Definition

Bradycardia refers to a slowing or reduction in heart rate. An adult heart at rest normally beats between 60 and 100 beats per minute. In bradycardia, the heart beats less than 60 times per minute.

Bradycardia is a serious condition in which the heart rate is extremely slow and the heart is unable to pump enough blood throughout the body. If this occurs, you may experience dizziness, weakness, or shortness of breath due to a lack of oxygen.

Bradycardia may or may not cause symptoms. Bradycardia that is symptomatic is called symptomatic bradycardia. Some bradycardias cause complications, and some do not.

A slow heart rate is not always a concern. For example, a resting heart rate of 40-60 beats per minute is common in some people while sleeping, particularly healthy young adults and trained athletes.

If bradycardia is severe, an implanted pacemaker may be needed to help the heart maintain its normal rate.

Causes

Bradycardia can be caused by:

• Damage to heart tissue due to aging
• Heart tissue damage due to heart disease or heart attack
• Congenital heart defects or abnormalities from birth
• Inflammation of the heart tissue (myocarditis)
• Complications of heart surgery
• Underactive thyroid gland (hypothyroidism)
• Imbalance of chemicals (electrolytes) in the blood, such as potassium or calcium
• Repeated pauses in breathing during sleep (obstructive sleep apnea)
• Inflammatory diseases of the body, such as rheumatic fever or lupus
• Medications, including tranquilizers, opioids, and medications used to treat heart rhythm disorders, high blood pressure, and certain mental health disorders

To better understand the causes of bradycardia, you must first understand the process that allows the heart to beat. The heart has four chambers: two atria and two ventricles.

Inside the right atrium, there is a group of cells called the sinus node. The sinus node is the natural pacemaker that generates the signals to start each heartbeat. Bradycardia occurs when these signals are slowed down or blocked.

Problems with the Sinus Node

Bradycardia generally starts in an area of the heart called the sinus node. In some people, a problematic sinus node can cause both slow and fast heart rates (bradycardia-tachycardia syndrome).

Atrioventricular (AV) Block

Bradycardia can also occur when the heart's electrical signals do not travel properly from the atriums to the ventricles. When this happens, it is called a heart block or atrioventricular block.

Heart block is divided into three main groups.

• First-degree heart block. This is the mildest form of heart block. At this level, all electrical signals from the atriums can reach the ventricles, but they are delayed. First-degree heart block rarely causes symptoms and usually does not necessitate treatment if there are no other issues with electrical signals
• Second-degree heart block. In the second degree, not all electrical signals reach the ventricles. Some beats slow down, resulting in a slower and sometimes irregular heart rhythm
• Third-degree heart block (total block). At this level, no electrical signals from the atriums reach the ventricles. When this occurs, the heart chambers typically beat on their own, albeit at a very slow pace

Risk Factor

Bradycardia is linked to heart tissue damage in some types of heart disease. Anything that increases the risk of heart problems may increase the risk of bradycardia. The risk factors for heart disease are:

• Advanced age
• High blood pressure
• Smoking
• Excessive alcohol consumption
• Use of illegal drugs
• Stress and anxiety

Healthy lifestyle changes or appropriate medical treatment can help lower the risk of heart disease.

Symptoms

Bradycardia, or a slower-than-normal heartbeat, can prevent the brain and other organs from receiving adequate oxygen. This condition can cause the following signs and symptoms:

• Chest pain
• Confusion or memory impairment
• Dizziness
• Easily fatigued during physical activity
• Fatigue
• Fainting or near fainting
• Shortness of breath

Diagnosis

To diagnose bradycardia, the doctor will examine you and listen to your heartbeat with a stethoscope. They will also ask about your symptoms and medical history.

The doctor may recommend tests to check your heart rate and see if you have a heart problem that causes bradycardia. Blood tests may be done to check for other conditions that cause a slowing of the heart rate, such as infection, hypothyroidism, or electrolyte imbalance.

Examination

An electrocardiogram, or ECG, is the main test for diagnosing bradycardia. An ECG measures the electrical activity of the heart and can show whether the heart is beating too slow, too fast, or not beating at all.

