2- Speckle Tracking Echocardiography (STE)
All measurements used in this analysis were made offline by a single investigator, blinded to the clinical data. The longitudinal strain was obtained from apical 4-chamber, 3-chamber and 2- chamber views. Apical 4-chamber and 2 view was used for LA strains measurements. The frame rate for images was adjusted between 60-80 frames/s. For 2 dimensional STE analysis, a line was manually drawn along the LA endocardium when the LA was at its minimum volume after contraction. The software then automatically generated additional lines near the atrial epicardium and mid-myocardial line, with a region of interest default width of 15 mm. Before processing, a cine loop preview feature visually confirmed that the internal line follows the LA endocardium throughout the cardiac cycle. If tracking of the LA endocardium was unsatisfactory, manual adjustments or changing software parameters (e.g. region of interest size or smoothing functions) was made. The software divided the LA endocardium into 6 segments. Segments in which no adequate image quality could be obtained were rejected by the software and excluded from the analysis. Overall, 1644 segments were analyzed (12 segments for each patient), and a total of 4.0 percent segments were excluded. LA peak strain just before mitral valve opening was taken as peak atrial longitudinal strain (PALS) and LA strain just before atrial contraction (onset of the P-wave on electrocardiography) was taken as peak atrial contraction strain (PACS), and conduit strain was obtained by subtracting the value of the peak atrial contraction strain from that of the peak atrial longitudinal strain.
On the LA strain curve, the time from the beginning of the QRS complex to the peak strain (reservoir strain) was measured for each segment. LA mechanical dispersion was defined as the standard deviation of time to peak positive strain from the 12 LA segments. Higher values of SD are thought to suggest a greater degree of LA dispersion12.