title: Feasibility of using an implantable system to measure thoracic congestion in an ambulatory chronic heart failure canine model.
abstract: BACKGROUND
  Noninvasive measures of impedance reflect alterations in thoracic fluid and pulmonary edema in acute animal and human studies.
  
  
  METHODS
  We evaluated the feasibility of using an implantable impedance measuring device and cardiac lead system to monitor intrathoracic congestion in a pacing-induced heart failure canine model. Three devices were implanted in each of five dogs: a modified pacemaker to measure impedance from a defibrillation lead implanted in the right ventricle; an implantable hemodynamic monitoring device to measure left ventricular end diastolic pressure (LVEDP) and a second pacemaker to deliver rapid (240 pulses per minute) ventricular pacing to induce heart failure.
  
  
  RESULTS
  All five dogs developed severe heart failure after 3-4 weeks of rapid pacing and recovered following pacing termination. The LVEDP increased and impedance decreased during pacing-induced heart failure and recovered after pacing cessation. At the end of pacing, there was a mean impedance reduction of 10.6 +/- 8.3% and a mean LVEDP increase of 18.1 +/- 4.5 mmHg compared to baseline. The impedance and LVEDP were inversely correlated (r =-0.41 to -0.85, all P < 0.05).
  
  
  CONCLUSIONS
  In the canine model, measurement of chronic intrathoracic impedance with an implantable system effectively revealed changes in thoracic congestion due to heart failure reflected by LVEDP. These data suggest that implantable device-based impedance measurement merits further investigation as a tool to monitor the fluid status of heart failure patients.
authors.affiliation: Medtronic, Inc., Minneapolis, Minnesota 55432, USA. li.wang@medtronic.com
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Stuart
authors.initials: S
authors.lastname: Lahtinen
authors.forename: Linnea
authors.initials: L
authors.lastname: Lentz
authors.forename: Nancy
authors.initials: N
authors.lastname: Rakow
authors.forename: Cameron
authors.initials: C
authors.lastname: Kaszas
authors.forename: Linda
authors.initials: L
authors.lastname: Ruetz
authors.forename: Lee
authors.initials: L
authors.lastname: Stylos
authors.forename: Walter H
authors.initials: WH
authors.lastname: Olson
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D004487:Edema / Q000503:physiopathology*; D017097:Electric Impedance; D005240:Feasibility Studies; D006333:Heart Failure / Q000503:physiopathology*; D010138:Pacemaker, Artificial; D011654:Pulmonary Edema / Q000503:physiopathology*; D035423:Thoracic Cavity