Final answer:
The nurse would administer diltiazem (Cardizem) as a medication for a sustained supraventricular tachycardia.
Step-by-step explanation:
When a nurse identifies a client's rhythm to be a sustained supraventricular tachycardia, the medication that the nurse administers is diltiazem (Cardizem). Diltiazem is a calcium channel blocker that helps to slow down the rate at which the heart beats. It is commonly used to treat supraventricular tachycardia and other heart rhythm abnormalities.