What Causes Bradycardia?

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Patient Presentation
A 17-year-old male long-distance runner came to clinic for his health supervision visit. He had no concerns and had recently run a marathon. He had no recent athletic injuries and was doing well in school. He was looking forward final year of cross-country in high school.

The pertinent physical exam revealed a heart rate of 56 beats/minute, blood pressure of 96/60, respirations were 12/minute. Weight was 25% and height was 75%. He looked healthy and thin. Heart showed normal rhythm with no murmur. He had no bruits. His heart rate was responsive to respiration and movement. The remainder of his examination was normal.

The diagnosis of a healthy male runner with bradycardia was made. The pediatrician noted that he had a lower heart rate. Previous heart rates had been in the 60-70s in the past few visits. He had no personal or family history of chest pain, dizziness, syncope, early cardiac death or cardiac issues. He denied taking any medications other than some antihistamines for some mild seasonal allergic rhinitis. The pediatrician discussed that this most likely was because he was highly trained. He cautioned the patient to be aware and to call if he developed any problems such as dizziness, syncope or chest pain.

Discussion
Bradycardia is a heart rate below what the lowest value that is normal for age. Infants and children have higher heart rates that slowly decrease with age to adult levels. It is usually noted as an incidental finding because of increased vagal tone. Reasons for cardiology referral include associated heart murmur, syncope especially if associated with exercise or unusual triggers, other signs such as chest pain or palpitations, family history of sudden cardiac death, congenital heart disease or familial heart disease, bradycardic medication use, or unusual symptoms associated with the concern. Severe bradycardia that causes poor cardiac output is a medical emergency. Fortunately most children have mild bradycardia which may have no symptoms or can manifest as dizziness, syncope, exercise intolerance or fatigue. Evaluation includes a good history and physical examination. Electrocardiogram may determine a rhythm abnormality but often an ambulatory Holter monitoring will be needed as the bradycardia and/or rhythm may be intermittent. Echocardiogram may be appropriate if congenital heart disease is suspected. Exercise stress testing is usually not need but can determine if the heart is appropriately responsive during exercise.

Learning Point
The differential diagnosis of bradycardia includes:

  • Athletes, well trained
  • Hypervagotonia this is a sinus bradycardia
    • Apnea and bradycardia in infants
    • Breathholding spells
    • Coughing
    • Emesis
    • Gastroesophageal reflux
    • Increased intracranial pressure
    • Obstructive sleep apnea
    • Stimulation of the nasopharynx or esophagus, or the rectum or perineum
  • Cardiac
    • Congenital heart disease
      • Atrial septal defect
      • Atrioventricular canal
    • Ischemic heart disease
    • Myocarditis/pericarditis
    • Sinus node dysfunction
    • Arrhythmias
      • Atrioventricular block
      • Long QT syndrome
    • Heart surgery
  • Electrolyte abnormalities
    • Hypo or hypercalcemia
    • Hypo or hyperkalemia
    • Hypoglycemia
    • Hypomagnesemia
  • Genetic
    • Carnitine deficiency
    • Glycogen storage disease
  • Hypoxia
  • Hypothermia
  • Immunologic
    • Systemic lupus erythematosus
    • Sjorgrens syndrome
  • Infectious
    • Chagas disease
    • Diphtheria
    • HIV
    • Lyme disease
    • Mumps
    • Rocky Mountain Spotted Fever
    • Rubella
  • Malnourishment
    • Anorexia nervosa
  • Medication
    • Acetylcholinesterase inhibitors
    • Alpha-adenergic agonists
    • Beta-adrenergic blockers
    • Calcium channel blockers
    • Clonidine
    • Lithium
    • Opioids
    • Parasympatheticomimetic drugs
  • Sleep
  • Relative bradycardia – pulse lower than expected for body temperature

Questions for Further Discussion
1. What Causes Tachycardia? A review can be found here
2. What medications should be avoided in long QT syndrome? A review can be found here
3. What are causes of sudden cardiac death? A review can be found here

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Arrhythmia

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Baruteau A-E, Perry JC, Sanatani S, Horie M, Dubin AM. Evaluation and management of bradycardia in neonates and children. Eur J Pediatr. 2016;175(2):151-161. doi:10.1007/s00431-015-2689-z

Ye F, Hatahet M, Youniss MA, Toklu HZ, Mazza JJ, Yale S. The Clinical Significance of Relative Bradycardia. WMJ Off Publ State Med Soc Wis. 2018;117(2):73-78.

Doyen B, Matelot D, Carre F. Asymptomatic bradycardia amongst endurance athletes. Phys Sportsmed. 2019;47(3):249-252. doi:10.1080/00913847.2019.1568769

Silva JN, Bradycardia in Children. UpToDate. Rev 9/3/19, accessed 4/1/20.

Author
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa

Published