Monitoring congestive heart failure by multi-vector cardiac impedance from implanted devices

For monitoring pulmonary edema secondary to Congestive Heart Failure (CHF), we investigated trends of impedance between implanted electrodes. ICDs were implanted in 16 dogs and 5 sheep. Right ventricles were paced (230–250 bpm) for several weeks. Impedance was measured every hour along 4 intrathoracic, 2 intracardiac and 4 cardiogenic vectors. Cardiac function was assessed biweekly by catheterization and echocardiography. Left Atrial Pressure (LAP) was measured daily by an implanted sensor. All animals developed CHF after 2–4 weeks of pacing (EF, 52 vs. 34%; LVEDV, 65 vs. 97 ml; LVEDP, 7 vs. 16 mm Hg; LAV, 17 vs. 33 ml; LAP, 7 vs. 26 mm Hg). Impedance decreased during CHF: LV-Can, 17±9%; LV–RV, 15±8%; LV–RA, 13±6%; RV-Can, 13±8%; RV coil-Can, 8±6%; RA-Can, 6±6%. The LV-Can decrease was greatest and correlated well with LAP (r2=0.73). All impedances were associated with circadian variability at the baseline, which diminished during CHF (5±2% vs. 2±1%). In CHF, cardiogenic impedances displayed reduced peak-to-peak amplitude and increased fractionation. As impedance decreased during CHF, left-heart trends were better correlated with LAP. Left-heart vectors may improve the detection of CHF compared to sensing by right-heart leads alone. This approach has important clinical implications for managing HF patients in ambulatory settings.