ABC | Volume 114, Nº3, March 2020

Original Article Sousa et al. Software: analysis of strain curves Arq Bras Cardiol. 2020; 114(3):496-506 Figure 5 – Simultaneous display of 18 strain curves of the left ventricle, six strain curves of the right ventricle and electrocardiographic curve; MVC: mitral valve closure; AVO: aortic valve opening; AVC: aortic valve closure; MVO: mitral valve opening. c) Hypothesis test of the differences between EchoPAC and D-Station GLS values Since the differences between the measurements had normal distribution, we used the paired t-test (significance level of 5%). Results are presented in Figure 10, with a p-value of 0.6798, indicating acceptance of null hypothesis, i.e ., equivalence between the methods. d) Bland-Altman agreement analysis 9,10 Figure 11 despicts the Bland-Altman plot, which indicates agreement between the two methods as they meet the third (c) validation criterion . There is an evidence of large % differences for absolute (module) values of GLS < 10%. Discussion Analysis of agreement between the methods Validation analysis results met the validation criteria, indicating equivalence between GLS values obtained by EchoPAC and D-Station. In a detailed analysis of the data, we can see that, for values lower than 10%, there was a trend of higher percentage difference. Intriguingly, all these subjects had important ventricular dysfunction with intraventricular dyssynchrony of left bundle branch block type. Such discrepancies may be precipitated by some factors, as follow: 1) Lowabsolute values result in higher percentage differences; 2) Ventricular dyssynchrony with left bundle branch block usually presents a stretching of the basal segment of the inferolateral and/or anterolateral wall at the beginning of systole, as well as erratic, mid- and telesystolic movements of the septum after the typical “septal flash”. Both can generate positive peaks. While D-Station defines systolic peak as the most negative value, regardless of the positive (or less positive) peak in case of exclusively positive curves, the EchoPAC assumes, as a rule for systolic peak (peak systolic strain), a positive peak 75% greater than the negative systolic peak mode value, as shown in Figure 4. Also, in EchoPAC, although manual adjustments are common in these cases, we decided not to make these adjustments aiming at greater accuracy of the method. In summary, discrepancies in the definition of systolic peak reduce the reproducibility of GLS between programs in patients with left bundle branch block. This issue should be addressed in future studies. However, these discrepancies do not have a negative impact, especially if we consider the intraobserver variability of GLS values reported in the literature (5.2%), 16 and inter-software discrepancies regarding speckle filtering and tracking. 17-19 Therefore, analysis of the results validates the D-Station as an alternative to EchoPAC. Potential Applications of the D-Station Software There are numerous potential applications of the D-Station software: simultaneous analysis of different chambers allows the study on the interaction between left and right ventricles, as well as left ventricle and left atrium, which may be relevant in heart failure with preserved ejection fraction, pericardial disease and interventricular dyssynchrony. 501