What is an ECG (electrocardiogram)?

An ECG is one of the tests commonly done when checking for high blood pressure.

ECG stands for electrocardiogram. The term suggests that it has something to do with electricity and the heart (cardio). It is therefore an examination of the heart. The history of the ECG goes back to 1882, when the physiologist Waller succeeded in recording the first ECG. Around 1900, the method was continually developed and refined so that it could be used in clinical practice. In 1924, the Dutchman Willem Einthoven received the Nobel Prize for his groundbreaking advances in the method. He is considered the inventor of the ECG.

How is an ECG performed?

For the ECG the upper body needs to be undressed and the forearms and lower legs must be accessible, because the ECG electrodes are either stuck on or attached to the skin with a slight suction. Both methods are completely painless. If there is a lot of body hair, the required areas are shaved so the electrodes can stick properly.

What types of ECG are there?

In doctors' offices three types are most commonly used: the resting ECG, the stress (exercise) ECG, and sometimes the long-term ECG. There are other types mainly used in hospitals or emergency services. We explain the variants commonly used in general practice.

Resting ECG

A resting ECG is done lying down and only takes a short time. The patient lies relaxed on the exam couch and the electrodes are attached. After a short wait to let the patient settle, the ECG is recorded.

Stress (exercise) ECG

A stress ECG shows the heart's activity during exertion and in the following recovery phase until the body returns to rest. The patient usually sits on a bicycle ergometer (stationary bike), has the ECG electrodes attached, and starts pedaling. The workload increases at set intervals until the person's individual limit is reached - then the recovery phase follows. The ECG is recorded the whole time so the heart's activity during exercise and in the subsequent recovery period can be observed.

Long-term ECG (Holter)

A long-term ECG is a small box connected by wires to electrodes that are stuck to the patient's chest. The patient then wears the device (hung around the neck or strapped on) and keeps it on continuously until the next day. During that time the ECG is recorded. This lets the doctor see how the heart behaved while the device was worn.

What does an ECG record?

Just before each heartbeat an electrical impulse forms in the heart and spreads like a wave across different areas of the heart, causing the heart muscle fibers to contract. This is called electrical conduction.

These weak currents can be measured through electrodes on the skin and displayed by the ECG device as lines, waves, and spikes - the so-called ECG trace. The ECG trace therefore maps the sequence of electrical activity in the heart.

Most practices use a 12-lead ECG, in which a total of twelve electrodes are attached to the upper body, arms and legs. This produces twelve different leads that are highly informative.

What does the doctor see on an ECG?

First of all, the heart rhythm can be seen - the more or less regular sequence of peaks. This also shows how fast the heart is beating. The shapes and sequences of the lines, waves, and peaks tell the doctor much more about the heart. The doctor can observe how electrical impulses are generated, spread, and subside. In addition to the heart rhythm and rate, this also allows the doctor to draw conclusions about the heart's atria and ventricles (whether the heart is enlarged, whether there is an acute or previous heart attack, and similar findings).

This makes the ECG an important and very informative test that can point the way to the next steps.

ECG devices for home use and smartwatches

Various compact ECG devices are available that are suitable for patients to use themselves. These devices record the heart rhythm over a short period - usually about 30 seconds - and some provide immediate feedback on whether any abnormalities are present. Most of these devices use a single lead and do not require adhesive electrodes. The device is held between the hands or against the chest, wrist, or ankle, allowing it to record the heart rhythm. The data are then transferred to an app or software, where they can be documented and, if necessary, presented to the doctor. These 1-lead ECGs provide limited information - they are primarily suitable for detecting abnormal heart rhythms (arrhythmias).

Other devices allow recording a 3-lead ECG using supplied cables and electrodes. That offers more possibilities for interpretation, but it also increases the chance of errors from incorrect electrode placement. Interpreting the recorded ECG is the doctor's responsibility, because it requires the appropriate training and experience.

Several smartwatches also offer ECG recording. These are simple single-lead ECGs that can give information about certain rhythm disturbances. They can be particularly helpful for detecting atrial fibrillation, which often occurs only sporadically.

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This article is from Tensana – the leading app since 2011, helping hundreds of thousands of people monitor their blood pressure every day. Our content is based on carefully researched, evidence-based data and is continuously updated (as of 11/2024).

Author Sabine Croci is a qualified medical assistant with many years of experience in internal medicine and cardiology practices as well as outpatient care, and has headed the specialist editorial team at Tensana since 2015. Thanks to her extensive additional qualifications as an emergency medical technician, first responder, and in various areas of therapy and emergency care, she provides well-founded, practical, and reliably verified information.