title: Internal defibrillation with minimal skeletal muscle activation: a new paradigm toward painless defibrillation.
abstract: BACKGROUND
  Shock-induced pain produces substantial morbidity in recipients of implantable cardioverter-defibrillators (ICDs). This pain likely derives from activation of skeletal muscle and associated nerves in the chest and abdomen. In an effort to develop a painless defibrillation system, we designed an electrode arrangement that incorporates a conductive sock placed around the heart to confine the electric shock field to cardiac tissue.
  
  
  OBJECTIVE
  The purpose of this study was to test whether cardiac defibrillation could be achieved without skeletal muscle activation using a novel electrode system.
  
  
  METHODS
  Eight adult mongrel dogs were studied. Force of skeletal muscle contraction was measured by strain gauges attached to the forelimbs during delivery of internal shocks ranging in energy from 0.1 to 31 J. Biphasic shocks were delivered (1) between a right ventricular coil and a subcutaneous dummy can (standard configuration), and (2) between a left ventricular coil and an epicardial electrode sock. Internal and external defibrillation thresholds (DFTs) were determined for each electrode configuration.
  
  
  RESULTS
  Shock-induced muscle contraction force was significantly lower using the sock electrode than with standard ICD electrodes at every shock energy level tested (P < .0001). Internal DFT was similar between electrode configurations (sock electrode: 8.6 +/- 4.2 J; standard: 11.0 +/- 6.3 J, P = .4), but muscle contraction force at DFT was greatly reduced with the new electrode system (1.8 +/- 2.0 kg vs 10.6 +/- 2.1 kg, P < .0001). The sock electrode rendered external defibrillation impossible, however, even at 360 J.
  
  
  CONCLUSIONS
  Skeletal muscle activation induced by ICD shocks can be greatly reduced using an electrode system that confines the electric shock field to the heart. Refinement of this strategy may allow for delivery of painless shocks by ICDs. Further development is needed to overcome implant complexity and the higher external DFT with this type of electrode system.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: Vinod
authors.initials: V
authors.lastname: Jayam
authors.forename: Menekhem
authors.initials: M
authors.lastname: Zviman
authors.forename: Venku
authors.initials: V
authors.lastname: Jayanti
authors.forename: Ariel
authors.initials: A
authors.lastname: Roguin
authors.forename: Henry
authors.initials: H
authors.lastname: Halperin
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Berger
mesh_terms: D000818:Animals; D017147:Defibrillators, Implantable; D004285:Dogs; D004554:Electric Countershock / Q000295:instrumentation / Q000379:methods; D017097:Electric Impedance; D004567:Electrodes, Implanted; D006329:Heart Conduction System / Q000503:physiopathology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010146:Pain / Q000503:physiopathology; D059408:Pain Management; D015203:Reproducibility of Results; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*