An 82 year old male with a history of hypertension presents to his primary care physician for a routine visit. He has had some generalized fatigue but attributed it to aging. His temperature is 37.0, blood pressures 110/60, heart rate 70, and respirations 20. Physical examination reveals normal lung sounds, an irregularly irregular rhythm, and no lower extremity edema. Laboratory studies including thyroid tests and a complete blood count are normal. Below is his ECG. Which of the following is the most appropriate therapy at this time?
A. Calcium channel blocker