3. Anti-arrhythmic drugs Flashcards
Name the 4 main classes of anti-arrhythmic drugs.
- Class I - Na+ channel blockers
- Class II - B-blockers
- Class III - K+ channel blockers
- Class IV - Ca channel blockers
Name an example of a Na+ channel blocker and describe its MOA.
FLECAINIDE (class Ic):
i. blocks myocyte Na+ channels…
ii. lengthens myocyte depolarisation (phase 0) - so lengthened refractory period…
iii. decreased HR
Name 3 arrhythmia types in which flecainide can be used. What precautions must be taken?
- Supraventricular tachys: AF and atrial flutter
- WPW syndrome
- 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.
Name 2 examples of beta-blockers and describe their MOA.
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
Name 3 arrhythmia types in which B-blockers can be used.
- Sinus and catecholamine-dependent tachycardias (action at SAN)
- Supraventricular tachycardias - control ventricle rate (action at AVN)
- AVN re-entry arrhythmias - cardioversion (action at AVN)
Name 2 examples of K+ channel blockers and describe their MOA.
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)
Why must heart rhythm be carefully monitored when a P is on amiodarone or other class III drugs?
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.
Name 2 examples of Ca2+ channel blockers and describe their MOA.
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.
Name 2 arrhythmia types in which Ca channel blockers can be used.
- Supraventricular tachycardia - control ventricle rate
2. AVN re-entry tachycardia - cardioversion
What is the MOA of ivabradine and why would it be used?
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.
What is the MOA of digoxin and why would it be used?
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.
Name a drug that can be used to treat vagal bradychardia.
Atropine: selective muscarinic antagonist - blocks vagal activity, increasing HR and AV conduction
Which drug can be used in cardioversion of RECENT ONSET A-Fib?
Vernakalant: blocks atrial-specific K+ channels
What is the MOA of lidocaine and when is it used?
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).
name 2 drugs that can be used to treat WPW syndrome whilst awaiting ablation
- flecainide
2. amiodarone (side effects)
