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1/ Why are EKG waves named starting with the letter P? What happened to letters A through O?

I’m guessing you’ve probably never wondered this, but if you’re curious, here’s a brief historical #medthread / #tweetorial on how the EKG waves got the names they did.
2/ The first electrical tracings of the heart were obtained in 1887 by A.D. Waller, a British physiologist and physician, who used a Lippmann capillary electrometer to capture the tracings.

3/ As a physiologist, Waller labelled the two waves on his initial tracing V1 & V2 based on their site of anatomic origin- the ventricle. He would continue, often rather adamantly, to refer to the electrical waves as A, V1, & V2 throughout his career.

4/ Building on this work, Willem Einthoven, a Dutch physician and the father of modern electrocardiography, would improve on the Lippmann electrometer and developed his own tracings with 4 deflections, which he labelled ABCD.
5/ Einthoven would further refine his tracing by mathematically correcting for the friction and inertia of the mercury used in the electrometer. In 1895, he published this corrected tracing superimposed on his original tracing, labeling it PQRST.

6/ While there are many theories, it is suspected that Einthoven, who initially studied mathematics, chose these letters based on the mathematical tradition of Rene Descartes who labelled successive points on a curve as P, Q, R, S, T

PMID: 4930789
7/ Cartesian tradition aside, labeling in this fashion also allowed Einthoven the distinct advantage of naming of additional undiscovered waves preceding or following the series, as is the case of the U wave.

8/ Einthoven would go on to further refine his methods of capturing electrocardiograms, including developing the string galvanometer, a 600lb machine that required immersion of one's extremities in saline bath electrodes.

9/ As Einthoven's technological advances were adopted in clinical practice, so too was his PQRST naming convention, much to the chagrin A.D. Waller.
10/ Einthoven's innovations with electrocardiography would eventually earn him the Nobel Prize in Physiology or Medicine in 1924. Many feel that Waller would have shared the prize, however, as he died in 1922, he was not eligible since the prize is not award posthumously.
11/ And thus ends my first #histmed #tweetorial. For a clearer read and to learn how the rest of the EKG waves got their names, I recommend starting with this article by J. Willis Hurst from Circulation in 1998.

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