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%; rvcoii-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 =b 2% vs. 2 =b 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.