Bradycardia is a slower than normal heart rate. The hearts of adults at rest usually beat between 60 and 100 times a minute. If you have bradycardia (brad-e-KAHR-dee-uh), your heart beats fewer than 60 times a minute.
Bradycardia can be a serious problem if the heart doesn't pump enough oxygen-rich blood to the body. For some people, however, bradycardia doesn't cause symptoms or complications.
An implanted pacemaker can correct bradycardia and help your heart maintain an appropriate rate.
Bradycardia care at Mayo Clinic
If you have bradycardia, your brain and other organs might not get enough oxygen, possibly causing these symptoms:
- Near-fainting or fainting (syncope)
- Dizziness or lightheadedness
- Shortness of breath
- Chest pains
- Confusion or memory problems
- Easily tiring during physical activity
When a slow heart rate is normal
A resting heart rate slower than 60 beats a minute is normal for some people, particularly healthy young adults and trained athletes. For them, bradycardia isn't considered a health problem.
When to see a doctor
A number of conditions can cause signs and symptoms of bradycardia. It's important to get a prompt, accurate diagnosis and appropriate care. See your doctor if you or your child has symptoms of bradycardia.
If you faint, have difficulty breathing or have chest pain lasting more than a few minutes, get emergency care or call 911 or your local emergency number. Seek emergency care for anyone with these symptoms.
In a normal heart rhythm, a tiny cluster of cells at the sinus node sends out an electrical signal. The signal then travels through the atria to the atrioventricular (AV) node and then passes into the ventricles, causing them to contract and pump out blood.
Bradycardia, shown on the right, is a slower heart rhythm that may occur because the sinus node in the heart may be discharging electrical impulses at a slower than normal rate. A heart with a normal heart rhythm is shown on the left. Bradycardia may also be due to other causes.
Bradycardia can be caused by:
- Heart tissue damage related to aging
- Damage to heart tissues from heart disease or heart attack
- Heart disorder present at birth (congenital heart defect)
- Infection of heart tissue (myocarditis)
- A complication of heart surgery
- Underactive thyroid gland (hypothyroidism)
- Imbalance of chemicals in the blood, such as potassium or calcium
- Repeated disruption of breathing during sleep (obstructive sleep apnea)
- Inflammatory disease, such as rheumatic fever or lupus
- Medications, including some drugs for other heart rhythm disorders, high blood pressure and psychosis
Electrical circuitry of the heart
Your heart comprises four chambers — two upper (atria) and two lower (ventricles). A natural pacemaker (the sinus node), situated in the right atrium, normally controls your heart rhythm by producing electrical impulses that initiate each heartbeat.
These electrical impulses travel across the atria, causing them to contract and pump blood into the ventricles. Then these impulses arrive at a cluster of cells called the atrioventricular (AV) node.
The AV node transmits the signal to a collection of cells called the bundle of His. These cells transmit the signal down a left branch serving the left ventricle and a right branch serving the right ventricle, which causes the ventricles to contract and pump blood — the right ventricle sending oxygen-poor blood to the lungs and the left ventricle sending oxygen-rich blood to the body.
Bradycardia occurs when electrical signals slow down or are blocked.
Sinus node problems
Bradycardia often starts in the sinus node. A slow heart rate might occur because the sinus node:
- Discharges electrical impulses slower than is normal
- Pauses or fails to discharge at a regular rate
- Discharges an electrical impulse that's blocked before causing the atria to contract
In some people, the sinus node problems result in alternating slow and fast heart rates (bradycardia-tachycardia syndrome).
Heart block (atrioventricular block)
Bradycardia can also occur because electrical signals transmitted through the atria aren't transmitted to the ventricles (heart block, or atrioventricular block).
Heart blocks are classified based on the degree to which signals from the atria reach your heart's main pumping chambers (ventricles).
- First-degree heart block. In the mildest form, all electrical signals from the atria reach the ventricles, but the signal is slowed. First-degree heart block rarely causes symptoms and usually needs no treatment if there's no other abnormality in electrical signal conduction.
- Second-degree heart block. Not all electrical signals reach the ventricles. Some beats are "dropped," resulting in a slower and sometimes irregular rhythm.
- Third-degree (complete) heart block. None of the electrical impulses from the atria reaches the ventricles. When this happens, a natural pacemaker takes over, but this results in slow and sometimes unreliable electrical impulses to control the beat of the ventricles.
A key risk factor for bradycardia is age. Heart problems, which are often associated with bradycardia, are more common in older adults.
Risk factors related to heart disease
Bradycardia is often associated with damage to heart tissue from some type of heart disease.
Therefore, factors that increase your risk of heart disease can also increase the risk of bradycardia. Lifestyle changes or medical treatment might decrease the risk of heart disease associated with the following factors:
- High blood pressure
- Heavy alcohol use
- Recreational drug use
- Psychological stress or anxiety
If bradycardia causes symptoms, possible complications can include:
- Frequent fainting spells
- Inability of the heart to pump enough blood (heart failure)
- Sudden cardiac arrest or sudden death
The most effective way to prevent bradycardia is to reduce your risk of developing heart disease. If you already have heart disease, monitor it and follow your treatment plan to lower your risk of bradycardia.
Prevent heart disease
Treat or eliminate risk factors that may lead to heart disease. Take the following steps:
- Exercise and eat a healthy diet. Live a heart-healthy lifestyle by exercising regularly and eating a healthy, low-fat, low-salt, low-sugar diet that's rich in fruits, vegetables and whole grains.
- Maintain a healthy weight. Being overweight increases your risk of developing heart disease.
- Keep blood pressure and cholesterol under control. Make lifestyle changes and take medications as prescribed to correct high blood pressure (hypertension) or high cholesterol.
- Don't smoke. If you smoke and can't quit on your own, talk to your doctor about strategies or programs to help you break a smoking habit.
If you drink, do so in moderation. For healthy adults, that means up to one drink a day for women of all ages and men older than age 65, and up to two drinks a day for men age 65 and younger.
Ask your doctor if your condition means you should avoid alcohol. If you can't control your alcohol use, talk to your doctor about a program to quit drinking and manage other behaviors related to alcohol abuse.
- Don't use recreational drugs. Talk to your doctor about an appropriate program for you if you need help ending recreational drug use.
- Manage stress. Avoid unnecessary stress and learn coping techniques to handle normal stress in a healthy way.
- Go to scheduled checkups. Have regular physical exams and report signs or symptoms to your doctor.
Monitor and treat existing heart disease
If you already have heart disease, there are steps you can take to lower your risk of developing bradycardia or another heart rhythm disorder:
- Follow the plan. Be sure you understand your treatment plan, and take all medications as prescribed.
- Report changes immediately. If your symptoms change or worsen or you develop new symptoms, tell your doctor immediately.
Nov. 13, 2019