Q. A 78-year-old female comes into your clinic today for evaluation of syncopal episodes. She has lost consciousness twice recently. The second episode occurred last week, and resulted in a minor head laceration and a trip to the emergency department where she received “four stitches”. A head CT performed at that time was interpreted as normal. Additionally, the patient reports occasional “fluttering” of her heart, which is associated with physical exertion. She denies any neurologic symptoms, history of seizures, or historical episodes of similar symptoms. On physical examination, her blood pressure is 165/90 mm Hg, heart rate is 75/min, respiratory rate 16/min, and oxygen saturation 97 percent on room air. Her lungs are clear bilaterally, with no ronchi, wheezes, or rales noted. Cardiac examination demonstrates a harsh, crescendo-decrescendo systolic ejection murmur, which is loudest over the second right intercostal space and radiates to her carotid arteries. You elect to perform an electrocardiogram (EKG) in the clinic today (see image). Based on this patient’s history and physical examination, and her EKG, what is the most likely cause of her symptoms?