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Thomas Komanek, Marco Rabis, Saed Omer, Jürgen Peters, Ulrich Frey

• \(\bf Background\) Echocardiographic quantification of ejection fraction (EF) by manual endocardial tracing requires training, is time-consuming and potentially user-dependent, whereas determination of cardiac output by pulmonary artery catheterization (PAC) is invasive and carries a risk of complications. Recently, a novel software for semi-automated EF and \(\it CO\) assessment (AutoEF) using transthoracic echocardiography (TTE) has been introduced. We hypothesized that AutoEF would provide EF values different from those obtained by the modified Simpson's method in transoesophageal echocardiography (TOE) and that AutoEF \(\it CO\) measurements would not agree with those obtained via \(VTI_{LVOT}\) in TOE and by thermodilution using PAC. \(\bf Methods\) In 167 patients undergoing coronary artery bypass graft surgery (CABG), TTE cine loops of apical 4- and 2-chamber views were recorded after anaesthesia induction under steady-state conditions. Subsequently, TOE was performed following a standardized protocol, and \(\it CO\) was determined by thermodilution. EF and \(\it CO\) were assessed by TTE AutoEF as well as TOE, using the modified Simpson’s method, and Doppler measurements via velocity time integral in the LV outflow tract (\(VTI_{LVOT}\)). We determined Pearson’s correlation coefficients \(\it r\) and carried out Bland–Altman analyses. The primary endpoints were differences in EF and \(\it CO\). The secondary endpoints were differences in left ventricular volumes at end diastole (LVEDV) and end systole (LVESV). \(\bf Results\) AutoEF and the modified Simpson's method in TOE showed moderate EF correlation (\(\it r\) = 0.38, \(\it p\) < 0.01) with a bias of -12.6% (95% limits of agreement (95%LOA): -36.6 – 11.3%). AutoEF \(\it CO\) correlated poorly both with \(VTI_{LVOT}\) in TOE (\(\it r\) = 0.19, \(\it p\) < 0.01) and thermodilution (\(\it r\) = 0.28, \(\it p\) < 0.01). The \(\it CO\) bias between AutoEF and \(VTI_{LVOT}\) was 1.33 l \(min^{−1}\) (95%LOA: -1.72 – 4.38 l \(min^{−1}\)) and 1.39 l \(min^{−1}\) (95%LOA -1.34 – 4.12 l \(min^{−1}\)) between AutoEF and thermodilution, respectively. AutoEF yielded both significantly lower EF (\(EF_{AutoEF}\): 42.0% (IQR 29.0 — 55.0%) vs. \(EF_{TOE Simpson}\): 55.2% (IQR 40.1 — 70.3%), \(\it p\) < 0.01) and \(\it CO\) values than the reference methods (\(CO_{AutoEF biplane}\): 2.30 l \(min^{−1}\) (IQR 1.30 - 3.30 l \(min^{−1}\)) vs. \(CO_{VTI LVOT}\): 3.64 l \(min^{−1}\) (IQR 2.05 - 5.23 l \(min^{−1}\)) and \(CO_{PAC}\): 3.90 l \(min^{−1}\) (IQR 2.30 - 5.50 l \(min^{−1}\)), \(\it p\) < 0.01)). \(\bf Conclusions\) AutoEF correlated moderately with TOE EF determined by the modified Simpson's method but poorly both with \(VTI_{LVOT}\) and thermodilution \(\it CO\). A systematic bias was detected overestimating LV volumes and underestimating both EF and \(\it CO\) compared to the reference methods.