A 16 y/o girl is brought to the ER by her soccer coach and a few teammates. Her coach told the doctor that during a routine practice that afternoon, the girl suddenly collapsed on the field. Her friends mentioned that following previous practices she c/o "feeling sort of dizzy" but never mentioned "passing out". Her friends explained that she has been spending less time with them lately; often going straight home after practice instead of going out for a snack with her teammates, as she used to do. The pt. states that she hads a "weird pain in her chest, felt dizzy and then just passed out". She describes several episodes of chest pain lately and apparently has been feeling more dizzy than usual. These feelings occcur throughout the day and not associated only with physical exercise. When the girls mother arrived at the ER, she was visibly frantic. "What happened?" I told you you were practicing too much--it's no wonder you passed out.--You play soccer more than 4 hrs a day". Mother corroborates the absence of any past physcial or psychiatric Hx but states that the pt "has not been herself lately--spending most of the weekend lying in bes instead of going out with her friends. I know she is not sleeping well-just last night I found her looking through the frig at 3 am." Physical Exam: Pt is a slight girl , 65 inches tall, weighing 135 lbs. Resting pulse 48 beats/min in a regular rhythm. B/P 115/60 seated and 120/67 standing. She appears well nourished and hydrated. She is clearly anxious and states that she feels "nervous" being in the hospital. The HEENT exam is significant for enlarged parotid glands bilaterally. The remainder of the physical is unremarkable. LABS: Sodium-138; K-2.7; Cl-82; Bicarb-35; Venous blood gasses=7.5 pH. All other labs WNL. with exception of Mg = 1.0. The ekg showed prominent U-waves and a prolonged QT interval. What is her Diagnosis? How does the medical workup confirm it? What is your plan of care