 Once the subjects are enrolled in the study, a 12-lead ECG will be performed instead of a 3 lead ECG before ICD interrogation baseline ECG. A 12 lead ECG will then be repeated while performing right ventricular pacing through the programmer at 100 beats per minute at the time of pacing threshold testing paced ECG. QRS durations from the baseline and paced ECG will be measured electronically in leads V3-V6. The measured QRS complexes should not be preceded by an atrial or ventricular premature complex. 