Arrhythmias: Anti-Arrhythmic Drugs & Surgery

Question 1

Name the classification system used for antiarrhythmic drugs

Answer 1

Vaughn Williams classification

Question 2

List the classes of in the Vaughn Williams classification

Answer 2

Ia, Ib, Ic
II
III
IV

Question 3

Give examples of antiarrhythmic drugs that don’t fit into the Vaughn Williams classification

Answer 3

Digoxin

Adenosine

Question 4

What is the target of class Ia drugs?

Describe its action

Answer 4

Voltage gated Na+ channel

Associate with and dissociate from Na+ channels at a moderate rate

Slow rate of rise of AP and prolong refractory period

Question 5

What is the target of class Ib drugs?

Describe its action

Answer 5

Voltage gated Na+ channel

Rapidly associate with and dissociate from Na+ channels

Prevent premature beats

Question 6

What is the target of class Ic drugs?

Describe its action

Answer 6

Voltage gated Na+ channel

Slowly associate with and dissociate from Na+ channels

Depress conduction
-ve inotropes

Question 7

What is the target of class II drugs?

Describe its action

Answer 7

β - adrenoceptor (antagonists)

Decrease SA and AV node depolarization rates

Question 8

What is the target of class III drugs?

Describe its action

Answer 8

Voltage-activated K+ channels (& some others)

Prolong phase 3 duration

(class III act on phase 3)

Question 9

What is the target of class IV drugs?

Describe its action

Answer 9

Voltage-activated Ca2+ channels

Slow conduction in SA and AV nodes

Less Ca2+ influx during phase 2

• ->
• ve inotropic effect

Question 10

Which classes of antiarrhythmics act on the atria?

Answer 10

Ic, III

Question 11

Which classes of antiarrhythmics act on the ventricles?

Answer 11

Ia, Ib, II

Question 12

Which classes of antiarrhythmics act on the AV node?

Answer 12

II, IV

adenosine, digoxin

Question 13

Which classes of antiarrhythmics act on the atria and ventricles, and AV accessory pathways?

Answer 13

Ia, Ic

Amiodarone, sotalol

Question 14

What phase of the action potential do class I drugs effect?

Answer 14

Phase 0 in fast response cells

as phase 0 is due to Na+

Question 15

What phase of the action potential do class II drugs effect?

Answer 15

Phase 0 in slow response cells

Question 16

What phase of the action potential do class III drugs effect?

Answer 16

Phase 3

as phase 3 is due to K+

Question 17

What phase of the action potential do class IV drugs effect?

Answer 17

Phase 2 in fast response cells
Phase 0 in slow response cells

(as these are due to Ca2+)

Question 18

In what states of the voltage dependant Na+ channel do class 1 drugs bind?

• Open
• Inactivated
• Resting

Answer 18

Class 1 drugs bind to voltage dependant Na+ channels in their open and inactivated states

They dissociate during the resting state

Question 19

Do class 1 drugs preferentially bind to myocytes with higher or lower firing frequencies?

Answer 19

They bind preferentially to areas of high firing frequency

Question 20

Why do class I drugs preferentially bind to ischaemic tissue and ectopic foci?

Answer 20

Ischaemia
-->
longer action potentials
-->
less time for Na+ channel in its resting state
-->
class I drugs are bound for longer
-->
Higher affinity for class I

(can be the same logic for ectopic foci)

Question 21

What is radiofrequency catheter ablation?

What does it target?

What can it be done straight after?

Answer 21

Ablation of cardiac tissue with catheter

Can target part of a reentrant circuit or a ectopic foci

Can be done in the same procedure as an electrophysiological study

Question 22

Describe a single chamber pacemaker

Answer 22

Only paces the right atria or right ventricle

Question 23

Describe a dual chamber pacemaker

Answer 23

Paces the right atrium and right ventricle

• used for AV node disease

Question 24

Describe an implantable cardioverter defibrillator (ICD)

Answer 24

Does:

• Pacing
• Cardioversion
• Defibrillation

Can get dual chamber ICDs

Question 25

What is the difference between an ICD and a pacemaker?

Answer 25

ICD can shock you back into rhythm

Pacemaker can’t

Question 26

What does a pacemaker do?

Answer 26

Paces the heart rate

Question 27

Describe direct current cardioversion (DCCV)

Answer 27

DC shocks via external electrodes

Need sedation/analgesia

Used during fibrillation to restore NSR

(antiarrhythmic drugs can be given at the same time)