Preprocessing ECG signals from 3 channels

I am using 3 ECG channels to read heartbeats, ECG1 (upper right corner of chest, under clavicle bone), ECG2 (upper left corner of chest, under clavicle bone) and ECG3 (left side of abdomen).

The outputs are 3 ECG signals which are differ from each other.

My question is which signal is considered as heartbeat signal or do I need to merge all the signals togather or process each one individually to get the exact heartbeat?

Answer 1

[Star Strider]

You have to have a fourth (reference or ‘ground’ electrode (ideally) to make any sense of those data. First, look up a reference on ‘vectorcardiography’. It’s too complicated to explain in detail here, so I’ll just provide an outline. You did not describe in sufficient detail your experimental setup, so my ability to reply to it is limited.

The cardiac electrophysiologic cycle traces a series of three principal 3D loops, corresponding to the P-wave, QRS complex, and T-wave. The scalar EKG (that you are recording) are projections of this loop on the axes between any two electrodes. Your ‘EKG1-EKG2’ correspond approximately to Lead I, ‘EKG1-EKG3’ to Lead II, and ‘EKG2-EKG3’ to Lead III of the standard scalar electrocardiogram.

Each lead is ‘correct’ and each will give you the ‘heartbeat’. The only way to merge them correctly is to combine them to form a vectorcardiogram. I went into this in considerable detail in Detecting QRS Complex in ECG Signal. I refer you to it.

See the appropriate sections of Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 9th Edition for a full discussion.

[Mouhannad Ali]

Thank you very much for the answer. The ECG device I am using it has only 3 electrodes (from bioradio), see the image.

and the output is (see the image):

so now as I understood, each output is represent the heartbeat (you can see that they differ from each other, just ch3 look as heartbeat). and in order to merge them I need to use vectorcardiography for 3 electrodes ??

Thank you again for helping

[Star Strider]

My pleasure.

The fourth ‘ground’ electrode is usually used with the differential amplifiers for the other leads to subtract out any ambient (and usually broad-band) noise that would be difficult to filter out with conventional signal processing techniques. It isn’t strictly necessary, but it helps.

Your ‘Channel 1’ is reversed from what I’d normally expect (the R-wave should be positive in Lead I), but the others appear normal, with ‘Channel 2’ looking like a normal Lead III and ‘Channel 3’ looking like a normal Lead II.

I would double-check the lead placement of the top two electrodes, since the may be reversed.

They are all relatively normal scalar EKG tracings otherwise. The only notable finding is relatively prominent P-waves and the presence of a U-wave (the slight elevation following the T-wave) that can be seen in hypokalemia. It’s a normal finding, but not usually as prominent as I see it here. That could also be due to your non-standard lead placement, since it’s more prominent in some leads than others when it’s present. It’s essentially a normal EKG.

Each output does represent the heartbeat, but to get the full effect, you need to combine them mathematically to a vectorcardiogram. (That will be a bit difficult to represent correctly because of your lead placement, but educational.)

Remember, the EKG tracings you’re seeing aren’t taken from one electrode, but represent the projection of the cardiac electrophysiological loop on a line connecting any two electrodes. So ‘Channel 1’ is the projection of the loop on a line connecting the top two leads, ‘Channel 2’ looks like it’s between the left clavicular lead and the abdominal lead, and ‘Channel 3’ looks like it represents the loop projected on a line from the right clavicular to the abdominal lead.

I strongly suggest that you read about the principles of electrocardiography. If I remember correctly, Webster’s biomedical instrumentation text has a good discussion of it, and any cardiovascular physiology text should as well. I was not able to find what I consider to be a good, free, online reference to refer you to. A thorough discussion of it here on MATLAB Answers is impractical.

As always, my pleasure.

[Mouhannad Ali]

That is very useful for me. Thank you again very much

[Star Strider]

Thank you. Again, my pleasure.