Abnormal heart rhythms Dr Trisha Macnair Not all abnormal heart rhythms (arrhythmias) are dangerous. In fact, an abnormal heartbeat is a common occurrence.

In this article

What causes them?

Symptoms

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.

There are a number of different rhythms which can cause specific conditions:

• 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 isn’t 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.

Patients may themselves identify problems with their heart rate or symptoms. When symptoms are identified, they may be sent to an A and E 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.

This article was last medically reviewed by Dr Jeni Worden in January 2010.