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Electrocardiogram (ECG): Definition, Function & Basic Principles – Electrocardiogram

by Thad Wilson, PhD
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    00:01 Now, we’re going to take on one of the more interesting parts of cardiac physiology.

    00:07 We’re actually going to talk very much about the electrocardiogram, which is your ability to monitor what the heart's electrical properties are from outside the body.

    00:21 So, in this case, what exactly is an electrocardiogram measuring.

    00:25 We usually abbreviate this as ECG.

    00:29 This is really pretty simple, although we try to make it into something that allows for a lot of diagnostic purposes associated with it.

    00:38 It really just involves a positive and a negative electrode.

    00:43 That's it. That's it.

    00:44 Pretty easy, right? Positive and negative electrode.

    00:48 But what does one positive and one negative electrode give us? It gives us one picture of the heart.

    00:56 What we can use, though, is maybe 10 or 12 electrodes and then we can get multiple pictures of this same structure.

    01:06 So, think of this like your house or your apartment.

    01:10 You can look at it from the street view.

    01:13 You can look at it from down the street.

    01:15 You can look at it from up the street. You can look at it from down the street.

    01:15 You can look at it from up the street.

    01:16 You can go in the backyard, look at it from the back.

    01:19 It all looks different even though it's the same apartment or house.

    01:24 And that's what all these different pictures of the heart give us.

    01:28 Different views of the same structure.

    01:34 So, how do these single positive and negative electrodes do that? Well, basically, you're looking at a mean vector.

    01:45 And the mean vector tells you in what direction the ECG is going to be traveling.

    01:52 If you are traveling towards a positive pole, you're going to get a positive deflection.

    01:58 If you're traveling a depolarization wave towards a negative pole, you’re going to get a negative deflection on the ECG.

    02:07 It's that simple.

    02:09 Now, notice that there are a lot of different vectors that are being generated as you have a depolarization.

    02:17 You know, you get one going to the right, one going to the left.

    02:20 We are only concerned with here the average or mean of all of those vectors.

    02:27 That determines if a positive charge is moving towards a positive pole.

    02:33 If that occurs, it’s a positive deflection.


    About the Lecture

    The lecture Electrocardiogram (ECG): Definition, Function & Basic Principles – Electrocardiogram by Thad Wilson, PhD is from the course Cardiac Physiology.


    Included Quiz Questions

    1. ECG
    2. MUGA Scan
    3. Exercise stress test
    4. Holter ECG
    5. ECHO
    1. … multiple myocardial fibers.
    2. … bundle of His.
    3. … AV node.
    4. … SA node.
    5. …Purkinje fibers.

    Author of lecture Electrocardiogram (ECG): Definition, Function & Basic Principles – Electrocardiogram

     Thad Wilson, PhD

    Thad Wilson, PhD


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