alt.hn

3/28/2025 at 1:05:52 PM

Excitable cells

 https://jenevoldsen.com/posts/excitable-cells/

by johannes_ne

4/1/2025 at 2:19:12 PM

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.

by eknkc

4/1/2025 at 3:48:24 PM

I had something similar for many years (triggered by an episode of afib brought-on by triggering my vagus nerve). The one thing that has helped me fully get rid of these (after YEARS of trial-and-error) was getting onto beta blockers (Propranolol).

These have COMPLETELY gotten rid of my ectopic beats and also helped me deal with the health anxiety.

If you ever want to talk, feel free to hit me up (contact info in profile).

by rdegges

4/1/2025 at 4:25:52 PM

Propranolol is such an underrated drug, or at-least it was when I first started using it twenty years ago (initially for hand tremors but I found it did more than settle just my hands). Glad others have been discovering its usefulness over the years.

I think they've even recently found use in cancer therapy [1].

Sir James Black the pharmacologist who developed it is an absolute legend [2].

1. https://www.tandfonline.com/doi/full/10.1080/2162402X.2023.2...

2. https://www.youtube.com/watch?v=ZPe0sLghRBQ&list=PLVV0r6CmEs...

by grumpy-de-sre

4/1/2025 at 8:09:01 PM

Yeah, I’ve been on propranolol and then metoprolol but they don’t seem to do much in terms of reducing ectopics. Currently on metoprolol though.

I’ve had an echo, stress ecg and then a ct angiogram. Everything is physically fine so at this point I mostly ignore them cause at least I know they are not an immediate danger.

Thanks!

by eknkc

4/1/2025 at 6:46:33 PM

> an episode of afib brought-on by triggering my vagus nerve

I get ectopic beats when I've got trapped gas in the stomach. Sounds weird, but generally when I get them I realize I need to stand up (because I've usually been sitting with bad posture which leads to the trapped gas) and have a large belch and then it calms down. I mentioned this to my doc and he said it was Roemheld syndrome ( https://en.wikipedia.org/wiki/Roemheld_syndrome ) which is vagus nerve-related.

by UncleOxidant

4/2/2025 at 7:58:58 AM

Yeah I got quite scared when it happened for the first time.

by benterix

4/1/2025 at 8:24:21 PM

Daily dose of magnesium supplements has made it tolerable for me, when beta blockers (carvedilol) didn't help much.

by throwaway7783

4/1/2025 at 3:29:15 PM

Many (most?) people get ectopic beats, but the threshold for noticing them seems to differ. Being stressed/anxious makes them more noticeable. There's a self-reinforcing feedback loop: the more you notice them & worry about them, the easier you will notice them ...

The thing about arrhythmias is that they can only cause damage while they're happening, but ectopics are only a problem for a single beat, which is not going to impact your oxygenation or blood pressure or anything else. Even a bunch of them every day won't cause any damage.

by elric

4/1/2025 at 4:40:33 PM

> Many (most?) people get ectopic beats, but the threshold for noticing them seems to differ.

This. Some of us have very high levels of proprioception. I can feel my pulse just by sitting quietly - I don't need to put my finger on my wrist to take it. Same with ectopic beats, I definitely feel them. And I find that there's a cycle to it - as you say there's a feedback loop: feel ectopic beat, become anxious, more ectopic beats, more anxious, etc. Then I have to try to actively forget about them. During those feedback times I'll have many ectopic beats / day (many per hour, even), but then some days later I'll realize I haven't had any for a while and I might go for weeks without noticing any.

by UncleOxidant

4/1/2025 at 5:52:55 PM

Apparently everyone gets them but the burden (% of beats being screwed up) is important. A high burden for prolonged periods means damage accumulation.

I had 2 24 hour monitors and one caught 700 eptopic beats in a day. Another couple months later, 15.000 in a day. The second one was a concern for the cardiologist. She ordered a couple more tests, started beta blockers asked for diet changes.

