Abnormal Heart Rhythms Arrhythmias

Authored by Dr Colin Tidy, 21 Sep 2017

Patient is a certified member of
The Information Standard

Reviewed by:
Dr Adrian Bonsall, 21 Sep 2017

Some normal variations

Sinus tachycardia

This means a normal heartbeat which is faster than usual - more than 100 beats a minute (bpm). This is usual when you exercise. It may also occur if you:

  • Are lacking in iron in the blood (anaemic).
  • Have a raised temperature (fever).
  • Have an overactive thyroid gland.
  • Are frightened (when you release adrenaline (epinephrine) into the bloodstream, which can speed up the heart).

Sinus bradycardia

This means a normal heartbeat which is slower than usual (fewer than 60 bpm). Many people who are very fit have a heart rate between 50 and 60 bpm - sometimes slower. It may also occur if you have an underactive thyroid gland. Read more about bradycardia.

Ectopic beats

These are extra heartbeats which occur out of sync to the normal regular rate. They are very common and are usually harmless. Most people with normal hearts have at least one ectopic beat a day. You do not normally notice them. Sometimes you may notice them as a slight thud in the chest if you are lying still in bed. Caffeine in tea or coffee, and alcohol may cause you to have more ectopic beats than usual. Some people with some types of heart disease have frequent ectopic beats.

What are arrhythmias?

An arrhythmia is an abnormal rate and/or rhythm of the heartbeat. There are various types but all are due to some problem with the electrical conducting system of the heart. Some arrhythmias are more serious than others. Some come and go (are intermittent); others are permanent unless treated. The main types of arrhythmia include the following:

Supraventricular tachycardia

In supraventricular tachycardia (SVT) the heartbeat is not controlled by the SA node (the normal timer of the heart). Another part of the heart overrides this timer with faster regular impulses. Read more about supraventricular tachycardia.

Atrial fibrillation

In atrial fibrillation (AF) many random electrical impulses 'fire off' from different parts of the atria. The atria then fibrillate. This means they only partially contract - but very rapidly (up to 400 bpm). Only some of these impulses pass through to the ventricles in a haphazard way. So, the ventricles contract between 160 and 180 bpm, but in an irregular way with varying force. See separate leaflet called Atrial Fibrillation.

Atrial flutter

Atrial flutter is similar to atrial fibrillation (AF). The atria contract at about 300 bpm but the ventricles are unable to beat that quickly and so beat at between 75 and 150 bpm.

Ventricular tachycardia

This is an uncommon arrhythmia. In this condition the ventricles beat faster than normal (between 120 and 200 bpm). The rate in the atria is normal. So, there is a trigger of electrical impulses somewhere in the ventricles which overrides the normal impulses coming down from the atria.

Ventricular fibrillation

In ventricular fibrillation (VF) many random electrical impulses 'fire off' from different parts of the ventricles. This is called fibrillation. This means the heart muscle only weakly contracts and this is not enough to push blood out of the heart. This is life-threatening and a common cause of the heart stopping (cardiac arrest). It is fatal unless corrected within a few minutes. It is a complication of various heart disorders, most commonly after a large heart attack (myocardial infarction).

Heart block

This occurs when the electrical impulses are partially or fully blocked between the atria and the ventricles. The SA node in the right atrium 'fires' at the normal rate but the rate at which the ventricles contract (pulse rate) depends on how many impulses get through to the ventricles.

  • First-degree heart block means there is a slight delay in each impulse going from the atria to the ventricles. But, each impulse does get through and the heart rate is normal.
  • Second-degree heart block means that some impulses from the atria are not conducted through to the ventricles. The rate that the ventricles contract can then be slow.
  • Third-degree, or complete, heart block means that no impulses are conducted through. The ventricles then contract at their own in-built rate of about 20-40 bpm. So, you have a very slow pulse.

Sick sinus syndrome

In this condition the SA node - the heart's natural pacemaker - becomes damaged. The heart then tends to beat slowly or miss a few beats. But, in some cases, the heart alternates between beating slowly for a while and then fast for a while.

What are the causes of arrhythmias?

There are various causes of abnormal heart rhythms (arrhythmias). They include the following:

Heart conditions

Many arrhythmias occur as a complication of a heart condition. For example:

  • Coronary heart disease (which causes angina and heart attacks). This reduces the blood supply to parts of the heart which may include parts of the conducting system. A damaged section of heart muscle (following a heart attack) can trigger an arrhythmia, or block electrical impulses.
  • Heart valve diseases can cause the heart muscle to enlarge which can trigger abnormal electrical activity. For example, AF is a common complication of mitral valve disease.
  • High blood pressure (hypertension) can put strain on the heart and cause arrhythmias.
  • Ageing (age-related degeneration) around the conducting fibres is one cause of complete heart block.
  • A disorder of the heart muscle (cardiomyopathy) can sometimes cause arrhythmias. See separate leaflets called Dilated Cardiomyopathy and Hypertrophic Cardiomyopathy.
  • Congenital:
    • Some arrhythmias are due to abnormalities in the electrical pathways, which are present from birth. One example is an extra electrical pathway which sometimes develops between the atria and ventricles. This can cause a type of SVT. (However, symptoms may not first start until you are a young adult.)
    • Some congenital heart defects are associated with certain arrhythmias. A congenital condition is one you have when you are born.
  • Inflammation of the heart and other less common heart disorders are other possible causes.

