Antiarrhythmic Drugs Flashcards
Class Ia Na+ channel blockers
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.
Quinidine
Class Ia Na+ channel blocker. Also blocks K+ channels, prolonging AP duration, is a vagal inhibitor, is an alpha-adrenergic receptor antagonist.
Procainamide
Class Ia Na+ channel blocker
Acute Ventricular Fibrillation/tachycardia
AR: Lupus Syndrome (33% of long term users)
Disopyramide
Class Ia Na+ channel blocker
Class Ib Na+ channel blockers
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.
Lidocaine
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.
Mexiletine
Class Ib Na+ channel blockers
Phenytoin
Class Ib Na+ channel blockers
Class Ic Na+ channel blockers
Propafenone, Flecainide, Encainide. Strongest slowing of upstroke rate, mildly prolong phase 2 = powerful prolongation of tissue refractory period. Encainide no longer used.
Propafenone
Class Ic Na+ channel blockers
Chronic Atrial Fibrillation
Half life of 2-11 hrs
AR: highly pro-arrhythmic, particularly with ventricular tachycardia
Flecainide
Class Ic Na+ channel blockers
Chronic Atrial Fibrillation
Half life of 12-27 hrs
AR: highly pro-arrhythmic, particularly with ventricular tachycardia
Encainide
Class Ic Na+ channel blockers
Class II Antiarrhythmic Drugs
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.
Class III Antiarrhythmic Drugs
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.
Ibutilide
Class III Antiarrhythmic Drug, blocks cardiac K+ channels.
Dofetilide
Class III Antiarrhythmic Drug, blocks cardiac K+ channels.
Used in: Chronic PSVT, Chronic Atrial Fibrillation
Sotalol
Class III Antiarrhythmic Drug, blocks cardiac K+ channels, also acts as a Beta-Blocker.
Used in: Chronic PSVT, Chronic Atrial Fibrillation
Bretylium
Class III Antiarrhythmic Drug, blocks cardiac K+ channels.
Amiodarone
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.
Class IV Antiarrhythmic Drugs
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
Verapamil
Class IV Antiarrhythmic Drugs: Calcium Channel Blocker
Half life of 7 hours
AR: hypotension, and potentially negative cardiac isotropy
Diltiazem
Class IV Antiarrhythmic Drugs: Calcium Channel Blocker
Adenosine
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.
Which drugs not to use for Acute Ventricular Fibrillation/tachycardia:
Classes I and IV
