A narrow QRS tachycardia with alternating R-R interval length in a 24 year old man

A 24-year-old man presented to the emergency room because of symptoms of dizziness and palpitations. He had these complaints before, but the episodes had never been documented electrocardiographically. Figure  1 shows the tachycardia recorded on admission. Intravenous adenosine administration resulted in termination of the tachycardia.
Source: Heart Rhythm - Category: Cardiology Authors: Tags: Josephson and Wellens ECG Lessons: A Monthly Visit to the 12 Lead ECG Source Type: research