Ectopic Foci and Abnormal Conduction – Heart Rate and Electricity

by Thad Wilson, PhD

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    00:01 Now, what happens if you don't get that conduction past the AV node? Remember, Purkinje fibers can beat on their own.

    00:12 They beat very slow, though, right? 30 to 40 beats per minute.

    00:17 That’s a slow, slow beat.

    00:21 But if you don't get enough information, they will take over and beat anyway.

    00:26 And these generate ectopic foci, a place in the ventricle, that decides, I didn't get enough information, I don't know when I should beat, I'm just going to beat anyway, you can't stop, I’m beating because, you know, why not? That's what happens.

    00:44 They take over their heart rate and they will beat on their own if they don't get enough signal.

    00:50 So, unless you get SA node, AV node signals down the ventricular myocytes and the Purkinje fibers will take over beating.

    01:00 This causes havoc.

    01:03 It makes the QRS complex very wide and creates a process called a premature ventricular complex.

    01:12 And these PVCs are seen very often in electrocardiogram.

    01:17 And the reason why they happen is because the Purkinje fibers did not get signal from the SA node or the AV node.

    01:27 You might ask, at this point, well, why don't they beat on their own anyway? I mean, because, you know, they have that intrinsic rhythm, right, 30 to 40 beats.

    01:38 The reason why they normally don't take over beating is because every time an action potential comes through, it resets the clock.

    01:48 So, if you have something like a sinoatrial node that beats 60 to 100 times per minute, it's going to reset the clock of the AV node and Purkinje fibers every time it happens.

    01:59 So, you'd have to have a block in the system for those other pacemaker cells to take over.

    About the Lecture

    The lecture Ectopic Foci and Abnormal Conduction – Heart Rate and Electricity by Thad Wilson, PhD is from the course Cardiac Physiology.

    Included Quiz Questions

    1. Wide QRS complex
    2. Irregular ventricular response
    3. Variation in P wave contour
    4. Absent QRS complex
    5. P wave after QRS complex
    1. Higher impulse rate of Purkinje fibers
    2. Increased vagal nerve activity
    3. Decreased sympathetic nervous system activity
    4. Hypocalcaemia

    Author of lecture Ectopic Foci and Abnormal Conduction – Heart Rate and Electricity

     Thad Wilson, PhD

    Thad Wilson, PhD

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