A 58-year-old man with a history of hypertension and coronary artery disease presents to the emergency department with palpitations and dyspnea. ECG shows atrial fibrillation with a ventricular rate of 145 bpm. Blood pressure is 110/70 mmHg, and he is haemodynamically stable. Troponin is negative. He has no prior antiarrhythmic therapy. Which of the following is the most appropriate first-line pharmacological agent for rate control in this patient?

Explanation

## Acute Atrial Fibrillation Rate Control: First-Line Approach ### Clinical Context This patient presents with haemodynamically stable atrial fibrillation (AF) with rapid ventricular response. The absence of haemodynamic instability (normal BP, no cardiogenic shock) means electrical cardioversion is not immediately mandated; pharmacological rate control is appropriate. ### Mechanism of Action & Drug Choice **Key Point:** In haemodynamically stable AF, intravenous calcium channel blockers (verapamil, diltiazem) or beta-blockers are first-line agents for acute rate control because they: - Rapidly slow AV nodal conduction - Have quick onset (IV: 2–5 minutes) - Maintain haemodynamic stability - Are safe in acute coronary syndromes (troponin negative here) ### Why Verapamil? | Agent | Onset | Route | Haemodynamic Effect | First-Line? | |-------|-------|-------|---------------------|-------------| | **Verapamil (IV)** | 2–5 min | IV bolus 5–10 mg | Minimal in stable AF | **Yes** | | Diltiazem (IV) | 2–5 min | IV bolus 0.25 mg/kg | Minimal in stable AF | **Yes** | | Beta-blocker (IV) | 5–10 min | IV metoprolol 5 mg | Negative inotropy | Yes (if LV intact) | | Amiodarone (IV) | 10–20 min | 300 mg bolus | Hypotension risk | No (2nd-line) | | Digoxin (IV) | 30–60 min | 0.5 mg + 0.25 mg | Minimal | No (slow onset) | | Flecainide (oral) | 1–2 hours | Oral 100 mg | Proarrhythmic | No (not for rate control) | **Clinical Pearl:** Verapamil 5–10 mg IV is the gold standard for acute rate control in haemodynamically stable AF. It achieves rate control in 80–90% of cases within 5–10 minutes. **High-Yield:** In acute AF with normal LV function and no acute MI, IV verapamil or diltiazem is preferred over amiodarone because amiodarone is reserved for: - Haemodynamically unstable AF (requires cardioversion first) - AF with accessory pathway (WPW syndrome) - AF refractory to AV nodal blockers ### Why Not the Other Options? **Amiodarone:** Although effective, it has slower onset (10–20 min), carries hypotension risk, and is a Class III agent best reserved for refractory or haemodynamically unstable cases. It is not first-line for simple rate control. **Digoxin:** Onset is 30–60 minutes—too slow for acute symptomatic AF. It is now reserved for sedentary patients or those with heart failure. **Flecainide:** A Class IC agent used for rhythm control (cardioversion), not rate control. It is contraindicated in acute coronary syndromes and can be proarrhythmic in AF. ### Algorithm for Acute AF Management ```mermaid flowchart TD A["Acute Atrial Fibrillation"]:::outcome --> B{"Haemodynamically stable?"}:::decision B -->|"No (shock, hypotension, chest pain)"|C["Electrical cardioversion"]:::urgent B -->|"Yes"|D{"Rate control or rhythm control?"}:::decision D -->|"Rate control (first-line)"|E["IV Verapamil or Diltiazem"]:::action D -->|"Rhythm control (if indicated)"|F["IV Amiodarone or Flecainide"]:::action E --> G["Reassess rate in 5-10 min"]:::outcome F --> H["Reassess rhythm in 20-30 min"]:::outcome ``` **Mnemonic:** **ABCD** for acute AF management: - **A**ssess haemodynamics - **B**lock AV node (verapamil, diltiazem, beta-blocker) - **C**ardiovert if unstable - **D**igitalize or add second agent if needed [cite:Harrison 21e Ch 226]