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  • - Atrial flutter is one of the heart arrhythmias

  • that's also known as just flutter.

  • It's one of the supraventricular tachycardias.

  • Now remember that the heart's dominant pacemaker

  • is the SA node and the SA node is going to send the signal

  • to the AV node which will then conduct the signal down

  • to the lower half of the heart

  • which makes the ventricles contract.

  • In case the SA node fails,

  • the heart has several backup pacemakers

  • called automaticity foci.

  • These backup pacers only fire in the event

  • that the signal from the SA node is not efficiently

  • or effectively reaching the AV node

  • and when they do fire, they fire at a rate between 60

  • and 80 beats per minute or BPM.

  • In atrial flutter,

  • there's a really irritable automaticity focus

  • and I'm drawing that here in purple.

  • This irritable focus is going to fire at a rate between 250

  • and 300 beats per minute,

  • which is a lot faster than the rest of the foci.

  • The electrical signal travels around in a circular pattern

  • and moves around again,

  • and again, and again, and again, and again.

  • So this causes the atria to contract at a rate between 250

  • and 300 beats per minute.

  • Every time the signal goes around

  • it's going to hit the AV node

  • and remember the AV node is what conducts the signal down

  • to the lower half of the heart

  • and makes the ventricles contract.

  • So you might think because of that,

  • the ventricles are also going to contract

  • at a rate between 250 and 300 beats per minute

  • but in reality the ventricles usually contract

  • at a slower rate around 150, beats per minute.

  • Now why is that?

  • That's because there's a built in mechanism

  • in the AV node called a refractory period.

  • Other tissues have this too.

  • After the AV node conducts the signal,

  • to the lower half of the heart,

  • there's a window of time also known as the refractory period

  • where the AV node can't fire again

  • even if it gets the signal to do so.

  • So this is sort of like a backup mechanism

  • to prevent the AV node from over-firing

  • which will then prevent the ventricles

  • from contracting too quickly.

  • So let's look at this in EKG.

  • With an atrial flutter EKG you're going to see

  • multiple P waves

  • and regular spaced QRS intervals.

  • By regular I mean that the space from this R to R interval

  • is going to be the same as this R to R interval

  • which is the same as this R to R interval.

  • Now why do we have these multiple P waves?

  • Remember, that there's an irritable automaticity focus

  • that's over-firing, so it's going to fire, fire, fire

  • but it won't conduct signal through the AV node

  • every time it fires because of the refractory period.

  • So for example here, we have the focus firing,

  • causing the atria to contract,

  • it hits AV node, conducts, makes QRS complex

  • and it tries to fire again

  • but because we're in the refractory period

  • it's not going to conduct through the AV node

  • and you're not going to get another QRS complex.

  • Instead you're going to see another P wave

  • when it tries to fire again.

  • In this particular example we have,

  • three P waves, for every QRS.

  • So this is called three to one conduction.

  • In atrial flutter you can also have two to one conduction,

  • where you'd have two P waves for every QRS

  • or even four or five P waves for every QRS

  • but this example is three to one conduction

  • and if you look closely you can appreciate

  • that the lines that the P waves make,

  • make a certain pattern

  • and they kind of resemble the teeth on a saw.

  • So classic A flutter is said to have a saw tooth pattern

  • and the saw teeth are the P waves.

- Atrial flutter is one of the heart arrhythmias

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心房粗動(AFL)|循環器系と疾患|NCLEX-RN|カーンアカデミー (Atrial flutter (AFL) | Circulatory System and Disease | NCLEX-RN | Khan Academy)

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    alex に公開 2021 年 01 月 14 日
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