Occurs due to an accessory conduction pathway allowing conduction re-entry between atrium and ventricle, e.g. in Wolff-Parkinson-White syndrome
ECG: regular, often without discernible P waves because they may be buried in the QRS or retrograde; fast, e.g. 150-200bpm
NB: this refers to orthodromic AVRT. Antidromic AVRT looks more like VT.
Management: vagal manoeuvres (1st), adenosine (2nd; not in severe asthma – use Ca2+ channel blocker, e.g. verapamil), β-blocker (3rd)