title: Evaluation of shock waveform configuration on the defibrillation capacity of implantable cardioverter defibrillators in dogs.
abstract: BACKGROUND
  Implantable cardioverter defibrillators (ICD) are programmed to detect ventricular arrhythmias and terminate them by delivering an electrical shock. A defibrillation threshold (DFT) at least 10 J below the maximum device output is recommended for successful therapy. Shock waveform configuration is a programmable parameter used to achieve a low DFT. It is hypothesized that a fixed-pulse configuration results in lower defibrillation energy requirements than a fixed-tilt configuration.
  
  
  METHODS
  10 mongrel dogs.
  
  
  METHODS
  ICD generator and transvenous lead were surgically implanted. Defibrillation threshold was determined using a protocol guided by the upper limit of vulnerability. Fixed-pulse and fixed-tilt (50%/50%) waveform configurations were tested in a random order. Plasma cardiac troponin I (cTnI) was measured for signs of myocardial injury.
  
  
  RESULTS
  The experiment was completed in 9 dogs. Overall mean DFT value was 424 ± 88 V (9.2 ± 3.9 J). Mean differences among voltage, energy and impedance at the DFT for fixed-pulse (422 ± 97 V, 9.1 ± 4.2 J, 62.6 ± 13.8 Ω) and fixed-tilt (426 ± 83 V, 9.3 ± 3.8 J, 62.8 ± 18.5 Ω) configurations were not statistically significant (All P > 0.21). Cardiac TnI concentration changed from 0.03 ng/mL (95% CI: 0.02-0.04) at baseline to 0.11 ng/mL (95 CI: 0.08-0.16) after DFT was obtained with the first waveform configuration and 0.19 ng/mL (95% CI: 0.13-0.28) at the end of the study period. There were no significant changes in heart rate, end-tidal CO2 and blood pressure over time (all P > 0.09).
  
  
  CONCLUSIONS
  The tested ICD device and lead placement reliably produced acceptable DFT values, based on a 10-J safety margin below the maximum device output. A benefit of fixed-pulse configuration could not be demonstrated over the standard fixed-tilt waveform. Signs of acute myocardial damage from repeated high-voltage shocks and episodes of ventricular fibrillation seemed of limited clinical significance.
authors: Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA. rpariaut@lsu.edu
authors: Romain
authors: R
authors: Pariaut
authors: Carley
authors: C
authors: Saelinger
authors: Jorge
authors: J
authors: Vila
authors: William
authors: W
authors: Deforge
authors: Patricia
authors: P
authors: Queiroz-Williams
authors: Hugues
authors: H
authors: Beaufrère
authors: Michael
authors: M
authors: Zimmerman
authors: Katrin
authors: K
authors: Saile
authors: Caryn A
authors: CA
authors: Reynolds
mesh_terms: D000818:Animals; D017147:Defibrillators, Implantable / Q000662:veterinary*; D004285:Dogs; D004554:Electric Countershock / Q000662:veterinary*; D004869:Equipment Safety / Q000639:trends; D019210:Troponin I / Q000235:genetics / Q000378:metabolism
chemical_list: D019210:Troponin I