What Is the Most Common Cause of Bradycardia?

Medically Reviewed on 11/16/2022
Cause of Bradycardia
Bradycardia doesn’t always result in symptoms, but a sluggish heartbeat is typical in most people, especially athletes.

Bradycardia can be due to extreme fitness (as seen in athletes). However, it is frequently linked to additional factors, such as:

What is bradycardia?

Bradycardia is a term used to describe an abnormally slow heart rate (the number of times the heart beats in a minute).

  • Adults’ resting heart rates typically range from 60 to 100 beats per minute (bpm). 
  • Bradycardia is characterized by heartbeats that are less frequent than 60 bpm.
  • In physically fit people, heart rates as low as 40 bpm are achievable.

Bradycardia, however, is typically a sign of cardiac problems. Your heart's electrical system transmits electrical signals to control your heartbeat. Any irregular alteration in the heartbeat's rhythm is referred to as an "arrhythmia." Bradycardia is the term for an arrhythmia that causes a slower-than-normal heartbeat.

Bradycardia can appear in various ways. It is usually common in healthy children and adults, particularly when they are sleeping. It can occasionally be brought on by a malfunction of the heart's internal electrical circuits or its internal timing. You may require treatment depending on the type and degree of the condition.

What causes bradycardia?

A low resting heart rate may occur in some older people, athletes, and people who exercise frequently, but it is not a medical problem. Bradycardia can also have more severe reasons, such as drug side effects, aging, cardiac problems, and other illnesses.

  1. Sick sinus syndrome: Develops when the heart's natural pacemaker, the sinus node, fails to consistently initiate each heartbeat. The heart rate is slow and erratic because it triggers some heartbeats but not all. Older adults are more likely to experience sick sinus syndrome; however, it can happen to anyone.
    • The following are risk factors for sick sinus syndrome:
  2. Heart block: Results when the electrical signal that contracts the atria (top chambers of the heart) does not always reach the ventricles.
    • Heart blocks are of two types:
      • 2:1 heart block occurs when the ventricles only contract once every two times the atria contract.
      • The upper and lower chambers of the heart are unable to communicate with one another when there is a complete heart block. Fortunately, the ventricles compensate for it as substitute pacemakers although the rate is not as regular and effective.
    • The following are risk factors for heart block:
      • Heart illness or a heart attack in the past
      • Exposure to specific poisons
      • Specific drugs, such as digitalis
      • Lyme illness
      • Congenital conditions
  3. Electrolyte imbalances: Your heart rate may be affected if you don't have adequate levels of electrolytes including calcium, magnesium, and potassium in your blood.
  4. Inflammation: Refers to pericarditis (inflammation of your heart's pericardium [the sac that surrounds and cushions your heart]), myocarditis (inflammation of your heart muscle), or endocarditis (inflammation of heart muscle’s inner lining).
  5. Rheumatic heart disease and rheumatic fever: When a bacterial illness such as strep throat is not treated right away, rheumatic fever may develop. A few years later, rheumatic heart disease develops because of the infection.
  6. Drugs: These include narcotic pharmaceuticals, lithium, beta-blockers, calcium-channel blockers, antiarrhythmia drugs, and antidepressants. Cannabis (marijuana), a substance used recreationally, can also cause bradycardia.
  7. Lyme disease: Caused by microorganisms that tick bites transmit. This infection, also known as borreliosis, might harm your heart if you wait too long to get treatment.
  8. Chagas disease: Like Lyme disease and caused by a parasite that you can catch from "kissing bugs," which are blood-sucking insects.

Other causes of bradycardia

  1. Severe hypothermia (cold) or hypoxia (not enough oxygen in the blood)
  2. Obstructive sleep apnea
  3. Hypothyroidism (underactive thyroid)
  4. High pressure inside the skull (increased intracranial pressure)
  5. Duchenne muscular dystrophy
  6. Long Q-T syndrome
  7. Scleroderma
  8. Lupus
  9. Anorexia nervosa (bradycardia may be caused by this eating disorder)


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What are the symptoms of bradycardia?

Bradycardia does not necessarily result in symptoms. A sluggish heartbeat may be typical and entirely healthy in some people, such as athletes.

The most typical signs of bradycardia include:

How is it diagnosed?

A physical examination combined with tests that gauge your heart rate and examine its rhythm can help a doctor identify bradycardia. 

Physical examination

During a physical examination, a medical professional will examine your body for any telltale symptoms of any diseases or issues. They will also examine your chest including auscultation to listen to the heartbeats.

Other tests

The following tests are the most likely to detect bradycardia:

  • ECG: Essential for detecting bradycardia as it can precisely follow the electrical activity of your heart. The electrodes used in this test are attached to your chest's skin and have several sensors within (typically 12). When your heart's electrical activity has been picked up by the electrodes, a wave will appear on a paper printout or computer screen.
  • Echocardiography or echo: Used to examine the functioning of heart chambers and valves by using electrodes and ultrasound technology.
  • Electrolyte levels: Evaluate your blood's concentration of electrolytes, including calcium, potassium, and magnesium.
  • Thyroid hormone concentrations: Bradycardia can be caused by hypothyroidism (reduced thyroid function).
  • Cardiac troponin: A particular type of protein called cardiac troponin is found in the cells of your heart muscle. Troponin leaks into your blood because of damage to those cells, which may suggest cardiac disease. Troponin is a crucial marker that medical professionals use to identify heart attacks.
  • Toxicology examination: Searches your blood for harmful chemicals. This test can detect various heart-harming compounds and prescription or illicit medicines that can cause bradycardia.

How is bradycardia treated?

Bradycardia may require different treatments that depend on the cause. Treatment also depends on the type of bradycardia you have and the severity of your symptoms.

Treatment for bradycardia may include:

  • Treat the underlying cause if it is fixable. For example, if a medicine is causing bradycardia, quitting a medication or altering its dosage, as directed by your healthcare physician, may resolve a bradycardia issue. Alternatively, if a disease such as an underactive thyroid is to blame, treating the thyroid may prevent bradycardia from recurring.
  • An intravenous or injectable medication, such as atropine, can increase your heartbeat more quickly. People receiving these medications may need monitoring and further care; therefore, treatments such as these are typically hospital-specific.
  • Temporary pacing, a gadget with electrical contacts that touch or adhere to the skin of your chest, is involved in this. These connectors enable a small electrical current to pass through your body and beat your heart. Temporary cardiac pacing is a successful short-term treatment for people who need a permanent pacemaker or whose bradycardia is anticipated to be transient.
  • A permanent pacemaker is a device that connects to your heart and is permanently implanted under the skin, typically in your chest. Your heart is monitored by the device, and if it starts to beat too slowly, electrical impulses are sent to speed up the heartbeat.
Medically Reviewed on 11/16/2022
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