title: The effect of electronic repositioning on left ventricular pacing and phrenic nerve stimulation.
abstract: OBJECTIVE
  Cardiac resynchronization therapy (CRT) improves survival and reduces heart failure symptoms. However, phrenic nerve stimulation and high pacing thresholds are common problems that limit CRT effectiveness. Current technology allows reprogramming of left ventricular (LV) pacing vectors, permitting 'electronic repositioning' to overcome both phrenic nerve stimulation and high pacing output without the need for re-operation.
  
  
  RESULTS
  Patients underwent prospective evaluation of a CRT system implantation with a bipolar LV. Optimal LV threshold and avoidance of phrenic nerve stimulation were determined at baseline and at 6 months. A subset of 48 patients underwent more detailed evaluation of pacing threshold and phrenic nerve stimulation at baseline and at 6 months. Between 2004 and 2007, 228 patients underwent CRT implantation (64 CRT pacemakers, 164 CRT defibrillators). At baseline, electronic reprogramming to determine an alternate configuration compared with standard LVtip to LVring found a ≥ 1.0 V reduction in pacing threshold in 80 patients (35%). Of the 17 patients who had an LVtip to LVring configuration and high pacing threshold (>5.0 V), 16 could be reduced by >1.0 V (94%) and 11 could be reduced by >2.0 V through electronic repositioning alone without repositioning the lead (65%). At implant, there were 48 patients with phrenic nerve stimulation at less than maximum pacing output (21%) using the standard LVtip to LVring configuration. In 37 cases (77%), there was at least one other configuration with no phrenic nerve stimulation, which prevented the need for lead revision.
  
  
  CONCLUSIONS
  Electronic repositioning is an important tool in the management of CRT patients which may help to lower thresholds, avoid phrenic nerve stimulation, and prevent unnecessary re-operations for LV lead repositioning.
authors.affiliation: Institut Universitaire de Cardiologie et Pneumologie de Québec, 2725 Chemin Sainte-Foy Québec, QC, Canada. jean.champagne@med.ulaval.ca
authors.forename: Jean
authors.initials: J
authors.lastname: Champagne
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Healey
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Krahn
authors.forename: Francois
authors.initials: F
authors.lastname: Philippon
authors.forename: Osnat
authors.initials: O
authors.lastname: Gurevitz
authors.forename: Anne
authors.initials: A
authors.lastname: Swearingen
authors.forename: Michael
authors.initials: M
authors.lastname: Glikson
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods; D058406:Cardiac Resynchronization Therapy / Q000009:adverse effects / Q000379:methods*; D004558:Electric Stimulation; D005260:Female; D006333:Heart Failure / Q000503:physiopathology / Q000628:therapy*; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010791:Phrenic Nerve / Q000502:physiology*; D011446:Prospective Studies; D012189:Retrospective Studies; D016896:Treatment Outcome