Arrhythmia

Arrhythmia means a disturbance of rhythm. The disturbance can be either in the rate or in regularity. Normal heart rate is determined by the activity of the sinu-atrial node, and is called sinus rhythm. At rest this is between 60 and 100 beats a minute, and it varies slightly as we breathe in and out (in children by up to 30 beats per minute). It increases with exercise, with our maximum recommended heart rate being 220 minus our age in years. A tachycardia is defined as a heart rate of more than a hundred per minute. This may be normal - a sinus tachycardia during exercise - or it may be abnormal as a result of heart disease, abnormalities in the conducting pathways of the heart (see the Wolf-Parkinson-White syndrome, in the heart and blood vessels disorders section), or conditions such as thyroid disease. An electrocardiogram (recording of the electrical activity of the heart) may help us to determine the origin of an abnormal tachycardia, but other investigations may be required.

The commonest abnormality of rhythm, that we all suffer, is the sensation of the heart "skipping a beat ". In fact it is a result of an extra beat arising in a part of the heart other than the sinu-atrial node, and therefore called an ectopic beat. While they are common in normal people they may be worsened by heart disease. They are increased by nicotine and caffeine and anxiety. There are reduced by exercise.

A heart rate below 60 beats per minute is termed a bradycardia. This may be normal in very fit people, but it may be due to a blockage in the conducting pathways between the atria and the ventricles. This is called heart block, and the heart rate can drop as low as 40 beats a minute, producing syncope or heart failure. It may require treatment using a pacemaker. Rarely, this can be congenital - which means present at birth.

The heart is made up of many individual muscle cells. In order for it to work as a pump these cells must contract together. If they contract individually, in an uncoordinated manner, called fibrillation, then the part of the heart affected fails to function as a pump. If it is the atria affected, causing atrial fibrillation, the pulse rate is irregular. In childhood this is rare (though not in the adult) but it may be caused by congenital abnormality, or as a result of rheumatic fever. It may be reversed by an electric shock - a process called cardio-version. If it is not reversed it may be controlled by drugs such as Digoxin from the foxglove plant. Since people with atrial fibrillation are at increased risk of suffering strokes, they may need treatment to thin the blood.
 
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