This 24-year-old man was in a nightclub. He had one drink and one joint of marijuana and shortly afterward developed severe palpitations, dyspnea and faintness. During the previous 6 months he had experienced palpitations 2-3 times a month, with chest discomfort:

• Wide QRS tachycardia at a rate of 246/min.
• Most likely, Antidromic AVRT (Atrioventricular re-entrant tachycardia)
• Less likely, atrial flutter with pre-excitation, ventricular tachycardia

The patient received IV Amiodarone and converted to sinus rhythm. The following ECG is recorded:

• Sinus bradycardia, 53/min.
• Wolff-Parkinson-White
• Posteroseptal accessory pathway (AP)

Comment: Short PR, typical delta wave of WPW. The delta wave is positive in I and aVL (AP is not left sided), isoelectric in V1 and positive in V2 (AP is septal), negative in II, III, aVF (AP is posterior). Thus, this ECG shows a typical pattern of a  right posteroseptal AP.

On the following day the patient is brought to the Electrophysiology Lab for EP studies.
A right posteroseptal bypass tract is demonstrated and successfully ablated.
The following ECG tracing is then recorded:

• Sinus Rhythm
• Early repolarization