Medical history is remarkable for two examinations with clinical application of diagnostic techniques for more than a hundred years and a long time. One is the X-ray examination, which finds a remarkable resemblance to the inventor roentgen, who in 1900 won the first Nobel Prize in physics; The other was electrocardiography, the inventor of which, Einthoven, was awarded the Nobel Prize in physiology or medicine in 1924.

1. The advent of ECG Technology

ECG Pioneer: Waller

In 1887, the Royal Society Mary's hospital held an epochal scientific presentation: Waller, Professor of physiology in the hospital, applied capillary electrometers to canine and human hearts to record electrocardiograms. Among the world-wide renowned physiologists at this scientific demonstration from observamore, including Einthoven at Leiden University in the Netherlands. At presentation, Waller successfully recorded the first human ECG on the spot, which had only ventricular waves V1, V2, and atrial P waves that failed to record. Waller's great and fruitful research results set the stage for the eventual advent of electrocardiographic technology.

Waller's founding shock and like magnetite generally captivated Einthoven, a young physiologist in the Netherlands. Thirteen years thereafter, ein thoven devoted fully to the study of recording electrocardiograms by capillary electrostatics. He improved several critical techniques to make the recorded figure clearer, and his recorded ECG showed atrial P waves, B and C waves of ventricular depolarization, and D waves of repolarization.

But there was a way that always made him insurmountable: the small movements above and below the mercury sulfuric acid interface in the capillary from which the ECG was recorded were influenced by various disturbances in the surrounding environment in addition to changes in the bioelectrics of the heart. Although his recorded ECG shape had changed from 2 waves to 4 waves, it still could not solve the problem that the ECG signal drowned in various interfering waves, making the technique only available for clinical use in a paced configuration.

After 13 years of unremitting effort Einthoven failed to see the dawn. In 1900, he decided to abandon capillary electrometer recording electrocardiographic technology and began searching for a new way out. Eventually, he was inspired by the string electrotonometer invented by ader in 1897 and determined to transform it for use in recording weak bioelectricity in the human heart. To increase the sensitivity of the rheometer, not only the magnetic field strength but also the chord weight is to be reduced. For this purpose, his drawn slender silver coated quartz chord lines (diameter only 2.1 μ m. Magni fi cation lens to see) suspended in the magnet between the two sides, when there are weak changes in the body surface ECG, the string thread swings, after the swing is magni fi ed 500 times, the ECG is recorded.

In 1901, Einthoven successfully recorded the first ECG with a string type ECG machine and named the waves P, Q, R, s, t, and u, which have been named to date.
In 1903, Einthoven published the paper on a new galvanometer and it is widely acknowledged that it marked the beginning of the era of the clinical application of electrocardiography. But at that time, the subject's two arms were to be soaked in two liquid tanks filled with saline, and to reduce interference, the recorder was to be 1.5 km away from the subject.

Einthoven's Laboratory

Chord current meter

2. Relay events over generations: final refinement of the lead system

The recording of the chordal ECG,  done by Einthoven in 1903, was only the first step forward, and of equal importance to it was the introduction and refinement of the ECG recording lead system.

When the ECG machine became available, more than a hundred recording lead systems at that time, some placed the probing electrode in the precordial area without a dry electrode on the forehead, some placed the dry electrode in the mouth, and others placed it in the esophagus. There was no uniform ECG lead system and the recorded ECG was bewildering and blinded.

1913: the standard bipolar limb leads

In 1906, ein thoven proposed the concept of bipolar limb leads, in which a high amplitude and graphically stable bipolar limb lead ECG (leads I, II, and III) could be recorded after two pairs of recording electrodes located in the patient's right arm, left arm, and left leg, respectively, whereas an equal triangular shape of the cardiac potential was formed after sequential attachment of three recording electrodes. Bipolar standard limb lead electrocardiography was not formally available until 1913 and was applied alone for 20 years.
unipolar limb lead

1933: Wilson's unipolar lead ECG

In 1920, Lewis in the United Kingdom challenged the bipolar limb conduction system: first, it produced low ECG amplitudes (severe attenuation) at greater distances from the heart; The second is that it does not reflect the ECG vector changes at the level of the heart. The technique of unipolar lead electrocardiography was soon started by Lewis, who placed the ECG unipolar probing electrodes on the V1 ~ V6 site of the precordial region and the 3 limb leads without stem electrodes as the central electrical end. This was proposed by Lewis and finally done by Wilson in 1933 with a unipolar lead ECG that defined the zero potential and the location of the central electrical end according to Kirchhoff's law of current. To this point, the ECG lead system has become a 12 lead system.

Unipolar leads

1942: final refinement of the standard 12 lead ECG

In Wilson's 12 lead system, the amplitude of ECG waveform in three unipolar limb leads, VL, VR and VF, is low, which is not easy to measure and observe changes. Further studies were done by Goldberger in 1942 when he recorded unipolar lead electrocardiograms from a limb that cut the connection to the central electrical end to form stemless electrodes with the connection of the other two limb leads. The miracle followed and the amplitude of the electrocardiogram doubled all at once, forming the so far unipolar pressurized limb leads: AVL, AVR, AVF leads.

To this point, the standard 12 lead system for recording the ECG is derived in its entirety: 3 bipolar limb leads (I, II, III, Einthoven, 1913), 6 unipolar precordial leads (V1-V6, Wilson, 1933), and 3 unipolar pressurized limb leads (AVL, AVR, AVF, Goldberger, 1942).

3. Clinical applications

In 1903, electrocardiography became available for clinical use. In 1906, Einthoven successively recorded atrial fibrillation, atrial flutter, ventricular premature beats and other electrocardiogram. In 1908, ECG began to be used for the diagnosis of atrial hypertrophy, ventricular hypertrophy, since then the application of ECG continues to expand, new ECG waves and ECG phenomena are successively discovered. Its protracted course resembled one lotus at a time and gradually entered the Sanskrit.

In 1930, the preexcitation syndrome was discovered, followed by the proposal of new clinical electrocardiographic disorders such as Leff disease, long and short QT syndrome, Brugada syndrome, sick sinus syndrome, early repolarization syndrome, J-wave syndrome, and epsilon wave.

Nowadays, ECG examination has become one of the four major routine examination programs in the clinic, and the application range has been beyond the diagnosis and treatment of cardiovascular disease, which is specific and highly sensitive for the diagnosis of cerebrovascular disease (e.g., nigra waterfall like T wave), respiratory disease (e.g., pulmonary embolism).