A large inherent delay between the ECG and EGM signals in the pacing system analyzer from Medtronic makes it unsuitable to estimate timing events during CRT implantation

Following an observation of pacing markers being placed after the beginning of the paced QRS complex when using the analyzer module 2290 of the Medtronic 2090 programmer, we decided to determine the delay between the EGM and the ECG channels and comparing it to the St Jude Merlin® programmer. We obtained ECG lead I simultaneously from both the ECG cable and by attaching the atrial clamps of the EGM cable on the left and right shoulder. We were then able to directly measure any delay. Then we compared measurements of start QRS to LV sense (qLV) in patients implanted with CRT in the last year where we had data on qLV at implant and at 6-month follow-up. At implant qLV was measured by the analyzer modules and at 6-month follow-up, it was measured in the pacing devices. We found that the delay between the EGM and ECG channels was 59 ± 4 ms in the Medtronic analyzer (ECG first) and 4 ± 3 ms in the St Jude analyzer (EGM first). In 16 CRT patients where the Medtronic analyzer had been used, the difference between qLV at implant and qLV at 6 months was 60 ± 27 ms whereas this difference was 2 ± 28 ms in 34 CRT patients where the St Jude analyzer had been used (p