Peculiar QRS morphology: an electrophysiological phenomenon

A female teenager presented with palpitations. The baseline rhythm on her ECG demonstrates sinus rhythm with normal PR interval of 120 ms, a mild degree of delta wave, RSR′ morphology in V1 with a precordial transition zone between V1 and V2. The frontal axis demonstrates normal QRS axis, in particular a positive lead III and aVF vectors, and negative aVR and aVL vectors, suggesting an overall inferior propagating QRS vector. Intermittently,...