Atrial Systole and Diastole – Cardiac Cycle

by Thad Wilson, PhD

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    00:01 Now let's talk a little bit about Atrial Systole.

    00:04 We kind of ended on it being the last little kick of volume into the left ventricle.

    00:11 It's initiated by the P wave from the ECG.

    00:15 It occurs, again, right at the end of ventricular diastole .

    00:23 We talked about it also producing a little bit of pressure on its own.

    00:27 The pressure that it induces involves squeezing in on the blood that's there right at the end.

    00:33 And that again, normally pushes about 10%, into the left ventricle to cause the full filling.

    00:41 So someone really doesn't need to have a lot of atrial systole under most circumstances.

    00:49 In fact, you could have a cardiac arrhythmia, known as atrial fibrillation, in which you the atrium really don't contribute much to ventricular filling.

    01:01 And you can be walking around, and you might not even know that person has this arrhythmia.

    01:07 On time though when atrial systole becomes very important around things like during exercise.

    01:14 We have large volumes of blood coming back to the heart, and the top part can help squeeze that blood into the left ventricle so that you can get a better contraction out.

    01:24 Because that way you can utilize the Frank-Starling mechanism to push more fluid out per stroke without utilizing any more energy.

    01:35 Atrial diastole occurs after atrial systole.

    01:39 Remember that this atrial kick is what creates the A wave.

    01:43 However, during the diastole portion of the atria, these are phases two through seven.

    01:49 There are two other waves we need to be concerned about.

    01:54 The first of these is known as the C wave.

    01:57 The C wave occurs during the contraction of the ventricles.

    02:01 This is actually a pressure reverberation that occurs.

    02:05 It either occurs during phase two as shown in the graph, or sometimes even a little bit into phase three.

    02:14 The other way we need to be concerned about is the V wave.

    02:17 The V wave occurs after you start to get blood filling the atria.

    02:23 It continues to fill the atria until suddenly the AV valves open and there is a sudden pressure fall.

    02:31 That's known as the V wave.

    02:35 So in terms of the atrial filling pressures, and the atrial contraction pressures, we can look at A, C, and V being those items that we want to make sure we have good feeling for why they are occurring.

    About the Lecture

    The lecture Atrial Systole and Diastole – Cardiac Cycle by Thad Wilson, PhD is from the course Cardiac Physiology.

    Included Quiz Questions

    1. Phase 1-2
    2. Phase 5-6
    3. Phase 3-4
    4. Phase 6-7
    5. Phases 5-7
    1. 40%
    2. 60%
    3. 50%
    4. 10%
    5. 30%

    Author of lecture Atrial Systole and Diastole – Cardiac Cycle

     Thad Wilson, PhD

    Thad Wilson, PhD

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