Rate Control in Atrial Fibrillation

Rate control slows the ventricular response in atrial fibrillation with drugs that block the atrioventricular node. It is the first approach in most older or minimally symptomatic people and is used alongside anticoagulation. A lenient target of a resting heart rate under 110 beats a minute is accepted at first, and a stricter target under 80 beats a minute is used for persisting symptoms or reduced ventricular function. The choice of drug depends on ejection fraction, blood pressure, lung disease, thyroid status and pregnancy.

Assessment. Check pressure, heart failure signs, ejection fraction by echocardiography, thyroid function, potassium, magnesium and creatinine. Look for pre-excitation, since atrioventricular nodal blockers are dangerous in Wolff-Parkinson-White syndrome.

Rheumatic mitral stenosis. Common in East Africa. A beta blocker or diltiazem lengthens diastole and is useful, and warfarin is needed rather than a direct oral anticoagulant.

Beta blocker, first line. Bisoprolol 1.25 to 2.5 mg orally once daily, increased to 10 mg daily; or metoprolol succinate 50 mg once daily, increased to 200 mg daily; or metoprolol tartrate 25 mg twice daily, increased to 100 mg twice daily.

Non-dihydropyridine calcium channel blocker. Diltiazem modified-release 120 mg orally once daily, increased to 360 mg daily; or verapamil modified-release 120 mg once daily, increased to 480 mg daily in divided doses. Avoid when ejection fraction is under 40%.

Digoxin. For sedentary people, heart failure or added to a beta blocker. Oral loading 0.5 mg, then 0.25 mg after 6 hours, to a total of up to 0.75 to 1 mg in 24 hours if needed. Maintenance 62.5 to 250 micrograms once daily (125 micrograms is usual). Target trough level 0.5 to 0.9 micrograms/L at least 6 hours after the dose.

Acute control. Metoprolol 2.5 to 5 mg intravenously over 2 minutes, repeated up to 15 mg. Diltiazem 0.25 mg/kg intravenously over 2 minutes, then 5 to 15 mg/hour. In heart failure or low pressure, amiodarone 300 mg intravenously over 1 hour, then 900 mg over 24 hours. Haemodynamic instability needs electrical cardioversion.

Thyrotoxic atrial fibrillation. Propranolol 10 to 40 mg orally three times daily until thyroid function is controlled.

Special groups. In pregnancy use metoprolol or digoxin and avoid atenolol. In older adults start at half dose. In creatinine clearance under 50 mL/min halve the digoxin dose. In hepatic impairment reduce metoprolol, propranolol and diltiazem. In asthma use diltiazem, and avoid beta blockers.

Monitoring. Resting and exercise heart rate, pressure, symptoms and ECG at each step, and 24 hour ECG recording to confirm control. Potassium and magnesium with digoxin. Digoxin level if there is toxicity, renal change or a new interacting drug.

Interactions. Verapamil and diltiazem with a beta blocker (heart block and heart failure). Amiodarone, verapamil, clarithromycin and ciclosporin raise digoxin levels, so halve the digoxin dose. Hypokalaemia increases digoxin toxicity.

Titration. Increase every 1 to 2 weeks, and lower the dose for a heart rate under 50 beats a minute.

Stopping. Do not stop a beta blocker suddenly. Stop a non-dihydropyridine calcium channel blocker if heart failure appears. Stop digoxin for toxicity: nausea, visual change, arrhythmia or a level over 2 micrograms/L.

Common errors. A rate-limiting calcium channel blocker in heart failure with reduced ejection fraction, combining it with a beta blocker, nodal blockers in pre-excitation, and no anticoagulation.

Referral and escalation. Refer for uncontrolled rate on two drugs, a rate-related fall in ejection fraction, or symptoms that suggest rhythm control or ablation.