How Willem Einthoven gave doctors a window on the heart

If the doctor has ever placed electrodes on the skin to record a trace of a heartbeat, then thanks to this gentleman - Willem Einthoven. His invention, the electrocardiogram (ECG), has been used for over 100 years and is still one of the most commonly used diagnostic tools in medicine.

He became interested in electrical heart activity after watching a demonstration of a raw electrocardiogram device developed by British physiologist August Waller. It was based on a capillary electrometer, one of the first instruments for detecting electric waves, consisting of a thin glass cylinder filled with mercury and sulfuric acid.

The Waller device did not generate very accurate recordings, so Einthoven developed better ones, which were called a string galvanometer. It consisted of a very thin quartz fiber covered with silver, which was conductive electricity from the heart. The filament passes between two solenoids, which causes it to move proportionally to the conducted current.

Einthoven made the first clinical recordings in 1902. The trail showed a wave shape with three peaks and two valleys in each heartbeat. Einthoven used the letters P, Q, R, S and T to designate these traits, the convention is still in force today.
Einthoven was convinced that ECG would be extremely valuable in clinical diagnosis. He identified different patterns from healthy people and people with heart disease such as arrhythmias, heart blocks and ventricular hypertrophy - the enlarged walls of the main chambers of the heart.

The medical community was initially skeptical about the usefulness of this technique, but Einthoven's work was eventually recognized by the Nobel Prize in Medicine in 1924.