title: Comparison of fixed tilt and tuned defibrillation waveforms: the PROMISE study.
abstract: BACKGROUND
  All modern defibrillation systems use biphasic shock waveforms. Typically a fixed tilt waveform is used for implantable defibrillators (ICDs), but a tuned waveform with duration based on shock impedance may be superior based on theoretical calculations.
  
  
  OBJECTIVE
  The objective of this study was to compare defibrillation efficacy of fixed tilt and tuned waveforms.
  
  
  METHODS
  PROMISE was designed as a prospective, within-patient, randomized study of defibrillation thresholds (DFTs) comparing a tuned (assuming a 3.5 milliseconds membrane time constant) versus a 50/50% tilt waveform. All patients had a left pectoral implant (active can) and testing was performed with a single coil shocking configuration ("SVC coil OFF"). DFTs were measured in random order with a binary search method in 52 patients, using the high-voltage lead impedance to select the pulse widths for both waveforms.
  
  
  RESULTS
  At the DFT, the tuned waveform had similar delivered energy (10.5 ± 6.3 vs 9.5 ± 5.5 J, P = 0.47), stored energy (13.6 ± 7.9 vs 11.3 ± 6.3 J, P = 0.06), peak current (7.5 ± 3.0 vs 6.8 ± 2.2 A, P = 0.09), and delivered voltage (451.0 ± 134.5 vs 411.5 ± 120.7 V, P = 0.05) compared with the 50/50% tilt waveform.
  
  
  CONCLUSIONS
  The DFTs for 3.5-millisecond time constant based tuned and 50/50% tilt waveforms are similar using a single coil, left pectoral active can.
authors.affiliation: Medical University of South Carolina, Charleston, South Carolina 29425-5920, USA. goldmr@musc.edu
authors.forename: Michael R
authors.initials: MR
authors.lastname: Gold
authors.forename: Jesus
authors.initials: J
authors.lastname: Val-Mejias
authors.forename: Frank
authors.initials: F
authors.lastname: Cuoco
authors.forename: Mukkaram
authors.initials: M
authors.lastname: Siddiqui
mesh_terms: D000368:Aged; D000465:Algorithms; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000295:instrumentation / Q000379:methods*; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D011446:Prospective Studies; D012815:Signal Processing, Computer-Assisted; D013318:Stroke Volume; D013997:Time Factors; D016896:Treatment Outcome; D014481:United States; D014693:Ventricular Fibrillation / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D016277:Ventricular Function, Left