The PMHNP working on an inpatient eating disorders unit is evaluating a 17-year-old girl with suspected anorexia nervosa. Her laboratory results reveal elevated serum cholesterol levels, elevated serum salivary amylase concentrations, and decreased fasting glucose concentrations. Which electrocardiography (ECG) changes will help confirm the diagnosis?

Choice A reason: ECG changes are commonly seen in patients with anorexia nervosa due to malnutrition and electrolyte imbalances, so "no significant changes" is incorrect. Choice B reason: Ventricular tachycardia is a life-threatening arrhythmia usually secondary to severe electrolyte disturbances, not a typical finding in early anorexia nervosa. Choice C reason: This is correct. Sinus bradycardia is a common cardiac manifestation in anorexia nervosa, reflecting physiologic adaptation to malnutrition, reduced metabolic demands, and increased vagal tone. It is a supportive finding for the diagnosis. Choice D reason: Torsades de pointes is associated with prolonged QT intervals and severe hypokalemia or other electrolyte disturbances. While it may occur in extreme cases, it is not a typical finding in initial anorexia nervosa evaluation.