Correlation of impedance cardiography with invasive hemodynamic measurements in patients with advanced heart failure: The BioImpedance CardioGraphy (BIG) substudy of the Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness (ESCAPE) Trial

Background: Impedance cardiography (ICG) is a noninvasive modality that uses changes in impedance across the thorax to assess hemodynamic parameters, including cardiac output (CO). The utility of ICG in patients hospitalized with heart failure is uncertain. Methods: The BioImpedance CardioGraphy in Advanced Heart Failure study was a prospective substudy of the Evaluation Study of Congestive Heart Failure and Pulmonary Artery Catheterization Effectiveness. A total of 170 subjects underwent blinded ICG measurements using BioZ (CardioDynamics, San Diego, CA); of these, 82 underwent right heart catheterization. We compared ICG with invasively measured hemodynamics by simple correlation and compared overall ICG hemodynamic profiles ("wet" [thoracic fluid content ≥47/kOhm in men and ≥37/kOhm in women] and "cold" [cardiac index ≤2.2 L min^-1m^-2) versus those determined by invasive measurements (wet [pulmonary capillary wedge pressure ≥22 mm Hg] and cold [cardiac index ≤2.2 L min^-1m^-2). We also determined whether ICG measurements were associated with subsequent death or hospitalization within 6 months. Results: There was modest correlation between ICG and invasively measured CO (r = 0.4 to 0.6 on serial measurement). Thoracic fluid content measured by ICG was not a reliable measure of pulmonary capillary wedge pressure. There was poor agreement between ICG and invasively measured hemodynamic profiles (κ ≤0.1). No ICG variable alone or in combination was associated with outcome. Conclusions: In hospitalized patients with advanced heart failure, ICG provides some information about CO but not left-sided filling pressures. Impedance cardiography did not have prognostic utility in this patient population.