EKG: This is what the electrocardiography shows

Electrocardiography, or EKG for short, graphically depicts the electrical processes in the heart muscle. This enables a variety of conclusions to be drawn about the function of the heart

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Routine: almost everyone in Germany receives an EKG sooner or later

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EKG - briefly explained

  • Every contraction (contraction) of the heart muscle is triggered by an electrical excitation. It follows a certain pattern that is repeated with every heartbeat.
  • The voltage changes that arise in the heart are recorded in the EKG on the skin with the help of electrodes. The ECG device amplifies these very weak signals and displays them as a curve, on a monitor or printed out on paper.
  • If interpreted correctly, the EKG provides important information about the function and health of the heart.
  • The abbreviation EKG stands for both the procedure, i.e. electrocardiography, and its visible result, the electrocardiogram.

Brief history of the EKG

As early as 1882, Augustus Desiré Wailer, an English physiologist, recorded the first EKG - from his dog Jimmy. It is primarily thanks to Willem Einthoven that the method also benefited people from the early 20th century. The Dutch doctor improved the technique and laid the theoretical foundations for reading the "heart writing", as they said at the time. For this achievement he received the Nobel Prize for Medicine in 1924. Today it is impossible to imagine everyday medical practice without the EKG.

The sinus accounts in the atria, the AV node, which forwards the excitation via special pathways into the ventricles

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How does an EKG work?

In order for the heart to continuously carry blood through the vascular system, both the heart chambers and the atria must contract and relax again at the right moment. In order to bring about this timed activity of the heart muscle cells, the "pump" has an excitation generation and excitation conduction system.

The sinus node occupies a key position in this system. This is where the electrical excitation occurs, which causes the muscle cells to contract. Because it drives the heart rhythmically and specifies the frequency of the heartbeat, the sinus node is also known as the body's own "pacemaker". It is located in the area of ​​the right atrium.

The electrical impulses emanating from the sinus node are propagated via the excitation conduction system. They first excite the two atria and then, after being passed on via the so-called AV node, the heart muscle cells of the two chambers. These throw the blood into the lungs and the body arteries (aorta). The AV node represents an electrical conduction channel between the atria and the ventricles, which is responsible for the fact that first the atria and then the ventricles are excited. In the course of each cycle, the excitation of the heart muscle cells regresses, again first in the atria and then in the ventricles.

During all these phases there are changes in the electrical voltage in the heart, which - albeit greatly weakened - are passed on to the surface of the body. These voltage fluctuations are continuously picked up by the EKG electrodes attached to the skin. The EKG device records the signals, amplifies them and then displays them as a curve. The printed out electrocardiogram shows this recurring electrical heart action, with the formation, transmission and regression of the excitation.

For the chest wall lead, six electrodes are placed according to a scheme

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How is an EKG done?

Before a routine examination, it will be clarified whether one is taking medication or suffering from underlying diseases, especially of the cardiovascular system. Both can influence the examination result. The normal resting ECG is usually made while lying down, sometimes also while sitting. As a rule, a total of ten electrodes are attached to the body: one on each arm and leg - the so-called limb leads - plus six more at fixed points on the chest, the chest wall leads. A gel improves the contact between the skin and the electrodes. Nowadays, suction electrodes are often used, which have better skin contact due to a weak negative pressure. Here, the moisture from a skin disinfectant spray is sufficient for good contact.

The subsequent writing of the ECG usually takes less than a minute. During this time you are usually asked

  • briefly not to speak
  • to breathe shallowly
  • and avoid large movements.

These activities can lead to incorrect impulses during the recording (artifacts) and thus reduce the quality of the recorded ECG. This makes it harder to correctly assess the EKG. After the derivation and documentation, the evaluation of the electrocardiogram follows. Important criteria are the absolute highs or the lows of the voltage fluctuations, their steepness and duration as well as the time intervals between them. A standardized EKG ruler helps to determine these parameters. For a better differentiation, the spikes in the technical language are identified with the letters: P-Q-R-S-T.

There are also computer programs that evaluate the EKG. They can help with the assessment, but not replace it.

The sinus rhythm: the normal curve of excitation and regression of the heart

© W & B / Jörg Neisel

EKG types and areas of application

There are three different types of ECG:

  • the most frequently performed resting ECG
  • the long-term ECG
  • and the exercise ECG

Long-term ECG and stress ECG are two special forms of electrocardiography. They are used for questions that cannot be adequately answered with a resting ECG.

