This article appears in the following Europace issue: Spotlight Issue: Cardiac Imaging in EP and CRT [View the issue table of contents]
IMAGING IN CRT
The role of tissue Doppler and strain imaging in predicting response to CRT
The Cardiovascular Institute, University of Pittsburgh, Scaife Hall 564, 200 Lothrop Street, Pittsburgh, PA 15213-2582, USA
Aims: Several echocardiographic methods have been proposed to assist in patient selection for cardiac resynchronization therapy (CRT). The prevailing hypothesis is that echocardiography may be superior to the electrocardiogram to qualify abnormalities in regional mechanical activation, because QRS widening is only a surrogate for ventricular dyssynchrony.
Methods and results: This review will focus on tissue Doppler (TD) and strain imaging, including their advantages and disadvantages for patient selection for CRT. Colour-coded TD remains to be one of the most promising means to quantify dyssynchrony. Tissue Doppler velocity data have a more favourable signal-to-noise ratio compared with TD strain or strain rate imaging. However, velocity data are affected by Doppler angle of incidence and passive or tethering motion. A newer promising method is speckle-tracking echocardiography to calculate strain. An opposing wall delay in peak TD velocity 
65 ms has been associated with clinical and ventricular response to CRT. The initial experience with speckle tracking used the short-axis view to calculate radial strain. An anterior-septal to posterior wall peak strain delay 130 ms has been associated with an ejection fraction response to CRT.
Conclusion: Although no ideal echo-Doppler method has yet been discovered to select patients for CRT, technical refinements and advances in understanding of pathophysiology continue to favourably impact on potential clinical applications.
Key Words: Echocardiography, Pacing therapy, Doppler ultrasound, Congestive heart failure
* Corresponding author. Tel: +1 412 647 6570; fax: +1 412 647 0568. E-mail address: gorcsanj{at}upmc.edu