Speckle tracking echocardiography: clinical applications in cardiac resynchronization therapy.

Cardiac resynchronization therapy (CRT) is a proven therapy for selected patients with heart failure, it has been shown to improve symptoms and left ventricular (LV) function and prolong survival. Despite proven benefit of CRT, a significant proportion of patients fail to respond to CRT. Multiple factors contribute to the non-response such as patient selection and device implantation including LV lead placement. Speckle tracking echocardiography (STE) derived strain imaging offers detailed characterization of LV function and provides indices of mechanical dyssynchrony, in addition, STE systolic strain could be used to identify area of scar, therefore applications of STE-derived strain imaging in CRT warrant a closer inspection. This review considers and summarizes different indices of mechanical dyssynchrony generated by STE-derived strain imaging and their relevance in patient selection for CRT and their prognostic values in predicting response to CRT. This review further examines applications of STE-derived strain imaging in optimizing LV lead position by detecting site of latest mechanical activation and presence or absence of transmural scar in a particular segment.