A nurse is assessing clients on a medical-surgical unit. Which client should the nurse identify as being at greatest risk for atrial fibrillation?

A. A 45-year-old who takes an aspirin daily: Daily aspirin use for cardiovascular prophylaxis does not increase risk for atrial fibrillation (AF). Age and comorbid cardiac conditions are stronger risk factors than aspirin use alone, making this client lower risk. B. A 50-year-old who is post coronary artery bypass graft surgery: Postoperative atrial fibrillation is common after cardiac surgery due to inflammation, atrial trauma, and autonomic changes. The risk of AF is highest in the immediate postoperative period, making this client the greatest risk. C. A 78-year-old who had a carotid endarterectomy: While advanced age and vascular disease increase AF risk, carotid surgery itself is less directly associated with triggering AF compared with cardiac surgery. The risk is elevated but not as acutely as post-CABG. D. An 80-year-old with chronic obstructive pulmonary disease: COPD increases the risk for AF due to hypoxia, pulmonary hypertension, and right atrial strain, but the onset is more gradual. Post-cardiac surgery AF presents a more immediate and higher-risk scenario in the acute setting.