HN Reader

I have frequent ectopic beats that I feel as a flutter / heavy beat on my chest. The doc says it won't kill me but it is extremely uncomfortable at times. This has been a great material to learn about the inner workings of heart cells.

BTW Here's an ECG from my Apple Watch showing 3 such beats (you can't miss them): https://link.ekin.dev/l1Vc3Gdf

If you happen to have these, just get checked out by a cardiologist. They are almost always benign but the frequency / daily amount are reasons for concern.

Exciting simulations! :) And an excellent explanation.

From time to time I get episodes of sudden tachycardia¹. It's a very strange feeling: one second everything is fine, the next my heart jumps in my throat and starts beating at 230 bpm (not a typo). After a while, just as quickly as it came, the tachycardia goes away and I'm back at whatever HR I was before the trigger. If it doesn't go away by itself, breathing in deep and holding my breath typically does the trick. It's like a light switch! A bit scary, but also very fascinating.

Thanks for explaining so well what goes on "under the hood"!

¹ https://en.wikipedia.org/wiki/Paroxysmal_supraventricular_ta..., I believe.

Thank you for all the kind responses.

I also want to make a similar article, where I calculate an ECG for the simulation, and then make and explain the changes necessary to make the ECG look realistic. A main challenge will be that the depolarization has to happen very fast relative to the repolarization, which may be computationally difficult for a cell-based simulation.

I'm rarely intimidated by a textbook but I was intimidated by a set of cardiology books I saw at the vet school. The topological structure of waves in the heart is

https://en.wikipedia.org/wiki/Spiral_wave

because cardiac cells circle around a loop with phase from 0 to 2π, contrast that the usual oscillator which has position p and momentum q. An oscillation in that space can rotate around the center and look like a phase but it's also possible to go right through the center, whereas for cardiac excitations the p variable is on the unit circle. This astonishing book covers the topology of this kind of thing:

https://archive.org/details/geometryofbiolog0000winf/page/n9...

particularly the cases where you have just one phase (e.g. jet lag or cell division or plant phenology) but it applies as well to those spiral waves where every element in the medium has a phase.

I had a benign irregular heartbeat (Premature Ventricular Contractions) for half my life. During one checkup the cardiologist said my heart had become enlarged to compensate, and if I wanted an energy boost I should get an ablation surgery.

The ablation was quite the experience as I was kept conscious throughout (and I felt euphoric thanks to the painkillers). A team of students carefully threaded a wire in through my femoral artery, guided it up to the inside of the heart and zapped the problematic cells. I could actually feel the moment they fixed it. One moment my rhythm was irregular, the next it was regular. They then ran a series of stress tests that included injecting me with something that pushed my heart rate above 200 bpm. That was uncomfortable. I was back to my normal routine 24 hours later and I did indeed have more energy.

Excellent article! Well written and the animations make it so much easier to understand. However I was unable to get the loops to go.

I am reworking the analysis of ECGs from an old contest, and I want help from an expert.

In 2000 the Computers in Cardiology challenge (CINC2000) provided ECGs from sleep studies of 70 patients and asked contestants to identify obstructive sleep apnea based on those ECGs. I was on the team that won.

Now I am reworking the problem for the second edition of a book (see https://www.fraserphysics.com/book.pdf), and I see great variety in those ECGs (see https://www.fraserphysics.com/all_ecgs.pdf). I suspect that some of that variety is due to lead placement, and some is due to pathology, but I'm not sure.

Is anyone here willing to help me out?

Learned about the heart today! Thank you!

I wonder what other types of cells / tissues can be simulated by cellular automata?

Absolutely fantastic. Well done!

As someone who had their life upended last year upon discovering I had AVNRT, this article is much appreciated. I'm still trying to understand the root cause of my arrhythmia, because two ablations and one daily medication later and I still have regular episodes.

It's wild how many different types of arrhythmia there are, and how they can be connected to many other systems in the body. It seems like mine might be related to my nervous system.

Oh this is interesting. Thanks!

I've survived ventricular fibrillation 3 times and have an implanted ICD. I never really understood why delivering high voltage shocks is that effective, and always have anxiety about "the time it won't work"

Trying to understand Author’s education. Have they done both Medicine & Engineering? Looking at their articles & github, they are sound in electro physiology, Anaesthesiology & software. Great intersection of knowledge.

Off topic, but I’v always wanted to download web pages like this that contain interactive plots for self-study or later reference. Solutions like SingleFile or Zotero never work though.

Any suggestions?

Anybody know similar article but about blood flow / hemorheology ?

As someone who lives with this reality moment to moment (thanks to a deeply bridged LAD coronary artery) it is interesting to see a visual representation of these effects.

I love this article. I had already learned all the facts in the article, but even so, the interactive animations helped me understand it better. Thank you.

Title reminded me of Tubular bells.