A 38-year-old man is in the Emergency Department complaining of palpitation of 45 min duration. Palpitation started suddenly with a sensation of rapid pounding in his precordium, accompanied by mild light-headeness. He had a similar brief episode a few months before:

• Narrow QRS tachycardia, 156/min
• P waves closely follow the QRS, They are negative in the inferior leads, positive in aVR and aVL
• Probably AVRT, less likely AVNRT

There is a 60-80 msec interval between QRS and P waves. This favours aVRT. (in AVNRT there is usually no gap between QRS and P)

There was no response to vagal stimulation. Sinus rhythm is restored after IV injection of Adenosine:

• Sinus rhythm
• Wolff-Parkinson-White

The narrow QRS tachycardia of ECG 1 was AVRT.