Page 20 - Delaware Medical Journal - July 2016

Impact of Catheterization Lab Computer
Software Settings on Hemodynamic
Assessment of Aortic Stenosis
Zaher Fanari, MD; Anitha Rajamanickam, MD; Mathew Grove, MD; Sumaya Hammami, MD, MPH; Cassie Walls, BS; Paul Kolm, PhD; William Weintraub, MD; Andrew J. Doorey, MD
Background: Accurate assessment of cardiac output (CO) is a critical measurement in the calculation of aortic valve area (AVA). Due to the known inaccuracy of estimated Fick calculations, many measure thermodilution (TD) CO also, due to previous studies showing better correlation with the gold standard direct CO. Previous studies have shown suboptimal correlation between both methods. Most physicians assume that the TD CO is chosen by catheterization laboratory software for AVA evaluation. Our study was performed to check which CO method is assigned by our popular computer software system [Philips Xper Connect (XIM)] for the AVA calculation and the impact of that on clinical decision.
Methods: We studied 100 consecutive patients who underwent right and left heart catheterization from 2009 to 2012 for assessment of AVA and who had both estimated Fick and TD CO calculated. Correlation of direct continuous VO2, assumed VO2 and TD based CO measurements were assessed by linear regression analysis and by variance component analysis.
Results: We found that whichever CO calculation was entered first to the software system became the determinative output used to calculate the AVA appearing on the final report. This was the estimated Fick method in 32 patients and
TD in 68 patients. The CO used for the final report depended solely on the timing of the oxygen saturation samples. AVA calculated using the two different methods varied widely, with weak correlations. (Pearson R=0.73, Intra-Class Correlation (ICC) =0.72). This discrepancy affected recommendation for surgery (AVA <1.0 cm2) in 18 cases (18 percent of patients).
Conclusion: Our widely used software has an arbitrary method of selecting the determinative CO to calculate the final AVA. For TD CO to ‘trump’ the Fick CO a complex series of computer commands needs to be performed. None of the physicians or technicians was aware of this software selection process, which affects critical treatment decisions.
Key Words: Computer Software; Hemodynamics; Cardiac Output; Aortic Stenosis
BACKGROUND
Cardiac output (CO) is one of the most important parameters of cardiac performance, an accurate assessment of which is a critical function of cardiac catheterization laboratories (CCL).1 This is especially true in valvular disorders – for example in patients with aortic valve area must be calculated using the CO measurements.2 A precise measurement of CO and, consequently, the degree of AS severity is crucial to ensure that only appropriate patients are referred for valve replacement and to prevent both premature and delayed aortic valve replacement.3
Over the past decades, many methods for CO measurement have been developed. One of the most widely used methods
is the Fick equation. This equation is based on the principle described by Adolfo Fick in 1870, according to which the total uptake or release of a substance by an organ is the product

concentration difference of the substance.4 The oxygen uptake

and the arteriovenous oxygen content difference. When oxygen consumption is directly measured, this is called a measured or direct Fick and is considered the gold standard. Alternatively CO can be calculated using estimated oxygen consumption, commonly called an “estimated” Fick. Another method to estimate CO is using the Thermodilution (TD) technique. In
this method an indicator curve is obtained after injection of the indicator (usually cold or warm saline) and this curve is used to estimate CO by using the Fick principle utilizing temperature instead of oxygen as the variable.5,6 While this method can show variability in measurement due to other underlying cardiac abnormalities such as tricuspid regurgitation,7,8 it has generally been shown to be nearly as accurate as a measured Fick, and superior to the estimated Fick method, even in those with severe valvular disease where tricuspid regurgitation is likely common.3
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Del Med J | July 2016 | Vol. 88 | No. 7
Abstract