Strange ECG signals during pacing

[candrews]

Hello, I have acquired body-surface ECG data using an ActiveTwo system during cardiac ventricular pacing. There is an unusual and unexpected waveform that immediately follows the pacing spike. Its shape resembles an exponential rise over 15 msec with a sudden sharp drop-off. Because of the sudden drop-off I am struggling to find a physiological explanation for this signal. Is there any possibility that this is an instrumentation artifact?

The signal is present with a varying amplitude in several channels. Its amplitude seems to be greatest in the electrodes near the heart, and it does not seem to appear at all in more distant electrodes where the pacing spike amplitude is very small. I am attaching an image of the waveform.

[Coen]

My initial guess is a electrode polarization artefact due to the stimulation currents. Are you using the older style BSPM strips with carbon electrodes, or the later Ag-AgCl electrodes ?

Best regards, Coen (BioSemi)

[candrews]

Hi Coen, thanks for your response. This study was performed using the newer Ag-AgCl electrodes. Also, I am not sure if it is relevant, but the CMS electrode was placed on the subject's right wrist, and the DRL was on the left wrist.

Thanks for your time,
-Chris

[Coen]

I would certainly begin with using the standard BSPM electrode configuration:

- CMS on torso approx in the center of all other electrodes
- DRL on right leg or right hip
- LA on left arm or left shoulder, RA on right arm or right shoulder, LL on left leg or left hip
- Use WCT (average of LA, RA and LL) as the reference for the torso electrodes

Best regards, Coen (BioSemi)

[candrews]

Thank you Coen. I'll first try to use the standard BSPM electrode configuration. If we still see a similar waveform at that point, we will carefully consider whether this may be due to a polarization artefact.

Best, Chris