Hacker News Reader

Comment by 01100011 | Hacker News Reader

Interesting to see that it uses bovine derived valves. Does anyone know the reason for that? Are real tissues less likely to cause issues with blood coagulation or have materials coatings caught up enough to solve that problem?

Does anyone know where modern thinking on the role of the heart is headed? I was intrigued to run across this article discussing the heart's role as more of a hydraulic ram and less of a pump:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/

I don't suppose the science is settled, but it is interesting that in the modern age we're still debating the function of such an important organ.

View on HN

Metal valves are only used in the young (i.e. under 50) because they are the most durable and can last a lifetime. The caveat is that lifelong blood thinners are needed because the metal provides a surface for clots to form. Bovine valves are the typical favorite because the body does not form clots on a bovine valve. They're usually sterilized and all cells killed so that it doesn't trigger tissue rejection. In the end, it's just a connective tissue matrix. Unfortunately, this means it is less durable and cannot heal from damage so they only last 10-15 years.

That’s not really true around selection of valve, it’s all about fitness.

A lot of younger people will have tissue valves, because they can have another one after (probably, if they don’t have too many Comorbidities) and it’s a better trade off than being anticoagulated. A though some of the newer anti coagulants are much less of a pain in the arse to be on than 10 years ago. Also they tick, which some people don’t like.

Similarly, many cardiologists would give a 80 year old a tissue valve because they probably won’t need another one and again the anti coagulation trade offs work in their favour

You’re right — what I said was an oversimplification and a little bit untrue. I agree fitness and Compton dotier are a huge factor in selection of valve type.

That said, in my experience, cardiologists are really hesitant to use a tissue valve in someone under 50, especially if it is an open heart procedure. With an open heart, the adhesions (scar tissue) on a revision surgery makes it far riskier and less likely to heal well. So the follow up for a valve replacement after 10-20 years becomes much more high risk. Not a problem if they’re 70 and they would be 90 at the time a replacement is needed. Much more of a problem if they’re 30 and will likely need 4-5 artificial valves in their lifetime.

The new thing is to first do a TAVR/TPVR, which involves cutting into an artery - most commonly the leg - and placing a valve by routing it through the artery into the heart. But, any revision will need to be an open heart procedure. So the first replacement is trans catheter, then the second is open heart. Thus, the third replacement gets much more risky. So, if someone is 50, the second replacement is at 65, and the third would be at 85, so not a huge issue. By contrast, if they’re 30, the high risk 3rd surgery will happen at 65.

I may be speaking from 7-8 years ago when we were still in the dawn of TAVIs but the cardiothoracic surgeons I worked with generally put tissue valves in <50, as TAVIs last less. So tou could do tissue valve, plan for a TAVI later, then probably something new will be there next time they need one

You’d need to ask a cardiologist of course, but I think for all intents and purposes, the science is in fact settled. The heart pumps blood.

In any field you see people using weak evidence to question strongly evidenced positions like in the linked article. I worked as a physicist for 7 years or so, and you frequently saw people using small deviations in experimental results to try and question general relativity, or parts of the standard model. Of course, when you see the few outliers lined up it seems convincing, but if you work professionally in the field you realize that that’s what they are - outliers. Just a handful of strange results in a literal flood of results that fit within and support the status quo.

And, fortunately or unfortunately, if you’ve seen it happen to someone, I think the evidence that the heart pumps blood is extremely convincing, having witnessed it first hand - if your heart stops, blood stops flowing. And we know that that is the correct order of causation, because to fix it, you shock the heart into pumping again.

You’d need FAR stronger evidence than failed drug trials (the vast majority of drug trials fail) or failed device trials (the vast majority of device trials fail) to seriously weaken that position, as far as I’m aware.

I think you misunderstood the parent comment's argument. What I believe they were saying is that continuous pumping (i.e. rotary pumps) may be less effective than beat-by-beat pumping (i.e. pulsatile pumps). The former result in a static continuous blood pressure while the latter result in a blood pressure waveform with a systolic and diastolic pressure. The argument I'm familiar with is that peaks and valleys in blood pressure trigger strengthening of arterial walls in a similar mechanism to muscle growth. But, there's a few different arguments and as far as I know, the science isn't completely settled.

Pulsating vessels are really important. There’s a bunch of evidence of the physiological benefits to having a pulse. Doesn’t mean you can’t, but it’s good for you, you evolved to have it. You can convince stem cells to differentiate into arterial wall just by exposing them to arterial flow. Just as you can get stem cells differentiate into osteoblasts by keeping them in a rigid structure. Smart fuckers

> There’s a bunch of evidence of the physiological benefits to having a pulse.

This is such a great statement on a couple of levels. That having no pulse and being alive is even possible is amazing.

How basic medical observations are done for these people is interesting to contemplate.

You use bovine or porcine generally. They last about 10 years. Metal valves last 30 years but require anti coagulation. Since porcine and bovine valves are zero from à immunogenicity standpoint, they’re ideal unless we could get human ones that are plugged into the circulatory system. Although with a pump heart you’re going to be on blood thinners anyway. And probably a few other things.

The dream of where the heart is headed is to growing new ones. The best heart is a human heart suited to you

If they only last 10 years.. they have to cut you open to replace them assuming you live a few decades??

They last 10 years ‘or so…’ some up to 17-20, so there’s a variability there, but they fail gracefully so you can monitor which is nice (as another commenter pointed out).

Tou can replace with transcutaneous valve replacement (like a stent, through a blood vessel) or open operation

mechanical heart valves require patients to be on blood thinners for the rest of their life, bovine and porcine heart valves are most similar to human heart valves in size and shape and they have very good reliability without requiring the patient to continue taking blood thinners.

It is fascinating that we can't reproduce the mechanical properties of a small biological valve, even a dead one (they are 'killed' before they are implanted).

When they finally do figure it out, imagine all the various applications to improve the longevity of ... well, everything.

We can't even design water pipes and valves that don't degrade over time. Limescale builds up and clogs the works. There's only a tiny amount of minerals in water, and yet that happens. Blood -- as they say -- is much thicker than water, and contains components specifically designed to clot. It's not wonder that this is a tricky problem to solve.

That's basically in galvanized pipe, or steel pipe.

yup that is correct. however non-mechanical valves last typically for 10 to 15 years, and will require a surgery past that time period.

some studies[1] have shown the mechanical valves are the safest choice.

1. https://med.stanford.edu/news/all-news/2017/11/mechanical-he...

There is also a difference in failure modes. Natural valves degrade performance overtime due to calcification of the valve, giving you warning and time to make decisions over replacement. Mechanical valves fail catastrophically by either remaining stuck open or having the valve plate shatter. If you ever stop hearing your valve click you need to get to a hospital ASAP

The vast majority of replacement valves implanted today also use animal tissue (bovine and pig). They are much more similar to the original valves than metal replacements.

Reply on news.ycombinator.com