A 23-year-old man was referred to the emergency room with complaints of dyspnoea and dizziness followed by rapid palpitations. He had no relevant medical history and was not using any medication. The family history was negative for arrhythmias and sudden death. Physical examination revealed a tachycardia of 160 beats/min with a normal blood pressure; also, a frog sign was visible. Initial laboratory tests and echocardiography did not demonstrate any abnormalities. After administration of adenosine 9 mg intravenously, the tachycardia was terminated and there was conversion to sinus rhythm.
His electrocardiogram is shown in Fig. 1. What is your diagnosis?
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