Continuous Monitoring of Intrathoracic Impedance and Right Ventricular Pressures in Patients With Heart Failure

Background—Hemodynamic monitoring using implantable devices may provide early warning of volume overload in patients with heart failure (HF). This study was designed to prospectively compare information from intrathoracic impedance monitoring and continuous right ventricular pressure measurements in patients with HF. Methods and Results—Sixteen patients with HF (age, 63.5±13.8 years; left ventricular ejection fraction, 23.2±11.3%; New York Heart Association, II and III) and a previous HF decompensation received both a cardiac resynchronization therapy defibrillator providing a daily average of intrathoracic impedance and an implantable hemodynamic monitor providing an estimate of the pulmonary artery diastolic pressure. At the end of a 6-month investigator-blinded period, baseline reference hemodynamic values were determined over 4 weeks during which the patient was clinically stable. A major HF event was defined as HF decompensation requiring hospitalization, IV diuretic treatment, or leading to death. Sixteen major HF events occurred in 10 patients. Within 30 days and 14 days before a major HF event, impedance decreased by 0.12±0.21 &OHgr;/d and 0.20±0.20 &OHgr;/d, respectively, whereas estimated pulmonary arterial diastolic pressure increased by 0.10±0.20 mm Hg/d and 0.16±0.15 mm Hg/d, respectively. During these periods, impedance decreased by 3.8±5.4 &OHgr; (P<0.02) and 4.9±6.1 &OHgr; (P<0.007), respectively, whereas estimated pulmonary arterial diastolic pressure increased by 5.8±5.7 mm Hg (P<0.002) and 6.8±6.1 mm Hg (P<0.001), respectively, compared with baseline. In all patients, impedance and estimated pulmonary arterial diastolic pressure were inversely correlated (r=−0.48±0.25). Within 30 days preceding a major HF event, this correlation improved to r=−0.58±0.24. Conclusions—Decompensated HF develops based on hemodynamic derangements and is preceded by significant changes in intrathoracic impedance and right ventricular pressures during the month prior to a major clinical event. Impedance and pressure changes are moderately correlated. Future research may establish the complementary contribution of both parameters to guide diagnosis and management of patients with HF by implantable devices.