Intrathoracic Impedance to Monitor Heart Failure Status: A Comparison of Two Methods in a Chronic Heart Failure Dog Model

In patients with heart failure (HF), a convenient and accurate assessment of HF status could enhance titration of medications and possibly reduce hospitalizations for fluid overload. This study examined the feasibility of monitoring HF status by measuring intrathoracic impedance with either an implantable cardioverter‐defibrillator or a pacemaker. Six canines were each instrumented with four devices: two capable of measuring intrathoracic impedance between a right ventricular coil electrode and the device case, one custom pacemaker for inducing HF, and an implantable hemodynamic monitor to measure left ventricular end‐diastolic pressure as an assessment of HF status. High‐rate ventricular pacing for 3–7 weeks induced HF, followed by a 4‐week recovery period. During high‐rate pacing, left ventricular end‐diastolic pressure was inversely correlated with impedance measurements from both systems (median r =−0.66; range r =−0.38 to −0.81). During recovery, the inverse correlation between left ventricular end‐diastolic pressure and impedance was enhanced (median r =−0.88; range r =−0.58 to −0.95). The two types of impedance measurements were highly correlated (median r =−0.68 during pacing and r =−0.91 during recovery). These results suggest that various methods of measurement of intrathoracic impedance over time could be used to monitor HF status.