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ECG Abnormalities – Electrocardiogram

by Thad Wilson, PhD
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    00:02 So, now, let's get into some of the pathologies.

    00:05 You can see what a normal ECG wave looks like.

    00:08 It has a normal P wave.

    00:10 It has a normal QRS complex.

    00:11 It has a T wave.

    00:13 These are all important electrical properties of the heart.

    00:18 If someone has a disorder called atrial fibrillation – the top portion of the heart is the atrium.

    00:28 And these two atrium will show up as the P wave.

    00:33 Therefore, if you have atrial fibrillation, you should see abnormalities with the P wave and you can see that.

    00:40 Usually, what happens is there's a lot of small jittery – what looks like noise in front of the QRS complex.

    00:49 That is denoted as atrial fibrillation.

    00:54 A first-degree AV block is a block and where you have a normal P wave, but it takes too long to capture a QRS complex.

    01:04 And how do you know it's too long? It’s greater than 0.2 seconds.

    01:09 That is a first-degree AV block.

    01:12 A second-degree AV block is more serious than a first.

    01:17 It means that there are certain times when you have a P wave and you don't capture a QRS complex.

    01:25 Therefore, there is some block in the AV system that's preventing it from getting through.

    01:32 A first-degree AV block is just slowing down.

    01:37 The second-degree AV block involves some QRS complexes that are not captured from that P wave.

    01:46 The most serious is a third-degree AV block and here you can see a number of P waves with no normal QRS complexes.

    01:57 If there are QRS complexes that are generated, they are generated ectopically and therefore, have a wide QRS complex.

    02:07 How do I know it's wide? It’s greater than 0.01 seconds.

    02:11 That’s where all those intervals become important.

    02:15 You have to be able to identify what the interval is and then know the normal numbers that are associated with it.

    02:25 PVCs can be seen quite often.

    02:27 These can happen if you have, again, a type III AV block, but you can also get PVCs to occur on a regular basis.

    02:37 And here, you can see some PVCs that are occurring in a sequence.

    02:41 And if you have them occur fast, that can be a ventricular tachycardia.

    02:47 You notice that there is no isoelectric line.

    02:50 You don't see any P waves.

    02:52 All you have are these PVCs.

    02:55 Even more serious than ventricular tachycardia is ventricular fibrillation.

    03:01 So, at least in ventricular tachycardia, you are getting contractions of the ventricles that was pushing out blood.

    03:09 In ventricular tachycardia, you have so many contractions happening, it's not pushing out enough blood per beat.

    03:18 And if you don't push out enough blood, it doesn't circulate to the tissues.

    03:22 And you end up having hypoxic tissues and actually could die in this condition, unless you were cardio-averted which means that you got put on a defibrillator and you received shocks, and that is the best way to get out a ventricular fibrillation.

    03:43 There are number of other ways to look at the ECG.

    03:47 And as you move through medicine, you will just deepen your understanding of what an ECG is.

    03:53 I'll go through one other pathology with you and this involves the STEMI myocardial infarction, which is a heart attack.

    04:01 And I go through it just because it is something that you all have heard about are heart attacks and be able to understand or to recognize someone who had a heart attack with an ECG is helpful.

    04:14 So, you can notice the normal QRS complex where you have a P wave, a Q, R and S, and then you have a T wave.

    04:24 This can change if you're exposed to severe ischemia induced by lack of blood flow to certain areas of the heart.

    04:33 What happens in ischemia is you have a decrease in membrane potential.

    04:40 What do I mean by a decrease in membrane potential? It’s lower than normal.

    04:45 So, if you have a lower-than-normal membrane potential, you start off on a lower level.

    04:53 You have a normal P wave.

    04:54 You might have a normal QRS complex.

    04:58 But then you don't return back to this low level, which you had, because of this ischemic event.

    05:06 And so, you end up being at a higher value for your ST segment.

    05:11 And then you have a normal T wave.

    05:14 This is called ST segment elevation.

    05:18 And one of the key reasons why ST elevation happens is because of a little bit of a trick on your eye, which looks like the ST segment is elevated, when actually it's the normal isoelectric line that is before the P wave or after the T wave, which is suppressed, because of ischemia and lack of oxygen to a certain portion of the heart.

    05:45 And so, this is just a very classic way to look at or to find out that someone has a heart attack if they show up with an ST segment elevation.


    About the Lecture

    The lecture ECG Abnormalities – Electrocardiogram by Thad Wilson, PhD is from the course Cardiac Physiology.


    Included Quiz Questions

    1. 1st-degree AV block
    2. 3rd-degree AV block
    3. Atrial fibrillation
    4. Ventricular fibrillation
    1. 0.20 seconds
    2. 0.40 seconds
    3. 0.02 seconds
    4. 0.25 seconds
    5. 0.002 seconds
    1. Normal P wave,ST-segment elevation, normal T wave
    2. Absent P wave, ST-segment elevation, normal T wave
    3. Normal P wave, ST-segment elevation, absent T wave
    4. Normal P wave, ST-segment depression, normal T wave
    5. Normal P wave, ST-segment depression, inverted T wave

    Author of lecture ECG Abnormalities – Electrocardiogram

     Thad Wilson, PhD

    Thad Wilson, PhD


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