A 62-year-old woman with a history of atrial fibrillation presents with palpitations and chest discomfort. Her ECG shows rapid atrial fibrillation with a ventricular rate of 140 bpm, normal QRS duration, and hemodynamic stability (BP 110/70 mmHg, no signs of heart failure). What is the drug of choice for rate control in this acute presentation?

Explanation

## Acute Atrial Fibrillation: Rate Control Strategy ### Clinical Context This patient has **hemodynamically stable** atrial fibrillation with a rapid ventricular response. The goal is rapid rate control (target HR <110 bpm at rest) to relieve symptoms and prevent tachycardia-induced cardiomyopathy. **Key Point:** In hemodynamically stable AF with normal QRS duration, **intravenous verapamil** (or diltiazem) is the drug of choice for acute rate control. It is faster-acting and more effective than digoxin in the acute setting. ### Why Intravenous Verapamil 1. **Onset:** 1–3 minutes IV; peak effect in 5–10 minutes 2. **Mechanism:** Non-dihydropyridine calcium channel blocker; slows AV nodal conduction 3. **Efficacy:** Achieves rate control in ~90% of hemodynamically stable patients 4. **Safety:** No risk of toxicity (unlike digoxin); can be repeated if needed 5. **Contraindication:** Avoid in patients with **pre-excitation** (WPW syndrome) or severe LV dysfunction ### Dosing - **IV verapamil:** 5–10 mg over 2 minutes; repeat 10 mg after 15–30 minutes if needed - **IV diltiazem:** 0.25 mg/kg over 2 minutes; alternative if verapamil contraindicated **High-Yield:** Verapamil is superior to digoxin in acute AF because: - Faster onset - More potent AV nodal blockade - No narrow therapeutic window - Effective even in high catecholamine states (exercise, stress) ### Why Not Digoxin? Digoxin is slower (onset 30 min–2 hours), less effective in acute AF (especially in high sympathetic tone), and has a narrow therapeutic index. It is now reserved for **rate control in sedentary patients** or those with **concurrent heart failure** (positive inotropic effect). ### Why Not Amiodarone or Ibutilide? - **Amiodarone:** Oral form is too slow for acute rate control; IV amiodarone is reserved for **hemodynamically unstable** AF or when rate control fails - **Ibutilide:** A Class III antiarrhythmic used for **rhythm conversion** (not rate control) in AF of short duration; not first-line for rate control **Clinical Pearl:** The distinction between **rate control** and **rhythm conversion** is critical. Verapamil controls rate; amiodarone or ibutilide convert rhythm. This patient is hemodynamically stable, so rate control is the priority. [cite:Harrison 21e Ch 276]