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. 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 ischaemic heart disease, abnormalities in the conducting pathways of the heart, 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. They 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.
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