title: Optimized first phase tilt in "parallel-series" biphasic waveform.
abstract: BACKGROUND
  A biphasic defibrillation waveform can achieve a large second phase leading-edge voltage by a "parallel-series" switching system. Recently, such a system using two 30-microF capacitances demonstrated better defibrillation threshold than standard waveforms available in current implantable devices. However, the optimized tilt of such a "parallel-series" system had not been defined.
  
  
  RESULTS
  Defibrillation thresholds were evaluated for five different biphasic "parallel-series" waveforms (60/15 microF) and a biphasic "parallel-parallel" waveform (60/60 microF) in 12 anesthetized pigs. The five "parallel-series" waveforms had first phase tilts of 40%, 50%, 60%, 70%, and 80% with second phase pulse width of 3 msec. The "parallel-parallel" waveform had first phase tilt of 50% with second phase pulse width of 3 msec. The defibrillation lead system comprised a left pectoral "hot can" electrode (cathode) and a right ventricular lead (anode). The stored energy at defibrillation threshold of the "parallel-series" waveform with first phase tilts of 40%, 50%, 60%, 70%, and 80% was 7.0 +/- 2.1, 6.1 +/- 2.8, 6.8 +/- 2.8, 7.2 +/- 2.9, and 8.4 +/- 3.1 J, respectively. The stored energy of the "parallel-series" waveform with a 50% first phase tilt was 16% less than the nonswitching "parallel-parallel" waveform (7.3 +/- 2.8 J, P = 0.006).
  
  
  CONCLUSIONS
  A first phase tilt of 50% maximized defibrillation efficacy of biphasic waveforms implemented with a "parallel-series" switching system. This optimized "parallel-series" waveform was more efficient than the comparable "parallel-parallel" biphasic waveform having the same first phase capacitance and tilt.
authors.affiliation: Department of Cardiology, Cleveland Clinic Foundation, Ohio 44195, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamanouchi
authors.forename: K A
authors.initials: KA
authors.lastname: Mowrey
authors.forename: M W
authors.initials: MW
authors.lastname: Kroll
authors.forename: J E
authors.initials: JE
authors.lastname: Brewer
authors.forename: A M
authors.initials: AM
authors.lastname: Donohoo
authors.forename: B L
authors.initials: BL
authors.lastname: Wilkoff
authors.forename: P J
authors.initials: PJ
authors.lastname: Tchou
mesh_terms: D000818:Animals; D017147:Defibrillators, Implantable; D004553:Electric Conductivity; D004554:Electric Countershock / Q000379:methods*; D013552:Swine