Cardiac dysrhythmia drugs

Question 1

Amiodarone:

Answer 1

useful for both supraventricular and ventricular arrhythmias. Analogue of thyroid hormone. Acts by blocking potassium channels, prolonging the action potential and refractory period and so resulting in a slowing of the heart rate, without altering the force of contraction. Can be used in Wolff Parkinson White syndrome.

Question 2

Sotalol:

Answer 2

blocks potassium channels, having the same effect as Amiodarone. The L isomer is a cardiac β1 adrenoceptor antagonist

Question 3

Adenosine:

Answer 3

leads to activation of potassium channels, a slowing of action potential duration and thus slowed heart rate. But has a very short plasma half-life so cannot be used chronically.

Question 4

Digoxin:

Answer 4

cardiac glycoside extracted from the foxglove plant. Can be used to slow AV node conduction and improve ventricular filling. Can also be used in heart failure. But, has a narrow therapeutic window (easily toxic).

Question 5

Propanolol, Atenolol:

Answer 5

β-blockers. Slows the rate of discharge of the SA node and also slow conduction through the AV node. Also useful in preventing arrhythmias following a heart attack

Question 6

Lidocaine (Lignocaine):

Answer 6

blocks the sodium channels that initiate the action potential, thus reducing the firing of action potentials (reduced heart rate). If it enters the CNS it can cause convulsions or coma. Also used as a local anaesthetic.

Question 7

Disopyramide, Procainamide, Flecainide:

Answer 7

also sodium channel blockers. But, these should all be avoided after heart attacks as they increase the risk of sudden death.

Question 8

Verapamil:

Answer 8

blocks L-type voltage-gated calcium channels. Slowing SA and AV node conduction, slowing heart rate. Dangerous in ventricular dysrhythmias and WolffParkinson-White syndrome, less cardiac output and AV node block.