title: Prospective randomized comparison of 65%/65% versus 42%/42% tilt biphasic waveform on defibrillation thresholds in humans.
abstract: BACKGROUND
  The waveform tilt of biphasic shocks yielding the lowest defibrillation threshold (DFT) is not well defined. Some evidence indicates that tilts less than 65% may improve DFTs.
  
  
  METHODS
  In 57 patients undergoing ICD implantation, DFTs were determined with truncated exponential biphasic waveform tilts at 65%/65% and at 42%/42%. An external defibrillator with custom software was used for testing. The effective capacitance of the defibrillator was 132-microF for both waveforms. DFTs were determined using a binary search method starting with 12 Joules (J). Patients were randomly assigned to initial testing with either one of the two tilts. Thirty patients (Group 1) were tested with a two electrode (active can to RV coil, or SVC coil to RV coil) and 27 patients (Group 2) were tested with a three electrode system (subcutaneous patch or active can + SVC coil to RV coil).
  
  
  RESULTS
  Groups 1 and 2 did not differ in age, ejection fraction or antiarrhythmic medications. Group 1 delivered energy DFTs were 10.1 +/- 5.5 J with the 65%/65% tilt and 10.1 +/- 5.9 J for the 42%/42% tilt (p = 0.92). In group 2 the average DFT for the 65%/65% tilt was 8.4 +/- 5.7 J and for the 42%/42% tilt was 8.1 +/- 5.3 J (p = 0.70). There were no significant differences in DFTs for either group. The system impedance for Group 1 was 64 +/- 12 ohms and for Group 2 was 39 +/- 6 ohms (p < 0.0001).
  
  
  CONCLUSIONS
  We found no differences in DFTs between 65%/65% tilt and 42%/42% tilt using either 2- or 3-electrode defibrillation systems. Further research is needed to optimize waveforms in order to minimize DFTs, which will result in smaller ICDs and/or greater safety margins for defibrillation.
authors.affiliation: Department of Medicine, Medical College of Virginia/Virginia Commonwealth University, Richmond, VA 23298-0053, USA.
authors.forename: Richard K
authors.initials: RK
authors.lastname: Shepard
authors.forename: Paul J
authors.initials: PJ
authors.lastname: DeGroot
authors.forename: Antonio
authors.initials: A
authors.lastname: Pacifico
authors.forename: Mark A
authors.initials: MA
authors.lastname: Wood
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Ellenbogen
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable; D004554:Electric Countershock; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D017180:Tachycardia, Ventricular / Q000628:therapy; D014693:Ventricular Fibrillation / Q000628:therapy*