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.
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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.
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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.
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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?
- Adenosine