## Acute Rate Control in Atrial Fibrillation **Key Point:** Intravenous verapamil is the first-line agent for acute rate control in haemodynamically stable AF because it rapidly slows AV nodal conduction and has a quick onset (1–5 minutes IV). ### Mechanism of Action - Non-dihydropyridine calcium channel blocker - Blocks L-type calcium channels in the AV node - Increases AV nodal refractoriness and slows conduction velocity - Reduces ventricular rate without converting AF rhythm ### Comparison of Rate-Control Agents in Acute AF | Agent | Route | Onset | Duration | Haemodynamic Effect | First-Line? | |---|---|---|---|---|---| | Verapamil | IV | 1–5 min | 30–60 min | Mild ↓BP, ↓CO | **Yes** (stable) | | Diltiazem | IV | 2–7 min | 30–60 min | Mild ↓BP, ↓CO | Yes (alternative) | | Digoxin | IV | 30–60 min | 4–6 hrs | Minimal ↓BP | No (slow onset) | | Amiodarone | IV | 5–10 min | Hours | ↓BP, ↓CO | No (rhythm control) | | Beta-blocker | IV | 5–15 min | Variable | ↓HR, ↓BP, ↓CO | Yes (if no contraindication) | **High-Yield:** In **haemodynamically stable** AF, the first-line agents are IV verapamil, IV diltiazem, or IV beta-blocker (e.g., metoprolol). In **haemodynamically unstable** AF, use synchronized DC cardioversion or IV amiodarone. **Clinical Pearl:** Verapamil is contraindicated in AF with pre-excitation (e.g., Wolff–Parkinson–White syndrome) because it blocks the AV node and may preferentially conduct through the accessory pathway, causing dangerously rapid ventricular rates. **Mnemonic:** **VERAPAMIL for VENTRICULAR rate control** — the V's match. Remember: verapamil slows the AV node, not the atrial rate. **Tip:** NEET PG often tests the distinction between rate control (verapamil, diltiazem, beta-blockers) and rhythm control (amiodarone, flecainide). In acute stable AF, rate control is the priority.
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