials: FA
authors.lastname: Schöndube
authors.forename: M
authors.initials: M
authors.lastname: Grossmann
authors.forename: H
authors.initials: H
authors.lastname: Dörge
authors.forename: F
authors.initials: F
authors.lastname: Stein
authors.forename: B
authors.initials: B
authors.lastname: Dohmen
authors.forename: A
authors.initials: A
authors.lastname: Moumen
authors.forename: K
authors.initials: K
authors.lastname: Erena
authors.forename: B J
authors.initials: BJ
authors.lastname: Messmer
authors.forename: P
authors.initials: P
authors.lastname: Hanrath
authors.forename: C
authors.initials: C
authors.lastname: Stellbrink
mesh_terms: D000818:Animals; D004553:Electric Conductivity; D004554:Electric Countershock; D013552:Swine