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 include (collectively referred to as “bradyarrhythmias”) :

• Sinus bradycardia—an unusually slow heartbeat due to heart disease, a reaction to medication, or normal causes (such as excellent fitness or deep relaxation)
• Sick sinus syndrome—an unusually slow heartbeat due to a malfunction of the heart’s natural pacemaker (sinoatrial node)
• 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

Heartbeat: Anatomy of the Heart

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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

A risk factor is something that increases your chance for getting a disease or condition. Risk factors for bradycardia include the following:

• Advancing age
• Hypothyroidism
• Drugs such as (most commonly used for):
  • Clonidine and other centrally acting alpha-2 adrenergic agonists ( high blood pressure )
  • Cholinesterase inhibitors ( Alzheimer’s disease )
  • Calcium antagonists (high blood pressure, heart disease)
  • Digitalis and other cardiac glycosides (heart failure and arrhythmias )
  • Lithium
  • Beta-blockers (high blood pressure, heart disease), also used in some eye drops
• Exposure to certain toxins
• Cardiac disease, such as:
  • Heart attack
  • Degeneration, calcification, or “wearing out” of the conduction system
  • Congestive heart failure
  • Valvular failure
  • Heart conditions that are inherited or present at birth (congenital heart defects)
• Electrolyte imbalances (high or low potassium levels)
• Sleep apnea
• Rarely seen with lupus or other collagen vascular diseases
• 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 (“syncope”)
• Dizziness, sensation of light-headedness
• Weakness
• Mild fatigue
• Sensation of your heart fluttering (palpitations)
• Shortness of breath
• Chest pain
• Low blood pressure (hypotension)

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, and perform a physical exam. In particular, the doctor will listen to your heart with a stethoscope.

Tests may include:

• Blood tests—to look for certain abnormalities that may explain the bradycardia (eg, electrolytes, glucose, thyroid function, and drug levels)
• Electrocardiogram (ECG, EKG)—a test that records the heart’s activity by measuring electrical currents through the heart muscle.
• Echocardiogram —a test that uses high-frequency sound waves (ultrasound) to examine the size, shape, and motion of the heart.
• Holter monitor or event monitor—a portable, continuous heart rhythm monitor that you wear as you perform normal daily activities.
• Exercise stress test —a test that records the heart’s electrical activity during increased physical activity.
• Nuclear scanning—radioactive material is injected into a vein and observed as it is distributed through the heart muscle to look for coronary artery disease.
• Coronary angiography —x-rays taken after a dye is injected into the arteries; this allows the doctor to look for abnormalities in the coronary arteries of the heart.

Treatment

If no underlying heart disease is detected, the heart’s response to exercise is normal, and there are no symptoms of low cardiac output, treatment may not be required. Your doctor may choose to monitor your heart rate and rhythm periodically. People with cardiac symptoms and conditions usually receive treatment.

Treatment for symptomatic bradycardia may include:

• Discontinuing any medications that slow the heart rate
• Diagnosis and treatment of any underlying conditions
• Intravenous (IV) atropine–this medication may be used to temporarily increase heart rate
• Artificial pacemaker–this device may be either temporarily or permanently implanted under the skin in the chest wall. Whenever the heart rate drops too low, the pacemaker takes over the job of providing the electrical impulses needed to establish and maintain a normal heart rhythm.

Prevention

To help prevent bradycardia:

• Treat underlying conditions that might lead to bradycardia.
• Carefully follow your doctor’s directions when using medications (especially those that can potentially cause bradycardia).
• Check with your physician or pharmacist before using any over-the-counter medication or natural supplement to assure that it will not interact with your other medications
• Follow general advice for preventing the development of heart disease, including:
  • Maintain an appropriate weight.
  • Consult your doctor about a safe exercise program.
  • Stop smoking.
  • Eat a healthful diet, one 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.