A Pilot Study Comparing Aortic Valve Area Estimates Derived from Fick Cardiac Output with Estimates Based on Cheetah-NICOM Cardiac Output

Abstract

Cardiac output during cardiac catheterization is often estimated using the modified Fick method (CO _Fick). In this proof-of-concept, prospective non-randomized study carried out in a single academic healthcare centre, we examined whether replacing CO _Fick in the Gorlin formula with Cheetah-NICOM monitor cardiac output (CO _Cheetah) could produce an accurate and precise estimate of aortic valve area in patients with severe aortic stenosis. In twenty-six subjects, CO _Fick and CO _Cheetah were obtained concurrently. A spot and 3-minute running average of CO _Cheetah was used. Bland and Altman analysis was used to derive bias, 95% limits of agreement (LOA) and confidence intervals (CI). The mean difference (bias) between AVA _Cheetah (average) and AVA _Fick was 0.11 cm ² and the 95% LOA were ±0.42 cm ². The 95% CI of the bias was 0.02–0.2 cm ². The bias and 95% LOA of AVA _Cheetah (spot value) were 0.14 ± 0.42cm ², with a 95% CI of 0.06–0.23 cm ². No proportional bias was present. AVA _Cheetah thus appears to be a reasonably accurate measure of AVA in patients with severe aortic stenosis compared to AVA _Fick measured using a modified Fick CO. However, the limits of agreement were not narrow enough to consider AVA _Cheetah and AVA _Fick interchangeable.