3. Anti-arrhythmic drugs

Question 1

Name the 4 main classes of anti-arrhythmic drugs.

Answer 1

1. Class I - Na+ channel blockers
2. Class II - B-blockers
3. Class III - K+ channel blockers
4. Class IV - Ca channel blockers

Question 2

Name an example of a Na+ channel blocker and describe its MOA.

Answer 2

FLECAINIDE (class Ic):

i. blocks myocyte Na+ channels…
ii. lengthens myocyte depolarisation (phase 0) - so lengthened refractory period…
iii. decreased HR

Question 3

Name 3 arrhythmia types in which flecainide can be used. What precautions must be taken?

Answer 3

1. Supraventricular tachys: AF and atrial flutter
2. WPW syndrome
3. Premature ventricular contractions

Must prescribe alongside AVN blocker (eg bisoprolol, digoxin) as slowing of AF would allow ventricles to speed up to match atrial rate.

Question 4

Name 2 examples of beta-blockers and describe their MOA.

Answer 4

BISOPROLOL and PROPANOLOL:

Block sympathetic stimulation at B-adrenoRs… decrease SAN/AVN catecholamine-dependent depolarisation (funny current - longer to reach threshold)…

• decreased HR (action at SAN)
• increase AVN APD and refractory period… slow AVN conduction

Question 5

Name 3 arrhythmia types in which B-blockers can be used.

Answer 5

1. Sinus and catecholamine-dependent tachycardias (action at SAN)
2. Supraventricular tachycardias - control ventricle rate (action at AVN)
3. AVN re-entry arrhythmias - cardioversion (action at AVN)

Question 6

Name 2 examples of K+ channel blockers and describe their MOA.

Answer 6

AMIODARONE and SOTALOL:

Block K+ channels… lengthen AP phase 3 (repolarisation in myocytes and nodes)… lengthen refractory period… decrease HR.

Amiodarone also has many other actions:

• B-blocker-like and Ca channel blocker-like effects at SAN and AVN (increases refractory period)
• Na channel blocker-like effect (slows intra-cardiac conduction)

Question 7

Why must heart rhythm be carefully monitored when a P is on amiodarone or other class III drugs?

Answer 7

Cause prolongation of QT interval (as this represents phase 3 of AP) so risk of torsades de pointes (type of V tach) and subsequent ventricullar fibrillation and death.

Ps with congenital or drug-induced long QT must NOT take K+ channel blockers.

Question 8

Name 2 examples of Ca2+ channel blockers and describe their MOA.

Answer 8

VERAPAMIL and DILITIAZEM:

Block Ca channels… elongate SAN and AVN phase 0 (depolarisation dependent on Ca influx)… lengthened refractory period… slow HR (depending on BP and baroR reflex) and AVN conduction.

Question 9

Name 2 arrhythmia types in which Ca channel blockers can be used.

Answer 9

1. Supraventricular tachycardia - control ventricle rate

2. AVN re-entry tachycardia - cardioversion

Question 10

What is the MOA of ivabradine and why would it be used?

Answer 10

Blocks SAN funny current… slows SAN AP firing… decreases HR.

Treatment of:
1. sinus tachycardia
2. heart failure and angina (in combination with B-blockers)
Avoids BP drop as doesn’t affect adrenoRs in vasculature.

Question 11

What is the MOA of digoxin and why would it be used?

Answer 11

Cardiac glycoside used as an adjunct (e.g. to beta-blockers) to decrease ventricular rates in atrial fibrillation/flutter.

Slows AVN conduction and thus HR.

Question 12

Name a drug that can be used to treat vagal bradychardia.

Answer 12

Atropine: selective muscarinic antagonist - blocks vagal activity, increasing HR and AV conduction

Question 13

Which drug can be used in cardioversion of RECENT ONSET A-Fib?

Answer 13

Vernakalant: blocks atrial-specific K+ channels

Question 14

What is the MOA of lidocaine and when is it used?

Answer 14

Lidocaine = class Ib drug that slows phase 0 (increases Na threshold for depolarisation) in fast beating or ischaemic tissue.

So can be used in acute ventricular tachycardia (esp. if ischaemia).

Have less pro-arrhythmic effect than class Ia (less QT prolongation).

Question 15

name 2 drugs that can be used to treat WPW syndrome whilst awaiting ablation

Answer 15

1. flecainide

2. amiodarone (side effects)

Question 16

What is the MOA of adenosine and which conditions can it be used for?

Answer 16

Natural nucleoside that:

• binds to A1 Rs and activates K currents in SAN and AVN… hyperpolarisation… decreased heart rate
• decreases Ca currents… lengthens AVN refractory period… short term slowing of AVN conduction

1. Converte re-entrant supraventricular tachycardias
2. Hypotension during surgery
3. Diagnosis of coronary artery disease (highlight perfusion defects)

Question 17

Which drugs could be used to terminate re-entrant SVT?

Answer 17

Acute (IV):

• adenosine
• verapamil
• flecainide

Chronic (oral):

• bisoprolol, verapamil
• sotalol
• flecainide
• amiodarone

Question 18

Name 3 drugs that could be used in VT.

Answer 18

1. metoprolol
2. lidocaine (esp. if ischaemic/scar related)
3. amiodarone