title: Ambulatory monitoring of congestive heart failure by multiple bioelectric impedance vectors.
abstract: OBJECTIVE
  This study was designed to investigate the properties of multiple bioelectric impedance signals recorded during congestive heart failure (CHF) by utilizing various electrode configurations of an implanted cardiac resynchronization therapy system.
  
  
  BACKGROUND
  The monitoring of CHF has relied mainly on right-side heart sensors.
  
  
  METHODS
  Fifteen normal dogs underwent implantation of cardiac resynchronization therapy systems using standard leads. An additional left atrial (LA) pressure lead sensor was implanted in 5 dogs. Continuous rapid right ventricular (RV) pacing was applied over several weeks. Left ventricular (LV) catheterization and echocardiography were performed biweekly. Six steady-state impedance signals, utilizing intrathoracic and intracardiac vectors, were measured through ring (r), coil (c), and device Can electrodes.
  
  
  RESULTS
  Congestive heart failure developed in all animals after 2 to 4 weeks of pacing. Impedance diminished gradually during CHF induction, but at varying rates for different vectors. Impedance during CHF decreased significantly in all measured vectors: LV(r)-Can, -17%; LV(r)-RV(r), -15%; LV(r)-RA(r), -11%; RV(r)-Can, -12%; RV(c)-Can, -7%; and RA(r)-Can, -5%. The LV(r)-Can vector reflected both the fastest and largest change in impedance in comparison with vectors employing only right-side heart electrodes, and was highly reflective of changes in LV end-diastolic volume and LA pressure.
  
  
  CONCLUSIONS
  Impedance, acquired by different lead electrodes, has variable responses to CHF. Impedance vectors employing an LV lead are highly responsive to physiologic changes during CHF. Measuring multiple impedance signals could be useful for optimizing ambulatory monitoring in heart failure patients.
authors.affiliation: Department of Cardiology, Methodist DeBakey Heart and Vascular Center, Methodist Hospital Research Institute, 6565 Fannin Street, Houston, TX 77030, USA. dkhoury@tmhs.org
authors.forename: Dirar S
authors.initials: DS
authors.lastname: Khoury
authors.forename: Mihir
authors.initials: M
authors.lastname: Naware
authors.forename: Jeff
authors.initials: J
authors.lastname: Siou
authors.forename: Andreas
authors.initials: A
authors.lastname: Blomqvist
authors.forename: Nilesh S
authors.initials: NS
authors.lastname: Mathuria
authors.forename: Jianwen
authors.initials: J
authors.lastname: Wang
authors.forename: Hue-Teh
authors.initials: HT
authors.lastname: Shih
authors.forename: Sherif F
authors.initials: SF
authors.lastname: Nagueh
authors.forename: Dorin
authors.initials: D
authors.lastname: Panescu
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D017097:Electric Impedance; D004567:Electrodes, Implanted; D006333:Heart Failure / Q000175:diagnosis* / Q000503:physiopathology; D006439:Hemodynamics; D018670:Monitoring, Ambulatory; D010138:Pacemaker, Artificial; D016278:Ventricular Function, Right