A client is admitted to the critical care unit (CCU) with a third degree complete heart block. A temporary transvenous pacemaker is inserted by the healthcare provider (HCP). An hour after pacemaker insertion, the device stops sensing the client's intrinsic heart rate. Which action should the nurse implement first?

A. Turn off the pacemaker. Turning off the pacemaker is not appropriate because the client has a third-degree heart block, which means their heart is not conducting impulses properly. Disabling the pacemaker could lead to severe bradycardia or asystole. The goal is to troubleshoot the issue rather than stopping pacing altogether. B. Check the sensitivity control. Loss of sensing means the pacemaker is not detecting the client's intrinsic heart activity, which can lead to inappropriate pacing or failure to respond to the heart’s natural rhythm. Adjusting the sensitivity setting ensures that the pacemaker can recognize the client's heartbeats and pace appropriately. This is the first step in troubleshooting pacemaker malfunctions related to sensing issues. C. Increase the milliamps (mA). Increasing the milliamps (mA) is used when there is failure to capture, meaning the pacemaker is delivering impulses but the heart is not responding. Since the problem here is failure to sense, adjusting the sensitivity setting is the correct first action. D. Position the client on the left side. Repositioning the client is sometimes recommended for displacement of a transvenous pacemaker lead, but in this case, the issue is sensing failure, not lead displacement. Checking and adjusting the pacemaker settings is a more appropriate first step before considering repositioning.