Antiarrhythmic drugs

Question 1

Class I
1) How do class I antiarrhythmics work?
2) Give an example of a class Ia, Ib, Ic drugs
3) What effect do class Ia drugs have on the duration of the action potential, and what degree of blockage of sodium channels do they cause?
4) What effect do class Ib drugs have on the duration of the action potential, and what degree of blockage of sodium channels do they cause?
5) What effect do class Ic drugs have on the duration of the action potential, and what degree of blockage of sodium channels do they cause?
6) What effect does prolonging the duration of the action potential have on the QT interval?

Answer 1

1) Sodium channel blockers. Blocking sodium channels causes a slower depolarisation (decreasing the slope in phase 0 if the cardiac action potential)
2) Class Ia = quinidine, procainamide. Class Ib = lidocaine, mexiletine. Class 1c = flecainide, propafenone
3) Prolong it, moderate effect
4) Decrease it, mild effect
5) No effect, marked effect
6) Increases it

Question 2

Class II
1) What drugs are class II antiarrhythmics?
2) Give an example of these drugs
3) How do they work?

Answer 2

1) Beta blockers
2) Atenolol, metoprolol, bisoprolol, metoprolol
3) Antagonise the effect of the SNS - reduction in cardiac conduction and cardiac conduction strength

Question 3

Class III
1) What drugs are class III antiarrhythmics?
2) In cardiac tissue, what are potassium channels responsible for?
3) How do these drugs therefore work?
4) Give an example of these drugs

Answer 3

1) Potassium channel blockers
2) Cardiomyocyte repolarisation through potassium efflux
3) Blockage of these channels prevent potassium release which slows repolarisation by increasing AP and refractory period duration and slows conduction. This is results in a prolonged QT interval.
4) Amiodarone, dronedarone, sotalol

Question 4

Class IV
1) What drugs are class IV antiarrhythmics?
2) How do they work?
3) Give an example

Answer 4

1) Non-dihydropyridine CCBs
2) Prevent the influx of calcium into cardiomyocytes which decreases conduction through the AV node
3) Verapamil, diltiazem

Question 5

Miscellaneous antiarrhythmic drugs
What are the 4 main miscellaneous antiarrhythmic drugs?

Answer 5

• Adenosine
• Cardiac glycosides (digoxin)
• Atropine
• Electrolyte supplements (magnesium and potassium salts)