Transthoracic echocardiography was performed in the left lateral decubitus position by experienced cardiac sonographer using a commercially available CX50 ultrasound machine (Philips Ultrasound System, Andover, MA, USA) according to the recommendation of the American Society of Echocardiography [24]. The data were saved digitally and analyzed offline using QLAB workstation (version 10.5, Philips Healthcare, Andover, MA, USA).

Ventricular volumes and areas were measured at end-systole and end-diastole to obtain left ventricular ejection fraction and RV fractional area change, respectively [25,26]. RA volumes were automatically calculated by the software using Simpson’s method. RA maximal volume (Vmax) was obtained in ventricular end-systole at the onset of tricuspid valve opening, pre-systolic volume (Vpre) was obtained preceding the P wave and minimal volume (Vmin) was obtained at the onset of tricuspid valve closure [26]. RA volumes were indexed to body surface area. RA total emptying fraction (EFtot) was calculated by (Vmax–Vmin)/Vmax, passive emptying fraction (EFpass) was (Vmax–Vpre)/Vmax, and active emptying fraction (EFact) was (Vpre–Vmin)/Vpre [27].

Peak early diastolic E-wave velocity, peak late diastolic A-wave velocity, peak tricuspid regurgitant velocity and pulmonary artery systolic wave acceleration time were obtained by pulsed-wave Doppler echocardiography. Due to the availability and feasibility of pulmonary artery systolic wave acceleration time in all subjects [28], mean pulmonary arterial pressure (mPAP) was assessed by pulmonary artery systolic wave acceleration time [29]. Systolic pulmonary arterial pressure was assessed using simplified Bernoulli equation: 4×peak tricuspid regurgitant velocity2 + 5 mmHg (an estimated central venous pressure) [29].

RV-focused apical four-chamber greyscale images were obtained using 2D speckle-tracking echocardiography with 70–90 frames per second. For evaluating RV longitudinal systolic function, tricuspid annular motion was calculated from average of tricuspid lateral and septal annular displacement using 2D speckle-tracking echocardiography [30], and RV global longitudinal strain (GLS) was assessed automatically in RV six segments by the software [31].

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