Group 2: Beta Blockers – Antiarrhythmic Drugs

00:01 Let's move on to the class 2 drugs. So, these are beta blockers.

00:04 Now, all beta blockers have a very complex interaction with the membrane.

00:09 First of all, all beta blockers do have anti-ischemic effects.

00:13 They reduce the myocardial oxygen demand by reducing heart rate for example.

00:18 Some beta blockers also have membrane stabilizing effects at the phase 0 point of the action potential.

00:26 All of the beta blockers will also affect the slow current. So, there is going to be an action on repolarization as well.

00:34 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.

00:45 Although sotalol is a beta blocker, I'm going to discuss it in the class III discussion.

00:52 So, in terms of these beta blockers, let's talk about the prototypical antiarrhythmic beta blocker, esmolol.

00:59 Now, esmolol is particularly useful because it can be given intravenously and it's quite fast acting and relatively short acting.

01:07 It reduces the cyclic AMP levels. It reduces the sodium current and it reduces the calcium current.

01:14 The actions are specific to the atrioventricular node.

01:18 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.

01:30 We call that dromotropy. So, esmolol and other beta blockers are negative dromotropic agents.

01:37 The word "dromos" refers to the Greek god or the patron god of racing.

01:43 So, dromos means race or fast. So, if you have negative dromotropy, you have a slower speed of conduction.