Does your doctor read your heart correctly
What is an EKG?
An EKG (electrocardiogram or electrocardiography) is an examination method in which the so-called heart action, the work 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. During the EKG, this weak electrical current is measured using electrodes on the extremities or chest. Depending on how the EKG electrodes are polarized, a distinction is made between bipolar and unipolar leads: A unipolar lead denotes a positive electrode with a neutral reference point. In contrast, electrodes with opposite polarity represent the bipolar lead.
The classic ECG is performed on the lying, relaxed patient and is therefore referred to as a resting ECG. This is in contrast to the stress ECG: Here, the ECG is recorded on the patient during physical exertion - on a treadmill or a bicycle.
Further information: Exercise ECG
You can read how a stress ECG is carried out in the article Stress ECG.
Another special form is the so-called long-term EKG (LZ-EKG), which records the electrical heart activity over 24 hours or even longer.
Further information: Long-term ECG
You can find out what advantages the long-term ECG has and how the measurement works in the article Long-term ECG.
Arousal formation and conduction in the heart
The heartbeat comes about through a special stimulus generation and 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. This is why the sinus node is also called the pacemaker of the heart. The impulse from the sinus node is transmitted to the entire musculature of the two atria, these contract and press the blood into the heart chambers.
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 is now spreading in the ventricles of the heart, the excitation in the atria is already receding, the muscles relax and the atria are filled with blood again. After the ventricles have been completely excited, the stimulus is completely regressed and the heart's action starts all over again.
With an extremity ECG, the doctor attaches three electrodes to the patient's body, which is why it is also referred to as a 3-channel ECG. The extremity leads include the bipolar Einthoven leads (I, II and III) and the unipolar Goldberger leads (aVR, aVL and aVF). This is in contrast to the chest wall lead, in which the doctor uses six different electrodes and places them on the chest wall (V1-6).
In the classic EKG examination, the EKG lead from the chest wall and both extremity leads are combined so that a total of twelve electrodes record the electrical stimuli. This is why the standard ECG is called a 12-lead ECG.
When do you do an EKG?
The electrocardiogram provides the doctor with information about the rhythm, the frequency and the generation, spread and regression of the heart. These are often changed in the following diseases, among others:
- Heart attack
- Coronary artery diseases
- Cardiac arrhythmias (atrial fibrillation and flutter, ventricular fibrillation and flutter)
- Inflammation of the heart muscle (myocarditis) or pericardium (pericarditis)
- Overdose and poisoning with certain drugs (e.g. neuroleptics)
- Deficiency or excess of certain minerals (for example potassium)
- Thickening of the heart wall (right or left heart hypertrophy)
Since some of these conditions are common emergencies, a mobile EKG is available in every ambulance.
Examination is important for these diseases
Read here for which diseases the examination can be useful:
What do you do with an EKG?
An EKG can be done in a doctor's office or in a hospital. During the resting ECG, the patient lies down relaxed on a couch with his torso stripped. Then the doctor or trained medical staff apply an electrically conductive gel to the EKG electrodes and stick them to the patient's skin, depending on the type of lead. The electrodes are connected to the ECG device via cables, which now records the heart's activity. The examination takes about two minutes. The individual phases of the heart's action are shown in characteristic, jagged curves on a strip of paper 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 each of 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 deductions are collected:
- Lead I: between right and left arm; the electrical excitation runs from right to left
- Derivation II: from the right arm to the left leg
- Derivation 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 in a unipolar manner. This results in:
- aVR: right arm
- aVL: left arm
- aVF: left foot
ECG: Chest wall lead according to Wilson
The doctor sticks six electrodes on the patient's chest, starting directly on the right of the sternum and going to the left side chest wall below the armpit. This is how he receives 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) sidewall of the left ventricle
If doctors suspect damage to the back wall, they stick the electrodes down to the left part of the back. This results in the additional leads V7, V8 and V9. They represent the electrical activity on the back wall of the left ventricle. In order to better depict the right heart, the leads V3-V6 can also be affixed 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 safe for the patient. With the stress ECG, on the other hand, the following problems can arise due to physical exertion, especially in patients who have a heart disease:
- Shortness of breath
- Rise or fall in blood pressure
- New arrhythmias (e.g. ventricular fibrillation)
- Chest pain or a feeling of tightness or tightness there (angina pectoris)
- Pulmonary edema (accumulation of fluid in the lungs)
Since the patient is cared for by medical specialists during the entire stress ECG, these problems can be recognized in good time and the examination can be terminated immediately.
More about the symptoms
The examination can be useful if the following symptoms occur:
What do I have to consider after an EKG?
After this EKG the doctor removes the electrodes. The contact gel can be easily removed with a paper tissue without leaving any residue. In principle, no specific precautionary measures need to be observed. The doctor will explain your findings to you based on the recordings and, if necessary, discuss therapy options with you.
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