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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. It only represents the average of the many depolarization vectors “seen” in the electric picture of the heart taken by those electrodes.
    2. If the depolarization wave travels toward a negative electrical pole you will get a positive deflection on the ECG.
    3. The ECG is not concerned with the polarity of the electrodes.
    4. The positive and electrical electrodes can be switched without having an effect on the ECG.
    5. A single pair of positive and negative electrodes can give multiple electrical views of the heart without repositioning of the electrodes.

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

     Thad Wilson, PhD

    Thad Wilson, PhD


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