Antiarrhythmics

Question 1

5 classes of antiarrhythmics

Answer 1

1. Na channel blockers
2. Beta blockers
3. K channel blockers
4. L-type Ca channel blockers
5. Adenosine and digoxin

Question 2

Class 1a agents

Answer 2

Moderate Na blockade
Ex: procainamide
Decreases the slope of phase 0 (decreases speed of propagation and conduction velocity)
Increases refractoriness via some K channel blockade

Question 3

Class 1b agents

Answer 3

Mild Na blockade
Ex: lidocaine, phenytoin
Mild effect on slowing the speed of propagation and the conduction velocity
Shortens the AP duration
In cells with automaticity, raises the threshold potential for excitability and decrease the slope of phase 4
Exclusively work on VENTRICULAR tissue

Question 4

Class 1c agents

Answer 4

Strong Na blockade
Ex: flecainide, propafenone
Strong effect on slowing the speed of propagation and the conduction velocity
Little or no effect on duration of AP
Primarily used for suppressing atrial arrhythmias
Contraindicated in the setting of structural or ischemic heart disease

Question 5

Class 3 agents

Answer 5

K channel blockers
Ex: amiodarone, dronedarone, sotalol
Prolong the duration of the AP (prolongs QT)
Amiodarone has Na and Ca blocker effects
Sotalol has beta blocker properties

Question 6

Class 2 and 4 agents

Answer 6

Beta blockers and L-type channel blockers
Ex: verapamil and diltiazem
Exert their effects on all types of arrhythmic mechanisms (decreasing automaticity, reducing effects of re-entry, decreasing triggered activity)
Effects on multiple types of arrhythmias

Question 7

Digoxin

Answer 7

Works primarily via its parasympathetic properties
Limited use given narrow therapeutic index
Causes triggered arrhythmias (via delayed after depolarizations)

Question 8

Adenosine

Answer 8

Potent inhibitor of the AV node (and a bit the sinus node)
Very short acting
Exerts its effects at all phases of the pacemaker AP
Hyperpolarization and shortening of the AP

Question 9

Main side effect for

1. Procainamide
2. Lidocaine
3. Flecainide
4. Sotalol
5. Amiodarone
6. Digoxin

Answer 9

1. Drug induced lupus
2. Neuropathy
3. Death (in ischemic low EF)
4. Torsades de Pointes
5. Pretty much everything (nerves, liver, thyroid, eyes, skin, lungs)
6. Triggered arrhythmias, colour vision abnormalities