Strain and Strain Rate Echocardiography

Myocardial function is eventually determined by the shortening and lengthening of myocardium, i.e., myocardial deformation or strain. The exact and direct measure of myocardial deformation has been dependent on the in vitro analysis of myocardial length. This is not an ideal physiological approach due to the change of the surrounding environment, and the process is rather tedious. Thus, this in vitro approach is primarily a research tool.

Thanks to recently developed imaging techniques, regional myocardial deformation can now be measured. Using the myocardial tagging technique, one can measure myocardial strain with high accuracy. Currently, this is used as the clinical standard for the noninvasive evaluation of regional function.¹ However, due to cost and long time needed for off-line analysis, myocardial tagging by MRI is not routinely utilized for clinical purposes. In 1998 and then in 2000, Heidelm² and Urheim,³ et al., reported that based on myocardial velocities by tissue Doppler imaging (TOI), the rate of myocardial deformation (strain rate or myocardial velocity gradient) can be calculated. In validation studies, Doppler-derived strain accurately reflected regional myocardial shortening and lengthening when compared to measurements by sonometric crystals. Since then, strain rate imaging (SRI) has been examined in animal and clinical studies for the assessment of cardiac function.