19 year old with palpitations

A 19-year-old college student presented with recurrent episodes of palpitations, dizziness, and shortness of breath lasting several minutes. He denied chest pain or syncope. On examination, his heart rate and rhythm were normal. A 12-lead ECG revealed a shortened PR interval and a delta wave. No structural abnormalities were noted on echocardiography. What is the ECG abnormality?