Intervendor Variability of Two-Dimensional Strain Using Vendor-Specific and Vendor-Independent Software

Background: Although two-dimensional (2D) strain is widely used to assess left ventricular mechanics, the strain values derived from vendor-specific 2D speckle-tracking software are different even for the same subjects and are therefore not interchangeable. The aim of this study was to test the hypothesis that vendor-independent software would produce lower intervendor variability between 2D strain measurements and overcome this limitation. Methods: Two sets of three apical images were acquired using two of three types of ultrasound machines (GE, Philips, and Toshiba) in 81 healthy volunteers (GE vs Philips in 26 subjects, Philips vs Toshiba in 31 subjects, and GE vs Toshiba in 24 subjects). Two-dimensional global longitudinal strain (GLS) was measured using vendor-specific software and two vendor-independent software packages (TomTec and Epsilon) in each set of apical images, and GLS values were directly compared with one another. Results: The upgrades of vendor-specific software yielded different values of GLS compared with the previous versions of the software. The correlations between the GLS values determined using vendor-specific software exhibited a wide range of r values (r = 0.23, r = 0.42, and r = 0.72), with significant bias, with the exception of one comparison. The vendor-independent software provided modest degrees of correlation (TomTec: r = 0.65, r = 0.65, and r = 0.77; Epsilon: r = 0.65, r = 0.74, and r = 0.77), with limits of agreement (range, +/- 3% to +/- 4.5%) that were not negligible. Conclusions: Although the vendor-independent 2D strain software provided moderate correlations between the GLS values of the ultrasound images obtained from the same subjects using different vendors, relatively large limits of agreement remain a relevant problem. These results suggest that the same ultrasound machine and the same 2D speckle-tracking software should be used for longitudinal analysis of strain values in the same subjects and for cross-sectional studies.