Final answer:
The nurse's first action in response to a client's ECG tracing showing a run of sustained ventricular tachycardia should be to assess airway, breathing, and level of consciousness.
Step-by-step explanation:
The nurse's first action in response to a client's ECG tracing showing a run of sustained ventricular tachycardia should be to assess airway, breathing, and level of consciousness. This is important to ensure that the client's vital functions are stable and that they can support any necessary interventions.