This stimulus skips from one muscle cell to another in a domino effect. The stimulus guidance system ensures that this is done in the right order: first the bosoms and then, after a short delay, the rooms. If it does not go well, a cardiac arrhythmia occurs.
Most heart diseases have consequences for the stimulus control system and therefore leave traces on an ECG.
In order to quickly recognize a heart attack, an ECG is an important study.

ECG Mountain
Stage The graph of an ECG can be compared to a mountain stage. Vertically, on the graph of the mountain stage is the height difference and on the ECG the power of the electric stimulus in voltage. Horizontally, at the mountain stage, the distance, on the ECG the duration in seconds.
What does a doctor see on an ECG?
An ECG provides a lot of information about heart disease. Is there even a case of heart disease? Or is it an innocent anomaly? Is it a cardiac arrhythmia or is it a heart attack from years ago? In case of chest pain, an ECG can show whether or not it is caused by angina pectoris.
Many heart diseases are only visible on the ECG when the heart is put under extra
strain. Therefore, an ECG is also often taken during an exercise test. An ECG has numerous applications, such as monitoring the heart rhythm in the ambulance or on cardiac monitoring. Most doctors and hospital staff recognize important abnormalities on the ECG such as a heart attack. But other heart diseases such as a cardiac arrhythmia or a heart attack from the past are sometimes difficult to spot on an ECG. Usually it takes a cardiologist.

photo An ECG with eight distractions: four on the chest, two on the upper arms and two on the lower legs.
Fixed points on
an ECG The electric wave through the heart begins in the sinus node, a group of muscle cells in the ceiling of the right bosom. This moment is not on an ECG. The moment the stimulus begins, the line is completely flat and horizontal. The first bump is caused by the electrical activity that spreads through the bosoms from the sinus node. This bump is called the P-top. Then the line becomes flat again, because the stimulus is briefly held up in the AV node. Then the stimulus activates the strong and thick muscle of both ventricles. At that time, the electrical activity is highest and the striking peak in the ECG occurs. The beginning of this peak is marked with the letter Q, the highest point with the letter R and the end with the letter S. The entire peak is called the QRS complex. After the QRS complex, the line becomes flat again, after which a second bump follows. This is caused by the electrical activity in the chambers as the heart muscle recovers and prepares for the next heartbeat. That second bump is the T-top.

Four phases
ECG Four
phases of a heartbeat A. The electrical stimulus begins in the sinus node located in the ceiling of the right bosom. Duration: about 0.11 seconds or less. Name: P-top.
B. After that, the electrical stimulus is briefly held up in the AV node. Duration: 0.2 seconds.

Name: PR segment.
C. The electrical stimulus spreads over the muscle wall of the chambers, which therefore squeeze vigorously. Duration: 0.08-0.10 seconds. Name: QRS complex.
D. Recovery phase. Name: T-top.
an ECG An ECG is quick and easy. First, electrodes are stuck on the skin. With an extensive ECG, there are several: two on the wrists, two on the ankles and six on the chest. For someone who is in a hospital bed and whose heart rate is observed, three or four electrodes are enough.
Why so many electrodes?
By measuring the electrical activity from different angles, a better picture is created, because the electrical stimulus moves in a certain direction, from the sinus node at the top right to the bottom of the heart. As a result, the different measuring points give different results, from which a trained ECG reader can make a lot of ground. The measuring points have fixed names: I, II, III and AVR, AVL, AVF for the ankles and wrists and V1 to V6 for the fixed measuring points on the chest. A device prints the heart rate chart on diamond paper. The smallest square on the paper is by default one millimeter high and one millimeter wide. The horizontal distance between two points is determined by the speed at which the window paper rotates through the device. In one second, the paper rolls exactly 25 millimeters further. A second is about the duration of a normal heart rate, from the beginning of the P-top to the end of the T-top. The power of the electrical stimulus is expressed vertically in voltage, with 10 millimeters standing for 1 millivolt.


