Review Question - QID 213583

A 36-year-old woman presents to the emergency department after she fainted at work. On presentation, she says that she started feeling lightheaded while moving some boxes with co-workers and fell to the floor. Her co-workers said that she recovered consciousness within 15 seconds and that she was coherent immediately upon waking up. She says that she has had several episodes like this in the past; however, this is the first time that she actually fainted. She has also occasionally felt palpitations though she says these never caused any problems. An electrocardiogram is obtained in the emergency department and the result is shown in Figure A. Which of the following pathologies most likely exists in this patient?