Bradycardia is a condition where your heart beats too slowly. It may be caused by a problem with the electrical system of your heart, which controls how fast your heart beats. The electrical signals that control your heart rate travel through the heart’s conduction system. This system includes the sinoatrial node (SA node), the atrioventricular node (AV node), and the bundle of His.
In bradycardia, the heart beats less than 60 times per minute.
Bradycardia can be a serious problem if the heart does not pump enough oxygen-rich blood to the body. For some people, however, bradycardia does not cause symptoms or complications. An implanted pacemaker can correct bradycardia and help the heart maintain a proper rhythm.
With bradycardia, the brain and other organs might not get enough oxygen, which could cause these symptoms:
- Fainting or fainting (syncope)
- Dizziness or vertigo
- Shortness of breath
- chest pain
- Confusion or memory problems
A resting heart rate slower than 60 beats per minute is normal for some people, especially healthy young adults and trained athletes. For them, bradycardia is not considered a health problem.
Case of sinus bradycardia
Sinus bradycardia is a type of slow heartbeat that originates in the sinus node of your heart. The sinus node is considered the pacemaker of the heart.
Sinus bradycardia does not always indicate a medical condition. In some people, the heart can still pump blood efficiently with fewer beats per minute. For example, healthy young adults or endurance athletes can often have sinus bradycardia.
It can also occur during sleep, especially when sleeping soundly. This is more common in older people.
Sinus bradycardia can also occur with sinus arrhythmia. Sinus arrhythmia occurs when the rhythm between heartbeats is irregular. For example, a person with sinus arrhythmia may have a variation in heartbeat as they inhale and exhale.
Sinus bradycardia and sinus arrhythmia can commonly occur during sleep.
Sinus bradycardia can be a sign of a healthy heart. But it can also be a sign of a faulty electrical system. For example, older people may develop a sinus node that does not function well enough to produce electrical impulses reliably.
Sinus bradycardia can start causing problems if the heart is not pumping blood efficiently to the rest of the body. Possible complications include fainting, heart failure, or even sudden cardiac arrest.
Bradycardia can be caused by:
- Damage to heart tissue associated with aging.
- Damage to heart tissue due to heart disease or heart attack.
- A heart condition present at birth (congenital heart defect).
- An infection of the heart tissue (myocarditis).
- A complication of heart surgery.
- An underactive thyroid gland (hypothyroidism).
- An imbalance of markers in the blood, such as potassium or calcium.
- A repeated disturbance of breathing during sleep (obstructive sleep apnea).
- An inflammatory disease, such as rheumatic fever or lupus.
- Medicines, including some medicines for other heart rhythm disorders.
- High blood pressure.
How does the heart work?
The heart has four chambers: two upper (atria) and two lower (ventricles). A natural pacemaker (the sinus node), located in the right atrium, normally controls the heartbeat by producing electrical impulses that trigger each heartbeat.
These electrical impulses travel through the atria, causing them to contract and pump blood into the ventricles. Then these impulses arrive at a group of cells called the atrioventricular (AV) node.
The AV node transmits the signal to cells that transmit the signal in the left and right ventricles, which causes the ventricles to contract and pump blood. The right ventricle sends oxygen-poor blood to the lungs and the left ventricle sends oxygen-rich blood to the body.
When does bradycardia occur?
Bradycardia occurs when electrical signals slow down or are blocked. Bradycardia often begins in the sinus node.
A slow heart rate can occur because of the sinus node:
- discharges electrical impulses slower than normal or fails to discharge at a steady rate;
- discharges an electrical impulse which is blocked before causing the atria to contract.
In some people, sinus node problems cause alternating slow and fast heart rates (bradycardia-tachycardia syndrome).
Bradycardia can also occur because the electrical signals transmitted by the atria are not transmitted to the ventricles.
In the mildest form, all the electrical signals from the atria reach the ventricles, but the signal is slowed down.
First degree disorder. The disorder rarely causes symptoms and usually needs no treatment if there are no other abnormalities in electrical signal conduction.
Second degree disorder. Not all electrical signals reach the ventricles.
Third degree disorder. None of the electrical impulses from the atria reach the ventricles. When this happens, a natural pacemaker takes over, but this results in slow and sometimes unreliable electrical impulses to control the rhythm of the ventricles.
Age. A key risk factor for bradycardia is age. Heart problems, often associated with bradycardia, are more common in older people.
Heart disease risk factors. Bradycardia is frequently associated with damage to heart tissue. Therefore, factors that increase the risk of heart disease may also increase the risk of bradycardia.
Lifestyle changes or medical treatment may reduce the risk of heart disease associated with the following factors: high blood pressure, smoking, excessive alcohol consumption, recreational drug use, psychological stress or anxiety.
If bradycardia causes symptoms, possible complications may include:
- fainting spells;
- inability of the heart to pump enough blood (heart failure);
- sudden cardiac arrest or sudden death.
Prevention of bradycardia
The most effective way to prevent bradycardia is to reduce the risk of developing heart disease by addressing risk factors: adopting a heart-healthy lifestyle by exercising regularly and following a diet healthy, low in fat, low in salt and sugar, rich in fruits, vegetables and whole grains, maintain a healthy weight, control maintain blood pressure and cholesterol.
The doctor will review your symptoms, medical and family history, and perform a physical exam.
He will also order tests to measure the patient’s heart rate, link a slow heart rate to symptoms, and identify conditions that may cause bradycardia.
Electrocardiogram. An electrocardiogram, also called an ECG, is a primary tool for evaluating bradycardia. Using small sensors (electrodes) attached to the chest and arms, it registers electrical signals as they travel through the heart.
Since an ECG cannot record bradycardia unless it occurs during the test, the doctor may instruct the patient to use a portable ECG at home. These devices include:
Holter monitor. Carried in your pocket or worn on a belt or across the body, this device records your heart’s activity for 24 to 48 hours.
The doctor will likely ask the patient to keep a diary for the 24 hours. The patient will describe any symptoms observed and note their time of onset.
Event recorder. This device monitors heart activity for a few weeks. Simply press a button to activate it when the patient experiences symptoms so that the device records heart activity during that time.
The doctor may use an ECG monitor while performing other tests to understand the impact of bradycardia. These tests include:
Tilt table test. The tilt table test is used to diagnose patients who faint because of a problem with the heart rate. It involves lying down on a special table while the table is tilted back and forth. The patient may feel dizzy or lightheaded during the test.
Stress test. The patient walks on a treadmill or rides a stationary bicycle to see if the parallel measured heart rate increases appropriately in response to physical activity.
Laboratory tests. The doctor will order blood tests to screen for conditions that could be contributing to bradycardia, such as infection, hypothyroidism, or electrolyte imbalance.
If sleep apnea is suspected of contributing to the bradycardia, the patient might undergo tests to monitor your sleep.
The treatment for bradycardia depends on the type of electrical conduction problem, the severity of the symptoms, and the cause of your slow heartbeat. If you have no symptoms, treatment may not be necessary.
Treat underlying disorders (e.g. hypothyroidism or obstructive sleep apnea).
Change in medications. Several medications, some of which are used to treat other heart conditions, can cause bradycardia. Changing medications or reducing doses may correct problems with a slow heart rate.
Pacemaker. When other treatments are not possible and symptoms require treatment, a pacemaker is needed. This battery-powered device the size of a mobile phone is implanted under the collarbone. The wires of the device are inserted into the veins and into the heart. Electrodes at the end of the wires are attached to heart tissue. The pacemaker monitors the heart rate and generates electrical impulses needed to maintain an appropriate rate.