Antiarrhythmic Drugs

Question 1

Class IA

Answer 1

Na-channel blockers

They slow the conduction velocity and prolong the refractory period. (Prolong QT-interval and QRS complex)

Quinidine: cinchonism (tinnitus)
Procainamide: Lupus-like syndrome
Disopyramide: anticholinergic side effects

Question 2

Class IB

Answer 2

Na-channel blockers

Lidocaine, Phenytoin and Mexiletine

Shorten phase 3 repolarization and decrease the duration of action potential.

Lidocaine: drug of choice in termination of ventricular tachycardia and prevention of ventricular fibrillation after acute myocardial infarction—CNS side effects include nystagmus and slurred speech.

Question 3

Class IC

Answer 3

Na-channel blockers

Suppress phase 0 in Purkinje and myocardial fibers. This causes a marked slowing of conduction in all cardiac tissues.

Used in atrial and ventricular tachycardia—also in Wolff-Parkinson-White Sydrome (WPWS)

Flecainide (blurred vision, dizziness and nausea)
Propafenone (avoid in asthmatic patients; bronchoconstrictor)

Question 4

Class II

Answer 4

ẞ-blockers—decrease the slope of phase 4 depolarization, prolong AV-conduction and decrease heart rate and contractility.

They are useful in tachyarrythmias causes by increased sympathetic activity.

Question 5

Class III

Answer 5

Potassium-channel blockers

Prolong the duration of the action potential without altering phase 0 of depolarization or the resting membrane potential. (Prolong effective refractory period)

Amiodarone, Dronedarone, Sotalol, Dofetilide, Bretylium, Ibutilide and Vernakalant

Question 6

Amiodarone

Answer 6

Class III anti-arrhythmic drug (K-channel blocker)

Onset of action: 2-3 days, but may take 1 to 3 weeks even with loading doses.

Elimination half life is 10-100 days.

Contains iodine and is structurally related to Thyroxine, it causes hypothyrodism.

Question 7

Dronedarone

Answer 7

Class III anti-arrhythmic drug (K-channel blocker)

Non-iodinated Amiodarone derivative. It is less lipophilic with lower tissue accumulation and shorter serum half-life than Amiodarone.

Question 8

Bretylium

Answer 8

Class III anti-arrhythmic drug (K-channel blocker)

Causes hypotension due to blockade of the efferent limb of the baroreceptor reflex.

It also inhibits NE release.

Question 9

IV Magnesium Sulfate

Answer 9

First-line treatment for Torsades de Pointes (TdP)—Magnesium helps stabilize the cardiac membrane and can help resolve TdP.

Sotalol may cause TdP and QT interval prolongation.

Question 10

IV Adenosine

Answer 10

Drug of choice for Acute Supraventricular Tachycardia