A patient in their 70s with a medical history of type 2 diabetes and hypertension presented to the emergency department with fatigue, light-headedness, and dyspnea on exertion during the previous week. On physical examination, the patient was alert and in no acute distress with a heart rate of 47 beats per minute and blood pressure of 148/59 mm Hg. The 12-lead electrocardiogram (ECG) is shown in Figure, A.