Canonical Question

Antiarrhythmic

V5 D7.iv Historical V4 G7.iii 1 appearance

Master answer

CLASS	ACTION	ELECTRO- PHYSIOLOGY	DRUGS	THERAPEUTIC INDICATIONS
I. Na – Channel Blockers
Ia	Intermediate dissociation	↓ phase 0 ↓↓ conduction v ↑ repolarisation ↑ APD	Quinidine Disopyramide Procainamide	Atrial and ventricular arrhythmias esp. post MI
Ib	Fast dissociation	↔,↓ phase 0 ↓ conduction v ↓ repolarisation ↓ APD	lignocaine phenytoin tocainide, mexilitine	Ventricular arrhythmias post MI, digoxin induced arrhythmias
Ic	Slow dissociation	↓↓↓↓ phase 0 ↓↓↓↓ conduction v ± repolarisation ↔ APD	flecainide ecainide, lorcainide	Refractory arrhythmias
II. β – Blockers
		↓ SA firing – ↓ rate, conduction	propranalol^* atenolol, esmolol	Rate control in AF, AT, Flutter and VT
III. K – Channel Blockers
		Delay phase 3 (repol) ↑ APD ↑ ERP	amiodarone bretylium, sotalol^{^}	AF / Flutter termination
IV. Ca – Channel Blockers
		↓ AV conduction ↑ PR interval ↓ rate/conduction	verapamil diltiazem	SVT and AF or Flutter
OTHERS (Some call this Class V)
	Blocks Na⁺/K⁺ _ATPase→ ↑Ca2⁺, ↓K⁺, ↑Ach	↑ contractility ↓ AV conduction	Digoxin	AF rate control Heart Failure
	Opens K⁺ channels via adenosine receptors	Hyperpolarizes myocardium ↓ AV conduction ↓ SA firing	Adenosine^# Ibutilide	Terminate SVT or reveal underlying rhythm in tachycardias
	Stimulates Na⁺/K⁺_ATPase	Membrane stabilization	Magnesium	VF / Torsades de pointes

Notes		* Propranalol also has Na blocking activity ^ l-sotalol has beta blocking and class III activities; d-sotalol is a pure class III agent. Commercially available sotalol is a racemic (equal part) mixture. # Amiodarone – blocks Na, Ca, K channels, and exhibits beta blockade.

The effect on the myocardial action potential of each class is:

	Class Ia	Class Ib	Class Ic	Class II	Class III	Class IV
Depolarisation rate (phase 0)	↓	↔ or ↓	↓↓↓↓	↔	↔	↓↓↑↔± ↔
Conduction velocity	↓↓	↓	↓↓↓↓	↓	↓	↔
Effective Refractory Period	↑↑↑↑	↓	↑	↓	↑↑↑↑	↔
Action potential duration	↑	↓	↔ or ↑	↑	↑↑↑↑	↓
Automaticity	↓	↓	↓	↓	↓	↔
P-R duration	↔	↔	↑	↔ or ↑	↑	↔ or ↑
QRS duration	↑	↔	↑↑↑↑	↔	↑	↔
QTc duration	↑	↔ or ↓	↑	↓	↑↑↑↑	↔

Sotalol Effects

l-sotalol has beta blocking and class III activities
d-sotalol is a pure class III agent
Commercially available sotalol is a racemic (equal part) mixture.
Class III Effects (K – channel blocking)
- Blocking of outward K⁺ channels slows cardiac repolarisation, which increases the cardiac refractory period.
- Delay phase 3 (repol), ↓ AV conduction,
- ↑↑↑↑ APD, ↑↑↑↑ ERP
- ↑↑↑↑ QTc
- ↓ automaticity
- ↓ ectopy
- ↓ defibrillation energy requirement
- May ↑ inotropy
Class II Effects (β – Blocker)
- Antagonizes β₁ & β₂ receptors
- ↓ SA firing – ↓ heart rate, conduction
can prolong the QT interval.
- can cause polymorphic ventricular tachycardia (Torsades de Pointes)
- recommended to be initiated in the inpatient setting to monitor the QT interval after each dose
can cause severe bradycardia necessitating drug discontinuation

Gladwin / Sakurai / JC 2020

Answer by Gladwin, JC, Sakurai

Exam appearances

Exam	Exact wording	Relationship	Success
2008B Q13	Classify antiarrhythmic drugs, including their mechanisms of action, and give an example of one drug from each group.	historical_member	—