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.