Anti arrhythmics

Question 1

Classes of Anti arrhythmics

Answer 1

1. Class 1A (procainamide)
2. Class 1B (lidocaine)
3. Class 1C (Flecainide)
4. Class 2 - beta blockers (Metoprolol, Propranolol)
5. Class 3 - K+ channel blockers (Amiodarone)
6. Class 4 - Non DHP Ca2+ channel blockers (Verapamil, Diltiazem)

Question 2

MOA of Procainamide

Answer 2

Class 1A

Blocks Na+ and K+ channels

Reduces rate of Phase 0 depolarisation → slows the initiation of depolarisation → reduces conductivity and automaticity

Lengthens phase 1-3 → Increase ERP (time where cardiomyocytes cannot undergo another action potential)

Increases APD (action potential duration)

Question 3

Clinical uses of procainamide

Answer 3

1. Supraventricular & Ventricular arrhythmias
2. Wolff-Parkinson-White syndrome

Question 4

Example of Class 1A drugs

Answer 4

Procainamide

Question 5

MOA of Lidocaine

Answer 5

Class 1B

-Inhibit Na+ channels in purkinje fibres, ventricular myocytes (not atrial)

Not as potent in blocking Na+ channel activity as class Ia

• Reduces rate of Phase 0 rise (though to a smaller extent)
• Shortens phase 3 repolarisation → reduces APD
• Reduces automaticity (little effect on conductivity)

Question 6

Clinical uses of Lidocaine

Answer 6

• Treating ischaemic arrhythmias
• Treat digoxin toxicity

Question 7

Example of Class 1B anti arrhythmics

Answer 7

Lidocaine

Question 8

MOA of Flecainaide

Answer 8

Inhibit Na+ channels in atrial, ventricular myocytes & purkinje fibre cells
Reduce rate of Phase 0 rise
Shortens phase 3 repolarisation
Reduces conductivity and automaticity

No/ little effect on APD/ERP

Question 9

Clinical uses of Flecainide

Answer 9

Refractory ventricular tachycardia that tends to progress to VF

Question 10

MOA of Class 2 anti arrhytmics

Answer 10

They are beta blockers

• Reduces phase 4 depolarisation, so that it takes longer before the drug can depolarise again
• Shape of graph does not change as it does not block any channels, but it reduces heart rate and contractility
• Reduces automaticity
• Prolonged AV conduction
• No changes to APD, ERP

Question 11

Clinical uses of Metoprolol, Propranolol

Answer 11

Tachycardia caused by sympathetic activation
Atrial fibrillation
Reduces sudden arrhythmic death post-MI

Question 12

Examples of Class 2 anti arrhytmics

Answer 12

Beta blockers - Metoprolol, Propranolol

Question 13

MOA of Amiodarone

Answer 13

K+ channel blockers –> Prolongs phase 3 repolarisation

Increases ERP and APD

Question 14

Clinical uses of Amiodarone

Answer 14

• Effective in maintaining normal sinus rhythm in patients with atrial fibrillation
• Effective in the prevention of reentrant ventricular tachycardia

Question 15

What class of anti arrhytmic is Amiodarone

Answer 15

Class 3 K+ channel blockers

Question 16

MOA of Verapamil, Diltiazem

Answer 16

Non-DHP Ca2+ channel blockers

• Prolongs phase 4 depolarisation
• Reduce AV node conductivity
• Increases ERP and APD
• Non DHP have higher selectivity for AV nodal calcium channels

Question 17

Clinical uses of Class 4 anti arrythmics

Answer 17

Supraventricular tachycardia
Hypertension
Angina