A nurse in an emergency department is performing triage on a group of clients. Which of the following clients should the nurse see first?

A. While this client may have a urinary tract infection with fever, this is not as immediately life-threatening as uncontrolled atrial fibrillation. B. Bruising in a client with cirrhosis can be expected due to impaired clotting, but it does not represent an immediate threat. C. Peripheral edema in heart failure is a chronic symptom and not an emergent condition. D. A new onset of atrial fibrillation with a rapid heart rate (152/min) can lead to hemodynamic instability, decreased cardiac output, and increased risk for thromboembolism. This client requires immediate evaluation and intervention.