Review Question - QID 212463

A 72-year-old man presents to his primary care physician with a 1-month history of occasional lightheadedness. He says that the episodes occur several times per week and resolve after he lies down. He also says that he has been experiencing palpitations in addition to mild chest discomfort. His past medical history is significant for hypertension and diabetes for which he takes lisinopril and metformin. He also had bilateral hip replacement operations 5 years ago without any significant complications. An electrocardiogram (ECG) is obtained, and the results are shown in Figure A. Which of the following characteristics describes the most likely cause of this patient's symptoms?