A 48-year-old man presents with palpitations and narrow complex tachycardia at 180 bpm. Vagal manoeuvres terminate the arrhythmia. An ECG post-termination shows a short PR interval of 100 ms and a delta wave. Which syndrome is this and what is the arrhythmia mechanism?

• A Brugada syndrome; abnormal sodium channel function
• B LGL syndrome; Mahaim fibre conduction
• C Wolff-Parkinson-White syndrome; accessory pathway causing orthodromic AVRT ✓
• D AV nodal re-entry tachycardia (AVNRT); dual AV nodal pathways

Explanation

Short PR interval with delta wave (ventricular pre-excitation) defines Wolff-Parkinson-White pattern; the clinical syndrome (WPW) includes symptomatic tachyarrhythmias. The most common arrhythmia is orthodromic AVRT, where the impulse conducts anterograde through the AV node and retrograde through the accessory pathway, producing a narrow complex tachycardia. Vagal manoeuvres slow AV nodal conduction and can terminate the re-entry circuit. AVNRT has no delta wave or pre-excitation.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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