12. drugs for arrhythmias

Question 1

Describe phases 0-4 of the cardiac action potential

Answer 1

0 - rapid depolarisation - Na+ influx
1 - short depolarisation - k+ efflux
2 - Delay in repolarisation - Ca2+ entry via L-type channels
3 - Rapid depolarisation - K+ efflux
4- Automaticity - slow depolarisation

Question 2

3 Major modes of action of anti-arhythmic drugs

Answer 2

1. Decrease slope of phase 4
2. Increase threshold potential - slow phase 0
3. Increase refractory period - lengthen action potential

Question 3

What do class I anti-arhythmic drugs do?

Answer 3

Sodium channel blockade

Question 4

What do class II anti-arhythmic drugs do?

Answer 4

catecholamine blockade

Question 5

What do class III anti-arhythmic drugs do?

Answer 5

Lengthening of refractoriness

Question 6

What do class IV anti-arhythmic drugs do?

Answer 6

Calcium channel blockade

Question 7

What are the 3 subtypes of Class I drugs and name examples?

Answer 7

1a - sodium channel blockade with lengthened refractoriness
quinidine, disopyramide and procainamide (Older drugs)

1b - sodium channel block with reduced refractoriness
lidocaine.
Binds and unbinds quickly.
Supresses premature beats

1c sodium channel block with little effect on refractory period
Flecainide.
Bind and unbind slowly.
General reduction in excitability. Supress re-entrant rhythms

Question 8

Example of Class II drug

Answer 8

Propranolol

Question 9

two examples of class III drugs

Answer 9

amiodarone

sotalol

Question 10

In what way can class III drugs be pro-arrythmic and when can this be dangerous?

Answer 10

Can produce a polymorphic ventricular tachycardia

Dangerous with other drugs that lengthen
QT interval:
Some antipsychotic drugs
If have disturbed electrolyte balance (hypokalaemia)
Also if have hereditary prolonged QT

Question 11

Class IV drugs

Answer 11

Verapamil

Dilitiazem

Question 12

What does adenosine do? 3

Answer 12

Slows the rate of rise of pacemaker potential
Slows conduction through AV node (negative dromotropic)
Terminates paroxysmal supraventricular tachycardias

Question 13

What does digoxin do?

Answer 13

Slows conduction through AV node - Acts directly on the heart to inhibit Na+/ K+ ATPase

Question 14

Drugs used to treat atrial fibrillation

Answer 14

Class II agents and Class IV agents

Question 15

Treatments for atrial flutter

Answer 15

Digoxin

D.C. shock

Class III agents: Amiodarone/sotalol for maintenance

Anticoagulants if long standing condition