Definition

Bradycardia is an abnormally slow heart rate. In adults, it is defined as a heart rate of less than 60 beats per minute. Different types of bradycardia are collectively referred to as bradyarrhythmias. They include:

• Sinus bradycardia—an unusually slow heartbeat due to heart disease, a reaction to medication, or harmless causes, such as excellent fitness or deep relaxation
• Sick sinus syndrome—an unusually slow heartbeat due to a malfunction of the sinoatrial node, which is the heart’s natural pacemaker
• Heart block (atrioventricular block or AV block)—an unusually slow heartbeat due to a slowing or blocking of electrical impulses in the heart’s conduction system

Causes

Bradycardia may be caused by:

• Normal responses to:
  • Deep relaxation
  • Being in excellent physical shape
• The heart’s natural pacemaker developing an abnormal rate or rhythm
• The normal electrical conduction pathway being interrupted
• Another part of the heart taking over as pacemaker

Risk Factors

Factors that may increase your chance of bradycardia include:

• Increased age
• Hypothyroidism
• Taking certain medications used to treat:
  • High blood pressure
  • Alzheimer’s disease
  • Heart disease
  • Heart failure and arrhythmias
• Exposure to certain toxins
• Cardiac disease, such as:
  • Heart attack
  • Wearing out of the heart’s conduction system
  • Heart failure
  • Heart valve failure
  • Heart conditions that are inherited or present at birth
• Electrolyte imbalances
• Sleep apnea
• Systemic lupus erythematosus or other collagen vascular diseases (rare)
• Head injuries
• Hypothermia
• Hypoglycemia
• Infectious diseases, such as:
  • Diphtheria
  • Rheumatic fever
  • Viral myocarditis
  • Lyme disease
  • Chagas disease

Symptoms

Some types of bradycardia produce no symptoms. Others may cause noticeable symptoms, such as:

• Fainting or loss of consciousness
• Lightheadedness
• Weakness
• Mild fatigue
• Irregular heart beat
• Shortness of breath
• Chest pain

Serious forms of bradycardia, such as complete heart block, are medical emergencies. They can lead to loss of consciousness or sudden cardiac arrest.

Diagnosis

The doctor will ask about your symptoms and medical history. A physical exam will be done. Your heart will be examined with a stethoscope.

• Your doctor may need you to have blood tests. These tests will look for problems that may explain the bradycardia.
• Your doctor may need to test your heart function. This can be done with:
  • Electrocardiogram (EKG)
  • Echocardiogram
  • A portable, continuous heart rhythm monitor that you wear as you perform normal daily activities
  • Exercise stress test
  • Nuclear scanning
  • Coronary angiography

Treatment

Treatment may not be required if you do not have cardiac symptoms and conditions. Your doctor may choose to monitor your heart rate and rhythm instead.

Treatment may include:

• Stopping any medications that slow the heart rate
• Diagnosing and treating any underlying conditions
• Medication to temporarily increase your heart rate
• An artificial pacemaker to establish and maintain a normal heart rhythm

Prevention

To help reduce your chnace of bradycardia:

• Treat any health conditions that might lead to bradycardia.
• Carefully follow your doctor’s directions when using medications, especially those that can cause bradycardia.
• Check with your physician or pharmacist before using any over-the-counter medication or natural supplement. Make sure it does not interact with your other medications.
• Follow general advice for preventing heart disease, including:
  • Maintain a healthy weight.
  • Consult with your doctor about a safe exercise program.
  • Avoid smoking.
  • Eat a healthy diet that is low in saturated fat and rich in whole grains, fruits, and vegetables.
  • Treat your high blood pressure and/or diabetes.
  • Treat your high cholesterol or triglycerides.

Heart Rhythm Society http://www.hrsonline.org/

Heart and Stroke Foundation http://www.heartandstroke.com

Fleg J. Arrhythmias and conduction disturbances. In: Beers MH, Berkow R, eds. The Merck Manual of Geriatrics (online). Merck & Co.;2000:486.

Hurst’s The Heart. 11th ed; 2004.

Explore arrhythmia. National Heart, Lung and Blood Institute, National Institutes of Health website. Available at:
http://www.nhlbi.nih.gov/health/health-topics/topics/arr
Updated July 1, 2011. Accessed January 18, 2013.