Narrow QRS tachyarrhythmias are sustained (more than 30 seconds) or non-sustained tachycardias with QRS 0.1 seconds or less. Always exclude structural heart disease; Holter ECG helps identify the arrhythmia.

Atrial fibrillation – acute onset (under 48 hours)

• Assess for heart failure, mitral stenosis, thyrotoxicosis, hypertension, age and other conditions.

• Consider anticoagulation with heparin or warfarin.

• Synchronised DC cardioversion in emergencies, especially haemodynamic instability, or consider it for a first episode.

Atrial fibrillation – non-acute or chronic (over 48 hours)

• No immediate DC cardioversion unless there is a hypotensive emergency.

• Anticoagulate with warfarin 2–5 mg PO once daily for at least a month, then elective cardioversion at a specialised hospital.

Atrial fibrillation with fast ventricular response (no aberrant conduction)

Anticoagulation

• C: Warfarin 2–10 mg PO every 24 hours (INR 2.0–3.0), OR S: rivaroxaban 15–20 mg PO every 24 hours (non-valvular AF).

Rate control – one of:

• D: Digoxin IV 0.25–0.5 mg, then 0.25 mg every 4–6 hours to a maximum of 1 mg; maintenance 0.125–0.25 mg every 24 hours; or digoxin 0.25 mg PO daily (use only in heart failure).

• B: Atenolol 50–100 mg PO every 24 hours (contraindicated in asthma).

• D: Diltiazem IV 15–20 mg over 2 minutes, may repeat after 15 minutes; maintenance 5–15 mg/hour IV infusion.

• S: Verapamil IV 5–10 mg over 2 minutes, may repeat after 30 minutes.

• DC cardioversion in selected cases after 4 weeks of anticoagulation.

Digoxin controls the rate only at rest. For long-term use combine D: digoxin 0.125–0.25 mg PO every 24 hours with B: atenolol 50–100 mg, S: bisoprolol 2.5–10 mg or C: metoprolol 25–50 mg every 24 hours, or use S: sotalol 80–160 mg every 12 hours. In the elderly and renal impairment adjust digoxin to trough levels (only after at least 10 days of treatment). Avoid digoxin when there is an accessory pathway.

Atrial fibrillation with aberrant conduction (e.g. WPW syndrome)

• Catheter ablation of the accessory pathway in symptomatic patients, especially with a short refractory period.

• Long-term anticoagulation unless contraindicated: C: warfarin 5 mg PO every 24 hours, OR S: rivaroxaban 15–20 mg every 24 hours, OR left atrial appendage occlusion (LAAO).

• Curative radiofrequency ablation for poor rate control or frequent/severe symptoms.

• Verapamil and digoxin are contraindicated in WPW syndrome.

Monitoring: keep the INR at 2–3; check every 3 months when stable and monthly if INR is below 1.5 or above 3.5. LAAO is for AF patients who cannot take oral anticoagulants and have CHA2DS2-VASc 2 or more, HAS-BLED 3 or more, or emboli despite adequate anticoagulation.

Atrial flutter

• P waves visible before the QRS, usually 2:1 block (rate about 150/minute), P waves usually negative in lead II; vagal stimulation may reveal blocked P waves.

• Synchronised DC cardioversion 200 J after sedation with A: diazepam IV 10–20 mg. If flutter has lasted over 48 hours, anticoagulate with warfarin for 4 weeks before cardioversion unless severe symptoms or heart failure need urgent cardioversion.

• No medicine is nearly as effective as DC cardioversion; anticoagulate sustained flutter.

• Recurrent flutter: refer – many are cured by radiofrequency catheter ablation.

Atrial tachycardia

• Rare and often incessant; P before QRS (often long PR) or hidden in T; may cause tachycardia cardiomyopathy.