title: Assessment of the Extravascular Implantable Defibrillator: Feasibility of Substernal Ventricular Pacing.
abstract: BACKGROUND
  The objective of this study was to assess feasibility of ventricular pacing and thresholds from within the substernal space to examine a new extravascular ICD configuration with pacing capabilities.
  
  
  METHODS
  In patients undergoing midline sternotomy, a duodecapolar diagnostic pacing catheter was positioned in the substernal space anterior to the pericardium, and a cutaneous patch in left lateral position. Different unipolar and bipolar pacing configurations were assessed. Strength-duration curves were performed to identify the optimal output, starting at 25 mA with a pulse width of 10 milliseconds.
  
  
  RESULTS
  Eight patients with mean age 69 ± 9 years were included. In 5, ventricular capture was achieved in ≥1 configuration. The mean bipolar pacing thresholds at PW 10, 5, 3, 1 milliseconds were 12.4 ± 3.7 mA (5 patients), 13.3 ± 5.8 mA (3 patients), 18.3 ± 5.7 mA (3 patients), and 25 ± 0 mA (2 patients), respectively. The 60-mm electrode spacing was the most successful bipolar configuration. Unipolar pacing was successful in 3 out of 4 patients with mean thresholds of 10 ± 0 mA at 10 milliseconds (3 patients), 15 ± 0 mA at 5 milliseconds (3 patients), 16.7 ± 2.9 mA at 3 milliseconds (3 patients), and 20 ± 7.1 mA at 1 milliseconds (2 patients).
  
  
  CONCLUSIONS
  Ventricular pacing from the substernal space in patients with midline sternotomy is feasible. Closed sternum studies are needed to determine pacing thresholds more accurately.
authors.affiliation: Department of Clinical and Experimental Cardiology, Amsterdam, the Netherlands.
authors.forename: Tom F
authors.initials: TF
authors.lastname: Brouwer
authors.affiliation: Department of Clinical and Experimental Cardiology, Amsterdam, the Netherlands.
authors.forename: Lonneke
authors.initials: L
authors.lastname: Smeding
authors.affiliation: Department of Clinical and Experimental Cardiology, Amsterdam, the Netherlands.
authors.forename: Wouter R
authors.initials: WR
authors.lastname: Berger
authors.affiliation: Department of Cardiothoracic Surgery, Heart Center, Amsterdam Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Antoine H G
authors.initials: AHG
authors.lastname: Driessen
authors.affiliation: Department of Clinical and Experimental Cardiology, Amsterdam, the Netherlands.
authors.forename: Joris R
authors.initials: JR
authors.lastname: DE Groot
authors.affiliation: Department of Clinical and Experimental Cardiology, Amsterdam, the Netherlands.
authors.forename: Arthur A M
authors.initials: AAM
authors.lastname: Wilde
authors.affiliation: Department of Clinical and Experimental Cardiology, Amsterdam, the Netherlands.
authors.forename: Reinoud E
authors.initials: RE
authors.lastname: Knops
mesh_terms: D000368:Aged; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects / Q000379:methods; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods; D022062:Electrophysiologic Techniques, Cardiac; D005240:Feasibility Studies; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D010138:Pacemaker, Artificial; D011446:Prospective Studies; D011474:Prosthesis Design; D013997:Time Factors; D016896:Treatment Outcome; D016276:Ventricular Function
keywords: ICD; implantable cardioverter-defibrillator; pacing; substernal