A client with atrial fibrillation is being evaluated for complications. Which condition is the nurse's priority concern?

Atrial fibrillation is a supraventricular tachyarrhythmia characterized by chaotic, uncoordinated atrial depolarization and a loss of effective atrial systole. This mechanical stasis of blood within the left atrial appendage promotes localized thrombus formation via Virchow's triad. Subsequent embolization of this clot into the cerebral circulation obstructs arterial flow, precipitating an acute ischemic stroke. A. Hypoglycemia: Depleted plasma glucose levels stem from endocrine imbalances, liver dysfunction, or mismatches in exogenous insulin therapy. Atrial tachyarrhythmias alter mechanical cardiac output and rhythm stability but do not directly impair systemic glucose metabolism. It remains a separate metabolic concern. B. Stroke: The absence of coordinated atrial contraction allows blood to pool and stagnate within the fibrillated left atrium, forming friable thrombi. Dislodgement of these fragments sends thromboemboli through the aorta directly into the cerebral vasculature, causing ischemic tissue infarction. This represents the most devastating complication. C. Infection: Microbial colonization and subsequent inflammatory cascades are driven by pathogen exposure, tissue injury, or compromised immunological defenses. While a systemic infection can trigger atrial fibrillation due to metabolic stress, the arrhythmia itself does not cause infectious processes. It is a cause, not a consequence. D. Dehydration: Intravascular volume depletion results from inadequate fluid intake, excessive gastrointestinal losses, or unchecked renal excretion. Atrial fibrillation impairs ventricular filling efficiency and reduces cardiac output but does not alter systemic fluid or electrolyte volumes. Volume status runs independently of this rhythm.