Saturday night broad QRS complex tachycardia in a young male

On a Saturday night, a 24-year-old male with palpitations was admitted to the Emergency Department. The arrhythmia started 8 h earlier while he was riding his bicycle. He had never experienced this sensation before. He admitted prior usage of cocaine, LSD and XTC. He denied the use of any drugs on the night of presentation. Physical examinations revealed no abnormalities except a very fast heart rate. The arrhythmia did not respond to carotid sinus massage. Laboratory investigation demonstrated no abnormalities. The ECG on admission is shown (Fig. 1). Spontaneously the rhythm changes (Fig. 2). What is your diagnosis?