Speckle-tracking strain analysis:
Speckle tracking strain echocardiography was used to determine RV lateral free wall average peak systolic strain . RV strain was measured using ECHOINSIGHT software (version 2.2.6.2230, Epsilon Imaging, Ann Arbor, MI). Based on the 4-chamber apical view, three successive RV cardiac cycles with a frame rate of 70-120/s were recorded. Right ventricular endocardial border was manually traced in still end-systolic frames, and the software performed automated tracking throughout the cardiac cycle. The automated tracking was visually verified and manually adjusted for adequate border delineation. Tissue velocities in the 2D plane are displayed throughout the cardiac cycle, representing magnitude and direction of motion. Finally, strain data was generated by analyzing the speckle pattern along the endocardial border in reference to one another. Longitudinal strain is defined as the percentage shortening of a regional area of interest (ROI) relative to its original length and is expressed as a negative value. The software further categorized the RV myocardium into six sections: basal RV free wall, mid-RV free wall, apical free wall, left basal septum, mid-left septum, and left apical septum and calculated the regional wall strain with the same manner. RV lateral free wall strain (average of the basal, mid, and apical free wall) was used in our analysis. Figure 1 demonstrated a representative case of RV dimension measurement.