The Amplitude of an ECG Strip (Nursing)

by Rhonda Lawes, PhD, RN

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    00:01 So let's talk about amplitude.

    00:03 Now, that is the height of the wave, when you looked at it as a graph.

    00:08 So the amplitude of an R wave is measured in millivolts.

    00:12 Well, that's convenient, right? Because we know one millivolt is how many millimeters? Good job, 10 millimeters.

    00:22 So amplitude is kind of how far that wave has moved the stylus above the ISO electric line.

    00:30 So the QRS duration, we have that mark there, the Q, R, S duration, that's how long it took.

    00:38 But amplitude is, how much energy did it take to move that stylus of that high? So amplitude is always measured from the isoelectric line to the peak of the QRS or the R wave, the very peak of the QRS complex.

    00:55 So take a look at this picture.

    00:57 Before we go on, you see, we have the isoelectric line, what color is it? Good, it's red.

    01:05 And that is the flat part of the ECG reading.

    01:09 Now amplitude is measured were? Correct at the very top of the QRS, which is the R wave.

    01:18 I want to talk to you about what things kind of impact amplitude? So let's start right in the middle with normal, always the best place to start.

    01:26 So look at a normal amplitude.

    01:29 That's going to give you an idea or a reference.

    01:32 Now, sometimes you have patients with a high amplitude.

    01:36 Now, this is if a patient has cardiac hypertrophy, they're most likely to have this high amplitude waveform.

    01:44 Now, think about that word hypertrophy.

    01:48 Why would that cause someone to have a higher amplitude than normal? Remember, that is the impulse moving through the ventricle.

    01:58 And if someone has cardiac, meaning heart; hyper, that's all a lot of extra; trophy is growth.

    02:06 So someone has an overgrown heart, it's going to be a lot more grown for it to be going through.

    02:12 And that's why you'll see a higher than normal amplitude.

    02:17 Now, let's look at the one on the left, this is a low amplitude.

    02:21 Now think about the leads that we put on a patient's chest.

    02:25 Usually, they're little stickers, and they're attached to a wire that goes to a monitor.

    02:30 But those are trying to pick up electrical signals through the chest wall.

    02:35 So anyone who has kind of a think of it as an altered chest wall, it's going to be harder for those signals to be picked up.

    02:43 That's why you have a lower amplitude.

    02:47 Higher, when you have like this really big heart that's hypertrophy.

    02:51 You're going to have a higher amplitude.

    02:54 But when it comes to a lower amplitude, that's because something has altered the chest wall.

    03:00 Now, examples of what could alter the chest wall, would be obesity.

    03:04 If a patient has extra body mass in between their chest wall and the heart, it's going to be harder for that signal to make it through.

    03:15 And the amplitude will be smaller.

    03:18 COPD. Ah, that should make sense.

    03:21 Remember, COPD patients get kind of barrel chested, right? So that's an alteration to their chest wall, that could cause a low amplitude.

    03:30 Now pericardial effusion is not necessarily the chest wall, right, that's extra fluid around the heart, but it also is going to make it harder for the signal to make it through.

    03:42 So we said, any alteration to the chest wall or something that makes the signal more difficult to make it through to the leads.

    03:49 But the term for that is increased resistance.

    03:53 So someone who has extra body mass in between the leads and the heart, someone has COPD, their chest wall has changed, or somebody who has extra fluid around their heart, that's going to lead to increased resistance to the current flow, and that results in a reduced amplitude.

    04:12 Okay, before you go on to the next one, those are three examples.

    04:17 Make sure you're clear and when it would be normal.

    04:21 Can you remember why it would be high? And try and give me three reasons it would be low.

    04:29 Do you wonder what you do in an example with low amplitude? The answer is you just try to do your best.

    04:36 Just try to get the best leads that you can and adjusting on your monitors so you can get an accurate ECG rhythm.

    About the Lecture

    The lecture The Amplitude of an ECG Strip (Nursing) by Rhonda Lawes, PhD, RN is from the course The Basics of ECG Strips (Nursing).

    Included Quiz Questions

    1. The distance from the isoelectric line to the peak of the R wave
    2. The distance from the lowest point of the S wave to the peak of the R wave
    3. The distance from the lowest point of the Q wave to the peak of the R wave
    4. The distance from the isoelectric line to the peak of the S wave
    1. A QRS complex with a higher than normal amplitude
    2. A QRS complex with a lower than normal amplitude
    3. An absent QRS complex
    4. A QRS complex with a flattened S wave

    Author of lecture The Amplitude of an ECG Strip (Nursing)

     Rhonda Lawes, PhD, RN

    Rhonda Lawes, PhD, RN

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