Questions and Answers
What is the general job of anti-arrhythmic drugs?
Increases potential to help reduce action potential and slow down beating of heart to stop arrhythmia.
What is excitability?
Changes in resting membrane potential.
What is conduction?
Slope of phase 0.
What is the refractory period?
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What is automaticity?
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Calcium channel blockade drugs will extend what interval in an ECG?
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Potassium channel blockade drugs will extend what interval in an ECG?
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Na+ channel blockers are in what class and what is their effect?
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Beta blockers are in what class and what is their effect?
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K+ channel blockers are in what class and what effect do they have?
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Ca++ channel blockers are in what class and what effect do they have?
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What general effect does adenosine have?
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What are general characteristics of Na+ channels?
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What are 3 Class 1a drugs?
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What is the general mechanism of Class 1a drugs?
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What are the ADRs of Quinidine?
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What are the ADRs of Procainamide?
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Study Notes
General Function of Antiarrhythmic Drugs
- Reduce action potential and slow heart rate to manage arrhythmias.
Key Concepts in Cardiac Electrophysiology
- Excitability: Refers to changes in resting membrane potential.
- Conduction: Defined by the slope of phase 0 of the action potential.
- Refractory Period: Comprised of phases 1 through 3 where the heart is less responsive to stimulation.
- Automaticity: Related to the slope of phase 4; involves Na+/Ca++ influx and K+ efflux, affected by SNS (increases slope) and PNS (decreases slope).
ECG Intervals Affected by Drug Classes
- Calcium Channel Blockers: Extend the P-R interval on an ECG.
- Beta Blockers: Also extend the P-R interval.
- Potassium Channel Blockers: Prolong the Q-T interval.
Antiarrhythmic Drug Classes
- Na+ Channel Blockers (Class I: IA, IB, IC): Decrease phase 0 upstroke rate and phase 4 slope; increase threshold for depolarization.
- Beta Blockers (Class II): Decrease phase 4 slope.
- K+ Channel Blockers (Class III): Increase action potential duration.
- Ca++ Channel Blockers (Class IV): Decrease phase 4 slope.
- Adenosine: Increases diastolic potential and opens K+ channels.
Characteristics of Sodium Channels
- Resting state: Closed, no ion movement.
- Activated state: Open, Na+ influx.
- Inactivated state: No ion conduction.
- Use-dependent blockade: Drug effect increases with faster activation rates.
Class IA Antiarrhythmic Drugs
- Examples: Quinidine, Procainamide, Disopyramide.
- Mechanism: Block Na+ channels in phase 0 and K+ channels, leading to prolonged refractory period.
- Clinical Use: Effective for supraventricular and ventricular arrhythmias.
Quinidine
- Class 1a antiarrhythmic and antimalarial derived from quinine.
- Administered mainly in sustained-release tablets; less commonly used IV due to hypotension risk.
- Commonly indicated for chronic control of both supraventricular and ventricular arrhythmias.
ADRs of Quinidine
- GI disturbances, tinnitus, visual disturbances (Cinchonism), and proarrhythmias like Torsade de Pointes.
- Possible drug interactions with digoxin, leading to increased toxicity.
Procainamide
- Class 1a antiarrhythmic with fewer anticholinergic effects compared to Quinidine.
- Indicated mainly for ventricular arrhythmias, with good oral bioavailability and short half-life.
- Pharmacokinetics involve renal excretion and biotransformation to active metabolite (N-acetylprocainamide).
ADRs of Procainamide
- High incidence of antinuclear antibodies (ANA) formation and lupus-like syndrome in some patients.
- Risk of agranulocytosis, psychotic reactions, and overdose management with sodium lactate.
Disopyramide
- Class 1a antiarrhythmic with unique clinical considerations (details not provided).
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Description
Explore essential concepts related to antiarrhythmic drugs, including their classes and functions. This quiz covers definitions and key terms that are critical for understanding how these medications affect heart rhythm. Test your knowledge and improve your grasp of antiarrhythmic pharmacology!