The long-term ECG

With a long-term EKG, you get a small, portable EKG device that continuously records the cardiac current curve, usually over 24 hours, sometimes over 48 hours or more. The measurement data are then read out on the computer and then evaluated cardiologically. The long-term ECG is mainly used to discover cardiac arrhythmias that only occur temporarily - and therefore may not occur in the period covered by the normal ECG. Activities and complaints that arise are logged during the investigation period. This allows abnormalities in the EKG to be related to corresponding events - for example, sporting activity.

Exercise is encouraged in the exercise ECG

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The exercise ECG

From a purely technical point of view, this EKG is written in exactly the same way as a resting EKG. The difference is that you exert yourself physically during the measurement on a so-called ergometer. The ergometer can either be a stationary bike or a treadmill. Age and fitness determine the initial load, which then increases gradually according to a specified scheme. The following parameters are monitored during exercise and subsequent recovery:

  • the EKG
  • the blood pressure
  • the pulse.

The purpose of the stress ECG is to identify cardiovascular diseases that only become noticeable during physical exertion. For example, circulatory disorders of the coronary arteries (coronary heart disease) or heart failure (heart failure). In addition, this form of electrocardiography can be used to determine the current physical performance in both healthy and sick people.
Especially in the case of elderly or sick people, it may be that such physical stress is not feasible. Then the stress is simulated with the help of a drug that makes the heart work faster and harder. During this time, the heart is examined using ultrasound (dobutamine stress echo).

This change in the ECG curve occurs in the event of an acute heart attack

© W & B / Jörg Neisel

When is an EKG done?

The heart rhythm and the spread of excitation in the heart are visible in the electrocardiogram. It is always made when there is a suspicion of diseases of the heart muscle itself or other factors that impair its function. This includes:

  • Arrhythmias such as atrial fibrillation, slow heartbeat (bradycardia) or heart stumbling (extrasystole)
  • Heart attack
  • coronary heart desease
  • Inflammation of the heart muscle (myocarditis)
  • Inflammation of the pericardium (pericarditis)
  • Certain electrolyte disorders, such as a potassium deficiency
  • Thickening of the heart wall, excessive stress on the right or left heart
  • Overdoses of some drugs
  • Some lung diseases, such as pulmonary embolism

For all of these diseases, electrocardiography also helps to monitor the course and check how well a treatment is working. In addition, the resting ECG is also a component in preparing for surgery if there are risk factors (such as shortness of breath when climbing stairs, frequent stabbing or pressure in the chest).

Very often, an EKG is also written upon presentation to the emergency room. Especially when it should be ruled out that there is a problem with the heart behind the symptoms - such as upper abdominal or back pain.

To put it simply: this is how the heart works

Are there any risks and side effects of an EKG?

Resting and long-term ECGs are completely painless, have no side effects and therefore do not involve any risks. Serious incidents are rare with exercise ECG, but they can happen. Therefore, the investigation is only carried out under supervision. It is canceled if the following symptoms occur:

  • dizziness
  • Chest pain
  • severe shortness of breath
  • excessive rise or fall in blood pressure

In the case of some diseases, the stress ECG may not be carried out at all. These include, for example:

  • acute myocarditis
  • a heart attack less than two weeks ago
  • very high blood pressure values ​​at rest
  • unstable angina.

This is a sharp, attack-like chest pain associated with coronary heart disease.

Prof. Markus Haass

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Consulting expert: Professor Dr. med. Markus Haass is an internist and cardiologist. He is a lecturer at the University of Heidelberg and since 2002 chief physician of the Department of Internal Medicine II with a focus on cardiology, angiology and internal intensive care medicine at the Theresienkrankenhaus Mannheim and since December 2015 medical director of the Theresienkrankenhaus and St. Hedwig-Klinik gGmbH in Mannheim, an academic teaching hospital of the university Heidelberg.

1. Herold G: Internal Medicine 2013, Cologne self-published
2. Professional Association of German Internists. Online: www.internisten-im-netz.de (accessed on July 24, 2013)
3. Wonisch M, Berent R, Klicpera M et al .: Practice guidelines for ergometry. In: Journal of Cardiology 2008, 15: 3-17
4. Ohly A: EKG finally understandable. Munich Urban & Fischer Verlag / Elsevier GmbH 2008

Important NOTE:
This article contains general information only and should not be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor. Unfortunately, our experts cannot answer individual questions.