Review Question - QID 109959

A 71-year-old man is brought to the emergency room by ambulance after he was found down by his wife. Upon arrival he is unresponsive, and advanced cardiac life support procedures are initiated. His wife says that he has been recently complaining of chest pain but was unable to provide more details about the nature of the symptoms. His past medical history is significant for Marfan syndrome and rheumatic fever as a teenager. After recovery of a pulse, an electrocardiogram is obtained in this patient, and the results are shown in Figure A. Which of the following is the most likely mechanism of action for a treatment that is contraindicated given the pattern of this patient's disease process?