Dr. Kent Morris, Norton Health Hospital in Louisville, KY
"Some of the newer software does have the ability to use both the bipolar signals and the unipolar signals in mapping, so the unipolar signals do matter. The unipolar noise level prior to installing the second CIS unit was somewhere around 0.12 - 0.15 mV which is certainly higher than I would like and after installing the unit was a little more acceptable in the 0.06 - 0.12 mV range so from slightly less to about half the noise level, but there was some variation and still some residual noise. Then we made a discovery.
We noticed that if you gain up the surface ECG leads, there was noise at the same frequency as on the unipolar channel. The unipolar signal is comprised of the distal pole on the mapping catheter to the surface ECG leads attached to the patient. So we started to suggest something external that the ECG cables were picking up. So we moved the x ray tube completely out from the patient as far back as possible and as we were moving the x ray tube out you could see the noise levels decrease. With the x ray tube as far back as possible the unipolar noise level was now generally less than 0.03 mV and the noise on the surface leads were pretty much gone. When we moved the x ray tube back in the noise returned to the previously mentioned levels. So at this point essentially all of the remaining noise appears to be emitted from the x ray tube. I would think that this is important for you to be aware of because otherwise it might appear that there is residual noise that your filters are not removing when in fact in our lab this appears pretty convincingly to be emitted radiation/noise."
"This makes the CIS units invaluable as a diagnostic tool because they essentially rule-out electrical sources of noise."