The left panel shows the concept of three-dimensional (3-D) area strain. Area strain expresses how the change in a regional area of the endocardium in a phase vs. that in the diastolic phase. Area strain is combined with both 3-D longitudinal and circumferential factors. The right panel shows an example of the strain dyssynchrony index using area tracking (ASDI). ASDI was calculated as the wasted energy per segment due to dyssynchrony and was determined by using the average difference between peak strain (ε-peak) and end-systolic strain (ε-ES) from 16 segments.