I still have a high burden as I can feel them but whatever..

by eknkc

4/2/2025 at 5:07:23 AM

I used to get them occasionally. A few years back I started doing loads of cardio exercise and I noticed a while back that I hadn't had the flutter for a long time. I always wondered if it was due to increased cardiac fitness.

by 0_____0

4/1/2025 at 5:34:49 PM

I had some of those, verified by ECG. Cut down on coffee a bit, they went away.

by ggambetta

4/1/2025 at 12:59:52 PM

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.

by pscanf

4/2/2025 at 7:57:06 AM

I have PSVT. I think it started for me around the age of 17 and was always pretty short-lived and infrequent, often with years between episodes. A couple years ago, chronic stress and lifestyle stuff began to catch up with me and the episodes started happening a few times a week, so I'm now prescribed Metoprolol as a pill in a pocket thing to deal with it. Generally speaking, as long as sleep, diet, and basic exercise are in order--and alcohol/caffeine consumption are kept low--it just doesn't happen. It also can almost always be remedied with some simple vagus nerve exercises. All of that can be tough to manage sometimes though, so I'm very seriously considering getting an ablation soon. The doctors have told me that it's not a particularly dangerous condition as long as you're an otherwise healthy individual, but it's definitely still terrifying and can't be good for you either.

by channel_t

4/1/2025 at 1:53:13 PM

I have the same condition. I was diagnosed at a very younger age with Wolff-Parkinson-White syndrome. It might be worth looking into.

https://www.mayoclinic.org/diseases-conditions/wolff-parkins...

by papascrubs

4/1/2025 at 3:20:48 PM

With WPW you MUST NOT take beta blockers (AFAIR), it may kill you.

I had just plain vanilla Afib and got ablation 2 years ago - best thing ever, cured instantly.

by limaoscarjuliet

4/1/2025 at 4:48:02 PM

Fortunately I don't think it's WPW in my case. Or at least, my cardiologist never mentioned it, so I assume it's some other condition that has similar symptoms.

by pscanf

4/1/2025 at 2:43:37 PM

Do you drink a lot of caffeine? A family member had this occasionally with no family history of issues, and the cardiologist had them wear a portable EKG for a few days that synced with an Android phone, with not much results. Finally the family member cut down from 4 espresso shots a day to just 1 cup of brewed, and the issue hasn't returned.

by TheJoeMan

4/1/2025 at 4:46:25 PM

Yeah, several cups of tea per day. I also recently had that test done, but nothing emerged as nothing occurred during the 24 hours I was monitored. Just like I expected, actually, as fortunately those episodes are very rare for me, not enough to warrant drastic lifestyle changes. (I can't give up my tea! :D )

by pscanf

4/1/2025 at 2:30:18 PM

A couple of years ago I woke with a minor headache that I ignored for various reasons all day, then skipped lunch as I had an important meeting later and lots to do ahead of it, and the headache got progressively worse. Just before the meeting I felt nauseous, threw up, and then started having the feeling of palpitations in my chest. I've always had them from time to time - that feeling that ones heart has skipped a beat or taken a couple of extra ones - but this time it wasn't going away after a couple of beats.

To cut a long story short, I went to hospital (instead of that meeting) and it turned out that it was atrial fibrillation and that while it feels medium terrifying it's not necessarily that big a deal.

It went away after a couple of days (if it had lasted longer they'd have done "electroconversion" to try to get it back into the proper ryhythm artificially). Apparently the real danger of this is that it might cause a blood clot which in turn could cause a stroke, but it's unlikely to be an issue in the short term.

They did put me on blood thinners and beta blockers between the occurrence and getting a full check up a month later, so I was very calm when we rescheduled that meeting.

Top tip: don't ignore a terrible headache; go to bed.

Edit: PS I think my heart rate was just above 100bpm at rest (possibly 120?), which was unnerving enough, so I can imagine how much more scary 230bpm must feel! You definitely win.

by dcminter

4/1/2025 at 4:55:06 PM

I fainted when I was an exercise class. I'd had too much to eat before then, my digestion was pretty slow then, also it was a crazy hot day in a building with a pool (high humidity) and an old HVAC system. Didn't help that I had a crush on the instructor and was trying even harder because of that.

Woke up on the ground feeling very relaxed. Got a medical workup that checked a lot of things, they had me wear a Holter monitor for a month. In the last 30 minutes of the study period they caught five bad heartbeats of A-Fib when I was sleeping. Funny one of my evil twin's schemes went south around then and I (we?) were feeling really bad about it. My cardiologist told me that the threshold was one bad heartbeat so I have A-Fib and have a risk of strokes, he recommended that I take a baby aspirin as it has a mild blood thinning effect.

