Correlating QLV Interval to Left Ventricular (LV) Lead Position in Patients Receiving Cardiac Resynchronization Therapy.

Measurements of the QLV interval is defined from the onset of the QRS width of the surface ECG to the first large positive or negative peak of the LV EGM during a cardiac cycle. Recorded EGM's will be measured at three distinct points (basal, mid, and distal) within each target vessel.