title: Defibrillation energy requirements using a left anterior chest cutaneous to subcutaneous shocking vector: implications for a total subcutaneous implantable defibrillator.
abstract: BACKGROUND
  Subcutaneous implantable defibrillators (ICDs) are being developed to facilitate ICD implantation.
  
  
  OBJECTIVE
  The purpose of this study was to estimate the human defibrillation energy requirement (DER) using a left chest cutaneous (Q) to subcutaneous (SQ) shocking vector.
  
  
  METHODS
  Twenty patients undergoing implantation of an indicated ICD were enrolled (15 males, age = 63 +/- 12 years; ejection fraction = 0.27 +/- 0.14). Defibrillation testing was performed using an investigational system consisting of an external defibrillator and a constructed connector to deliver a shock between a pectoral SQ can and a cardiac apical Q electrode. Two attempts at defibrillation using this configuration were allowed. Stage 1 testing started at 70 J with a step-down/step-up to 50 or 100 J, respectively. Stage 2 testing began at 50 J with a step-down/step-up to 30 or 70 J.
  
  
  RESULTS
  During stage 1, a 70-J shock was successful in 7/9 (78%) patients. A second attempt was successful in 7/7 patients using a 50-J shock. In the two remaining patients, a second attempt using a 100-J shock was successful. During stage 2, a 50-J shock was successful in 10/11 (91%) patients. The protocol could not be completed in 2/11 patients. Of the remaining nine patients, a second defibrillation was successful in seven (78%) using a 30-J shock.
  
  
  CONCLUSIONS
  The defibrillation energy requirement (DER) of this study vector was 50 J or less in most patients. This low DER supports further investigation of a totally SQ-ICD. However, the DER of 100 J in two patients indicates that further investigation is needed regarding DER variability and safety margins.
authors.affiliation: Section of Cardiology, Department of Internal Medicine, University of Chicago, Illinois 60637, USA. mburke@medicine.bsd.uchicago.edu
authors.forename: Martin C
authors.initials: MC
authors.lastname: Burke
authors.forename: James A
authors.initials: JA
authors.lastname: Coman
authors.forename: Adam W
authors.initials: AW
authors.lastname: Cates
authors.forename: Curtis C
authors.initials: CC
authors.lastname: Lindstrom
authors.forename: David A
authors.initials: DA
authors.lastname: Sandler
authors.forename: Susan S
authors.initials: SS
authors.lastname: Kim
authors.forename: Bradley P
authors.initials: BP
authors.lastname: Knight
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011474:Prosthesis Design; D019919:Prosthesis Implantation / Q000379:methods; D014693:Ventricular Fibrillation / Q000628:therapy