• Usually paroxysmal, often in young people with a normal heart; AV nodal re-entry or WPW syndrome; P waves usually hidden by the QRS.

Acute management

• Vagal manoeuvres: Valsalva or carotid sinus massage, with the patient supine and relaxed.

• If vagal manoeuvres fail: S: adenosine IV (or IO) 6 mg over 1–3 seconds followed by a rapid 20 ml normal saline flush; if no conversion in 1–2 minutes give 12 mg, and repeat 12 mg once if needed (30 mg total).

• If nothing works and the patient is hypotensive: DC shock.

Prevention of recurrent paroxysmal atrial fibrillation (specialist initiated)

• Only with severe symptoms despite the measures above: S: amiodarone 200 mg PO every 8 hours for 1 week, then 200 mg every 12 hours for 1 week, then 200 mg every 24 hours.

• Halve the warfarin dose and monitor INR closely until stable; avoid digoxin with amiodarone.

Long-term treatment

• Teach the patient vagal manoeuvres (Valsalva is the most effective).

• Infrequent, non-incapacitating symptoms: B: atenolol 50–100 mg PO every 24 hours, OR S: verapamil 80–120 mg PO every 8 hours (normal heart).

• Verapamil and digoxin are contraindicated in WPW syndrome.

• Refer to a specialised cardiac centre for mapping and radiofrequency ablation.