Tachycardia in a 39-year-old Woman

VIDEO: The patient says her "heart was beating out of her chest." Complains of dyspnea, faintness. PMH, here. Your Dx?

A 39-year-old woman is seen in the ED with palpitations, dyspnea, faintness. C/o myalgias, alopecia, memory loss x1 year. PMH: PCOS, hyperthyroid. Meds: none. Vitals: HR, 160 bpm; RR, 24; BP, 172/104. 


Can you make a diagnosis?