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 1 – D-Station algorithm. ECG: electrocardiogram. Reading of entries and text files with strain curves and strain rate Definition of points on the electrocardiographic curve Separation into phases and parameters calculation Presentation of the strain curves/strain rate and strain parameters program are illustrated in Figure 1. D-Station does not replace pre‑existing platforms, but rather expands the possibilities of post-processing. Separation into phases Each strain curve corresponds to one or more cardiac cycles in certain region of the cardiac chamber and can be divided into the mechanical phases of this cycle. According to previous studies, 4 definition of these phases relies on the times of opening and closing of the aortic and mitral valves, on the time of electrical events, obtained fromelectrocardiogram (ECG) waves, as well as the time of the onset of the first and the second QRS complex, and onset of P-wave. 5,6 The ECG curves match well with the strain curve and the strain rate (SR) in the files. Considering the onset of the cardiac cycle at the onset of the QRS complex, six phases were defined, as follow (in order of occurrence): electrical mechanical coupling (EMC), isovolumic contraction (IC), ejection phase (Ejec), isovolumic relaxation, early filling (E), atrial contraction (A). A detailed description of definitions of each phase of the cardiac cycle is provided in the supplementary material. Algorithm of reading of the signs and parameters calculation The program entries are: 1) time of opening and closing of aortic and mitral valves; 2) raw data files containing the strain curves or strain rate; 3) identifier of the test; and 4) visualization option selected by the user. Further information can be found in the software manual, presented in the supplementary material of the study. Six visualization options are available in the current version of the software: • Strain - LV (left ventricular strain), strain rate - LV (left ventricular SR) and ECG; • Strain - LV , strain - LA (left atrial s train ) and ECG; • Strain - LV , strain rate - LA and ECG; • Strain - LV , strain - RV (right ventricular strain) and ECG; • Strain - LV , strain rate - LV and ECG, where SR is obtained from the strain curves; • Test option (CircAdapt interface): strain - LV and strain rate - LV In all these options, curves are exhibited simultaneously as shown in Figure 2. From raw data containing information of three-, four-, and two-chamber planes, left ventricular strain curves can be visualized, according to the model of the 18 segments proposed by the American Heart Association (AHA). 7 Processing of the raw data sheets consists in changing the format to optimize the software functioning. In addition, due to small changes in heart rate on ECG curves, the four‑chamber apical view was adopted as standard. After formatting of the sheets, a picture containing strain, SR and ECG curves is exhibited. The user should then define three points in the figure – the onset of QRS complex, the onset of P-wave and the onset of the second QRS complex. Based on the values obtained form these points and timing of the opening and closing of the valves, it is possible to determine each phase of the cardiac cycle. The D-station terminal exhibits the time points of each of these phases, as well as the values of each calculated parameter. The user can decide between a picture containing the curves of cardiac chambers of interest (Figure 3) or the picture containing the points used in the parameters’ calculation. Event timing and calculated parameters Each of the longitudinal strain curves presented in Figure 3 has an important event for the calculation of the software’s parameters: the peak systolic strain, defined as the peak value during systole, according to the EACVI/ASE. 7 The peak systolic strain of each segment is used for calculation of GLS, defined as the arithmetic mean of peak systolic strain values of all segments. All these possibilities of post-processing allow and/or facilitate the analysis of new parameters, including the strain/ SR of left and right atrium, right ventricular strain and diastolic recovery (diastolic stunning) 8 for example. Algorithm for recognition of the peak systolic strain The D-Station defines the peak systolic strain as the most negative strain value between the onset of the QRS and the AVC. This contrasts with the EchoPAC software, which determines the peak systolic strain according to the criterion presented in Figure 4. Validation of the D-Station: database and statistical analysis To validate the D-Station software, files containing strain curves of 48 individuals were obtained from the database of the Division of Echocardiography of Hospital Beneficiencia Portuguesa de São Paulo . We did not perform a sample calculation, and hence a convenience sample was selected by retrospective analysis of the database. All tests were performed 497