title: Relative efficacy of different tilts with biphasic defibrillation in humans.
abstract: OBJECTIVE
  The goal of this study was to assess if tilt bears any impact on defibrillation efficacy of biphasic shocks.
  
  
  BACKGROUND
  Although it has been shown that biphasic waveform may increase the defibrillation efficacy, this pulsing method has not been as extensively studied in patients, and information regarding the effect of different tilts is lacking.
  
  
  METHODS
  This study consisted of two similar but distinct protocols including 33 patients undergoing transvenous defibrillator implant. In 17 patients (Part I) defibrillation threshold was obtained delivering biphasic waveforms with 50%, 65%, and 80% tilt in random fashion. Similarly, in 16 patients (Part II) testing of biphasic waveform with 40%, 50%, and 65% tilt was performed in random order. The electrode system used consisted of two transvenous leads and a subcutaneous patch in all 33 patients.
  
  
  RESULTS
  In Part I, tilt of 50% demonstrated a defibrillation threshold significantly lower than 65% tilt (7.5 +/- 4.3 J vs 9.7 +/- 5.0 J; P = 0.04) and 80% tilt (7.5 +/- 4.3 J vs 11.7 +/- 5.9 J; P < 0.01). Similarly, 65% tilt provided a lower defibrillation threshold than 80% tilt (9.7 +/- 5.0 J vs 11.7 +/- 5.9 J; P = 0.02). In Part II, no significant difference was observed in terms of defibrillation threshold between 40% tilt and the two tilts of 50% and 65%. However, as in Part I, 50% tilt provided a significant reduction of the energy to defibrillate as compared to 65% tilt (6.3 +/- 3.6 J vs 9.0 +/- 4.8 J; P < 0.01). The 50% tilt resulted in better defibrillation efficacy than 65% tilt independent of the lead system used for testing (Medtronic Transvene and CPI Endotak-C).
  
  
  CONCLUSIONS
  Biphasic shocks with 50% tilt required less energy for defibrillation than 40%, 65%, and 80% tilts. However, in the clinical setting a programmable tilt may be preferable to account for some patient-to-patient variability.
authors.affiliation: Electrophysiology Laboratory, University of Wisconsin-Milwaukee Clinical Campus, Wisconsin, USA.
authors.forename: A
authors.initials: A
authors.lastname: Natale
authors.forename: J
authors.initials: J
authors.lastname: Sra
authors.forename: D
authors.initials: D
authors.lastname: Krum
authors.forename: A
authors.initials: A
authors.lastname: Dhala
authors.forename: S
authors.initials: S
authors.lastname: Deshpande
authors.forename: M
authors.initials: M
authors.lastname: Jazayeri
authors.forename: K
authors.initials: K
authors.lastname: Newby
authors.forename: A
authors.initials: A
authors.lastname: Wase
authors.forename: K
authors.initials: K
authors.lastname: Axtell
authors.forename: W L
authors.initials: WL
authors.lastname: VanHout
authors.forename: M
authors.initials: M
authors.lastname: Akhtar
mesh_terms: D000328:Adult; D000368:Aged; D017147:Defibrillators, Implantable; D004562:Electrocardiography / Q000295:instrumentation; D004567:Electrodes, Implanted; D005260:Female; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D012984:Software; D017180:Tachycardia, Ventricular / Q000503:physiopathology / Q000628:therapy*; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*