Time to Calm the Fick Down? A Systematic Review and Meta-Analysis of Thermodilution Compared to Direct Fick in Tricuspid Regurgitation.

Background: Many clinicians consider thermodilution (TD) as a means to measure cardiac output (CO) to be unreliable in patients with tricuspid regurgitation (TR). No systematic appraisals of this clinical issue have been conducted. We hypothesized that the level of inaccuracy of using TD in patients with TR, compared to the direct Fick (DF) method, to determine CO, is overstated.

Methods: We performed a systematic search of 6 major literature databases for the period from 1946 to July 2023. Studies were included if they included CO measurements determined with both TD and the DF method in patients with vs without TR. Meta-analysis of the correlation between the measurements determined by TD vs the DF method was performed, stratified by the presence of TR.

Results: A total of 1064 studies were identified, of which 8 met the inclusion criteria. Four of the studies were included in the pooled analysis. The presence of TR did not affect the correlation between CO measurements determined by TD vs the DF method (moderate-to-severe TR:  = 0.90, 95% confidence interval 0.76, 0.96; mild or no TR,  = 0.86, 95% confidence interval 0.71, 0.93). Many studies had high levels of heterogeneity and risk of bias.

Conclusions: The accuracy of CO measurements made using TD, compared to the gold-standard DF method, may not be meaningfully affected by the presence of moderate-to-severe TR. Given the high levels of heterogeneity and risk of bias of the included studies, these findings should be replicated in a modern cohort.