Let's talk about the group 5 drugs. Let's start with
adenosine. So adenosine is actually an endogeneous compound.
We actually have adenosine in our bodies. Now adenosine
acts on the purine receptor. It completely blocks conduction
in the AV node. It causes quite significant membrane
hyperpolarization and it increases the potassium current.
It is a very short duration of time. Now, when I say short
duration I mean short duration. We think that it lasts
in the blood for maybe 6 or 7 seconds because it's not broken
down in the liver and it's not broken down in the kidney,
it's actually broken down by red blood cells. Now one of the
major side effects of using adenosine is chest pain.
When we are talking about adenosine, I do want to mention
one thing. How you give this drug is really important.
And as you go on to your clerkship and work on code teams you
have to know that adenosine has to be given IV push with a follow up.
So you take your adenosine syringe, you get it ready. When you
are told to give it you give it and you push it hard as you can
into the IV line. Then you take a saline flush and you flush
it after that. You need to get that drug into the heart
as quickly as possible because it has such a short duration
of action. The other thing I am going to warn you about
is that the patients will complain of chest pain like you've
never seen. So the first time I ever gave adenosine
as a medical student. I push this adenosine, the patient had
a supraventricular tachycardia with a heart rate of around
175 and the monitor went flat for about 6 seconds. And I tell
you, if you are standing there as a medical student,
and you cause a flat line on a patient, the patient is
looking at you, the nurses think you killed the patient,
and you are standing there as the only person and then all of
a sudden the patient starts to complain of severe chest pain.
This is chest pain like no other, it's the wrath of God kind
of chest pain that these patients complain about and then
the heart rate comes back. And then it comes back very slowly.
That's what it's like giving this drug but you can save lives
because it's very effective. Let's move on to magnesium.
Magnesium, obviously you know it's a divalent cation,
but it actually is great at depressing ectopic pacemakers. And
it is the drug of choice for a rhythm called torsades de pointes.
And i'll explain torsades de pointes later. Potassium is
actually an antiarrhythmic too. It also will depress ectopic
pacemakers but it also can be proarrhythmic. It can also cause
a reentry arrhythmia. In fact the KGB used to use potassium
to kill people that they just didn't like and it was a very
easy way to get rid of patients or enemies of the state
without actually having any kind of identifiable problem when
they do autopsies. So potassium kills and in fact
it's now a restricted drug, or vial of liquid I
suppose you could call it, in most intensive care units.
Always measure your potassium levels because each class of
these drugs, whether it's class I or class III are kind of
dependant upon the potassium level and having altered potassium
levels can actually induce more arrhythmia in conjunction with
some of these medications.