An ECG is a recording of the electrical activity of the heart. The normal heart displays a specific pattern of activity during each beat. A wave of nerve stimulation that causes the heart to contract starts in the natural pacemaker of the left atrium (upper chamber) and spreads to the right atrium, and then passes through a special conducting pathway to the ventricles (lower chambers). A recording made of the wave pattern typically shows a small ‘blip’ as the atria contract, then a gap, followed by a larger peak as the ventricles contract. If the heart is not functioning normally – if its beats are irregular, for example, or if the nerve impulses are conducted through the heart too slowly -the pattern of the waves is altered. This makes the
ECG useful in diagnosing blocks to contraction, palpitations, fibrillation, coronary thrombosis, angina and cardiac arrest.
When an ECG is taken, electrodes are attached to the person’s wrists and ankles by rubber bands and to various positions on the chest by a suction pad, so that different ‘views’ of the heart’s activity can be recorded. Wires from the electrodes lead to the ECG machine, or electrocardiograph, which produces a graphical record of the wave forms. A routine ECG recording takes only a few minutes and is sufficient for most needs, but it cannot detect every abnormality of heart functioning. It may be, for example, that the heart’s rhythm is normal at rest and only becomes abnormal when it is working hard. In this case, a recording is taking during exercise, usually while the person walks on a moving belt (treadmill), the speed of which is adjustable to vary the effort needed. This is often called an ‘exercise ECG’. Sometimes a person has intermittent irregularities of the heartbeat, perhaps causing occasional periods of giddiness for a few minutes. Unless these actually occur when a recording is being carried out they will not be revealed. It may then be necessary for a full 24-hour record of the heart’s activity to be obtained. For this the person wears the standard electrodes and a small, portable, ECG machine on a belt, which monitors the heart’s activity continuously and records it. Both EEG and ECG recordings are relatively simple, non-painful examination methods that can reveal a number of irregularities and disorders. As such they are helpful diagnostic tools.