- An arrhythmia is any deviation from the normal rhythm of the heart. The normal heart rhythm is called sinus rhythm.
- Arrhythmias are important as they cause unpleasant symptoms, which may progress to serious complications. Some may even be life-threatening.
- Arrhythmias may result from most heart diseases and can occur without apparent cause.
- The details given by the patient, plus examining the pulse and listening to the heart sounds, will make a clinical diagnosis.
- Arrhythmias are best treated by referral to a specialist cardiologist. Any identified underlying disorder contributing to the arrhythmia must be treated in its own right.
- With appropriate treatment, most arrhythmias will revert to normal sinus rhythm.
What causes it?
The heart has what is called a natural pacemaker – a series of cells which generate electrical currents in the wall of the heart. This natural pacemaker is called the sino-atrial node (SA node) and is situated in the wall of the right atrium.
This SA node controls the rate and rhythm of the whole heart. It is under the control of the autonomic part of the nervous system, which is not under conscious control but which is responsible for the control of bodily functions such as the beating of the heart, intestinal movements, sweating, the production of saliva and other similar functions.
Any condition or substance affecting the autonomic system can thus affect the function of the SA node.
The SA node generates electrical impulses which spread to the atria and ventricles through specialised conducting tissues. This causes the two parts of the heart to contract normally. Arrhythmias, which may be continuous or intermittent are the result of disturbances either of the generation of these impulses, or of their conduction.
Different types of arrhythmias include:
- Ectopic beats, also called extrasystoles. These are heartbeats which are due to an impulse generated somewhere else in the heart outside the SA node. If they originate in the atria, they are called supraventricular. If they arise in the ventricles, they are called ventricular. They may be produced by any heart disease, caffeine or from smoking. They are common in normal people who may be unaware of them, or may feel that the heart has "missed a beat".
- Bradycardia, in which the heart rate is slower than normal, and tachycardia, in which the heart rate is faster than normal.
- Fibrillation is a rapid and chaotic beating of the many individual muscle fibres of the heart. This stops the heart from maintaining its effective and synchronous contraction, which is vital to its function. The affected part of the heart ceases to pump blood.
- Heart block, which is often associated with slow heart rates. This is a condition in which conduction of the electrical impulses generated by the SA node is impaired, causing the pumping action of the heart to slow down.
Associated risk factors include:
- underlying heart disease, e.g. coronary artery disease or valve dysfunction
- stimulants - either exogenous, e.g. caffeine, or endogenous, e.g. thyroid hormone
- advancing age
- certain medications, e.g. theophylline
Symptoms and signs
The symptoms include:
- palpitations, which is the term used for a conscious perception of an abnormal heart rhythm
- chest pain
- worsening of angina or heart failure
- extreme fatigue
In the more serious arrhythmias, the Stokes-Adams syndrome or cardiac arrest may occur. The Stokes-Adams syndrome is a temporary loss of consciousness that occurs when blood flow stops due to fibrillation of the ventricles of the heart or because the heart stops beating. This syndrome may complicate heart block.
Cardiac arrest describes the stopping of effective pumping action of the heart. This most commonly occurs when the muscle fibres of the ventricles start to beat rapidly without pumping any blood (ventricular fibrillation) or when the heart stops beating completely (asystole).
Who is at risk?
Arrhythmias may result from most heart diseases and can occur without apparent cause. Often, degeneration of the conducting system of the heart is related to advancing age or is associated with heavy smoking.
Some non-cardiac disorders are associated with arrhythmias, e.g. thyroid dysfunction.
Mostly, though, the patient has some type of underlying heart problem, e.g. valve disease, coronary artery disease, heart failure, damage from a heart attack, cardiomyopathies or congenital defects. Some patients have abnormal conduction pathways causing a tachyarrythmia.
How is it diagnosed?
The details given by the patient, plus examining the pulse and listening to the heart sounds, will make a clinical diagnosis. A 12-lead ECG will confirm and/or clarify the particular type of arrhythmia.
As some arrhythmias are intermittent, they may not be present when the ECG is done. In these cases, cardiologists can do Holter monitoring. Here the patient wears a mini ECG recorder for 24-48 hours while he/she carries on with normal activities. Any arrhythmia occurring during that time will be recorded for analysis.
How is it treated?
Arrhythmias are best treated by referral to a specialist cardiologist. Any identified underlying disorder contributing to the arrhythmia must be treated in its own right. The goal of therapy is to eliminate symptoms and/or prevent a potentially serious outcome such as a life-threatening arrhythmia and sudden death.
The arrhythmia will need to be normalised, by being slowed down, speeded up or made more regular. This may require emergency treatment. Treatment of the arrhythmia can be with medication, e.g. beta blockers or amiodarone. Very slow heart rates and heart block may need temporary or permanent pacemakers. In some patients, the abnormal pathway can be identified and destroyed, allowing the SA node impulses to flow along the normal pathways again.
The type of treatment used will depend on the type of arrhythmia, and the technical expertise available to the cardiologist. Careful monitoring during treatment is essential, as some of the drugs can paradoxically worsen the condition.
What is the outcome
With appropriate treatment, most arrhythmias will revert to normal sinus rhythm. Some types not responding to drug treatment may benefit from invasive techniques, such as ablation of the SA node with pacemaker insertion.
Atrial fibrillation (AF) is a common arrhythmia, and is often resistant to treatment. It may persist even after correction of related underlying cardiac problems, e.g. valve replacement or bypass surgery, especially if AF has been present for a long time.
If, with treatment, the patient becomes symptom-free, despite continued AF, then a recognised outcome is to merely control the ventricular rate (using beta blockers or digoxin), plus effective anticoagulation with warfarin. Because AF results in no effective atrial contraction, there is a very high risk of clots forming in the heart, with a possible fatal outcome – hence the need for warfarin to be used for as long as the AF persists.
Advancing age, the presence of congenitally abnormal conduction pathways, and congenital heart defects cannot be prevented. However, stimulants can be avoided, while stopping smoking will decrease the autonomic stress on the heart. Weight loss, too, will indirectly relieve the load on the heart.
When to see a doctor
If you experience any of the symptoms described above, a doctor should be consulted as soon as possible.
Should a known heart problem, or any of the associated risk factors already exist and symptoms of an arrhythmia develop, a cardiologist should be consulted urgently.
Reviewed by Dr A.G. Hall (B.Soc.Sc.(SW), MB,Ch.B)