Bradycardia & Eating Disorders: How Low is Too Low?

Bradycardia, or low heart rate, is a common and potentially serious complication of eating disorders, affecting up to 95% of individuals with anorexia nervosa. Bradycardia warning signs include fatigue, dizziness, chest pain, and, in severe cases, life-threatening arrhythmias. Distinguishing between bradycardia due to an eating disorder vs. having an "athletic heart" is crucial, as malnourished individuals may require hospitalization for medical stabilization. Nutritional rehabilitation and weight restoration are key to reversing bradycardia and ensuring long-term recovery.

Low Heart Rate in Eating Disorders

Bradycardia is one of the most common medical complication in patients with anorexia nervosa, affecting up to 95% of patients per one study. 

What is bradycardia?

Bradycardia is an abnormally low heart rate, including any heartbeat under 60 beats per minute (bpm) compared to a normal heart rate range of 60-100 bpm.

Bradycardia typically occurs alongside substantial weight loss. While it is most common in patients who are severely underweight, it can also occur in those who are not underweight but have lost a significant amount of weight, like with those with atypical anorexia, with adolescents’ heart rates being more affected by losing a significant amount of weight

However, bradycardia does not usually cause symptoms, highlighting the need for healthcare professionals to evaluate patients at risk for this potentially serious complication and other cardiac complications.

Causes of bradycardia

The cause of bradycardia in those with eating disorders may be related to increased vagal (parasympathetic) tone and as an adaptive response to the energy deficit, but this is unclear, as not all studies have found an increased parasympathetic tone.

The parasympathetic nervous system slows the heart in an attempt to conserve energy and keep the rest of the body functioning normally. As the heart rate slows down, the heart is unable to pump oxygen-rich blood back to the body, causing:

• Fatigue
• Dizziness or lightheadedness
• Shortness of breath
• Chest discomfort
• Syncope (passing out)
• And more sinister arrhythmias in severe situations!

Bradycardia & hypotension

Bradycardia is often linked with hypotension (low blood pressure) due to the similar underlying pathophysiology. A weakened heart from prolonged malnutrition struggles to pump blood throughout the body, resulting in low blood pressure. The increased parasympathetic tone along with the compensatory reduced metabolic needs contribute to the low blood pressure observed in malnourished individuals. Other contributors can include medications to treat many of the comorbid conditions with eating disorders as well as decreased blood return to the heart upon standing due to sarcopenia. Patients with abnormally low blood pressure can experience:

• Dizziness
• Nausea
• Fatigue
• Blurred vision
• Cold or clammy skin
• Confusion
• Tachycardia (elevated heart rate)

Identifying & treating bradycardia

It can be difficult to determine whether a low heart rate requires monitoring or needs immediate attention. Without doubt, heart rates of less than 40 bpm (or 45 bpm for adolescents) require hospital admission and cardiac monitoring as described in the 2023 American Psychiatric Association Practice Guidelines for the Treatment of Patients with Eating Disorders.

• Under 60 bpm: A heart rate of under 60 bpm is considered slower than normal for most adults, although athletic adults and young adults may experience a resting heartbeat of under 60 bpm that drops even lower during sleep. If an individual with an eating disorder has a heart rate under 60 bpm, an evaluation may be warranted.
• Under 50 bpm: A heart rate consistently below 50 bpm is more likely to be a cause for concern. However, some healthy, active adults have heart rates under 50 bpm, particularly endurance athletes. Per the American Psychiatric Association, individuals with eating disorders who have a heart rate lower than 50 bpm may require medical hospitalization for assessment and treatment.
• Under 40 bpm: A heart rate consistently under 40 bpm is most likely a cause for concern in malnourished individuals and requires additional medical monitoring.

The “athletic heart” myth

Individuals with a severe eating disorder may already be aware of their low heart rate, and some may attribute it to having an “athletic heart.” While they may be exercising frequently, and may even be performing at a higher athletic level, a bradycardic heart and an athletic heart are different.

The low heart rate of an eating disorder patient is not the result of athletic conditioning. Few medical providers are well-trained in understanding eating disorders and often take the explanation of an “athletic heart” at face value. When combined with other symptoms of an eating disorder, bradycardia warrants further evaluation.

Testing for bradycardia

One way to distinguish between the two is to ask patients to mildly exert themselves. Patients with bradycardia secondary to malnutrition will show an abnormally elevated heart rate (tachycardia) with minimal activity, such as walking across the room or standing up from a lying position. On the contrary, an athletic heart will not have as exaggerated an increase in heart rate with these activities.

You can also confirm the health of the heart by ordering ultrasound imaging. In patients with severe eating disorders imaging may show small, thin cardiac chambers that wouldn’t be seen in healthy athletes.

Treatment for bradycardia

Bradycardia typically resolves with nutritional rehabilitation and improved body weight by treating the underlying eating disorder.

Patients with eating disorders, a heart rate less than 40 bpm and/or hypotension should be hospitalized for medical stabilization. At this stage of cardiac distress, patients are likely experiencing other serious medical complications related to their illness, and medical stabilization in a specialized inpatient medical setting may be necessary prior to entering an eating disorder treatment program.

References

• Mehler PS, Watters A, Joiner T, Krantz MJ. What accounts for the high mortality of anorexia nervosa? Int J Eat Disord 2022;55:633-6.
• Sachs K, Harnke B, Mehler PS, Krantz MJ. Cardiovascular complications of anorexia nervosa: A systematic review. Int J Eat Disord 2016;49(3):238-48.
• Westmoreland P, Duffy A, Rienecke R, et al. Causes of death in patients with a history of severe anorexia nervosa. J Eat Disord 2022;10:200.
• Yahalom M, Spitz M, Sandler L, et al. The significance of bradycardia in anorexia nervosa. Int J Angiol 2013;22:83-94.