Table 1. Comparison between 2D and 3D speckle-tracking analysis of LV myocardial strain by vendor-specific software (EchoPAC, GE Healthcare) [adapted from (18)].

Characteristics	3D strain	2D strain
Acquisition	One apical 3D full volume	Three parasternal and three apical 2D views
Heart rate	Regular (6-beat LV full volume)	Regular (consecutive 2D LV planes)
Feasibility in sinus rhythm	Good	Very good
Reliance on good image quality	Yes (++)	Yes (+)
Temporal resolution*	34–50 volumes/s	40–80 frames/s
Parameters	All strains (longitudinal, radial, circumferential)	All strains (longitudinal, radial, circumferential)
Two-directional (area) strain†	Yes	No
Bull’s-eye map‡	Dynamic	Static
Calculation of global strain	Simultaneous segmental values§	Non simultaneous segmental peaks§
Radial strain	Calculated from area strain (by the law of volume conservation)	Measured
Out-of-plane motion of speckles	No	Yes
Positive peak rule||	No	Yes
Drift compensation¶	No	Yes
Definition of end-systole	Time of LV minimal volume	Time of aortic valve closure

*, a higher range is advisable in tachycardia to avoid undersampling (40% of the heart rate); ^†, reflects a combination of longitudinal and circumferential strain; ^‡, bull’s-eye maps of 2D longitudinal strain display one snapshot with peak values of segmental strain; bull’s-eye maps of 3D strain parameters display simultaneous segmental strain values continuously throughout the cardiac cycle; ^§, with 2D longitudinal strain bull’s-eye, peak segmental values are displayed irrespective of their reciprocal timing during systole; with 3D strain bull’s-eye, simultaneous segmental strain values are displayed in each frame; ^||, in the bull’s-eye display, positive strain is displayed during systole for a certain segment only if the positive peak strain exceeds 75% of the peak negative strain value in the same segment; ^¶, all segmental strain curves are “forced” by the software to return to baseline at end-diastole. ECG, electrocardiogram.