Antiarrhythmic drugs

Question 1

Class I drugs

Answer 1

IA: Procainamide, Quinidine
IB: Lidocaine, Mexiletine, Tocainide
IC: Flecainide, Encainide, Moricizine, Propafenone

• Block Na-channels in tissues that are frequently depolarizing

Question 2

Quinidine

Answer 2

• Class IA
• Block fast and active form of Na-channels
• Decrease velocity of phase 0
• Slow conduction velocity in atria, Purkinje fibers and ventricular cells
• Decrease QRS duration in ECG
• Increase AP duration and ERP (due to class III activity)
• May be used in wide variety of arrhythmias; atrial, AV-junctional, and ventricular tachyarrhythmias
• Cause cinchonism (headache, vertigo, tinnitus), cardiac depression, GI upset, autoimmune reactions
• May cause Torsade de pointes

Question 3

Lidocaine

Answer 3

• Class IB
• IV or IM
• Block fast and inactive refractory Na-channels
• Prevent the channels to go back to resting state –> shortens phase 3 repolarization
• Selectively affects ischemic or depolarized Purkinje and ventricular tissue
• Reduces AP duration, may prolong ERP
• Useful in acute ventricular arrhythmias, especially in post-MI
• The least cardiotoxic drug of conventional anti-arrhythmias

Question 4

Flecainide

Answer 4

• Class IC
• Block any Na-channels
• Markedly slows phase 0 depolarization
• Increase QRS on ECG
• Approved for refractory ventricular tachycardias
• May progress to VF, resulting in “sudden death”

Question 5

Class II drugs

Answer 5

• Propranolol
• Metoprolol
• Esmolol
• Beta-blockers

Question 6

Propranolol

Answer 6

• Class II drug
• Block cardiac beta-adrenoceptor and reduce cAMP, which result in reduction of both sodium and calcium currents
• Prolong phase 4 depolarization
• Suppress abnormal pacemakers –> decrease heart rate and contractility
• PR interval i usually prolonged
• Used as a prophylactic drug in post-MI patients (reduce the incidence of sudden arrhythmic death)

Question 7

Class III drugs

Answer 7

• Amiodarone
• Sotalol
• Dronedarone
• Dofetilide
• Block K-channels
• Can induce Torsades de pointes

Question 8

Amiodarone

Answer 8

• Class III drug
• Block K-channel, thus slow phase 3 repolarization
• Increase AP and ERP
• Increase QT in ECG
• Amiodarone have class I, II, III and IV actions, and therefor considered the most efficacious of all anti arrhythmic drugs
• Approve only in arrhythmias that are resistant to other drugs
• Contains iodine - can cause hyper-, hypothyroidism, pulmonary fibrosis, GI disturbances, microcrystalline deposits in cornea and skin - blue skin (smurf skin), tremor, Torsades de pointes

Question 9

Sotalol

Answer 9

• Class III drug
• Block K-channels and has potent nonselective beta-blocker activity
• Prolong phase 3 repolarization
• Increase AP and ERP
• Increase QT in ECG
• Recommended for atrial flutter and fibrillation
• Used for long-term therapy to decrease the rate of sudden death in post-MI patients
• Can cause Torsades de pointes

Question 10

Class IV drugs

Answer 10

• Verapamil
• Diltiazem
• Nifedipine (used in hypertension)
• Ca-channel blockers

Question 11

Verapamil and Diltiazem

Answer 11

• Class IV drug
• Bind only to open, depolarized channels
• Block L-type Ca-channels, therby decrease phase 4 depolarization and conduction velocity
• Decrese SA and AV nodal activity
• Increase ERP
• PR interval is increased
• Used in supraventricular tachycardias
• Convert atrioventricular nodal reentry to normal SR
• May cause AV block

Question 12

Adenosine

Answer 12

• Normal component of the body, but in high doses markedly slows or completely blocks conduction in the AV node
• Hyperpolarize the tissue and reduce Ca current
• Increase ERP
• Drug of choice in abolishing AV nodal arrhythmias and in paroxysmal supraventricular tachycardias
• Only 15 s of action
• Cause flushing, chest pain and hypotension