ECG leads to a quick diagnosis

A 19 year old man presented to the emergency department with a two hour history of palpitations and chest discomfort. He had no important medical history and took diphenhydramine occasionally for hay fever. He denied smoking, drinking alcohol excessively, and using drugs. On examination he seemed breathless, his pulse was irregular at 140 beats per minute and his blood pressure was 145/60. On further examination of his cardiovascular, respiratory, and abdominal systems no abnormality was detected.

His 12 lead electrocardiogram is shown in the top half of fig 1. The next day this patient was reviewed on the post take ward round on the coronary care unit. His 12 lead electrocardiogram is shown in the lower half of fig 1.

(1) What do the electrocardiograms show?

(2) How would you treat this patient in the short term?

(3) What long term treatment would you offer?