All right, so we’ve covered our irregular rhythms.
We’re now gonna move on to our regular narrow complex rhythms.
So like I said before,
when you have a regular narrow complex rhythm,
your next question is
are there P-waves?
If there are no P-waves present,
you're dealing with one of the super ventricular tachycardias.
So paroxysmal SVT or supraventricular tachycardia
is kind of a catch-all term for a few different diagnoses
that shares some common pathophysiology.
paroxysmal SVTs are triggered by premature atrial beats
So the atria for whatever reason contract prematurely
and this sets off a cycle that produces a rhythm disturbance.
There are a number of metabolic risk factors
for supraventricular tachycardia
Hyperthyroidism, use of stimulants like cocaine,
caffeine can trigger SVT,
ethanol can do it as well.
In order to get SVT though
in the setting any of these risk factors,
you have to have some form of re-entry pathway
to be able to maintain this abnormal rhythm.
So there's a couple common types of SVT,
these are not the only ones,
but the two most common ones
are AV Nodal Reentrant Tachycardia or AVNRT
and in AVNRT,
you have bidirectional pathways in the AV node.
So the normal AV node only conducts in one direction, down.
Down from the atria to the ventricles.
However, if you have bidirectional pathways
that allow conduction back from the ventricles to the atria,
you can have a circuit form
that basically creates an electrical loop
driving very, very fast ventricular rates
as electricity goes from the atria to the ventricle
and then directly back up from the ventricle to the atrium.
There’s also AVRT or Atrioventricular Reentrant Tachycardia
and in this situation,
there is an accessory pathway
that creates a loop between the normal AV nodal pathway
and the abnormal accessory pathway.
So how do you diagnose paroxysmal SVT?
So first and foremost,
you have to have a narrow QRS complex like we said,
your QRS has to be less than a hundred and twenty milliseconds.
You have to have a rapid regular rate.
So here, you can see the QRS' which I've marked
are coming along every seven millimeters.
So your RR interval is seven millimeters and constant.
That gives us a rate of about 200.
And then lastly,
you have to have absent or abnormally conducted P-waves
So the arrows denote where P-waves should be
before each QRS complex but you can see we’re basically
just getting QRST, QRST, QRST
and we’re not able to see P-waves.
So these are the diagnostic criteria for SVT.
What are we gonna do about SVT?
we’re gonna start off with some non-pharmacologic management.
So many cases of supraventricular tachycardia
can be treated with vagal maneuvers.
any maneuver that you perform
that increases parasympathetic tone
is gonna decrease the heart rate
and potentially terminate the SVT.
So a couple of the maneuvers that are commonly done
is the valsalva,
so you basically get the patient to hold their breath
and bear down as though they’re having a bowel movement
and they wanna hold that for 15 or 20 seconds if they can.
That raises parasympathetic tone
and in some cases can terminate the SVT.
Another vagal maneuver
that’s commonly performed is carotid massage.
Now, before you do carotid massage,
you wanna auscultate the carotids
and make sure you’re not hearing any bruits
and obviously you only wanna do one side at a time
because occluding both carotids at once is not a good idea.
What you're gonna do is put your fingers
over the carotid artery high up in the neck
and you're gonna apply firm but gentle pressure
continually for about 15 or 20 seconds.
Again, this will raise parasympathetic tone
and might terminate the SVT.
If your vagal maneuvers don't work and by the way,
for patients who have a history of paroxysmal SVT in the past,
they typically learn these maneuvers
and will have attempted them at home
before the even come into the hospital.
But if vagal maneuvers don’t work,
of course, you’re gonna cardiovert your patient
if they’re unstable
but your initial medical management is gonna be adenosine.
Now, adenosine works
by completely blocking conduction through the AV node
for a very short period of time,
about three to five seconds is its plasma half-life.
So it completely blocks nodal conduction
but the effect of it goes away very, very quickly.
One of my favorite cardiology mentors when I was an intern
described adenosine to me as control-alt-delete for the heart.
So basically, what you're doing is just shutting down
all of the wacky electrical conduction pathways and hoping
that the normal pathways will take back over when you restart.
If adenosine doesn't work,
were gonna move on to AV nodal blocking agents.
Again, calcium channel blockers, beta blockers
can be helpful for refractory cases.
They basically will block conduction through the AV node
and hopefully decrease the ventricular rate.
I do wanna emphasize again,
that these agents are contraindicated
in wide complex tachycardia.
In situations like WPW,
remember, your AV nodal blocking agents
are not gonna block your accessory pathway
and they could potentially accelerate your tachycardia.
So in wide complex rhythms,
please do not give calcium channel blockers
or beta blockers 'cause they can be very harmful.
All right, our last scenario is
our regular, narrow, complex rhythm that has P-waves
and if you have P-waves,
you’re dealing with a sinus tachycardia.
So just a quick review on sinus tach,
your rhythm is gonna be regular so your RR interval
is gonna be the same from beat to beat, to beat,
in this case 11 millimeters.
You’re of course going to have a narrow QRS complex
and you're gonna see a P-wave preceding every single QRS
and you can see that denoted here.
PQRS, PQRS all coming along at a regular rate.
I wanna emphasize that sinus tachycardia is not a dysrhythmia.
It's not a disease on to itself to be treated.
It’s a symptom of some other underlying problem.
There is some physiologic derangement
that’s driving the tachycardia
and your goal should not be to slow down the heart rate,
it should be to identify and treat that underlying problem.
So in summary,
I'll just remind you of a couple of key points
about each rhythm we talked about.
Ventricular tachycardia is a wide complex rhythm
with which patients should be cardioverted if unstable,
otherwise, they can be managed medically.
all wide complex tachycardia is vtec until proven otherwise.
Atrial fibrillation is our narrow,
complex irregularly irregular rhythm.
Again, we're gonna cardiovert unstable patients
but the mainstay of management
is gonna be AV nodal blockers
like calcium channel or beta blockers
Atrial flutter, we identify by the saw tooth atrial waves
and the management is the same as it is for atrial fibrillation.
And then lastly,
paroxysmal SVT is characterized by a narrow QRS complex,
a regular rate, and absent or abnormal P-waves.
Once again, cardioversion for any unstable patient
but the mainstay of medical management is gonna be adenosine.
So once again,
if the patient’s unstable, cardiovert them.
If they have hypotension or shock,
altered mental status, ischemic chest pain,
or evidence of acute heart failure,
you wanna make sure you terminate that rhythm quickly.
is always gonna be treated by addressing the underlying cause
never treat sinus tachycardia as a primary rhythm disturbance.
Thank you very much.