What is an ECG (electrocardiogram)?

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

Ausschnitt eines EKG (Elektrokardiogramm)

ECG stands for electrocardiogram. The name shows it has to do with "electro" and the heart (cardio) so it is a test of the heart. The history of the ECG goes back to 1882, when the physiologist Waller managed to record the first ECG. Around 1900 the method was further developed and refined so it could be used clinically. In 1924 the Dutchman Willem Einthoven received the Nobel Prize for his groundbreaking improvements to 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 may be 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 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 12lead ECG, where twelve electrodes are attached to the chest, arms and legs. This provides twelve different leads that are highly informative.

What does the doctor see on an ECG?

First of all, the heart rhythm is visible the more or less regular sequence of the spikes. From this you can also tell how fast the heart is beating. The shapes and patterns of the lines, waves and spikes tell the doctor even more about the heart. They can observe the formation, spread and recovery of the electrical impulses. From this, besides rhythm and heart rate, the doctor can also draw conclusions about the heart's atria and ventricles (for example whether the heart is enlarged, or whether there is a recent or older heart attack), and so on.

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

There are various compact ECG devices available that patients can use themselves. These devices record the heart rhythm for a short period usually about 30 seconds and some give immediate feedback on whether any abnormalities are present. Most of these devices use a single lead and dont require sticky electrodes. You hold the device between your hands, against your chest, on your wrist or on your ankle to record the rhythm. The data are then sent to an app or software where they can be stored and, if needed, shared with a doctor. The diagnostic value of these single-lead ECGs is limited they are mainly useful for detecting rhythm problems (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 comes from BloodPressureDB – the leading app since 2011 that helps hundreds of thousands 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 in outpatient care, and has led BloodPressureDB's specialist editorial team since 2015. Thanks to her extensive additional qualifications as a paramedic, first responder and in various therapy and emergency areas, she provides solid, practical and reliably reviewed information.