Disturbed heart rhythm

Irregular heart rhythms monitored by electrocardiogram

Disturbed heart rhythm, or arrhythmia, occurs when the heart's natural pacemaker develops an abnormal rate or rhythm, the normal blood flow is blocked or another part of the heart takes over as pacemaker.

Normal heartbeats occur at between 60 and 100 beats per minute for adults when resting.

They start in the right atrium, or upper chamber, of the heart sending an electrical signal which spreads to a connecting point to the ventricles, or lower chambers.

The atria contract first, followed by the ventricles a fraction of a second later.

Too slow or too fast

Heartbeats can be too slow, known as bradycardia. A heartbeat of less than 60 beats per minute can cause fatigue, dizziness, light-headedness or fainting.

A heart beat which is too fast, tachycardia, can produce palpitations and is also responsible for dizziness, light-headedness and fainting. Rapid heart-beating in the ventricles can be life threatening.

Ventricular fibrillation, where the lower chambers quiver and the heart cannot pump any blood, leads to collapse and sudden death unless medical treatment is immediately provided.

In atrial fibrillation, where the two upper chambers of the heart - the atria - quiver instead of beating properly, blood is not properly pumped out of the heart. As a result it may form clots and if the clot becomes lodged in an artery in the brain, a stroke may result.

The American Heart Association says around 15% of strokes are caused in this way.

Symptoms

Patients may themselves identify problems with their heart rate or symptoms.

Professor John Camm, professor of clinical cardiology at St George's Hospital, London, said: "Often the patient with a cardiac arrythmia will make specific complaints such as 'I feel my heart beating rapidly' or 'I feel my heart beating slowly and irregularly'.

"Sometimes they have taken their pulse and complain of a slow or fast pulse rate.

"And sometimes they have symptoms which are related to their fast pulse rate such as feeling faint or blacking out. Similarly, a slow heart rate can have these symptoms."

When symptoms are identified, they may be sent to an accident and emergency department or an electrocardiogram may be taken to build up a picture of the heart rhythm defect.

Patients may also be given a recorder to take readings over a 24 hour period or when they notice abnormalities.

The results are analysed by a computer and a decision taken on treatment.

In the case of slow heartbeats, a cardiac pacemaker may be fitted. If the heartbeat is fast, drugs or a procedure which destroys the heart's defective conduction system with radiofrequencies may be used to correct the problem.