Abstract
Abstract Background Two-dimensional echocardiographic strain measurements have limited reproducibility, hampering the ability to detect subtle changes in repeated examinations. This is partly related image acquisition, including apical foreshortening and suboptimal transducer rotation and/or tilt, resulting in non-standardized imaging planes. However, the impact of image acquisitions on measured global longitudinal strain (GLS) values has not been quantified in large studies due to the labor-intensive task of measuring apical foreshortening and characterizing the imaging plane. Recent advances in echocardiographic image analysis based on deep learning (DL) may shed new light on this problem by enabling measurements of apical foreshortening and estimation of transducer angulation without human intervention. Purpose To quantify the effect of apical foreshortening and transducer rotation/tilt on GLS values. Methods To isolate the effect of foreshortening and transducer rotation/tilt on GLS values, 1395 patients without cardiac pathology were included in the analysis. For each patient, GLS was measured in the three apical views (four chamber, two chamber, long-axis) using commercial software. The same recordings were automatically analyzed using DL to obtain indicators of apical foreshortening (apex displacement in the long axis and short axis directions) and of the transducer rotation and tilt relative to the heart. Correlations between strain values and the foreshortening/rotation/tilt indicators were calculated. When significant correlation was detected, a regression analysis was performed to quantify the absolute change in GLS that can be related to foreshortening and transducer rotation/tilt. The first and last 5% quantiles of each DL indicator were excluded from these analyses. Results For each view, GLS was significantly correlated (p<0.05) with at least one of the foreshortening or transducer angulation indicators (Fig. 1). The regression analyses suggested that apical foreshortening and suboptimal transducer rotation/tilt can cause GLS variations up to 1.3 percentage points, representing a relative change of 6.5%. Conclusions Apical foreshortening and transducer rotation/tilt quantified using automatic DL methods were related to GLS values in a large dataset. The magnitude of the relationship suggests that apical foreshortening and transducer rotation/tilt can limit the usefulness of GLS measurements, especially in the context of repeated examinations where detecting small relative changes is important. Overall, this retrospective analysis confirms the importance of minimizing apical foreshortening and of standardizing transducer angulation to reduce minimal detectable changes in GLS and improve its reproducibility.