Feasibility of using an implantable system to measure thoracic congestion in an ambulatory chronic heart failure canine model.
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.
Wang
Li
L
Medtronic, Inc., Minneapolis, Minnesota 55432, USA. li.wang@medtronic.com
Lahtinen
Stuart
S
Lentz
Linnea
L
Rakow
Nancy
N
Kaszas
Cameron
C
Ruetz
Linda
L
Stylos
Lee
L
Olson
Walter H
WH
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