Comparison of cardiac indices during pregnancy between noninvasive automated device and two-dimensional echocardiography: a longitudinal study

Objective To determine the correlation, precision, mean percentage difference and agreement between cardiac indices (stroke volume [SV], cardiac output [CO], SV index [SVI], and cardiac index [CI]) measured by noninvasive cardiac output monitor (NICOM®, Cheetah Medical, Boston, MA, USA) and 2-dimensional transthoracic echocardiography (2D-TTE) across gestations in Chinese pregnant women.Methods This was a prospective longitudinal study performed in women with singleton pregnancy at 11–14+6 (n = 152), 19–24+6 (n = 152), 30–34+6 (n = 141), and 35–37+6 (n = 103). Cardiac indices, including CO and SV, were obtained by NICOM®, which uses thoracic bioreactance, and 2D-TTE. CI and SVI were calculated from CO and SV adjusted for body surface area. The measurements of cardiac indices obtained using NICOM® were assessed relative to that of 2D-TTE by calculating correlation coefficient, bias, precision, mean percentage difference, and 95% limits of agreement, adjusted for repeated measurements.Results Comparison of the SV and SVI measurements by the two approaches showed significant moderate correlation in the first trimester (r = 0.2–0.3; p = .01). Overall, the SV and SVI measurements obtained using NICOM® relative to that obtained by 2D-TTE revealed a bias of −12.1 mL and −6.1 mL/m2 (95% confidence interval [CI]: −44.5 to 20.2 and −24.8 to 12.5), respectively. Comparison of the CO and CI measurements by the two approaches showed significant moderate correlation in the first trimester (r∼0.2; p = .01). Overall, the CO and CI measurements obtained using NICOM® relative to that obtained by 2D-TTE revealed a bias of −0.50 L/min and −0.18 L/min/m2 (95% CI: 2.26–3.27 and −1.79 to 1.39), respectively. Mean percentage difference for all cardiac parameters in all three trimesters were more than 30%.Conclusions In Chinese pregnant women, NICOM® has underestimated cardiac indices (SV, CO, SVI, and CI) compared to that measured by 2D-TTE. The mean percentage differences for all cardiac indices are more than 30%, which are higher than the clinically acceptable limit. Future research is needed to determine whether adjustment factors should be applied to the proprietary algorithms used by the NICOM® for the estimation of SV and CO in the Chinese pregnant population.