- 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.