 Currently, the indications for CRT include end-stage heart failure class II-IV with an EF 35, and a QRS duration 120ms. The QRS duration is used as an indicator of the degree of ventricular electromechanical dyssynchrony, however, a growing number of studies have postulated its inability to predict response to therapy. As a result, other measures of mechanical dyssynchrony are being sought to guide therapy. The vast majority of these studies have examined clinical, cardiac, electrocardiographic, and device-specific indices, however, a widely accepted predictor of response to CRT is lacking. 