Impedance cardiography for cardiac output estimation: reliability of wrist-to-ankle electrode configuration

Non-invasive measurement of cardiac output (CO) may become an important modality for the treatment of heart failure. Among the several methods proposed, impedance cardiography (ICG) has gained particular attention. There are 2 basic technologies of ICG: thoracic and whole-body ICG whereby the electrodes are applied either to the chest or to the limbs. The present study is aimed to test the effectiveness of the Non-Invasive Cardiac System (NICaS), a new ICG device working with a wrist-to-ankle configuration.

To evaluate the reliability of NICaS derived CO (NI-CO), 50 CO measurements were taken simultaneously with thermodilution (TD-CO) and modified Fick (Fick-CO) in 35 cardiac patients, with the TD-CO serving as the gold-standard for the evaluation. Overall, 2-tailed Pearson's correlation and Bland-Altman limits of agreement between NI-CO and TD-CO were r=0.91 and -1.06 and 0.68 L/min and between Fick-CO and TD-CO, r=0.80 and -1.52 and 0.88 L/min, respectively. Good correlation was observed in patients with loading conditions altered by nitroglycerin and also in patients with moderate valvular diseases.

Agreement between NI-CO and TD-CO is within the boundaries of the FDA guidelines of bio-equivalence. NI-CO is applicable for non-invasive assessment of cardiac function.