Fig. 4

Longitudinal strain curves of a CRT responder. a and b shows the longitudinal strain curves for a responder at baseline and 6-month follow up respectively. The patient’s LVEF improved from 25 to 47%. QRS was recognized by software as the beginning of systole. Since the negative peak before AVC was automatically recorded as the peak strain, the global strain (GS) by software was − 7.9% at baseline and − 5.3% at follow-up. These findings were contrary to the LVEF improvement. However, after studying the EC within LV_Ej and the MLS throughout the cardiac cycle, we found that MLS was slightly improved, while EC and ECR were significantly improved