In this lecture we’re gonna talk about common tachyarrhythmias.
So what is a tachyarrhythmia?
Very simply, to have a tachyarrhythmia,
you must be first tachycardic,
meaning, your ventricular must rate must be over a hundred.
Secondly, you have to be having an arrhythmia,
so you have to be in a non-sinus cardiac rhythm.
Now, the term tachyarrhythmias incorporates
many different cardiac rhythms
and they might be stable or unstable.
And we’re gonna talk about the differences
in how you manage the two.
So unstable tachyarrhythmias,
are situations in which
a tachyarrhythmia is present
and the patient has some sign of hemodynamic instability
So this is gonna include hypotension or shock,
altered mental status or loss of consciousness,
ischemic chest pain or dyspnea
or acute decompensated heart failure.
Basically, any situation in which lack of systemic perfusion
is causing end organ damage.
The treatment of all tachyarrhythmias
is the same when the patient is unstable.
Unstable tachyarrhythmias are life threatening events
and you have to assume
that the patient is in danger of cardiac arrest.
So we’re gonna do the same thing
for all of these patients.
We’re gonna give them all oxygen.
We’re gonna monitor them.
We’re gonna establish IV access
and do frequent blood pressure checks.
We’re gonna address our ABCs.
So we’re gonna manage the airway if we need to.
And provide any support that’s necessary
for respiratory distress.
But the most important thing we’re gonna do
is perform emergent synchronized cardioversion.
If a patient is having an unstable tachyarrhythmia
the most important thing you can do for that patient
is to terminate that rhythm
and get back into a normal perfusing rhythm.
So electricity is gonna be the answer
for all unstable tachyarrhythmias.
Now, if possible,
we wanna provide sedation or analgesia for our patient
before performing cardioversion.
'Cause this you can imagine 200 joules to the chest
is not really comfortable.
So if you have time and the patients' condition permits it,
it’s definitely better to provide sedation,
but if the patient is too unstable for that,
terminating the rhythm is the most important thing you can do.
So again, cardioversion is indicated
for all unstable tachyarrhythmias
regarding of what the underlying rhythm is.
If the patient’s unstable and they’re in a tachyarrhythmia,
you need to shock them.
So it’s really important when you’re confronted
with a tachyarrhythmia
to identify specifically what cardiac rhythm your patient is in.
The reason for that is that
you’re gonna manage different rhythms in different ways.
So you have to understand what rhythm you’re dealing with
in order to provide the right treatment for the patient.
The approach to rhythm identification is always the same.
Whenever you’re looking at a cardiac rhythm,
the first question you’re gonna ask yourself is,
is this a fast rhythm or a slow rhythm?
Now, if it’s a slow rhythm,
you’re dealing with sinus bradycardia or maybe a bradydysrhythmia
In which case,
we’re gonna cover all of that in another lecture.
So don’t worry about that right now.
If it’s a fast rhythm
which is what we’re talking about in this lecture,
the two possibilities are sinus tachycardia or a tachydysrythmia.
Now, if it's sinus tachycardia,
we’re not gonna treat that as a rhythm disturbance.
Our goal is gonna be to identify the underlying cause
and address that.
But if the patient is having a dysrhythmia
they're in a non-sinus rhythm,
then we need to identify specifically what rhythm they're in.
The next question we’re gonna ask ourselves
in order to do that is,
is it a wide complex rhythm or a narrow complex rhythm?
Now, when I talk about wide or narrow,
I’m talking about the QRS complex
and just as a reminder from basic cardiology,
a wide complex rhythm is any situation in which the QRS complex
is more than 3 millimeters wide
or a 120 milliseconds on the ECG.
So if it’s a wide complex rhythm,
that suggests ventricular origin of the rhythm.
It has to be coming from some place below the AV node,
typically within the ventricles.
The other possibility is that it could be a supraventricular rhythm
with abnormal conduction through the heart.
And we’ll talk a little bit more about that shortly.
The possibilities for wide complex rhythms
are either ventricular tachycardia
or supraventricular tachycardia with aberrant conduction
Now, if we’re dealing with a narrow complex rhythm
that tells us that the origin of the rhythm is super ventricular.
It’s above the level of the ventricles,
because in order to produce a narrow complex rhythm
the heart has to use the fast conduction pathways
which allow rapid depolarization of the heart
producing a narrow QRS complex.
The next question if we identify a supraventricular rhythm is
is this a regular rhythm or is it an irregular rhythm?
If it’s irregular,
we’re gonna be thinking about things like atrial fibrillation
or atrial flutter with variable conduction.
If it’s a regular rhythm,
we’re gonna ask ourselves
whether or not there are P waves present,
if there are, we’re back to sinus tachycardia
and again, we’re not dealing with the primary rhythm disturbance.
But if there are no P waves present,
we’re dealing with the paroxysmal supraventricular tachycardia
and we’re gonna talk a lot more about that in slides to come.
Sinus rhythm or tachyarrhythmia,
if you’re looking at a fast rhythm.
if you have a tachyarrhythmia is
is it wide or is it narrow?
If it’s wide,
we’re dealing with a ventricular origin.
So again, wide complex rhythms
are those that have QRS duration
of longer than a 120 milliseconds or 3 millimeters.
If the QRS rate is greater than 100,
you have a tachycardia.
So wide complex,
wide QRS' plus fast heart rate
equals wide complex tachycardia.
So the path of physiology of wide complex tachycardia
is pretty easy to understand.
Narrow QRS complexes originate above the level of the AV node.
And these narrow complex rhythms use the His-Purkinje system,
which as you recall is a normal conduction system in the heart
that allows very rapid depolarization
of the entire myocardium producing a narrow QRS complex.
the impulses move quickly through this system,
the depolarization of the heart is efficient,
it happens quickly
and that gives you a nice, sharp, narrow QRS complex.
By contrast, when the QRS complex is wide,
the rhythm could be originating
either above or below the AV node.
In both cases however,
the normal conduction pathways,
the His-Purkinje system is not being used.
The electrical impulses are sort of travelling
from one myocyte to the next in a very inefficient manner.
This takes a long time to depolarize the entire heart.
It’s a slow process.
Meaning, that the QRS complex takes longer to be completed.
So it appears as wide on the ECG.
The vast majority of wide complex tachycardias
are ventricular tachycardia.
So 90% of patients who you see with wide complex rhythms
are gonna be in V-tach.
There is a small percentage of patients though about 10%
who have super ventricular rhythms with abnormal
or aberrant conduction.
Now, an easy way to understand this is
is to think about bundle branch blocks.
If you have a baseline bundle branch block,
you’re gonna have a wide QRS complex
even when you’re just hanging out in normal sinus rhythm.
Clearly, if you go into rapid atrial fibrillation
or sinus tachycardia,
your QRS complexes are still gonna be wide, right?
Now, that’s a supraventricular rhythm
with abnormal conduction because of your bundle branch block.
So it’s a sort of an easy way to think about it,
although there are definitely other situations
which we’re gonna cover
where you can see
wide complex supraventricular rhythms.