Antiarrhythmic Drugs

Question 1

Class Ia Na+ channel blockers

Answer 1

Quinidine, procainamide, disopyramide. Slowed and reduced upstroke (class I), and delay of repolarization causes a prolonged repol (class III). Also prolongs refractory period. Use dependent.

Question 2

Quinidine

Answer 2

Class Ia Na+ channel blocker. Also blocks K+ channels, prolonging AP duration, is a vagal inhibitor, is an alpha-adrenergic receptor antagonist.

Question 3

Procainamide

Answer 3

Class Ia Na+ channel blocker

Acute Ventricular Fibrillation/tachycardia

AR: Lupus Syndrome (33% of long term users)

Question 4

Disopyramide

Answer 4

Class Ia Na+ channel blocker

Question 5

Class Ib Na+ channel blockers

Answer 5

Lidocaine, Mexiletine, Phenytoin. Mildly slow upstroke, prolong refractory period, but do NOT prolong phase 2 of the AP. Purest form of class 1 on the fast response. Lidocaine is the most important for arrythmias.

Question 6

Lidocaine

Answer 6

Class Ib Na+ channel blockers

Used in Acute Ventricular Fibrillation/tachycardia

Half life of 1-2 hrs

AR: least cardiotoxic agent of class I drugs. Side effects: parasthesia, tremors, seizures agitation and confusion.

Question 7

Mexiletine

Answer 7

Class Ib Na+ channel blockers

Question 8

Phenytoin

Answer 8

Class Ib Na+ channel blockers

Question 9

Class Ic Na+ channel blockers

Answer 9

Propafenone, Flecainide, Encainide. Strongest slowing of upstroke rate, mildly prolong phase 2 = powerful prolongation of tissue refractory period. Encainide no longer used.

Question 10

Propafenone

Answer 10

Class Ic Na+ channel blockers

Chronic Atrial Fibrillation

Half life of 2-11 hrs

AR: highly pro-arrhythmic, particularly with ventricular tachycardia

Question 11

Flecainide

Answer 11

Class Ic Na+ channel blockers

Chronic Atrial Fibrillation

Half life of 12-27 hrs

AR: highly pro-arrhythmic, particularly with ventricular tachycardia

Question 12

Encainide

Answer 12

Class Ic Na+ channel blockers

Question 13

Class II Antiarrhythmic Drugs

Answer 13

Beta Blockers: Propanolol, Metoprolol, Esmolol. Beta-adrenergic receptor blockers. These reduce I(f) current, L-type Ca current. and K+ current. This reduces the rate of diastolic depolarization in pacing cells, reduces upstroke rate, and slows repolarization, particularly in AV nodal myocytes. Refractory period is prolonged in SA and AV cells, and pacing rate is reduced. These are used to terminate arrhythmias that involve AV nodal re-entry, and to control ventricular rate during atrial fibrillation.

Used in: Chronic PSVT, Acute Ventricular Fibrillation/tachycardia

AR: Hypotension, aggravation of heart failure, bronchospasm and impotence.

Esmolol has a half life of 10 minutes since it is metabolized by red cell esterase.

Question 14

Class III Antiarrhythmic Drugs

Answer 14

Ibutilide, Dofetilide, Amiodarone, Sotalol, Bretylium. These drugs block cardiac K+ channels, causing a prolongation of fast response phase 2 (which causes increased Na+ inactivation) and a prominent prolongation of the refractory period. Very potent, especially against re-entrants.

Question 15

Ibutilide

Answer 15

Class III Antiarrhythmic Drug, blocks cardiac K+ channels.

Question 16

Dofetilide

Answer 16

Class III Antiarrhythmic Drug, blocks cardiac K+ channels.

Used in: Chronic PSVT, Chronic Atrial Fibrillation

Question 17

Sotalol

Answer 17

Class III Antiarrhythmic Drug, blocks cardiac K+ channels, also acts as a Beta-Blocker.

Used in: Chronic PSVT, Chronic Atrial Fibrillation

Question 18

Bretylium

Answer 18

Class III Antiarrhythmic Drug, blocks cardiac K+ channels.

Question 19

Amiodarone

Answer 19

Class III Antiarrhythmic Drug, blocks cardiac Na+ channels, markedly reduces conduction velocity and increasing refractory period. Also decreases the rate of diastolic depolarization (phase 4) in automatic cells, reducing firing rate.

Used in: Chronic PSVT, Chronic Atrial Fibrillation, Acute Ventricular Fibrillation/tachycardia

Half life of 13-100 days

AR: bradycardia and heart block. Dose related effects: thyroid dysfunction, corneal deposits, pulmonary fibrosis and skin discoloration. Problems exacerbated by long half life.

Question 20

Class IV Antiarrhythmic Drugs

Answer 20

Calcium Channel Blockers: Verapamil, Diltiazem. Use-dependent blockers of L-type Ca Channels in nodal cells, but also function in fast response myocytes. Slow the Calcium dependent upstroke (slowing conduction velocity of AV node), and they also prolong the refractory period, thereby they can suppress re-entrant arrhythmias, particularly in the AV node. Slowed repolarization (phase 3) results indirectly from L channel block: the reduced amplitude of the AP activates fewer K+ channels.

Used in: Chronic PSVT

Question 21

Verapamil

Answer 21

Class IV Antiarrhythmic Drugs: Calcium Channel Blocker

Half life of 7 hours

AR: hypotension, and potentially negative cardiac isotropy

Question 22

Diltiazem

Answer 22

Class IV Antiarrhythmic Drugs: Calcium Channel Blocker

Question 23

Adenosine

Answer 23

increases K+ current, while also decreasing both L-type Calcium current and I(f) in SA and AV nodes. Similar in function to Beta Blockers, but is not one.

Used in: Acute Paroxysmal supraventricular tachycardia (PSVT).

Half life is less than 10 seconds, given as an IV bolus

AR: flushing (20%), chest burning and shortness of breath, brief AV block.

Question 24

Which drugs not to use for Acute Ventricular Fibrillation/tachycardia:

Answer 24

Classes I and IV