Electrocardiography (EKG) is a non-invasive and painless test aimed at assessing the work of the heart and showing possible disorders in the functioning of the organ. The principle of collecting the ECG signal is based on recording the potential difference (voltage) between the electrodes placed on the chest and on the patient's limbs. The voltage discrepancy results are recorded electronically or on an EKG paper tape in the form of an electrocardiogram. The test results are then analyzed and interpreted by a specialist doctor. Electrocardiography is recommended prophylactically to every person over the age of 40 as a control periodic examination due to the possibility of detecting diseases within the circulatory system that may be asymptomatic.
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Indications for electrocardiography
First, an ECG test is recommended for people diagnosed with cardiovascular diseases, such as atherosclerosis, arrhythmia, cardiac conduction disturbances, inflammation of the heart muscle or pericardium, ischemic heart disease or acquired / congenital heart defects. In the case of ECG measurement in a patient diagnosed with a cardiovascular disease, it is used as a control in order to assess the progress of the disease, changes due to the condition, and the effectiveness of the treatment process. Electrocardiography also allows for premature detection of a heart attack on the basis of disturbing premises such as a feeling of burning or pain in the chest, shortness of breath, severe weakness, feeling anxious or pale with excessive sweating. Testing is also recommended
in the case of people at high risk, i.e. those with
a family history of heart disease or related medical conditions. An EKG is also performed
in people with suspected cardiovascular diseases, performing professions characterized by increased physical activity, taking medications for cardiovascular diseases and before exercise tests.
Contraindications and preparation for the examination
Electrocardiography is a completely safe, non-interfering test
in any way in the patient's body, so it can be carried out in any person without reservation. It does not require any special preparation, but is recommended in the relationship
with examination:
- not consuming cold drinks and coffee before the test is performed;
- avoiding heavy meals due to the risk of increased pressure in the abdominal cavity as a result of an overfilled stomach;
- not smoking for at least one hour prior to the start of the test;
- one day before the examination, no alcohol consumption and cessation of intense physical exertion;
- rest and relaxation for a while before starting the test;
- shaving off dense hair on the chest prior to examination to avoid disturbance in wave conduction or problems with electrode placement;
- it is necessary to inform the doctor carrying out the procedure before starting the procedure about the medicines you are taking, especially those affecting the heart (e.g. affecting the rhythm of the heartbeat);
- not having interviews during the examination;
- not changing position or moving during the measurement;
The recommendations are designed to eliminate factors that could adversely affect or interfere with electrocardiographic measurements, making the results less accurate. For this reason, any factors that may raise blood pressure or disturb the heart in any way should be avoided before the procedure.
How is an EKG performed?
Electrocardiography is a short test that takes only a few minutes together
with electrodes connected to the patient's body. The subject must undress from the waist up to expose the chest and expose the wrists and ankles. All metal parts (e.g. jewelry, watches, glasses, etc.) must be removed prior to testing. Then the patient takes a supine position with the arms stretched along the silhouette. The electrodes are placed in the number of six on the chest, they are in the form of suction cups.
In turn, four electrodes in the form of metal clips are attached to the wrists and ankles. The places where the sensors are attached are wiped with an alcohol solution before the individual tips are mounted. This is to improve the electrical conductivity. Proper placement of the electrodes is important, each of which is assigned a specific point on the body. Red clip connects to right wrist, yellow to left wrist, black (ground)
with the right ankle and green with the left ankle. Low current is released through the electrodes, flows through the patient's body, and returns as a trace on the graph. ECG results are recorded and analyzed and interpreted. The cardiologist then determines the further course of the procedure
depending on the final results.
What is the result of the electrocardiogram and its interpretation?
The ECG test result is recorded on graph paper, thanks to which it is possible to count the heart rate and the duration of individual cycles. Currently, electronic forms of electrocardiogram recording and its analysis in specialized medical programs are also available. An ECG curve is made up of many repeating parts. One particular particle is equal to one cycle of the heartbeat from the moment the blood is pumped into the atria, through the contraction of the atria and the heart chambers, until the blood is pumped out of the organ. The electrocardiogram is difficult to interpret and requires a great deal of experience to be able to read the result correctly.
The EKG graph consists of many components within the heartbeat cycle, including:
Isoelectric line
It provides a reference basis for changes in the graph in the form of deviations. It is a horizontal line that appears when there is no activity. It is usually designated for the segment of PQ markers.
- Waves - deflections from the isoelectric line (positive for upward deflections; negative for downward deflection):
- P wave - an expression of atrial depolarization (positive in all 11 leads, except for aVR (negative));
- QRS complex - corresponds to the depolarization of the ventricular muscle (at this time also the atrial repolarization occurs, which is obscured by the QRS complex);
- U wave (not for every graph) - corresponds to late repolarization of papillary muscles;
- T wave - corresponds to ventricular repolarization;
- Segments - the duration of the isoelectric line between individual waves:
- PQ segment - expresses the time of depolarization conduction through the atrioventricular (AV) node;
- ST segment - defines the period of initial repolarization of the ventricular muscle;
- Spacing:
- PQ interval - expresses the time of depolarization conduction through the entire stimulus-conducting system of the heart, i.e. from the sinoatrial node to the Purkinje fibers, and the resulting depolarization of the atria;
- ST interval - expresses the time of slow and fast repolarization of the ventricular muscle (second and third phase of repolarization);
- QT interval - expresses the action potential time of the ventricular muscle (depolarization with repolarization);
The ECG test can be performed at any age and is the primary diagnostic method used to assess the work of the heart.
Sources:
- A (not so) brief history of electrocardiography, www.ecglibrary.com [dostęp online dnia 2020-06-07].
- Baranowski R., Wojciechowski D. (red.). Atlas EKG. Gdańsk 2012. VIA MEDICA.
- ECG library, www.ecglibrary.com [dostęp online dnia 2020-02-07].
- ECGSIM, www.ecgsim.org [dostęp online dnia 2020-02-07]. Program symulacyjny demonstrujący zależność pomiędzy elektryczną aktywnością serca a wykresem EKG.
- EKG Academy. Learn, Practice, Reference, Clinical Skills Education, 2016 [dostęp 2020-06-07].
- Hampton R. J., Ścibiorski C. EKG w praktyce. Warszawa 1999. Wydawnictwa Lekarskie PZWL.
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- Konturek S. Fizjologia człowieka. Układ krążenia. Kraków 2001. Wydawnictwo Uniwersytetu Jagiellońskiego, s. 51-54.
- Ocena morfologiczna elektrokardiogramu. [W:] Barbara Dąbrowska, Andrzej Dąbrowski: Podręcznik elektrokardiografii. Warszawa 2005. Wydawnictwo Lekarskie PZWL, s. 54-55.
- Sekcja Elektrokardiologii Nieinwazyjnej i Telemedycy PTK, senit.pl [dostęp online dnia 2020-06-07].
- Składowe prawidłowego elektrokardiogramu. [W:] Tomasz Tomasik, Adam Windak, Anna Skalska, Jolanta Kulczycka-Życzkowska: Elektrokardiografia dla lekarza praktyka. Kraków 1996. Uniwersyteckie Wydawnictwo Medyczne "Vesalius", s. 21-35.
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