Problem: A 19-year-old male has sustained a spinal cord injury following a diving accident. His heart rate has been in the 50s since injury, and he has been alert and oriented. The ICU nurse notes that the patient's HR has been slowly declining to the 40s. The patient is less alert and his oxygen saturation is in the high 80s. The NP orders a dose of IV atropine, which results in no change in the patient's HR. What is the next step in treating his bradycardia?