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Chapter 17 AntiArrhythmic Drugs


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What is the mechanism of Class I Anti Arrhythmics?
Block the fast Na channel responsible for phase 0 depolarization.
What is the mechanism of Class II Anti Arrhythmics?
Beta adrenergic receptor blockers
What is the mechanism of Class III Anti Arrhythmics?
Prolongers of the Action Potential without effecting initial phase 0 depolarization (i.e. usually outward K blockers).
What is the mechanism of Class IV Anti Arrhythmics?
Block Slow L Type Calcium Channels
Describe 2 mechanistic ways Antiarrhythmics treat increased automaticity.
1. prolong phase 4 depolarization; 2. increase the refractory period
Describe 2 mechanistic ways Antiarrhythmics treat reentrant pathways.
1. increase tissue refractory period; 2. na channel blockade
Describe Class IA's effect on Na channel. Usefulness?
Increased threshold, moderate Na channel block. Has little effect on SA node so good for increased automaticity and prolongs refractory period so good for reentry circuits.
What are Class IA's effect on EKG?
Prolonged QRS and QT
List 3 Class IA Drugs. For each list common side effects.
Quinidine (oral only, anitcholinergic, hypotension);
Procainamide (can be IV, beware NAPA, SLE like); Disopyramide (oral,no dig/GI, > anticholinergic, > -inotropic effect)
Why is quinidine and digoxin a risky mix?
Quinidine raises blood digoxin levels by decreasing body's clearance and volume of distribution of the later.
Describe Class IB's effect on Na channel. Usefulness?
Shortens the Action Potential duration and refractory period. This is effect is more pronounced leading to blockade in ischemic cells. Ventricular arrhytmias with little atrial effect.
List 4 Class IB Drugs and their relavant side effects.
Lidocaine (IV only, CNS);
Tocainide (oral, CNS/GI, agranulocytosis);
Mexiletine (oral, CNS/GI);
Diphenylhydantoin (antiseizure,IV/oral, CNS/GI)
Describe Class IC's effect on Na channel. What is the problem with this class?
Most potent Na channel blocker. Can increase mortalitiy with underlying heart abnormalites!
List 2 Class IC Drugs and their relevant side effects.
Flecinide (oral, aggravation of CHF/V Arr);
Propafenoen (weak Beta adrenergic block)
Common EKG finding in Class II Drugs.
prolonged PR interval due to prolonged AV nodal conduction.
What are the clinical uses of Beta blocker (Class II) antiarrhytmics?
Tachyarrhytmias (excess catecholamines); atrial flutter and fibrillation; supraventricular arrhytmias
Amiodarone is a Class III Drug. What is the relevant action and side effects of this drug?
Amiodarone (many effects, many adverse reactions, VD, -Inotrope, ~60 day elimination, pulmonary toxicity, thyroid dysf(x),GI)
List 5 Class III Drugs.
Amiodarone, Sotalol, Bretylium tosylate (IV), Ibutilide (IV, atrial flutter conversion), Dofetilide (oral, atrial flutter conversion)
List 2 common Class IV Drugs.
Verapamil, Diltiazem; CCBs so most potent in SA & AV nodes
What is the most efective drug for the rapid termination of reentrant PSVT?

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