title: Strength duration curve for epicardial left ventricular stimulation.
abstract: BACKGROUND
  The strength duration curve for endocardial stimulation has been extensively studied. Little information is available on the left ventricular epicardial strength duration curve. In view of the large number of patients treated with resynchronization therapy, left ventricular epicardial stimulation parameters have practical importance.
  
  
  METHODS
  Twelve patients who underwent implant of a biventricular defibrillator were available for at least 4 months of follow up and accurate determination of strength duration curves were studied. Strength duration curves were constructed at 30 days (subacute phase) and 4 or more months (chronic phase) after the implant for right ventricular endocardial, left ventricular epicardial unipolar, and left ventricular bipolar stimulation. The goal was to determine the chronaxie, which correlates with the most economical stimulation.
  
  
  RESULTS
  There was no significant difference between the right ventricular endocardial and left ventricular epicardial bipolar chronaxie (P = 0.57 subacute and 0.6 chronic) or right ventricular endocardial and left ventricular unipolar chronaxie (P = 0.93 subacute and 0.92 chronic). Most chronaxie values were lower than the factory default values.
  
  
  CONCLUSIONS
  The left ventricular unipolar or bipolar epicardial chronaxie is not significantly different from the right ventricular endocardial chronaxie. Both values are lower than the pulse duration used as default setting in most devices as well as in clinical practice. Individual determination of the chronaxie could lead to energy savings.
authors.affiliation: Temple University Hospital, Philadelphia, Pennsylvania 19140, USA.
authors.forename: Monique
authors.initials: M
authors.lastname: Scally
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Heston
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Rudnick
authors.forename: Florin T
authors.initials: FT
authors.lastname: Deger
authors.forename: Richard M
authors.initials: RM
authors.lastname: Greenberg
mesh_terms: D002304:Cardiac Pacing, Artificial / Q000379:methods*; D002907:Chronaxy; D003327:Coronary Disease / Q000503:physiopathology / Q000628:therapy*; D017147:Defibrillators, Implantable; D004056:Differential Threshold; D005260:Female; D006801:Humans; D008297:Male; D010138:Pacemaker, Artificial; D016277:Ventricular Function, Left