Antiarrhythmics

Question 1

How do you generate an AP in cardiac myocytes? - make reference to the phases

Answer 1

• 0: VGNC > influx of Na+ > rapid depolarisation
• 1: K+ efflux > slight repolarisation
• 2: Ca2+ influx > plateau
• 3: K+ efflux > rapid repolarisation phase
• 4: return to RMP by Na+/K+ATPase

Question 2

How do you generate the pacemaker potential? - make reference to the phases

Answer 2

• 4: HCN channels open Na+ influx > funny current - intial slow depolarisation
• threshold potential reached
• 0: influx of Ca2+ through L type Ca2+ channels > depolarisation
• 3: efflux of K+ > repolarisation

Question 3

What is the Vaughan Williams classification?

Answer 3

• class I: block voltage gated Na+ channels
• class II: beta blockers
• class III: potassium channel blocker
• class IV: calcium channel blocker

Question 4

What are the sub types of class I antiarrhythmics?
Examples

Answer 4

Class IA - procainamide
Class IB - lidocaine
Class IC - flecainide

Question 5

Example of class IB antiarrhythmics

Answer 5

Lidocaine

Question 6

What are the uses of lidocaine?

Answer 6

Ventricular tachycardia
Not in atrial arrhythmias

Question 7

What is the mechanism of action of lidocaine?

Answer 7

Class IB antiarrhythmic
- Weakly blocks voltage gated Na+ channels
- Decreases AP duration + effective refractory period

Question 8

Adverse effects of lidocaine

Answer 8

Drowsiness + dizziness
N + V

Question 9

Example of class IC antiarrhythmics

Answer 9

Flecainide

Question 10

What are uses of flecainide?

Answer 10

Supraventricular arrhythmias
Premature ventricular contractions
Wolff- Parkinson White syndrome

Question 11

What is the mechanism of action of flecainide?

Answer 11

Class IC antiarrhythmic
- blocks voltage gated Na+ channel
- slows phase 0/depolarisation
- prolong QT interval
- normal effective refractory period + AP

Question 12

What are the adverse effects of flecainide?

Answer 12

• Drowsiness + dizziness
• N+V
• pro-arrhythmia + sudden death with chronic use

Question 13

Examples of class II antiarrhythmics

Answer 13

beta blockers
Bisoprolol
Propanolol
Atenolol
Metoprolol

Question 14

What are the uses of class II antiarrhythmics?

Answer 14

Supraventricular tachycardias
Heart failure
After MI

Question 15

What is the mechanism of action of class II antiarrhythmics?

Answer 15

Beta blockers
- block B adrenoreceptors
- decrease sympathetic activity on heart > reduces cAMP levels > reduces Ca2+ influx
- slows AP
- prolongs repolarisation at AV node
- increased PR interval

Question 16

What are the adverse effects of class II antiarrhymics?

Answer 16

Hypotension
Fatigue
Bronchospasm

Question 17

What are contraindications of class II antiarrhytmics?

Answer 17

Asthma
Acute heart failure
Partial AV block

Question 18

What the important drug drug interactions of class II antiarrhymics

Answer 18

B agonists
Verapamil + Diltiazem - CCBs

Question 19

Examples of class III antiarrhythmics

Answer 19

potassium channel blockers
Amiodarone + sotalol

Question 20

What are the uses of class III antiarrhythmics?

Answer 20

Broad anti-arrhythmic activity
(most arrhythmias)

Question 21

What is the mechanism of action of class III antiarrhythmics?

Answer 21

potassium channel blockers
- block potassium channel > prolong repolarisation by inhibiting K+ efflux > prolonged AP duration

Question 22

What are the adverse effects of amiodarone?

Answer 22

• Pulmonary fibrosis
• Hypo/hyperthyroidism
• Photosensitivity
• Hepatitis
• Increased LDL cholesterol
• Optic neuritis > transient blindness

Question 23

What are contraindications of amiodarone?

Answer 23

Active thyroid disease
Heart block

Question 24

What are the important drug drug interactions of class III antiarrhythmics

Answer 24

Amiodarone increases [plasma] of digoxin,warfarin + verapamil

Question 25

Examples of class IV antiarrhythmics

Answer 25

**CCBs** - non dihydropyridine Verapamil Diltiazem

Question 26

What are uses of class IV antiarrhythmics?

Answer 26

Control ventricles during Supraventricular tachycardia Convert SVTs

Question 27

What is the mechanism of action of class IV antiarrhythmics?

Answer 27

**calcium channel blockers** - block calcium channels - decrease conduction through AV node > shorten phase 0 + prolonged repolarisation at AV node - increased PR interval - pronged plateau phase in cardiac myocytes - prolong depolarisation + repolarisation

Question 28

What are the adverse effects of class IV antiarrhythmics?

Answer 28

Constipation Bradycardia Heart block

Question 29

What are important drug drug interactions of class IV antiarrhythmics?

Answer 29

Beta blockers

Question 30

What are the 2 pathways causing arrhythmia?

Answer 30

- generate abnormal impulses - conduct impulses abnormally

Question 31

Do you treat arrhythmias via rate or rhythm control?

Answer 31

Most patients - rate control Rhythm control in younger patients

Question 32

Examples of Class V antiarrhytmics

Answer 32

Digoxin Adenosine Ivabradine

Question 33

What affect does digoxin have on the heart?

Answer 33

- cardiac glycoside - positive inotrope - AV node blockage

Question 34

What affect does ivabradine have on the heart?

Answer 34

Pacemaker current inhibitors Slows heart rate

Question 35

What effect does adenosine have on the heart?

Answer 35

Stimulates A1 adenosine receptor > AV blockage Short lasting

Question 36

Mnemonic to remember antiarrhythmics

Answer 36

**Some Block Potassium Channels** - **Class I**: block Sodium channels - **Class II**: Beta blockers - **Class III**: block Potassium channels - **Class IV**: block Calcium channels

Question 37

How to remember the action of Class I antiarrhythmics

Answer 37

- **IA** - After - prolongs AP - **IB** - Before - shortens AP - **IC** - normal AP

Question 38

How do you use the names of B blockers to determine their selectivity?

Answer 38

A-N β1 O-Z β1 and β2 Not “olol” ending α and β

Question 39

Full name of HCN channels

Answer 39

Hyperpolarisation-activated cycling nucleotide gated channels