Antiarrhythmics

Question 1

List the 4 classes of drug used to treat arrythmias (and their sub-classes if applicable)

Answer 1

Class I - Na+ channel blockers
- Class IA
- Class IB - e.g. Lidocaine
- Class IC - e.g. Flecainide
Class II - B-blockers - e.g. Propranolol
Class III - K+ channel blockers - e.g. Amiodarone
Class IV - Calcium channel blockers - e.g. Verapamil, Diltiazem

Question 2

What is the mechanism of action of Lidocaine?

Hence what is its major indication?

Answer 2

Use-dependent Na+ channel blocker - only blocks open Na+ channels, so particularly targets damaged myocardium firing lots of APs - many channels open.
Particularly used to prevent VF after MI

Question 3

What is the mechanism of action of B-blockers in terms of anti arrhythmic effects?
Link this to its indications

Answer 3

• Block B1-adrenoreceptors in the heart - decreased sympathetic activity. Therefore decrease slope of pacemaker potential - takes longer to reach AP threshold - slows heart.
  Therefore can be used after MI, as MI increases sympathetic activity.
• Also slow conduction at AV node - prevents supraventricular tachycardia.

Question 4

What is the mechanism of action of potassium channel blockers?
What is their major indication?

Answer 4

• Prolong AP by lengthening the refractory period - delays next AP
• Wolf-Parkinson-White syndrome

Question 5

State the mechanism of action of calcium channel blockers

Answer 5

• Decrease slope of pacemaker potential

- Decrease AV nodal conduction

Question 6

What is the mechanism of action of Adenosine?

Answer 6

• Acts on a-1 adrenoreceptors at AV node

- Enhances K+ conductance - hyperpolarisation - briefly stops heart so it resets –> used in arrhythmic emergencies

Question 7

What class of antiarrhythmic is lidocaine? 
List some ADRs

Answer 7

Class IB

GI upset, CNS symptoms such as dizziness, seizure etc…

Question 8

What class of antiarrhythmic is Amiodarone?
List 4 ADRs

Answer 8

Class III

• Pulmonary fibrosis
• Hepatotoxicity
• Neuropathy
• Thyroid dysfunction

Question 9

Name one class IC antiarrythmic and state 3 ADRs

Answer 9

Flecainide

• Pro-arrhythmic
• GI upset
• Blurred vision

Question 10

What is the mechanism of Digoxin?

List 2 ADRs

Answer 10

• Increases vagal activity - therefore decreases AV conduction and decreases HR
• Can cause bradycardia and GI upset

Question 11

Name 2 calcium channel blockers

Answer 11

Verapamil

Diltiazem