First of all let’s figure out what is it (not in general but for Electrophysiologist) and what are common sources for signal quality issues.
So what the majority of EP-physiscians are calling noise is any additional signal on the ECG or EGM which should not be there. In the ideal world Surface ECG and intracardiac EGM’s must contain only the electrical activity coming from the heart and nothing else.
However we are not living in the ideal world and apart of electrical activity of the heart there are many other activities (internal or external) which can be recorded by an EP system and overlay normal ECG/EGM traces.
Far-field. Simply saying this is a summary of all electrical activity in the human body which you are not measuring during the study. Every single cell, especially neurons and myocites are generating some electrical signals - a single cell cannot generate enough to make it visible, however overall electrical activity of the entire body is something you see on the screen. in case of cardiac EP study we are measuring only activity in cardiomyocites - so any other activity will be interpreted as “noise” and this is far-field. For Electroencephalography - all the signals from every cell except the brain will be far-field. For EMG - every activity except muscles one - Far-field etc..
The main thing you should know about it - it is unavoidable - if there is no far-field - that means there is no electrical activity - read no life.
When do you see it? - on every signal which is amplified enough to make it visible.
Normally it has quite low amplitude - much lower than signals you need - so it is not a problem to distinguish.
Pacing artifacts - this is again something which you should expect and it is not causing regular noise, but artifacts. First of all you should expect them on the channel you’re actually pacing (obviously) and at other channels, but with much lower amplitude.
Another thing to keep in mind is that you should expect higher artifact amplitude if you are pacing with higher output AMP and wider artifact, if your pulse width is high. If your problem is within this description - that is something unusual which has to be solved by a noise troubleshooting expert.
Mains noise. This is the most frequent and easiest to identify type of noise. Just in case - this is a regular ripples with 20ms cycle length (for 50Hz) which is present on a single channel, several catheters or everywhere. Based on the frequency it is easy to conclude that it is coming from mains power which has 50Hz frequency (in Europe).
Every modern EP system is equipped with the notch filter, which main purpose is to clean up this type of noise. So the first tip would be - please check if it is enabled.
However in some cases it is not enough or the notch filter must be turned off for a purpose - and here it becomes more tricky to find out the exact source of the problem and again - in this case you better ask for an expert advise.
Mid (200 Hz - 2kHz) and Higher Frequency (over 10kHz) noises.
Those are coming from various electronic devices in your lab and here is no common rule for troubleshooting - every lab is different so you definitely need an experienced engineer to sort it out.
Those 4 are not covering all kinds of noises, however the majority of signal quality issues are described here.
We’ve just found what is it and where it comes from, but why it is sometimes not getting solved?
The answer is consists from 2 parts:
1. All real problems from groups 2 to 4 are often the result of poor integration or compatibility issues between different equipment installed in the lab. And very often every piece of equipment belongs to a different vendor.
Whether everything is working fine - it’s ok, however when it comes to a signal quality issue - engineers from a single vendor will not be able to solve the issue.
The best scenario is that after a few not successful attempts from different vendors - they will decide to perform a joint visit - and this may help. However in practice it is nearly impossible to organise and this process ends up with the “fingerpointing”.
2. All engineers are normally testing devices as a standalone and without the patient on the table - and in 99% of noise issues all tests are passing successfully. So you get the answer that the system is fine. And, surprisingly, those techs are absolutely right!
Standalone system they have tested is perfectly fine. However the problem still may come from poor integration (see above), but also from clinical/application side - and that is something what normal engineer will never find, especially if he is not familiar with the procedure you’re doing.
As a conclusion, we will give you the only advice - if you are having a real problem and want to solve fast and calm - you need a noise expert with dual technical and medical background and he should not work for a single vendor.
SinusTec experts are matching those criteria and having nearly 100% success rate within noise troubleshooting - so just fill the survey and get advised