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

Introduction: For monitoring pulmonary edema secondary to Congestive Heart Failure (CHF), we investigated trends of impedance between implanted electrodes. Methods: 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. Results: 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. Conclusions: 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.