However, ECG cannot detect bradycardia unless it happens during the examination. Therefore, your doctor may recommend a portable device, such as:

• Holter monitors. This device can be put in a pocket or worn on a belt and carried around. It records heart activity continuously for 24 hours or more
• Event recorder. This is similar to a Holter monitor but only records at specific times for a few minutes at a time. They are worn longer than Holter monitors, usually 30 days. When you experience symptoms, press a button to see your heart's electrical recordings. Some devices automatically record when they detect an irregular heart rhythm

The ECG examination may be accompanied by other tests to understand how the bradycardia arose in your heart. These tests include:

• Tilt table test. This test helps doctors understand how bradycardia causes fainting. You lie on a special table, which is tilted as if you were standing. The tilt test is performed to determine whether the change in position causes fainting
• Exercise stress test. An ECG may be used to monitor the electrical activity of the heart while riding a stationary bike or walking on a treadmill. If you are having difficulty exercising, certain medications may be prescribed to stimulate the heart in the same way that exercise does

A sleep study may be recommended if the doctor suspects a link between bradycardia and obstructive sleep apnea.

Management

Bradycardia treatment is determined by the severity of the symptoms and the cause. If bradycardia does not cause symptoms, treatment may not be necessary.

Management of bradycardia includes lifestyle changes, medication, or the insertion of an implantable pacemaker. If the bradycardia is caused by a disease, such as thyroid disease or sleep apnea, treating the disease may help.

Medications

Many medications, including those used to treat other heart diseases, can cause bradycardia. Always tell your doctor about all of the medications you are taking, including those purchased without a prescription. If the medication you are taking causes bradycardia, your doctor will recommend a lower dose or a different medication.

Surgery or Other Procedures

When other treatments are ineffective and bradycardia symptoms worsen, a pacemaker is required to regulate the heart rhythm. A pacemaker works only when necessary. When the heart beats too slowly, the pacemaker sends electrical signals to speed up the heartbeat. 

A pacemaker must be implanted through surgery. Several special wires are inserted into a large vein in the groin and guided to the heart via X-ray. The wire is guided to the appropriate area of the heart, while the other end is connected to a heart rate generator implanted under the skin of the groin.

Complications

Possible complications of bradycardia include:

• Frequent fainting
• Heart failure or the inability of the heart to pump enough blood around the body
• Sudden heart attack
• Sudden death

Prevention

Although bradycardia cannot generally be prevented, there are strategies to reduce the risk of heart disease, such as:

• Regular exercise. Your doctor will recommend an exercise schedule that suits your condition
• Eat a healthy diet. Choose a low-fat, low-salt, low-sugar diet, rich in fruits, vegetables, and whole grains
• Maintain an ideal body weight. Being overweight increases the risk of developing heart disease
• Keep blood pressure, blood sugar, and cholesterol under control. Make lifestyle changes and take medications as prescribed by your doctor
• Do not smoke. If you need help quitting smoking, consult with your doctor about suitable strategies or programs
• Limit alcohol consumption. If you are unable to control your alcohol use, consult with your doctor about a quit-drinking program and managing other alcohol-related behaviors
• Manage stress. Uncontrolled emotions can affect heart rate. Regular exercise, joining a support group, or experimenting with relaxation techniques like yoga are some ways to relieve stress
• Regular health check-ups. See your doctor on a regular basis and report any new signs or symptoms to them

Monitor and Treat Heart Disease

If you already have heart disease, there are ways to reduce your risk of developing bradycardia or other heart rhythm disorders.

• Follow your doctor's medication regimen. Make sure you understand your doctor's treatment plan and take all of your medications as prescribed
• Report changes immediately. If your symptoms change, worsen, or new symptoms appear, inform your doctor right away

When To See a Doctor? 

Bradycardia symptoms can be caused by a variety of factors. It is critical to receive a timely, accurate diagnosis and appropriate treatment. Consult a doctor if you have symptoms of bradycardia.

If you faint, have difficulty breathing, or experience chest pain that lasts more than a few minutes, call an emergency number or go to the emergency room for immediate care

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