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ECG: reasons, process and significance

by Josephine Andrews
Published: Last Updated on 444 views

ECG stands for electrocardiogram and refers to an examination method in which the electrical activity of the heart is measured. The so-called heart action is derived via electrodes and recorded in the form of curves. The doctor can use this to assess whether the heart is functioning properly. Here you can read everything about the ECG, how the examination is carried out and which patients it is used on.

What is an ECG?

An ECG (electrocardiogram or electrocardiography) is an examination method in which the so-called heart action, the working cycle of the heart, is measured. The heartbeat is triggered by an electrical excitation that is clocked by the so-called sinus node and spreads through the heart muscle cells. This weak electrical current is measured in the ECG via electrodes on the extremities or chest . Depending on how the ECG electrodes are polarized, a distinction is made between bipolar and unipolar leads: A unipolar lead designates a positive electrode with a neutral reference point. On the other hand, electrodes with opposite polarity represent the bipolar lead.

The classic ECG is performed on a lying, relaxed patient and is therefore referred to as a resting ECG. In contrast to this is the stress ECG : Here, the ECG is derived from the patient during physical exertion – on a treadmill or a bicycle.

Further information: Stress ECG

You can read about how a stress ECG is carried out in the article  Stress ECG .

Another special form is the so-called long-term ECG (LZ-EKG), which records the electrical activity of the heart over 24 hours or longer. 

Further information: long-term ECG

You can find out what advantages the long-term ECG has and how the measurement is carried out in the article  long-term ECG .

Excitation formation and excitation conduction in the heart

The heartbeat comes about through a special stimulus generation and stimulus conduction system : It begins with an electrical impulse in the so-called sinus node, an area in the right atrium of the heart that sets the pace, so to speak. That is why the sinus node is also known as the pacemaker of the heart. The impulse from the sinus node is transmitted to the entire musculature of the two atria, which contract and press the blood into the ventricles.

The electrical impulse then reaches the so-called AV node , which transfers the electrical stimulus from the atria to the ventricles. These then contract and transport the blood into the large body vessels. While the stimulus spreads through the ventricles, the excitation in the atria is already receding, the muscles relax and the atria fill with blood again. After the chambers of the heart have been fully stimulated, the stimulus also returns here completely and the heart action starts all over again.

ECG leads

With an extremity ECG, the doctor attaches three electrodes to the patient’s body, which is why it is also called a 3-lead ECG. Limb leads include the bipolar Einthoven leads (I, II, and III) and the unipolar Goldberger leads (aVR, aVL, and aVF). In contrast to this is the chest wall lead, in which the doctor uses six different electrodes and places them on the chest wall (V1-6).

In the classic ECG examination, the ECG lead from the chest wall and both extremity leads are combined so that a total of twelve electrodes record the electrical stimuli. Therefore, the standard ECG is called a 12-lead ECG.

When is an EKG done?

The electrocardiogram provides the doctor with information about the heart’s rhythm, frequency, and the generation, propagation and regression of excitation. These are often altered in the following diseases, among others:

Since some of these diseases are common emergencies, a mobile ECG is available in every ambulance.

What do you do with an EKG?

An EKG can be performed in a doctor’s office or in a hospital. During the resting ECG, the patient lies relaxed on a couch with their upper body bare. Then the doctor or trained medical assistant applies an electrically conductive gel to the EKG electrodes and sticks them to the patient ‘s skin depending on the type of lead . The electrodes are connected via cables to the ECG device, which now records the heart’s activity. The examination takes about two minutes. The individual phases of the heart’s action are depicted in characteristic jagged curves on a paper strip against a time axis. Each rash represents a specific phase of the heartbeat.

Further information: ECG: Evaluation

You can read about the types of spikes and waves, what they should look like and what they mean in the article  ECG: Evaluation .

ECG: limb leads

In the Einthoven derivation, the doctor sticks an electrode on the patient’s wrists and a reference electrode above the ankle of the left leg. The electrodes are connected in a bipolar manner. The following derivations are collected:

  • Lead I: between right and left arm; the electrical excitation runs from right to left
  • Lead II: from the right arm to the left leg
  • Lead III: from the left arm to the left leg

With the Goldberger lead, the doctor also sticks the electrodes to the wrists and ankles of the left leg, but in contrast to the Einthoven lead, he connects them unipolarly. This results in:

  • aVR: right arm
  • aVL: left arm
  • aVF: left foot

ECG: chest wall lead according to Wilson

The doctor places six electrodes on the patient’s chest, starting just to the right of the breastbone and ending on the left lateral chest wall below the armpit. This is how he gets the leads V1 to V6, each of which is responsible for a specific area of ​​the heart muscle:

  • V1 and V2: anterior wall of the heart chambers
  • V3 and V4: Anterior wall of the left ventricle
  • V5 and V6: (deep) side wall of the left ventricle

If doctors suspect damage to the back wall, they stick the electrodes to the left part of the back. This results in the additional leads V7, V8 and V9. They represent the electrical activity on the posterior wall of the left ventricle. In order to better image the right heart , leads V3-V6 can also be glued mirror-inverted to the right side of the chest wall (V3r-V6r).

What are the risks of an EKG?

The resting and long-term ECG are non-invasive and painless examination methods that are not dangerous for the patient. With a stress ECG, on the other hand, physical exertion can cause the following problems, especially in patients with heart disease:

Since the patient is cared for by medical specialists throughout the entire stress ECG, these problems can be identified in good time and the examination stopped immediately.

What do I have to consider after an ECG?

After the EKG , the doctor removes the electrodes. The contact gel can be easily removed with a tissue without leaving any residue. Basically, there are no specific precautions to be taken. The doctor will use the leads to explain your findings and, if necessary, discuss treatment options with you.

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