Learning Objective
By the end of this section, learners should be able to describe the mechanism of action of Class IV antiarrhythmic drugs and explain their effects on SA and AV nodal conduction in the management of supraventricular tachyarrhythmias.
CLASS IV: Ca²⁺ CHANNEL BLOCKERS
Class IV antiarrhythmic drugs act by blocking slow L-type calcium (Ca²⁺) channels in cardiac nodal tissue.
Mechanism of Action
- Block slow cardiac Ca²⁺ channels
- ↓ Phase 0 depolarization in slow-response fibers
- ↓ Phase 4 depolarization
- ↓ SA nodal automaticity
- ↓ AV nodal conduction velocity
Activity
Drugs
- Verapamil
- Diltiazem
Clinical Uses
- Supraventricular tachycardias (SVTs)
- Rate control in atrial fibrillation and atrial flutter
Adverse Effects
- Constipation (Verapamil)
- Dizziness
- Flushing
- Hypotension
- AV block
Activity
Drug Interactions
- Additive AV nodal block when combined with:
- β-blockers
- Digoxin
- Verapamil displaces digoxin from tissue-binding sites → ↑ digoxin toxicity
