ABC | Volume 110, Nº2, February 2018

Original Article Ferreira et al Alternative method to calculate simplified EOA proj Arq Bras Cardiol. 2018; 110(2):132-139 IBM SPSS Statistics version 23 (IBM, Vienna, Austria) and GraphPad Prism version 7.0 (GraphPad Software, La Jolla California, USA) were used for statistical analysis. Results Baseline characteristics Between September/2011 and November/2015, 22 patients [15 (68%) men, mean age 72 ± 9 years] with classical LFLG AS underwent a low dose dobutamine stress echocardiography in order to evaluate the true severity of the AS. No major adverse events were reported. Table 1 shows the baseline clinical and echocardiographic features of these patients as well as the hemodynamic evolution with dobutamine infusion. 8 (36%) patients reached the AHA/ACC criteria for true severe aortic stenosis, 11(50%) patients maintained the valve area – gradient discordance present at baseline and 3 (14%) patients showed a progression of hemodynamic indices suggestive of pseudo severe aortic stenosis. No patient ended up the stress exam with inversion of the area – gradient mismatch (ie, aortic valve area > 1,0 cm 2 and Vmax ≥ 4 m/s). Flow rate at baseline and at peak dobutamine i n f us i on wa s ca l cu l a t ed us i ng bo t h t he c l a s s i c Q classic = 1000 × LVOT VTI × CSA LVOT ET and the alternative equations (Q alternative = CSA LVOT × Vmean LVOT × 100) in all patients. Only 9 (41%) patients achieved a flow rate variation with dobutamine infusion assessed by both methods ≥ |15|%, enabling the simultaneous determination of the simplified projected aortic valve area at normal flow rate by the classic and the alternative formulas. Table 2 shows the baseline and peak dobutamine echocardiographic characteristics of this subset group of patients. A scatter plot showing the classic simplified projected aortic valve area values against the respective alternative simplified projected aortic valve area values was built (Figure 1). As suggested by the scatter plot, a strong linear association between the two methods of calculation was found – r (7) = 0,99, p < 0,001. Simple regression was conducted to find the best line that predicts the simplified projected aortic valve area calculated by the alternative method from the simplified projected aortic valve area calculated by the classic method. The results were statistically significant, F (1,7) = 245,5, p < 0,0001. The identified equation to understand this relationship was: alternative EOA proj = 1.00 (95% CI 0.85 – 1.15) x Classic EOA proj + 0,036 (95% CI -0.111 – 0.182). The adjusted R 2 was 0.97, meaning that 97% of the variance of the alternative EOA proj can be explained by classic EOA proj . A Bland-Altman analysis was performed to assess agreement between the two methods of EOA proj calculation. In Figure 2 the Y axis shows the differences between the two paired EOA proj measurements (alternative method – classic method) and the X axis represents the average of these measurements Alternative method + Classic method 2 .Normaldistribution of the differences between paired measurements was verified by use of the Shapiro-Wilk test for normal distribution (test statistics = 0,854, df = 9, p = 0,082). There is no trend in increases in the variability of the differences in relation to their mean. The calculated bias (the average of the paired differences) is 0.037 cm 2 (95% CI 0.004 – 0.066), meaning that on average EOA proj calculated by the alternative method measures 0.037 cm 2 more than EOA proj calculated by the classic method. This bias is statistically significant ( t = 2.619, df = 8, p = 0.031). The calculated 95% limits of agreement between the two methods are -0,04 and 0,12, which means that for 95% of the individuals, the EOA proj calculated by the alternative method would be between 0,04 cm 2 less and 0,12 cm 2 more than the EOA proj calculated by the classic method. Discussion The EOA proj is defined as the EOA of the aortic valve that would have occurred at a hypothetical standardized flow rate of 250 mL/s. This new echocardiographic index was developed in order to overcome the variable and unpredictable effect of dobutamine in flow rate. 4 In fact, patients with classic LFLG AS undergoing DSE have a wide variable response in terms of flow rate progression, which may be due to multiple factors including the variable presence of myocardial contractile reserve, the unpredictable chronotropic response to dobutamine and the potential development of left ventricle dyssynchrony with dobutamine infusion 3 Such variability in flow rate response may impose an insurmountable obstacle in the interpretation of ambiguous changes in mean pressure gradient and EOA. By normalizing the EOA at a hypothetical flow rate of 250 mL/s, the EOA proj enables direct comparison of AS severity in patients with classic LFLG AS that present different flow rate profiles with dobutamine infusion. In addition to make the interpretation of DSE results easier, this new parameter has also been shown to be related to actual AS severity (calcification at surgery) and to have an important value in mortality prediction. 4,7 In order to calculate the EOA proj , EOA is plotted against the mean transvalvular flow rate at different stages of DSE. The slope of this curve – called compliance – is then used to predict EOA at 250 mL/min. 4 A simplified version of the original formula substitutes the curve slope for an easier to calculate quotient Peak EOA – Rest EOA Peak Q – Rest Q . Thus, the simplified version of the EOA proj formula can be expressed as Peak EOA – Rest EOA Peak Q – Rest Q EOA proj = EOA basal + × (250 – Q rest ) . 8 Both the original and simplified version of the EOA proj formulae recommend the calculation of flow rate as the quotient between stroke volume and ET which requires 3 different measurements: 1) LVOT diameter (LVOT D ); 2) LVOT velocity-time integral (LVOT VTI ) and 3) ET measured at the aortic velocity spectrum. Both LVOT D and LVOT VTI are measures routinely done in DSE protocols performed for classic LFLG AS evaluation as they are needed to calculate EOA of the aortic valve by the continuity equation. However, the need for ET measured at the aortic velocity spectrum adds the requirement for an extra measurement in the usual protocol of DSE. Furthermore, this flow rate 134