Inter-vendor variability and reproducibility of subcostal left ventricular longitudinal strain

Left ventricular longitudinal strain (LVLS) performed using subcostal windows is a novel alternative for patients who require strain imaging but have poor apical windows. We investigated the reproducibility and inter-vendor variability of subcostal LVLS. One hundred and twenty-four echocardiographic studies were analysed from 73 women with early stage HER2-positive breast cancer. Speckle tracking strain was performed offline using EchoPAC and TomTec on subcostal 4-chamber and 3-chamber views to obtain subcostal 4-chamber (SC4_LS) and 3-chamber (SC3_LS) LVLS which was then averaged (SCav_LS). Reproducibility of subcostal single chamber and averaged LVLS were assessed. Measurements between platforms were compared. Strain was reported in absolute magnitude. EchoPAC measurements of SC3_LS (20.5 +/- 2.4% vs. 21.2 +/- 2.5%, p = 0.002) and SCav_LS (20.9 +/- 2.1% vs. 21.2 +/- 2.1%, p = 0.02) were lower than TomTec measurements while SC4_LS was similar (21.3 +/- 2.7% vs. 21.3 +/- 2.5%, p = 0.94). Mean differences between EchoPAC and TomTec were <= 0.6% strain units for all subcostal LVLS measurements; SCav_LS showed the narrowest limits of agreement (LOA) (mean difference - 0.3%, LOA - 3.2 to 2.6%). EchoPAC and TomTec measurements of SCav_LS showed good correlation (r = 0.76, p < 0.001). Intra-observer and inter-observer analysis showed good reproducibility. Inter-observer variability was lower than inter-vendor variability; SCav_LS was most reproducible: inter-observer relative mean error was 3.6% for EchoPAC and 4.3% for TomTec and inter-observer LOA were +/- 2.1% for EchoPAC and +/- 2.6% for TomTec. Averaged subcostal LVLS was highly reproducible with inter-observer variability comparable to GLS. Inter-vendor differences in averaged subcostal LVLS were small but statistically significant.