What is an arrhythmia?
An arrhythmia is an abnormality of heart rhythm or heart rate in which the rhythm is irregular or the rate is excessively slow or fast.
What causes an arrhythmia and who is at risk?
Normally the heart beats regularly at about 70 beats per minute, although it can beat very fast during and following exercise or with fear or anxiety. It can also beat very slowly in healthy athletes at rest. Occasional irregular beats are also normal and can be more frequent after drinking coffee and in early pregnancy.
Arrhythmias result from damage to or an abnormality of the heart’s electrical conduction system, which is responsible for setting the rate and rhythm of the heart. The most common cause is coronary artery disease, especially a heart attack, which interferes with the conduction system. Another common cause is an overactive thyroid (a gland in the neck that produces a hormone that controls the rate of the body’s chemical reactions). Certain medicines can also cause arrhythmias:
- antidepressants such as amitriptyline can cause a life-threatening arrhythmia when taken in higher doses than prescribed,
- medicines such as terfenadine and astemizole used to treat hay fever can cause a life-threatening arrhythmia when taken at higher doses than prescribed, or when taken with other medicines (especially a commonly used antibiotic called erythromycin). Terfenadine can also cause a fatal arrhythmia when taken with grapefruit juice.
A few types of arrhythmias are inherited.
What are the common symptoms and complications of an arrhythmia?
Normally the heart fills with blood between each heart beat, and then pumps this blood out of the heart with each heart beat. The blood supplies the body with the oxygen and nutrients it needs. An arrhythmia can interfere with the heart filling with blood and so the heart pumps out less blood than normal with each beat. If this quantity is a lot less than normal, symptoms occur due to the lack of oxygen reaching the body. The first part of the body affected is the brain and this results in dizziness and faintness. If the lungs do not receive enough blood there is difficulty breathing, and if the heart does not receive enough blood there is heart pain (angina) and may be heart failure.
There are many types of arrhythmia:
- atrial fibrillation (rapid, irregular beats of the upper chambers of the heart) is common in the elderly and also in people who have an overactive thyroid gland; it is not usually life-threatening, but can cause deteriorating heart function,
- ventricular arrhythmias (rapid, irregular beats initiated in the lower chambers of the heart) are most common in people who have had a heart attack or who have heart disease, and are life-threatening. They are the most frequent cause of death in developed countries and are common in the first few days after a heart attack. This is why people who have had a heart attack are monitored for a few days afterwards.
The other main symptom of an arrhythmia is palpitations. This is an awareness of the heart beat, which may seem to be excessively fast or irregular. However, palpitations do not necessarily indicate that there is an arrhythmia unless they are excessively fast or irregular. Palpitations with a normal heart rate are normal, as is an awareness of an occasional missed beat.
How do doctors recognize an arrhythmia?
Many arrhythmias can be seen on an electrocardiogram (ECG). This is an electrical recording of the heart that is obtained by placing small round plates on the chest and recording the electrical activity of the heart. Some arrhythmias only occur intermittently (especially those associated with heart disease) and in this situation continuous monitoring is required to detect the arrhythmia. This can be done at home by wearing a portable recording machine. The times when symptoms are noticed are noted. In this way a continuous recording can be obtained over 24 hours, and the times of the symptoms can be compared with the recording and any arrhythmia diagnosed.
What is the treatment for an arrhythmia?
Self-care action plan
Most arrhythmias cannot be prevented by self care, but a self-care action plan to reduce the risk of developing coronary artery disease and subsequent arrhythmia, and the heart disease that can cause them, involves:
- stopping smoking (which speeds up the heart rate),
- eating a healthy, low-fat, high-fibre diet,
- taking daily exercise as advised by a doctor,
- avoiding stress and anxiety,
- avoiding alcohol (which dulls the nervous system) and coffee (which stimulates the nervous system) if prone to arrhythmias,
- avoiding medicines that might cause arrhythmias (antidepressants such as amitriptyline and the anti-hay fever medicines terfenadine and astemizole).
A variety of prescribed medicines are used to treat arrhythmias. The most commonly used is digoxin. This is used to slow the rate of atrial fibrillation, and so increase heart filling and the amount of blood the heart pumps out with each beat. All anti-arrhythmia medicines can cause life-threatening side effects. They must be used as instructed by a doctor, and any unusual or new symptom must be reported to the doctor immediately.
Atrial fibrillation due to an overactive thyroid reverts to a normal rhythm once the overactive thyroid has been treated.
Electric shock treatment
Some types of arrhythmia that occur after a heart attack are treated by ‘electric shock’. A controlled electric current is passed through the heart and this shocks the heart out of its abnormal rhythm and returns it to a normal regular rhythm.
Pacemakers are used if there is a block in the electrical conduction system of the heart that means that the heart is unable to beat fast enough to supply enough blood to the body. The pacemaker provides the electrical stimulus to make the heart beat faster. It consists of a control box and leads that connect the box to the heart. These leads are inserted into the heart through veins. The pacemaker may be temporary and used only for a few days after a heart attack, or it may be permanent. In permanent pacemakers the control box is a small, specially designed box powered by a lithium battery, and is usually implanted on the front of the left side of the chest.
A few rare types of arrhythmia caused by an abnormal electrical conduction pathway, which is often inherited, are treated by destroying the abnormal part of the pathway using an electric current or a radiowave.
A general anaesthetic is not usually needed for either inserting a pacemaker or destroying the abnormal part of a conduction pathway.
What is the outcome of an arrhythmia?
The outcome of an arrhythmia depends on its type and cause. Many arrhythmias cause few, if any, symptoms, and most can be treated successfully.