Echopac workstation

To further compare in vivo and in vitro conditions, strain measurements were performed both in the silicone phantom and in the in vivo heart. 3D-PTV data was used to extract strain in the silicone phantom. The strain is calculated as $$\gamma =(L-L_0)/L_0,$$ where L₀ is the initial length of interest and L is the length at a certain time instance.
In vivo strain measurements were performed using 2D transthoracic echocardiography from the apical four-chamber view at rest (Vivid 9 echocardiography scanner, GE Medical Systems, Horten, Norway). Deformation imaging by speckle tracking is a technique, which is an angle-independent method avoiding limitations related to translational cardiac motion. The endocardial border was traced and the region of interest was adjusted to the myocardial wall. Wall motion was tracked over the cardiac cycle. Myocardial speckle tracking was digitally analyzed using Echo Pac Work Station (GE Medical Systems).

The LV global longitudinal strain (GLS) was calculated in the longitudinal three-chamber, two-chamber, and four-chamber views by 2D-speckle-tracking echocardiography with high-quality ECG gated images. The frame rate was set at between 50 and 90 frames/s, and a minimum of three cardiac cycles were obtained for each loop. The images were analyzed using software with the EchoPAC workstation (version 112, GE Healthcare, USA). The left ventricular endocardial border was manually traced in the end systole. Subsequently, software generates a speckle-tracking region-of-interest (ROI) to include the entire myocardium between the endocardium and the epicardium. The left ventricular was divided into 18 myocardial segments. Longitudinal strains for each segment were recorded and presented as a bull's eye. The strain values for all the segments are recorded and averaged to obtain the global longitudinal strain. GLS is presented as a percent change (%). Negative values of GLS indicate myocardial contraction. The predefined cutoff for subclinical left ventricular systolic dysfunction in patients with septic shock was defined by a GLS ≥ −15% (less negative than −15%) according to the previous studies [14 (link)–16 (link)].

A complete echocardiographic examination of the heart was performed by two experienced veterinarians (ADP, MB) according to the guidelines [28 (link)]. A Vivid E9 echocardiographic system (General Electrics Healthcare, Milwaukee, WI, United States) with a 5–10 MHz transducer was used. A limb ECG lead II was recorded simultaneously. Loops and images were analyzed using an offline Echo-PAC workstation (GE Healthcare, Europe). In all cats, the following echocardiographic parameters were measured: two-dimensional left atrial measurements from the right parasternal long and short-axis view; left ventricular M-mode or 2-D measurements from the right parasternal short-axis view; spectral and color flow Doppler velocities from the left apical view; and tissue Doppler annular velocities from the left apical view.
Normal cats were considered according to previously published feline echocardiographic references, and hypertrophic cardiomyopathy was diagnosed if the LV wall was thicker than 6 mm [29 (link),30 (link),31 (link)]. All animals with systemic hypertension, hyperthyroidism, aortic stenosis, neoplastic infiltration or other congenital and acquired diseases were excluded from the study. Restrictive cardiomyopathy was diagnosed when normal LV walls with biatrial enlargement and restrictive mitral inflow pattern was detected [32 (link),33 (link)].

A complete transthoracic echocardiogram was performed using a GE VIVID E9 ultrasound system (GE Ultrasound, Horten, Norway) equipped with a phased-array transducer (M5S). Standard echocardiographic parameters were obtained according to the principles described in the ASE/EACVI recommendations [7 (link)]. Left ventricular ejection fraction (LVEF) was measured using the apical biplane Simpson’s method. LV dysfunction was defined as LVEF < 52% for men and LVEF < 54% for women, consistent with the current recommendations [7 (link)]. Left ventricular diastolic function and the severity of valvular regurgitation (AR, MR, TR) and aortic stenosis (AS) were assessed using an integrated method consistent with the established practice guidelines [8 (link),9 (link),10 (link)]. The systolic pulmonary artery pressure (SPAP) was estimated using TR peak velocity and right atrial pressure, which was estimated by the inferior vena cava diameter in a long-axis subxiphoid view and its response to inspiration. All echocardiograms were stored digitally, and further offline analysis was performed using an EchoPAC workstation (v201, GE Healthcare, Horten, Norway).

All patients underwent echocardiography at the time of enrollment. Patients were examined in the left lateral decubitus position using a GE VIVID E95 ultrasound system (GE Ultrasound, Horten, Norway) equipped with a phased-array transducer (M5S). Standard echocardiographic parameters were obtained according to the guidelines of the American Society of Echocardiography (ASE) and the European Association of Cardiovascular Imaging (EACVI) recommendations (12 (link), 13 (link)). Data acquisition was obtained from the parasternal long- and short-axis views and the three standard apical views. Three consecutive cardiac cycles were recorded during quiet respiration for each view. Grayscale recordings were optimized for LV evaluation at a rate of 50–80 frames/s, and only patients with these parameters were included in the subsequent analyses. All echocardiograms were digitally stored, and further offline analysis was performed using a commercial EchoPAC workstation (v204, GE Healthcare, Horten, Norway).