Equivalence of the Bioimpedance and Thermodilution Methods in Measuring Cardiac Output in Hospitalized Patients with Advanced, Decompensated Chronic Heart Failure

Background: An accurate and reliable noninvasive method for determining cardiac output/cardiac index would be valuable for patients with acutely decompensated advanced systolic heart failure.

Objectives: To determine whether a correlation exists for cardiac output and index determined by using bioimpedance and thermodilution in patients with acutely decompensated complex heart failure and if differences between results with the 2 methods could be explained by the patients' advanced condition.

Methods: Cardiac output and index were determined by using bioimpedance and thermodilution in 33 patients. Echocardiographic and electrocardiographic data were assessed to determine if differences between results with the 2 methods could be explained by the patients' advanced condition. Concordance correlation coefficients and Bland-Altman agreement between methods were calculated.

Results: Four patients were excluded from analysis because reliable measurements could not be obtained; the remaining 29 patients constituted the study population. Mean cardiac outputs determined by thermodilution and bioimpedance were 5.48 and 5.40 L/min, respectively (rhoc = 0.89, P < .001), and mean cardiac indexes were 2.67 and 2.65 (rhoc = 0.82, P < .001). Mean bias (limits of agreement) between data pairs was 0.08 (-0.18 to 0.35) L/min (P = .52) for cardiac output and 0.03 (-0.097 to 0.16; P = .61) for cardiac index. Six data pairs (21%) had an absolute percent difference greater than 15%. Of these, 50% had a higher thermodilution value.

Conclusion: Determinations of cardiac output and index by both methods were significantly correlated. Mean bias between the 2 methods was small, suggesting clinical utility for bioimpedance in patients with complex decompensated heart failure.