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Here are excerpts from an unknown ECG lead. I find it weird that the "baseline" changes after the T wave and doesn't return until after the following QRS complex. Is that normal/expected for any lead?

sec 82-92

zoom sec 88-90

Click for better resolution. I've got another 10 minutes of the ECG, if that would be helpful.

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Also, I should note that I'm quite inexperienced when it comes to cardiology, so this is probably a basic question -- so don't upvote me too much :) –  Andrey Dec 21 '11 at 22:26
    
What frequencies are the high pass and low pass filters set at? –  jonsca Dec 22 '11 at 1:58
    
@jonsca: I've applied a 5-point moving average. As there was no baseline drift I don't think I had applied any other filters, so that would be from the data acquisition tool. It was sampled at 360 Hz. Here are the non-averaged graphs for these intervals: 80-92 sec, 88-90 sec –  Andrey Dec 22 '11 at 8:48
    
@jonsca: Ok, looks like I had highpassed it at 0.5 Hz. –  Andrey Dec 22 '11 at 8:49
    
It looks like some kind of line noise or artifact on the unfiltered plot. See if your software has a notch filter for 50/60Hz (depending on Europe or the States). Put that on, then try your moving average, but remember a "boxcar" filter is always going to distort your plot a bit. I'm not an expert on ECG, but I would hedge my bets on this being non-physiological. –  jonsca Dec 22 '11 at 12:32
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up vote 3 down vote accepted

I am not sure if I understand your question correct. What I can see here is a clear ST depression, that might be indicative of myocardial ischemia/infarction. The underlying mechanism is the shortage of oxygen in myocytes leading to elevation of resting potential and slowing of the depolarization -- this accounts for the elevated baseline after T.

I am not at all an ECG expert, but I have seen the misplaces T-P segment many times while at medical school. It wasn't indicative for diagnosis, whereas all other segments were.

So, why are you worrying about this segment?

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Thanks! Then I know that the TP elevation is fine. About the ST depression, is it clear because there's a large vertical distance between the isoelectrical line (measured at P onset) and right after S, or also because of the horizontal ST segment? –  Andrey Dec 23 '11 at 18:51
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