Abstract 820: Usefulness of Monitoring Congestive Heart Failure by Multiple Bioelectric Impedance Vectors
Bioelectric impedance is useful in detecting changes in pulmonary congestion and cardiac function. We examined the utility of simultaneously measuring multiple intrathoracic and intracardiac impedance signals by a cardiac resynchronization therapy (CRT) system for monitoring congestive heart failure (CHF). We implanted CRT systems in 15 normal dogs using standard leads. An additional LA pressure lead-sensor was implanted in 5 dogs. Continuous RV pacing (230–250 bpm) was applied over several weeks. Catheterization and echocardiography were performed biweekly. Multiple intrathorcaic and intracardiac impedance vectors were measured via ring (R), tip (T), coil (C), and Can electrodes. The system measured both steady-state impedance (Zs), which monitored changes in geometric and resistive parameters, and cardiogenic impedance (Zc), which monitored beat-to-beat variations during mechanical deformation of the heart. All animals developed CHF after 2– 4 weeks of pacing starting from baseline (EF, 43 vs. 31%; LV end-diastolic volume, 65 vs. 95 ml; LV end-diastolic pressure, 6 vs. 16 mmHg; LA volume, 18 vs. 31 ml; LA pressure, 8 vs. 26 mmHg). Zs decreased significantly during CHF in all measured vectors: LVR-Can, −17%; LVR-RVR, −15%; LVR-RAR, −11%; RVR-Can, −12%; RVC-Can, −7%; RAR-Can, −5% (LVR-Can reflected the largest change, p < 0.05). All Zs vectors decreased exponentially, but at varying time constants (7–13 days); the LVR-Can vector depicted the fastest rate of change (p < 0.008). Select Zs vectors reflected changes in LV end-diastolic volume; LVR-Can yielded the highest correlation (r = −0.83, p < 0.001). Zs was inversely related to LA pressure; the LVR-Can produced the highest correlation (r= −0.84, p < 0.001). Peak-to-peak Zc decreased significantly during CHF compared to baseline in all vectors tested (LVR-RVR, 18 vs. 11Ω; LVR-RAR, 20 vs. 13Ω; RVR-RVT, 38 vs. 13Ω). Changes in Zc via RVR-RVT correlated with EF (r = 0.72, p = 0.028). Intrathoracic and intracardiac impedance, acquired via different CRT system leads, have variable responses to CHF. Employing a LV lead improves physiologic monitoring by impedance. Cardiogenic impedance reflects dynamic changes in cardiac function during CHF.