Contrast-enhanced echocardiographic measurement of longitudinal strain: accuracy and its relationship with image quality.

The importance of left ventricular (LV) global longitudinal strain (GLS) is increasingly recognized in multiple clinical scenarios. However, in patients with poor image quality, strain is difficult or impossible to measure without contrast enhancement. The feasibility of contrast-enhanced GLS measurement was recently demonstrated. We sought to determine: (1) whether contrast enhancement improves the accuracy of GLS measurements against cardiac magnetic resonance (CMR) reference, (2) their reproducibility compared to non-enhanced GLS, and (3) the dependence of accuracy and reproducibility on image quality. We prospectively enrolled 25 patients undergoing clinically indicated CMR imaging who subsequently underwent transthoracic echocardiography (TTE) with and without low-dose contrast injection (1-2 mL Optison/3-5 mL saline IV, GE Healthcare). GLS was measured from both non-contrast and contrast-enhanced images using speckle tracking (EchoInsight, Epsilon Imaging). These measurements were compared to each other and to CMR reference values obtained using feature tracking (SuiteHEART, NeoSoft). Inter-technique comparisons included linear regression and Bland-Altman analyses. A random subgroup of 15 patients was used to assess inter- and intra-observer variability using intra-class correlation (ICC). Contrast-enhanced GLS was in close agreement with non-enhanced GLS (r = 0.95; bias: - 0.2 ± 1.5%). Both inter-observer (ICC = 0.88 vs. 0.82) and intra-observer variability (ICC = 0.91 vs. 0.88) were improved by contrast enhancement. The agreement with CMR was better for contrast-enhanced GLS (r = 0.87; bias: 1.1 ± 2.2%) than for non-enhanced GLS (r = 0.80; bias: 1.3 ± 2.7%). In 12/25 patients with suboptimal TTE images that rendered GLS difficult to measure, contrast-enhanced GLS showed better agreement with CMR than non-enhanced GLS (r = 0.88 vs. 0.83) and also improved inter-observer (ICC = 0.83 vs. 0.76) and intra-observer variability (ICC = 0.88 vs. 0.82). In conclusion, contrast enhancement of TTE images improves the accuracy and reproducibility of GLS measurements, resulting in better agreement with CMR, even in patients with suboptimal acoustic windows. This approach may aid in the assessment of LV function in this patient population.