Echocardiographic assessment of dyssynchrony: moving forward.

Correction of mechanical dyssynchrony is believed to be the primary mechanism by which cardiac resynchronization therapy (CRT) improves clinical status and reduces left ventricular (LV) volume.1 The use of QRS duration as a surrogate for mechanical dyssynchrony has been intensely investigated, based on the suspicion that a direct measurement of mechanical rather than electric dyssynchrony might be more relevant in CRT. Indeed, although the majority of patients improve after CRT using the current treatment criteria, significant numbers of patients do not appear to derive a detectable benefit, either clinically or structurally.2 Conversely, there are patients with normal QRS who manifest mechanical dyssynchrony by echocardiographic techniques.3 Therefore, various imaging-based methods of detecting segmental systolic timing have been developed to enhance the sensitivity and specificity of patient selection criteria for response to CRT.1,4