What is bradycardia?

Bradycardia is a type of abnormal heart rhythm, or arrhythmia. It occurs when the heart beats very slowly — less than 60 beats per minute.

A normal heartbeat begins with an electrical impulse from the sinus node, a small area in the heart's right atrium (right upper chamber). The electricity travels through the heart and causes the muscle to contract between 60 and 100 times each minute.

What are the symptoms of bradycardia?

Sometimes bradycardia causes no symptoms and your doctor may not need to treat it. Others may experience the following:

• Fainting (syncope)
• Dizziness
• Weakness or fatigue
• Disturbed sleep

Babies with bradycardia may act sleepy and lack interest in feeding.

What causes bradycardia?

Some children and elderly people, as well as athletes and people who exercise often, may have a low resting heart rate that is not a medical condition. Other, more serious causes of bradycardia include drug reactions, advanced age, conditions of the heart and other ailments.

Sick sinus syndrome

Sick sinus syndrome occurs when the sinus node — the heart's natural pacemaker — doesn't reliably trigger every heartbeat. It triggers some heartbeats but not all, so the heart rate is slow and irregular. Sick sinus syndrome is more common in elderly people but may occur at any age.

Risk factors for sick sinus syndrome include:

• Blood pressure medications
• Age over 70
• Previous heart surgery
• Atherosclerosis

Heart block

Heart block occurs when the electrical signal that contracts the atria (upper chambers of the heart) doesn't always travel to the ventricles (lower chambers).

• A 2:1 heart block means that for every two contractions of the atria, there's only one contraction of the ventricles.
• Complete heart block means there is no communication between the upper and lower chambers of the heart. Fortunately, the heart is designed with two backup "pacemakers" inside the ventricles.
• Congenital heart block is present at birth.

Risk factors for heart block include:

• Previous heart disease or heart attack
• Exposure to certain toxins<
• Certain medications, including digitalis
• Lyme disease

Other causes of bradycardia

• A response of the vagus nerve affecting the heart (see Reflex Syncope in the Syncope article)
• High pressure inside the skull (intracranial pressure)
• Heart attack
• Obstructive sleep apnea
• Certain medications
• Hypothyroidism (underactive thyroid)
• Severe hypothermia (cold) or hypoxia (not enough oxygen in the blood

How is bradycardia diagnosed?

Bradycardia can sometimes be diagnosed in your physician's office with an electrocardiogram (ECG or EKG). But when bradycardia is an occasional event, a regular ECG may be normal. If this is the case, your doctor may give you an ECG monitor to wear at home that will record your heart rhythm over time. These include:

• Holter monitor: a portable ECG worn for one to seven days
• Event monitor: a portable ECG worn for one or two months but only triggered when your heart rhythm becomes abnormal or when you manually activate it

• Implantable monitor: a tiny event monitor inserted under your skin and worn for several years to record events that only seldom take place

How is bradycardia treated?

• Treatment of any underlying conditions
• During a heart attack, medications to stimulate heartbeat
• Insertion of a pacemaker under the collarbone, which delivers regular electrical pulses through thin, highly durable wires attached to the heart

Learn more about arrhythmias or visit the Johns Hopkins Electrophysiology and Arrhythmia Service.