Based on these observations, techniques have been developed to correct dyssynchrony. Cardiac resynchronization therapy (CRT) has been shown to improve subjective and objective parameters in heart failure patients with QRS duration > 120msec. However, there is a group of heart failure patients who did not respond to CRT. Also it has been noted that approximately 30% of heart failure patients with QRS duration > 120 msec do not have actual mechanical dyssynchrony by tissue doppler imaging. The electromechanical discrepancy of ventricular dyssynchrony has been suggested as the possible explanation for the lack of response. Also, there are heart failure patients with normal QRS duration who do have mechanical dyssynchrony. These findings bring more emphasis to the importance of mechanical dyssynchrony than electrical dyssynchrony, which is measured by QRS duration on surface EKG.