ECG: Everything You Need To Know About Electrocardiogram
Photo by Stephen Andrews:

The electrocardiogram is an examination that records the electrical activity of the heart, as the heartbeat progresses.

Indeed, the heart, like all muscles, contracts under the influence of successive electrical impulses (polarizations and repolarizations), which can be detected and recorded.

In reality, the electrocardiogram refers to the trace of the electrical activity obtained; the test is called electrocardiography (ECG).

Why have an electrocardiogram?

The ECG is an essential examination in cardiology. It may be prescribed in many situations:

  • in case of chest pain
  • to detect arrhythmias (heart rhythm disorders)
  • to detect other heart disorders such as coronary heart failure (blockage of the arteries supplying the heart), the presence of damaged areas in the heart (due to a lack of irrigation or a recent heart attack), dilation of the heart, etc.
  • to monitor cardiac activity in cases of known heart disease
  • in case of emergency admission for chest pain
  • during a pre-operative assessment

In all these situations, the electrocardiogram is abnormal.

The exam

This is a non-invasive and painless examination.

The principle is simple. By sticking electrodes to the surface of the skin, on the chest, it is possible to record the difference in “potential” (electrical difference) between two diametrically opposed points with respect to the heart, and thus to record the electrical activity of the heart.

In practice, to perform an ECG, many electrodes (between 12 and 15) are used, placed on the chest but also on the arms and legs.

If necessary, the skin is first washed and dried, and shaved, to allow better adhesion. The electrodes are fixed using adhesive stamps.

The ECG is recorded, most often lying down, for 5-10 minutes, sometimes longer. The plot is done automatically on a roll of paper that unfolds gradually.

What results can be expected from an electrocardiogram?

The normal ECG has a so-called “sinus” tracing, with different electrical periods.

The doctor will interpret the traced obtained to detect any abnormalities, these may concern:

  • frequency (normally between 60 and 100 beats per minute)
  • the nature of the rhythm (e.g. absence of one of the normal elements of the curve);
  • the amplitude of certain waves;
  • the duration of the interval between others.

Depending on the results, he may guide the diagnosis and request, if necessary, the performance of additional examinations such as a stress ECG.

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