Non-heart causes

  • Certain medicines and excess thyroid hormone (hyperthyroidism) can sometimes trigger an arrhythmia.
  • In some cases the cause is not clear. For example, some cases of AF and SVT occur out of the blue in otherwise healthy hearts. A section of the conducting fibres just becomes faulty and can trigger fast impulses.

What are the symptoms of arrhythmias?

Symptoms can vary, depending on the severity of the condition. If the abnormal heart rhythm (arrhythmia) comes and goes (is intermittent), the symptoms develop suddenly and can go just as suddenly. Symptoms can include:

  • The sensation of having a 'thumping heart' (palpitations). But note: sensations of palpitations are also common in people who do not have an arrhythmia. This is why it is important to see a doctor for correct diagnosis.
  • An abnormally fast, slow, or irregular pulse.
  • Dizziness or feeling faint.
  • Shortness of breath.
  • Chest pains which sometimes develop.

Some arrhythmias are more serious than others. A heart rate that is very fast or very slow can result in too little blood flowing through the heart. In some cases this can lead to heart failure, or you may collapse.

It can be very difficult to detect an arrhythmia in a young child, when the only clue may be a change in behaviour or a problem with feeding.

Do I need any tests?

Sometimes a doctor can easily diagnose that you have an abnormal heart rhythm (arrhythmia) by taking your pulse and examining you.

However, some people have symptoms which come and go (are intermittent) and which may or may not be due to an arrhythmia. For example, some people who have the sensation of a 'thumping' heart (palpitations) may have ectopic beats, or may be just more aware of their normal heartbeat.

Some people have dizzy spells, or fainting attacks which may be due to an intermittent arrhythmia. Tests can help to confirm if you have an arrhythmia and to find which type it is.


A heart tracing (electrocardiogram, or ECG) test is painless and harmless. Small metal electrodes are stuck on to your arms, legs and chest. Wires from the electrodes are connected to the ECG machine.

The electrical impulses in your heart can be detected by the ECG machine which records them on to a paper or computer. An ECG can confirm if you have an arrhythmia at the time of the test. Different arrhythmias cause different ECG patterns, so this test can often clarify the type of arrhythmia.

Ambulatory electrocardiogram

If you have an intermittent arrhythmia, this may not be detected by a standard ECG done at one particular time. You may then be advised to have an ambulatory ECG. This test records the electrical activity of your heart when you are walking about (ambulatory) and doing your normal activities.

Wires from electrodes placed on your chest are connected to a small lightweight recorder. The recorder is attached to a belt which you wear around your waist. The electrical activity is usually recorded for 24-48 hours.

You will be given a diary to record the times when you develop any symptoms (such as palpitations). The ECG tracing is analysed at the end of the test. But, any times you record where symptoms occurred will be most carefully analysed to see if there was an arrhythmia to account for the symptoms.

Exercise electrocardiogram

Sometimes an ECG is taken whilst you exercise on a treadmill or bike to try to provoke symptoms which may be an intermittent arrhythmia.

Other more sophisticated tests may be advised in difficult cases.

What are the treatments for arrhythmias?

Each type of abnormal heart rhythm (arrhythmia) has specific treatment options. Also, treating any underlying cause - such as coronary heart disease, or high blood pressure (hypertension) - may also be important in controlling certain arrhythmias. The following are the sort of treatments which may be considered:


Various medicines can interfere with the electrical impulses in your heart. They are often used to prevent intermittent arrhythmias, or to control the heart rate in AF.

Catheter ablation treatment

Catheter destruction (ablation) treatment is an option for some cases of SVT, ventricular tachycardia and AF. A small wire (catheter) is passed via a large vein in your leg into the chambers of your heart. It is guided by special X-ray techniques. The tip of the catheter can destroy a tiny section of heart tissue that is the source or trigger of abnormal electrical impulses. This treatment is suitable only if the exact site of the trigger can be found by special tests, and be found very accurately by the catheter tip.


This may be an option for some types of tachycardia - for example, in some cases of AF which have recently developed and some cases of ventricular tachycardia. Whilst under anaesthetic, you are given an electrical shock over the heart. This may revert the abnormal rhythm back to normal.

Artificial pacemakers

These are used in cases of complete heart block and in certain other situations. An artificial pacemaker is a small device which is inserted just under the skin on the upper chest. Wires from the pacemaker are passed through veins into the heart chambers. The pacemaker can then stimulate the heart to maintain a regular normal heartbeat.

Implantable cardioverter defibrillators

Implantable cardioverter defibrillators (ICDs) are sometimes used in difficult cases. They are small devices which are similar to pacemakers and are inserted under the skin in the upper chest. Wires are passed through a vein to the heart. The device monitors the heartbeat. If it detects a change to an abnormal rhythm, the device can send a short electrical shock to the heart to stop the abnormal rhythm.

Further reading and references

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