Final answer:
The nurse should immediately assess the activation status of the device, heart rate cutoff, and number of shocks it is programmed to deliver.
Step-by-step explanation:
The nurse should immediately assess the activation status of the device, heart rate cutoff, and number of shocks it is programmed to deliver. This is the most important priority as it ensures the device is functioning properly and has the correct settings to respond to any potential cardiac events. Assessing the client's anxiety level, presence of a Medic-Alert card, and knowledge of postdischarge physical activity restrictions are also important, but they are not as critical as ensuring the proper functioning of the device.