title: Disparity in left ventricular stimulation among different pacing configurations in cardiac resynchronization therapy.
abstract: BACKGROUND
  Cardiac resynchronization therapy (CRT) demands high energy utilization due to continuous biventricular pacing. Current technology allows 6 pacing configurations for a bipolar left ventricular (LV) lead. Understanding the energy requirements for each configuration will allow optimization of pacing output.
  
  
  RESULTS
  Pacing impedance, LV voltage threshold at 1.5 ms (rheobase) and 0.4 ms and chronaxie were obtained in 6 LV configurations in 49 consecutive patients undergoing CRT implantation or replacement. Strength-duration curves were derived using the Lapicque formula. Pacing impedances and voltage thresholds at 1.5 and 0.4 ms, calculated minimum threshold energy at chronaxie, current drain, energy thresholds at 0.4 ms, and strength-duration curves were statistically different between LV configurations (P<0.05). The lowest threshold energy requirements were found in Tip→right ventricular (RV) coil and Tip→Can configuration. Energy strength-duration curves involving the ring as the cathode (Ring→RV, Ring→Can, and Ring→Tip) had the highest LV thresholds. The pacing configuration with the lowest energy threshold correlated 89% of the time with the lowest voltage threshold at 0.4 ms. The probability to reach LV thresholds <1.5 V at 0.4 ms was increased from 51% with 2 LV configurations to 67% with 6 LV configurations.
  
  
  CONCLUSIONS
  Pacing impedance, LV thresholds, minimum threshold energy at chronaxie, current drain, voltage, and energy strength-duration curves were statistically different between LV pacing configurations. LV pacing configuration with the lowest voltage threshold does not always reflects the lowest energy threshold, particularly in the presence of a low impedance configuration. The availability of 6 LV configurations increases the probability of optimizing LV pacing output.
authors.affiliation: McGuire VA Medical Center and Virginia Commonwealth University/Pauley Heart Center, Richmond, VA 23249, USA. jose.huizar2@va.gov
authors.forename: Jose F
authors.initials: JF
authors.lastname: Huizar
authors.forename: Karoly
authors.initials: K
authors.lastname: Kaszala
authors.forename: Jayanthi
authors.initials: J
authors.lastname: Koneru
authors.forename: Marcin
authors.initials: M
authors.lastname: Kowalski
authors.forename: Leroy R
authors.initials: LR
authors.lastname: Thacker
authors.forename: Mark A
authors.initials: MA
authors.lastname: Wood
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Ellenbogen
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004562:Electrocardiography; D005260:Female; D005500:Follow-Up Studies; D006333:Heart Failure / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000150:complications / Q000503:physiopathology / Q000628:therapy*