A 52-year-old man with rheumatic mitral stenosis (MVA 1.2 cm²) presents with new-onset atrial fibrillation and a ventricular rate of 110 bpm. He is haemodynamically stable. What is the drug of choice for rate control in this patient?

Explanation

## Rate Control in AF with Mitral Stenosis **Key Point:** In atrial fibrillation complicating mitral stenosis, digoxin is the preferred first-line agent for rate control because it combines AV nodal blockade with a positive inotropic effect, making it uniquely suited to haemodynamically compromised patients and those with structural heart disease. ### Why Digoxin is Preferred **High-Yield:** Digoxin has a dual mechanism in this setting: 1. **AV nodal blockade** — slows ventricular rate 2. **Positive inotropic effect** — maintains cardiac output despite the stenotic mitral valve This is critical in mitral stenosis, where the left atrium is already enlarged and pulmonary congestion is a risk. Negative inotropes (beta-blockers, calcium channel blockers) can precipitate acute decompensation. ### Comparison of Rate-Control Agents in Mitral Stenosis | Agent | AV Nodal Block | Inotropic Effect | Safety in MS | Notes | |-------|---|---|---|---| | **Digoxin** | ✓✓ | Positive | Excellent | First-line in MS + AF | | Metoprolol | ✓✓ | Negative | Caution | Risk of pulmonary oedema | | Diltiazem | ✓✓ | Negative | Caution | Negative inotrope | | Verapamil | ✓✓ | Negative | Caution | Negative inotrope | **Clinical Pearl:** Beta-blockers and non-dihydropyridine calcium channel blockers are contraindicated or used with extreme caution in mitral stenosis because their negative inotropic effects can unmask haemodynamic compromise and precipitate pulmonary oedema in a patient with a fixed mitral valve area. **Warning:** Do not confuse this with AF in other structural lesions (e.g., aortic stenosis, hypertrophic cardiomyopathy), where beta-blockers may be preferred. In mitral stenosis specifically, digoxin is the gold standard. ### Additional Considerations - **Anticoagulation:** All AF patients with mitral stenosis require anticoagulation (warfarin preferred over DOACs in moderate-to-severe MS due to reduced efficacy of DOACs in this subgroup). - **Rhythm control:** If digoxin alone is insufficient, add a class IC antiarrhythmic (flecainide) or class III agent (amiodarone) rather than switching to a negative inotrope. - **Digoxin dosing:** Loading dose 0.5–1 mg over 24 hours; maintenance 0.25 mg daily (adjust for renal function and age).