Questions and Answers
What is the main effect of Class 3 antiarrhythmic drugs?
Name one Class 3 antiarrhythmic drug.
Amiodarone
Which drugs are classified as Class 4 antiarrhythmics?
Sotalol has both β-blocking and action potential prolonging actions.
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Amiodarone can cause adverse effects on the ______, ______, and ______.
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What is the primary action of non-dihydropyridine (NDHP) drugs?
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Dihydropyridine (DHP) drugs primarily affect the ______.
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What is the mechanism of action of Verapamil?
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What is the clinical application of Adenosine?
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What is the therapeutic use of Magnesium in relation to arrhythmias?
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Atropine is used to treat bradycardia by producing a vagal block to increase heart rate.
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Study Notes
Class 3 Antiarrhythmic Drugs
- Potassium (K+) channel blockers, prolong phase 3 repolarization, increasing QT interval.
- Key drugs include Amiodarone, Ibutilide, Dofetilide, Dronedarone, and Sotalol (AIDDS).
- All can induce torsades de pointes; Amiodarone carries the lowest risk.
Class 4 Antiarrhythmic Drugs
- Calcium (Ca2+) channel antagonists affecting cardiac function.
- Causes decrease in SA nodal automaticity, AV nodal conduction, and ventricular contractility.
- Primary drugs: Verapamil and Diltiazem.
Amiodarone
- Multi-channel blocker impacting K+, Na+, and Ca2+.
- Adverse effects include pulmonary toxicity, thyroid dysfunction, and liver damage; monitoring required every 3 months.
Ibutilide and Dofetilide
- Class III K+ channel blockers indicated for atrial and ventricular arrhythmias.
- Specifically block the rapid component (IKr) of the delayed rectifier K+ current, slowing repolarization.
Sotalol
- Exhibits both β-blocking and action potential-prolonging properties.
Non-Dihydropyridine (NDHP) Drugs
- Includes Verapamil and Diltiazem, primarily affecting the heart.
- Induces vasodilation, resulting in lower blood pressure.
Dihydropyridine (DHP) Drug
- Nifedipine is the primary example, mainly targeting the vasculature.
- Not utilized as an antiarrhythmic agent.
Calcium Channel Blockers (CCBs)
- Have minimal impact on smooth muscle outside the cardiac context.
- Skeletal muscle is not affected under conventional CCB treatment.
- Reduce the responsiveness of Ca2+ channel pores to voltage depolarization.
Verapamil
- Mechanism of Action: Reduces SA automaticity leading to decreased heart rate; slows AV conduction, increasing PR interval.
- Ineffective on ventricular arrhythmias due to no impact on Na+ conduction.
- Clinical Uses: Prevention and conversion of nodal arrhythmias (PSVT), rate control in atrial fibrillation.
- Adverse Effects: Includes headache, flushing, dizziness, ankle edema, constipation, and potential exacerbation of heart failure.
- Contraindications: Sick sinus syndrome, pre-existing AV nodal disease, WPW syndrome with atrial fibrillation, ventricular tachycardia.
Adenosine
- Treats paroxysmal supraventricular tachycardia (PSVT), particularly reentry mechanisms involving accessory pathways.
- Extremely short half-life (10-15 seconds); administered IV to central vein.
- Activates A1 receptors in SA and AV nodes, opening K+ channels and facilitating K+ efflux.
- Also activates A2 receptors in vasculature, leading to nitric oxide (NO) release through endothelial Ca2+ modulation.
Magnesium
- Functions as a muscle relaxant.
- Mechanism of Action: Acts as a cofactor for ATP-dependent enzymes and inhibits calcium channels.
- Therapeutic Uses: Effective for torsades de pointes, perioperative atrial fibrillation, and digitalis-induced arrhythmias.
Atropine
- Utilized for bradycardia treatment.
- Functions by producing a vagal block to increase heart rate.
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Description
This quiz focuses on the properties and effects of Class 3 and Class 4 antiarrhythmic drugs. It covers potassium and calcium channel blockers, their mechanisms of action, key medications, and associated risks. Test your knowledge on the pharmacology of these crucial cardiac drugs.
