is what we are doing, aren't we?
Now, couple of definitions have become important
for us. We are tachy, so it has to be above 100.
Put you in the cateogry. If it is less
than 100 and the P wave looks abnormal and
I will tell you what this abnormality of the
P wave is in a second. Be careful because
remember if you find the EKG and here we are
going to push you a little bit, but you can
handle it. If you take a look at an EKG, you
are going to look for a P wave preceding the
QRS complex, an upright QRS complex, especially lead II.
And then that gives you sinus type of rhythm.
You take a look at the rate. Take a look at
axis deviation and the P wave should be well
as you would expect a P wave. However, when
I show you the P wave upcoming, you will notice
that the P wave is going to look rather dysmorphic.
Not fibrillated. Not fluttered meaning saw-tooth,
but fibrillated or, in other words, it is
wandering. It is going to look dysmorphic.
If you find a dysmorphic type of P wave and
if you find the heart rate to be almost within
normal range, you will not call it multiatrial
tachycardia, you will call it wandering atrial
pacemaker and it really comes down to a simple
definition such as less than 100 beats per
minute. Next, what about the ECGs? We will see now
we get into a dysmorphic or P waves in which
its morphology has been altered. And when I it
show to you, it would be quite obvious, but
before we get there though, a couple of other
definitions that you want to keep in mind.
In one strip of EKG, on the same lead, you
need to find at least three distinct P waves
and by distinct I do not mean wave,
like fibrilation. I do not mean two, like
sawtooth. No. Three distinct each P wave
looks a little bit more different than the
other. So rather distinct in morphology
of whom? The P wave. Do not touch the QRS
complex because this is SVT. Hope that is
clear. Spend a little bit of time with that
last bullet point there because that really
is going to be the description or the distinguishing
point in words of an SVT known as multifocal
atrial tachycardia. And then less than 100
beats per minute would be your wandering atrial
pacemaker. What do you want to do? You'll correct the
underlying issue, of verapamil now in terms
of drugs up until now when we try to control
that rhythm, we tried to cardiovert and we
can do our cardioversion by medicine or medical
cardioversion. And if that is not effective,
your next step of management would have to
be electrical cardioversion. Right? When we did our
other SVTs including afib and atrial flutter,
we tried to cardiovert medically and we did
so by slowing things down. We did that by
giving digoxin. We did that by giving metoprolol,
a beta-blocker. Right? Now, verapamil, which is a
calcium-channel blocker much more specific
for the heart. Think V, verapamil; V, ventricle.
It slows down the heart rate or it tries to
convert your abnormal distinct P wave into
a proper normal sinus rhythm. Is that clear?
Do you understand the concept of cardioversion
now? Now if it is calcium-channel blocker,
you try to control that heart rate. Well let
me one more time bring this up and I am going
to keep reinforcing this until you fully understand
when we do pharmocologically with antiarrhythmics
as to what you are dealing with. Earlier when
we were talking about SVTs and I was talking
to you about that phase 403 because we
were talking about heart rate, which would
be the pacemaker. That phase 4, which was
funny with the sodium channel. I told you
specifically that has to be ligand-gated,
the only effective or should I say a more
effective antiarrhythmic class that work on
that phase 4 was that class II, which was
a beta-blocker. "Dr. Raj, really it is not making
sense. It is not sticking." It has already,
believe it or not. When? When you did autonomic
nervous system, when you did CNS physiology,
you looked that the autonomic nervous system
and you looked at the parasympethetic nervous
system, how do you slow down that heart rate?
Can you picture that? 403, parasympethetic,
acetylcholine, working on antireceptors on
the heart and how do you slow that heart rate?
By causing a decreased gradient of phase 4.
Are you seeing this? And if you're not, listen
to what I am saying. Go draw it
out or go look at it where you take a look
at your action potential and slowing down
of your heart with parasympethetic and you
worked through your phase 4. Is that clear?
Acetylcholine, that has to be ligand-gated.
Is that clear? That has to be cleared. Now
that was when we were dealing with phase 4.
Now let us talk about phase 0 of your pacemaker,
heart rate. What is phase 0 as a pacemaker?
You see how it is an integrating stuff. Stick
with me. Phase 0 in a pacemaker potential
is going to be your calcium channel. So, therefore,
a drug or a class of antiarrhythmic that might
have work here would be something like a calcium
channel blocker. Let us continue. What are
the drugs? Well. Beta-blockers to a certain
extent could be used. Same concept. You are
trying to slow down that heart rate. What
phase? Phase 4. You know that. It decreases
heart rate. And do not use dig in the treatment
of MAT, though. That is important. Multifocal
atrial tachycardia, there are too many other
factors that are in play in which digoxin
might actually not be effective. Keep that
in mind whereas digoxin was a drug that you
definitely thinking about using or considering
when dealing with afib and atrial flutter.
And that is another huge distinction point.
That last bullet point right there with digoxin.
Hope that is clear. Let us continue.
So I want you to take a look at the bottom ECG
lead and with that strip, you are paying attention
to the P wave, does that look fibrillated
to you? So what are you doing now? When you
are going through these lecture series with
SVTs, supraventricular tachycardia, is comparing
atrial fibrillation, atrial flutter and now
multifocal atrial tachycardia. Please do
that for me. It is the best way to then identify
each one. Is this the P wave is not fibrillated?
It is definitely not saw-tooth and on the same
lead, you will find three different rhythms
in which the P wave is rather distinct, even
within the same lead. This then gives you
multifocal atrial tachycardia with a beat
per minute or heart rate above 100, tachy.
If by chance it falls below 100, then you
start thinking about the alternate diagnosis
of wandering HO pacemaker. Let us continue.
This particular SVT is WPW. So we have now