Cardiac complications are common in anorexia nervosa (AN), with sinus bradycardia occurring in up to 95% of patients^1,2. The mechanism of bradycardia in AN has yet to be clearly elucidated.

The predominant hypothesis posits that bradycardia is due to an increased cardiac vagal tone^3,4, with a direct relationship observed between vagal tone and percent weight loss⁴. Additionally, sympathetic response may be altered through down-regulation of cardiac beta-adrenoceptors⁵. The physiologic response of lowering the resting heart rate through an increase in parasympathetic activity and sympathetic down-regulation leads to energy conservation in the fasting state of AN.

Current guidelines recommend that patients with AN and “severe” sinus bradycardia—defined as heart rate <50 beats/min during the day or <45 beats/min at night—should be admitted to the hospital for cardiac monitoring and gradual weight gain⁶. Fortunately, bradycardia associated with AN is reversible with weight gain^7,8.

References

1. Portilla MG. Bradycardia: an important physical finding in anorexia nervosa. J Ark Med Soc 2011;107:206-208. https://www.ncbi.nlm.nih.gov/pubmed/21739848
2. Katzman DK. Medical complications in adolescents with anorexia nervosa: a review of the literature. Int J Eat Dis 2005; 37:S52-S59. https://onlinelibrary.wiley.com/doi/full/10.1002/eat.20118
3. Petretta M, et al. Heart rate variability as a measure of autonomic nervous system function in anorexia nervosa. Clin Card 1997; 20: 219-224. https://www.ncbi.nlm.nih.gov/pubmed/9068906
4. Kollai M., et al. Cardiac vagal hyperactivity in adolescent anorexia nervosa. Eur Heart J 1994;15:1113-1118. https://www.ncbi.nlm.nih.gov/pubmed/7988604
5. Kaye WH, et al. Isoproterenol infusion test in anorexia nervosa: Assessment of pre-and post-beta-noradrenergic receptor activity. Psychopharm Bull 1990.
6. Golden NH, et al. Eating disorders in adolescents. J Adolesc Health 2003;33: 496-503. https://www.ncbi.nlm.nih.gov/pubmed/14642712
7. Gottdiener JS, et al. Effects of self-induced starvation on cardiac size and function in anorexia nervosa. Circulation 1978;58: 425-433. https://www.ncbi.nlm.nih.gov/pubmed/679432
8. Olivares JL, et al. Cardiac findings in adolescents with anorexia nervosa at diagnosis and after weight restoration. Eur J Pediatrics 2005;164:383-386. https://www.ncbi.nlm.nih.gov/pubmed/15909184

Contributed by Marissa K Shoji, Medical Student, Harvard Medical School