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Why understanding the origins of EKGs may help you catch that trout... 🎣🫀

Updated: Oct 28

Here's a hint: It all starts with the P wave 🧐.


Two surgeons at Bridger Veterinary Specialists work on a complicated fracture with an EKG monitor in the background. The anesthetist monitoring the case is off to the right, out of the picture.

“Do you know why they call it a p-wave?” said the surgeon next to me.


"Uhh.... No. I have no idea," I said.


And he went on, "seems weird they'd start in the middle of the alphabet and not the beginning, right?"


Doubt is the origin of wisdom. - Rene Descartes

Mother Trucker. I hate when surgeons ask me physiology questions I don't know the answer to. I mean, I'm a board-certified anesthesiologist. I should know everything there is to know about EKGs (electrocardiograms), right?

A normal electrocardiogram (EKG or ECG) labeled with the appropriate points, P, Q, R, S and T. An EKG measures voltage over time through the heart.

I look at them all day long. I hear their beeps in my dreams. But never once did it dawn on me to ask myself the question, why does the conventional naming of waves on a normal EKG go P, Q, R, S and T?


And now a surgeon (of all people!), who just pieced a shattered dog's pelvis back together, scrubs out of surgery and asks me this?!


It all starts with a "P" (an abbreviation of "le point") that Descartes wrote about 400 years ago.


The Snell-Descartes Law. Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the phase velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.

But that's the cool thing about working with super smart people. They always challenge you.


Only the contest made me a poet, a sophist, an orator. - Plato

So off I went that night on googling why they call it a P wave. And the story is quite beautifully interconnected over 300 years of science and mathematics. It's also the foundational discovery of refraction - something we see every day on the water as anglers.


The Snell-Descartes Law: a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air

(1). 


It turns out that Descartes figured out refraction about 400 hundred years ago. And when he started creating his geometry explanations, he started with P for Point.


Fast forward 300 years and William Einthoven started experimenting with what now became the modern day EKG. He won the Nobel Prize for figuring out the geometry of it, but to do it, he had to read a fair amount of Descartes' work (4).


Einthoven used P as the starting letter for the first wave on the EKG, well, because that's what Descartes used. Einthoven also speculated that if he chose letters from the middle of the alphabet, then there would be letters available before and after it if new waves were discovered.


Which leads us to fishing, particularly the visualization of fish under water.


Fishing guides would argue you need polarized glasses to see trout underwater. But I'd argue you need polarized glasses, the Snell-Descartes Law, and a whole hell of a lot of patience if you're new to spotting fish in the stream. Like literally, it took a guide 10 minutes of him pointing until I saw the flash of the trout fin.


A fisherman has to correct his angle of entry when spearfishing to account for the Law of Refraction (3).






















Snell's Window


I don't really think it's fair to talk about the Snell-Descartes Law without mentioning the concept of Snell's Window. If you've ever spent a lot of time at the bottom of the well of a deep pool, you know exactly what this is, and it actually has a name...


Snell's window is a phenomenon by which an underwater viewer sees everything above the surface through a cone of light of width of about 96 degrees. This phenomenon is caused by refraction of light entering water, and is governed by Snell's Law. The area outside Snell's window will either be completely dark or show a reflection of underwater objects by total internal reflection (5).


A diver viewed from below who appears inside of Snell's window. By U.S. Navy photo by Mass Communication Specialist 1st Class Jayme Pastoric - This image was released by the United States Navy with the ID 110607-N-XD935-191 (next). Public Domain, https://commons.wikimedia.org/w/index.php?curid=15450843


We're all a lot more similar than we think.


You may think you look really different from a fish. You may say that fish have a 2 chambered heart, and mammals have a 4 chambered heart. But when it comes to EKG tracings, and assessing electrical activity of the heart, well, we all have a P, Q, R, S and T. So please keep being kind to your fellow humans and your fellow fish! 🐟


Here are a couple interesting fish EKG papers if you'd like to read more.


Zebrafish Electrocardiography (ECG): A Minimally Invasive Assay to Evaluate Cardiac Function (https://app.jove.com/v/20079/zebrafish-electrocardiography-ecg-a-minimally-invasive-assay-to-evaluate-cardiac-function)


Comparison of human and zebrafish electrocardiograms (ECG). (Top) ECG of an adult zebrafish at 23 C (kindly provided by prof. Tzung Hsiai). (Bottom) ECG of a healthy 43-year old human male. For direct comparison of zebrafish and human ECGs both recordings are shown in the same time scale. Similar to the human electrocardiogram, P, QRS and T waves are clearly distinguishable in the zebrafish ECG (6).

Stay wild and free!


Winston & Ashley















References




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