This 25-year-old woman has been referred to the EP clinic. In the past 5 years she has had episodes of rapid palpitation of sudden onset and termination, lasting up to one hour. The episodes were infrequent (about once a year), until recently, when they had been occurring almost every month. During the episodes she felt weak and presyncopal:

• Sinus rhythm
• Wolff-Parkinson-White
• Pattern compatible with anteroseptal accessory pathway

Comment: In favor of the anteroseptal location of the accessory pathway:  negative delta wave in V1; negative QRS complex in V1-V3; positive delta wave with prominent broad R waves in III and aVF.  EP studies confirmed the anteroseptal location, very close to the His bundle. (Mauricio S. Arruda et al. Development and Validation of an ECG Algorithm for Identifying Accessory Pathway Ablation Site in Wolff-Parkinson-White Syndrome; J. Cardiovasc Electrophysiol Vol.9, pp.2-12, January 1998)