Bradycardia means a slow heart rate (pulse). Bradycardia can be caused just by being very fit, especially in young people. However, bradycardia may also be caused by problems affecting the heart. Bradycardia may also have other causes such as an underactive thyroid gland. Some medicines may slow your heart and cause bradycardia.
Bradycardia often does not need any treatment but if treatment is needed then the outcome (prognosis) is usually very good. However, the outcome will also depend on the underlying cause of your slow heart rate.
A normal heartbeat and conducting system
The heart needs a small electrical current to pass through the heart in a very set pattern. This is called the heart's conduction system.
The heart has four chambers - two atria and two ventricles. The walls of these chambers are mainly made of special heart muscle. The chambers have to squeeze (contract) in the correct order for the heart to pump blood correctly with each heartbeat.
The sequence of each heartbeat is as follows:
- The sinoatrial node (SA node) in the right atrium is a tiny in-built 'timer'. It fires off an electrical impulse at regular intervals (about 60-80 per minute when you rest and faster when you exercise). This controls your heart rate. Each impulse spreads across both atria. This causes them to contract and pump blood through one-way valves into the ventricles.
- The electrical impulse gets to the atrioventricular node (AV node) at the lower right atrium. This acts like a 'junction box' and the impulse is delayed slightly. Most of the tissue between the atria and ventricles does not conduct the impulse. However, a thin band of conducting fibres called the atrioventricular bundle (AV bundle) acts like 'wires' and carries the impulse from the AV node to the ventricles.
- The AV bundle splits into two - a right and a left branch. These then split into many tiny fibres (the Purkinje system) which conducts the electrical impulse throughout the ventricles. This makes the ventricles contract and pump blood through one-way valves into large arteries:
- The artery going from the right ventricle (pulmonary artery) takes blood to the lungs.
- The artery going from the left ventricle (aorta) takes blood to the rest of the body.
- The heart then rests for a short time (diastole). Blood coming back to the heart from the large veins fills the atria during diastole:
- The veins coming into the left atria bring blood from the lungs (full of oxygen).
- The veins coming into the right atria bring blood from the body (needing oxygen).
What is bradycardia?
Bradycardia means that your heart beats very slowly. For most people, that heart rate is between 60 and 100 beats per minute when resting.
A slow heartbeat (fewer than 60 beats per minute) may sometimes be normal and can be a sign of being very fit. Top athletes may have a pulse rate of fewer than 40 beats per minute. This normal slow heartbeat doesn't cause any problems and does not need any treatment.
However, sometimes bradycardia is caused by an underlying medical condition and does cause symptoms. Bradycardia may be a sign of a problem with the heart's electrical system. It means that the heart's natural pacemaker isn't working right or that the electrical pathways of the heart are disrupted. In severe forms of bradycardia, the heart beats so slowly that it doesn't pump enough blood to meet the body's needs. This can cause symptoms and can be life-threatening.
How common is bradycardia?
Bradycardia is common but most often affects young people who are very fit and the bradycardia is harmless. Bradycardia caused by serious conditions is more common in older people, especially those aged over 65 years.
What are the causes of bradycardia?
Bradycardia is caused by something that interrupts the normal electrical impulses controlling the rate of your heartbeat.
There are many possible causes of bradycardia. Bradycardia may be normal, especially in young very fit people. Otherwise the possible causes include:
- Damage to your heart as you become older.
- Abnormal conduction of the electrical impulse that stimulates the heart to pump blood around your body - for example, sick sinus syndrome or heart block. See separate leaflet called Abnormal Heart Rhythms (Arrhythmias) for more details.
- Damage to the heart caused by a heart attack (myocardial infarction).
- High blood pressure (hypertension)
- Congenital heart disease. (A congenital condition is a condition that you are born with.)
- Infection of heart tissue (myocarditis).
- A complication of heart surgery.
- Underactive thyroid gland (hypothyroidism).
- Medications: some medicines can cause bradycardia - for example, beta-blockers or digoxin.
What are the symptoms of bradycardia?
Bradycardia may not cause any symptoms. However, bradycardia may cause you to feel:
- Dizzy or light-headed. You might even experience faints or sudden collapse.
- Short of breath, especially with exercise.
- Very tired.
- A pain in your chest or a thumping or fluttering feeling in your chest (palpitations).
- Confused or that you are having trouble concentrating.
How is bradycardia diagnosed?
Bradycardia is diagnosed simply by taking your pulse rate and finding a very slow heartbeat.
You will then need further tests to find out the cause of the bradycardia. Your doctor will ask you questions about your symptoms, measure the rate and rhythm of your heartbeat, measure your blood pressure and examine your heart.
The first tests will include blood tests and a tracing of your heart (electrocardiogram).
Bradycardia often comes and goes, so you may need a portable (ambulatory) electrocardiogram. This device is very light. You wear the monitor for a whole day or sometimes longer. The device records your heart rhythm while you go about your daily activities.
What are the treatments for bradycardia?
Always obtain emergency help if you or someone near you has collapsed or if you have symptoms of a heart attack, such as severe chest pain or severe shortness of breath. Call your doctor right away if your heart rate is slower than usual and you feel like you might pass out, or you notice increased shortness of breath.
The treatment depends on the underlying cause and the symptoms. If the bradycardia isn't causing any symptoms there is no need for any treatment unless treatment is needed for the underlying cause of the bradycardia.
If damage to the heart's electrical system causes your heart to beat too slowly, you may need to have a pacemaker. A pacemaker is a device placed under your skin that helps correct the slow heart rate. People who have a pacemaker can lead normal, active lives; however, this will also depend on the underlying condition.
If another medical problem, such as hypothyroidism or an imbalance of salts (electrolytes) is causing a slow heart rate then treating the cause will often cure the bradycardia.
If a medicine is causing your heart to beat too slowly, your doctor may lower the dose of the medicine or change it to a different medicine.
Can bradycardia cause any complications?
For most people, bradycardia will not cause any complications. Any complications will depend on the underlying cause of the slow heart rate.
If severe bradycardia isn't treated, it can lead to serious problems. These may include sudden collapse, fits (seizures) or even death.
What is the outcome (prognosis)?
The outcome will depend on the underlying cause of bradycardia. If treatment is needed, the treatment is usually very effective and the outcome is very good.
Can bradycardia be prevented?
Bradycardia can be caused by heart disease so healthy lifestyle advice is very important. This includes healthy eating, not smoking, reducing body weight (if overweight) and taking regular exercise. See separate leaflet called Preventing Cardiovascular Diseases for more details.
Dr Colin Tidy
Dr Colin Tidy
Dr Hayley Willacy