Comparison of estimations versus measured resting oxygen consumption in patients with heart failure and reduced ejection fraction undergoing right heart catheterization

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Paul J. Chase (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Paul Davis

Abstract: Affecting close to 6 million people in the United States, heart failure (HF) represents the final stage of several diseases of the heart and is commonly defined as a reduction in the heart's ability to circulate blood. Cardiac output during right heart catheterization is an important variable used in patient selection for advanced therapies, such as cardiac transplantation and left ventricular assist device implantation. It is common practice to utilize the Fick method to determine the cardiac output (cardiac output = oxygen consumption [VO2]/arteriovenous oxygen difference) inputting estimated VO2 from one of three published empirical formulae. However, these estimation equations have not been validated in patients with HF. The purpose of this study was to determine the accuracy of three widely used equations for the estimation of VO2 compared to direct breath-by-breath measurement of VO2 and determine to what extent clinically significant error occurs in patients with HF and reduced ejection fraction (HFrEF). Forty-four patients with HFrEF undergoing routine cardiac catheterization (65.9% male, 65.9% Caucasian, 64.5 ± 10.7 years old) performed 10 minutes of ventilatory gas exchange immediately following catheterization procedures, and averaged results of the last five minutes were compared to the derived estimations by: LaFarge & Miettinen, Dehmer et al. and Bergstra et al. (estimated - measured). Single-sample t-tests found the mean difference between the estimation of LaFarge & Miettinen was not significant (-10.3 ml/min ± 6.2 SE, p=0.053), but significant differences were found with Dehmer et al. (16.0 ml/min ± 6.4 SE, p=0.008) and Bergstra et al. (40.6 ml/min ± 6.4 SE, p<0.001). Bland-Altman plots demonstrated limits of agreement outside of acceptable limits with trends towards overestimation in patients with low VO2 and underestimation in patients with higher VO2 for all equations. Bland-Altman plots and single-sample t-tests of dichotomous groups (sex, pulmonary hypertension and aldosterone antagonist medication) did not identify a subgroup where any of the equations were acceptable. The rate of &ge25% error in the estimates of the LaFarge & Miettinen, Dehmer et al. and Bergstra et al. equations occurred in 11%, 23% and 45% (respectively) of the patients. Clinically significant error (misclassification) in the cardiac index derived from the Lafarge & Miettinen, Dehmer et al. and Bergstra et al. equations for three clinically important classifications: cardiogenic shock - 20.5%, 22.7% and 31.8%; hypoperfusion - 15.9%, 15.9% and 25%; abnormal - 13.6%, 13.6% and 15.9%, respectively. Exploring possible HFrEF-specific equations, linear regression modeling was performed with 34 patients. Two models were developed: (Model 1) VO2=-10.76+(127.74*body surface area)+(aldosterone antagonist [prescribed=1, not prescribed=-1]*22.15); (Model 2) VO2=149.4+(sex [male=1, female=-1]*25.41)+(aldosterone antagonist [prescribed=1, not prescribed=-1]*28.34). Bland-Altman plots and t-tests with the remaining 10 patients yielded limits of agreement outside of acceptable limits despite lack of significant differences between the estimated and measured VO2 for Model 1 and Model 2 (11.0 ml/min ± 10.7 SE, p=0.165; 12.4 ml/min ± 0.249, p=0.249). These findings do not support the use of these empirical formulae to estimate the resting VO2 in patients with HFrEF undergoing right heart catheterization. The direct measurement of the resting VO2 should be the primary method applied to the Fick equation for cardiac output.

Additional Information

Language: English
Date: 2014
Cardiac Output, Heart Failure, Resting Oxygen Consumption, Right Heart Catheterization
Cardiac catheterization
Cardiac output $x Measurement
Oxygen consumption (Physiology)
Heart failure $x Treatment

Email this document to