G without deviations

Reading an
ECG An ECG gives a lot of information, but is not easy to use. Small deviations of a few millimeters can be very important, striking deviations just not. It requires a trained eye to properly assess the information. However, a trained eye may also be wrong, which is why the so-called Minnesota criteria set out what is normal and what is not. A cardiologist knows those criteria from the outside. Recognizing myocardial infarction
On an ECG, an acute heart attack can be identified by an abnormality in the line between the QRS complex and the T-top, or the ST segment.

This line is higher than normal during a heart attack. Doctors speak of elevation of the ST segment and distinguish between a heart attack and a heart attack without elevation of this segment.
The increase in the ST segment is due to the fact that part of the heart muscle no longer receives oxygen due to myocardial infarction.
This is visible due to increased electrical activity in the recovery phase after the chambers contract.

ECG Heart Attack
Heart Attack: ST Segment Is Elevated. Right: ECG without deviations.
Chest pain (Angina pectoris)
If someone has chest pain, a doctor cannot always tell directly whether it is angina pectoris. The pain can also be caused by something other than poor blood flow of the heart muscle. The ECG provides important information for diagnosis, especially when it comes to the stable form of angina pectoris. This form only occurs with effort. A person who reports to the doctor with chest pains will therefore probably be subjected to an exercise test.
If the pain is indeed caused by angina pectoris, it becomes visible during the exercise
test. On the ECG, during the attack, the line between the QRS complex and the T-top, the so-called ST segment, is lower than normal. The doctor will carry out further examination. If the person undergoing the exercise test does not suffer and the ECG remains normal, the risk is small that the chest pain is caused by angina pectoris. However, for various reasons, the doctor may decide to further investigate.
ECG Chest

Chest pain (Angina pectoris): ST segment is reduced. Right: ECG without deviations.
block A cardiac arrhythmia can be recognized in most cases on an ECG. An example of arrhythmia is the heart block. A heart block occurs when in the stimulus guidance system the AV-knot no longer conducts the electrical stimulus from the bosoms to the chambers. The rooms no longer get the stimulus that starts in the sinus knot, but still contract. Heart muscle cells can also create an incentive themselves.
With a heart block, the electrical stimulus occurs in the muscle cells of the
chambers. The result is that bosoms and chambers will each contract in their own rhythm. On the ECG this becomes visible because the intervals between the P-top (contraction of the bosoms) and the qrs complex (contracting of the chambers) are no longer related. The P-top and the QRS complex no longer follow each other but each show their own rhythm.

ECG Heartblock
Heartblock. The P-top (bosoms) and the QRS complex (rooms) follow their own rhythm. Right: ECG without deviations.
research Some abnormalities in the electrical activity of the heart muscle occur only occasionally. At other times, the ECG is normal. That's why the doctor will sometimes have a Holter exam done. This study was named after the American physician Norman J. Holter who first applied it.
In the Holter study, the lab technician applies electrodes to the chest that are connected to a cabinet that the person undergoing the examination carries for a longer period of
time. Usually a Holter examination takes 24 hours, but sometimes it takes longer, up to 48 hours or even a week. It is important to keep a diary. For example, any deviations in the ECG may be associated with what someone has done during that period and with the complaints he has had. The result of a Holter study is an extensive ECG with a minimal chance of missing any abnormalities. Implantable Loop Recorder (ILR)
In some abnormalities, it is necessary to follow the heart rhythm even longer.

Then a device is applied under the skin, called an Implantable Loop Recorder (ILR). An example of such an abnormality is someone who inexplicably loses consciousness for a short time. Then an ILR is an option to investigate whether an arrhythmia is the cause.

ECG Willem Einthoven
One of the first experiments with the registration of electrical activity in the heart muscle by Willem Einthoven, the discoverer of the ECG (early twentieth century).
Willem Einthoven
The ECG as a medical research was developed in the early years of the twentieth century by the Dutch cardiologist Willem Einthoven. His influence is still noticeable in clinical practice. For example, Einthoven was the first to use the letters P, Q, R, S and T for the phases of the heartbeat and determined the placement of electrodes on the chest. Willem Einthoven was awarded the Nobel Prize in Medicine in 1










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