Let's move on to the class 2 drugs.
So, these are beta blockers.
Now, all beta blockers have a very complex
interaction with the membrane.
First of all, all beta blockers
do have anti-ischemic effects.
They reduce the myocardial oxygen demand by
reducing heart rate for example.
Some beta blockers also have membrane stabilizing effects
at the phase 0 point of the action potential.
All of the beta blockers will also affect the slow current.
So, there is going to be an action on repolarization as well.
And there is one beta blocker, it's sotalol,
that has action potential prolongation,
because in a way,
it's acting like a class III antiarrhythmic.
Although sotalol is a beta blocker,
I'm going to discuss it in the class III discussion.
So, in terms of these beta blockers, let's talk about the
prototypical antiarrhythmic beta blocker, esmolol.
Now, esmolol is particularly useful because
it can be given intravenously
and it's quite fast acting and relatively short acting.
It reduces the cyclic AMP levels. It reduces the sodium
current and it reduces the calcium current.
The actions are specific to the atrioventricular node.
In terms of the ECG changes with these medications,
you often will see a prolongation of the PR interval,
which represents the conduction
through the AV node being delayed.
We call that dromotropy. So, esmolol and other beta blockers
are negative dromotropic agents.
The word "dromos" refers to the Greek god
or the patron god of racing.
So, dromos means race or fast. So, if you have
negative dromotropy, you have a slower speed of conduction.