This 23-year-old woman since her teens has suffered from episodes of rapid palpitation of sudden onset and termination, lasting 20-40 minutes, terminating spontaneously. She is referred to the EP clinic because of a recent episode that lasted 4 hours. She is in the Emergency Dept. where she is successfully treated with IV adenosine:

• Sinus rhythm
• Preexcitation (Wolff-Parkinson-White, WPW) – Left bypass tract

The patient undergoes successful ablation of a left postero-lateral bypass tract. The following ECG is recorded at the end of the procedure:

• Sinus rhythm
• Preexcitation (WPW) no longer present