Around the beginning of the next year I developed a deep vein thrombosis which got cleared up with Eliquis, a blood thinner. The emergency room referred me to my primary care doc who ran all sorts of tests and couldn't find a reason for the DVT so he decided to keep me on Eliquis indefinitely, the cardiologist figured that covered the A-Fib so I dropped the aspirin because the combination could cause excessive bleeding.

I have one of those credit card Kardia EKGs and haven't seen an A-Fib episode yet. For the decade before I got that workup I did crazy amounts of cardio (helped me stay sane under incredible pressure) and around the time my evil twin was out I was getting up in the morning before sunrise, hiking 6 miles, going to the gym during the day, going out in the evening and hiking another 6 miles. My cardiologist says I have "Athlete's heart" with an abnormally low resting heart rate (drops below 50 at night when I get a good night's rest) and I shouldn't do more than an hour of cardio a day, so I don't.

by PaulHoule

4/1/2025 at 4:55:26 PM

Yeah, the first time it happened (about 15 years ago) I thought "that's it, I'm dead". Heart things are unnerving indeed! Best of luck with your AFib!

by pscanf

4/1/2025 at 5:56:38 PM

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.

by johannes_ne

4/2/2025 at 4:11:49 AM

Also cool would be the inverse. Going from ECG to plausible simulated RD dynamics.

by fraserphysics

4/2/2025 at 1:51:14 PM

Indeed, but that problem is just so much more complex.

by johannes_ne

4/1/2025 at 4:28:02 PM

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.

by PaulHoule

4/1/2025 at 4:35:25 PM

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.

by randerson

4/1/2025 at 11:54:20 AM

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

by lofties

4/1/2025 at 12:35:17 PM

I was able to do it by clicking in a few places in quick succession evenly spread out.

by samwho

4/1/2025 at 12:43:38 PM

Try clicking in one place repeatadly and adjust clicks slightly to always go next to the fastest refractory cell possible. This works like a charm to induce arrhytmia

by jcattle

4/1/2025 at 1:23:15 PM

I was able to consistently start a loop in one click by clicking on the edge between grey and white (slow and fast refractory) cells ASAP after a normal beat.

If I'm fast enough, the wave can't spread to the grey cells so it only goes in direction around the red cells and starts a loop.

(But you can't do this on the first image with a Defibrillate! button because there are no slow cells.)

by leereeves

4/1/2025 at 4:10:28 PM

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?

by fraserphysics

4/1/2025 at 11:49:25 AM

Learned about the heart today! Thank you!

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

by Kalabasa

4/2/2025 at 12:58:56 AM

I think many types can if you broaden the definition of automata to include 'reaction diffusion' you can even simulate things like the Schrödinger equation under a RD scheme! (there are some examples in gollygang/Ready).

RD was invented by Alan Turing as a way to model animal coat patterns too, and I think it's exceptionally good at that (I did a talk at Houdini Hive SiggraphAsia2019 about it: https://youtu.be/K_7TkoIkFhk?si=afhcjZ8TeysNJxRH)

by danwills

4/1/2025 at 4:26:56 PM

I was thinking the same thing. I need more simulations like this!

by owenpalmer

4/2/2025 at 1:00:39 AM

Definitely have a look at gollygang/Ready I reckon! There are some really fascinating things in the pattern library (including some that I contributed).

https://github.com/GollyGang/ready

by danwills

4/1/2025 at 10:36:40 AM

Absolutely fantastic. Well done!

by samwho

4/1/2025 at 4:17:37 PM

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.

by mjamesaustin

4/1/2025 at 3:54:24 PM

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.

by the_arun

4/1/2025 at 4:31:03 PM

Thank you all for the interest in the article and the kind feedback.

I'm a medical doctor with an interest in engineering and coding. My PhD was quite focused on signal analysis and coding, and my supervisor is a medical engineer.

by johannes_ne

4/1/2025 at 4:14:18 PM

I don't know the author, but I will note that my cardiologist got an Electrical Engineering degree before going to medical school and views it as a huge advantage when dealing with the heart.

by mjamesaustin

4/1/2025 at 11:51:20 AM

Anybody know similar article but about blood flow / hemorheology ?

by agumonkey

4/1/2025 at 12:15:59 PM

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.

by EncomLab

4/2/2025 at 1:02:49 PM

Title reminded me of Tubular bells.

by bobowzki

4/2/2025 at 1:12:40 AM

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?

by BenFranklin100

4/1/2025 at 4:14:53 PM

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"

by dheera

4/1/2025 at 1:28:36 PM

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.

by leereeves