Usefulness of monitoring congestive heart failure by multiple impedance vectors

Introduction: We investigated trends in intrathoracic impedance measured between multiple implanted electrodes for monitoring pulmonary edema secondary to congestive heart failure (CHF) in an experimental model. Methods: Biventricular ICDs were implanted in 16 dogs and 5 sheep. Continuous RV pacing (230-250 bpm) was applied over several weeks. Meanwhile, impedance was measured every hour along 4 intrathoracic and 2 intracardiac vectors. Four cardiogenic impedance vectors were also monitored. Cardiac function was assessed biweekly by catheterization and echocardiography. Left atrial (LA) pressure was measured daily by an implanted LA pressure sensor. Results: All animals developed CHF after 2-4 weeks of pacing as evidenced by changes in function (EF, 52 vs. 34%; LV end-diastolic volume, 65 vs. 97 ml; LV end-diastolic pressure, 7 vs. 16 mmHg; LA volume, 17 vs. 33 ml; LA pressure, 7 vs. 26 mmHg), clinical symptoms, or autopsy. Steady state impedance decreased during CHF: LV-Can, 17±9%; LV-RV, 15±8%; LV-RA, 13±6%; RV-Can, 13±8%; RVcoil-Can, 8±6%; RA-Can, 6±6%. Change in LV-Can impedance was greater than that of RA-Can, RV-Can, and RVcoil-Can (P