A 23-year-old female with...

A 23-year-old female with no past medical history presented to the emergency department after a syncopal episode. She was eating dinner with her family when she suddenly felt faint and lost consciousness, resulting in bruising on her forehead and cheek as she fell to the floor. Paramedics were called, and an ECG was obtained as given in the image. Her medical history includes exercise-induced asthma and frequent urinary tract infections. She uses albuterol as needed, takes a daily oral contraceptive, and recently completed a course of levofloxacin. She does not smoke cigarettes or drink alcohol but smokes marijuana a few times a week. Her family history is unremarkable. On examination, she appeared scared but otherwise showed no signs of distress. Her heart rate was 104 bpm, and her blood pressure was 96/60 mm Hg. A cardiac examination revealed premature beats, while the rest of her examination was unremarkable. Laboratory results showed a thyroid stimulating hormone (TSH) level of 42 IU/mL, a potassium (K) level of 3.8 mEq/L, and a magnesium (Mg) level of 1.9 mg/dL. Kindly suggest an appropriate diagnosis, cause, and treatment for this patient.