Final answer:
Vagal stimulation is the appropriate intervention when a client's rhythm changes from normal sinus rhythm to supraventricular tachycardia on an ECG monitor.
Step-by-step explanation:
When a nurse observes a client's rhythm changing from normal sinus rhythm to supraventricular tachycardia on an ECG monitor, the nurse should prepare to assist with vagal stimulation. Vagal stimulation is a technique that can be used to slow down the heart rate and restore normal sinus rhythm. This can be done by applying pressure to the carotid sinus or using a Valsalva maneuver.