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
2016B Q21	Classify anti-arrhythmic drugs by mechanism of action, giving examples of each (75% of marks). Describe the electrophysiological and ECG effects of sotalol (25% of marks).	historical_member	—