If a doctor has ever placed electrodes on your skin to record a trace of your heartbeat, you have Willem Einthoven to thank. His invention, the electrocardiogram (ECG), has remained in use for over 100 years, and is still one of the most widely used diagnostic tools in medicine.
He became interested in the electrical activity of the heart after seeing a demonstration of a crude electrocardiogram device developed by Augustus Waller, the British physiologist. It was based on the capillary electrometer, one of the first instruments to detect electric waves, consisting of a thin glass cylinder filled with mercury and sulphuric acid.
Waller’s device did not produce very accurate recordings, so Einthoven developed a better one, which was called a string galvanometer. It consisted of a very thin quartz filament coated in silver, which conducted the electrical current from the heart. The filament passes between two electromagnets, which cause it to move in proportion to the current it is carrying.
The lightness of the filament made it extremely sensitive. “Einthoven achieved such amazing technical perfection that many modern electrocardiographs do not attain equally reliable and undistorted recordings,” wrote Serge Barold in a 2003 paper about Einthoven’s work.
Einthoven made his first clinical recordings in 1902. The trace showed a waveform with three peaks and two troughs in each heartbeat. Einthoven used the letters P, Q, R, S and T to denote these features, a convention still followed today.
Einthoven was convinced that the ECG would be hugely valuable for clinical diagnosis. He identified different patterns from healthy people and those with heart conditions such as arrhythmias, heart blocks and ventricular hypertrophy – enlarged walls of the heart’s main chambers.
The medical community was initially sceptical about the technique’s utility, but Einthoven’s work was eventually recognised with a Nobel Prize in Medicine in 1924.
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Willem Einthoven’s life
Einthoven was born in Indonesia – then the Dutch East Indies – in 1860. His father, a doctor, died when he was just six, but he chose the same career, studying medicine at the University of Utrecht in the Netherlands. Soon after he graduated, he was appointed as professor of physiology at Leiden University. He died of cancer in 1927.