A 35-year-old woman with a history of acute rheumatic fever presents with severe mitral stenosis and atrial fibrillation. She is haemodynamically stable and has no contraindications to anticoagulation. What is the drug of choice for rate control in this patient?

Explanation

## Rate Control in Mitral Stenosis with Atrial Fibrillation **Key Point:** In a haemodynamically stable patient with mitral stenosis (MS) and atrial fibrillation (AF), **beta-blockers (e.g., metoprolol)** are the preferred first-line agents for rate control. They effectively slow the ventricular rate both at rest and during exertion by blocking AV nodal conduction, and they are well tolerated in haemodynamically stable MS. **Clinical Pearl:** Digoxin was historically favoured in MS + AF, but its role has been significantly downgraded in modern guidelines (ACC/AHA 2014, Harrison's 21e). Digoxin provides poor rate control during exercise (sympathetically driven AF), has a narrow therapeutic window, and its positive inotropic effect is clinically modest and not the primary rationale for use in this setting. It is now reserved for patients with concomitant systolic heart failure or when beta-blockers/CCBs are contraindicated. **High-Yield:** The classic teaching that "digoxin = drug of choice in MS + AF" applies specifically to haemodynamically **unstable** patients or those with reduced EF. In a **stable** patient without heart failure, beta-blockers (metoprolol, atenolol) are preferred per current evidence-based guidelines. ### Why Metoprolol (Beta-Blocker) is Preferred in Stable MS + AF 1. **Effective AV nodal blockade** → controls ventricular rate at rest AND during exercise 2. **Haemodynamically well tolerated** in stable MS (no significant reduction in CO when used carefully) 3. **Guideline-supported** — ACC/AHA and ESC guidelines list beta-blockers as first-line for rate control in AF with MS in stable patients 4. **Reduces heart rate** → prolongs diastolic filling time → improves transmitral gradient and symptoms ### Why Digoxin is NOT First-Line Here - Poor rate control during physical activity (sympathetically mediated AF overrides vagomimetic effect) - Narrow therapeutic window with risk of toxicity - Modern guidelines relegate it to adjunctive or second-line therapy ### Comparison of Rate-Control Agents in Stable MS + AF | Agent | AV Node Effect | Exercise Rate Control | Safety in Stable MS | Comment | | --- | --- | --- | --- | --- | | **Metoprolol** | ↓↓ | Excellent | **Preferred** | First-line per ACC/AHA guidelines | | **Diltiazem** | ↓↓ | Good | Acceptable (stable) | Alternative if beta-blockers not tolerated | | **Verapamil** | ↓↓ | Good | Acceptable (stable) | Use with caution; more negative inotropy | | **Digoxin** | ↓ | Poor | Second-line | Reserved for HF or refractory cases | [cite: Harrison's Principles of Internal Medicine, 21e, Ch. 282; ACC/AHA 2014 Valvular Heart Disease Guidelines]