The Texas Medical Center is moving ahead on its Bivacor rotary pump artificial heart.[0] It does not appear that Bivacor is a bridge to a transplant, but rather an end point. They kept a cow alive for many months a few years ago. Since it is a continuous rotary pump, the patient will have no pulse with this device.
One of the inventors behind Bivacor is Dr. Billy Cohn, an elite heart surgeon with a strong bent toward innovation. He would have an idea, hit his garage to cut up some plastic mesh, seal it, sterilize it, and be trying it in a patient in a few days. He jokes about Home Depot being his best source of medical equipment. In fact, he tells a hilarious Home Depot story in the middle of his standard talk on medical innovation.[1]
The Bivacor pump does have a pulse-like output, so I suspect some of the issues with earlier rotary pumps might not be so prevalent. Because it's a rotary pump though I suspect there's still issues with cell damage as they pass parts of the rotating assembly. The video claims that wide clearances reduce the risks of clotting from cell damage, but it's a reduction - not outright removal. See around the 3:40 to 4 minute mark on the video at https://www.bivacor.com/
Your small vessels are not grown to tolerate a constant pressure. You get aneurysms, clotting is super dangerous because they generally form and sit rather than getting sucked/pushed into the heart to potentially get broken up. Most importantly, forget your potential organ failure you wont notice until there's a lot of damage, and all the numbness you'll get, it's the brain function affects that bother me. Sluggish, memory problems, et al that accompanies tiny thromboses.
A rotary pump is an endgame-solution. It keeps you alive, at a cost and you die the end anyway (obviously).
Exactly. This is the cause of the phenomenon known as "pump head" that anesthesiologists refer to when patients are on long periods of support on heart lung bypass machines. These machines are peristaltic pumps with a continuous flow. Check out Ventriflo, a new type of pump intended for use in this area that has a biomimetic flow and pressure profile. Www.ventriflo.com
There's also Scandinavian Real Heart (https://realheart.se) from Sweden. They are developing a "total artificial heart" with two chambers and two pumps for a natural blood flow (and pulse).
Longterm animal tests are expected to commence after this summer.
I remember reading, years ago, about someone who was temporarily fitted with a rotary pump. He said his hearing required some adjustment, apparently we sort of constantly hear blood rushing without being aware of it, but that somehow changes when your pulse is gone.
How do these pumps affect blood pressure? Does it become constant? That can't be good for the elasticity of arteries & veins?
The sensation when your heart stops is sudden and terrible. It feels very quiet and you know for sure that something very bad is imminent.
I’m not sure if it comes from the absence of sound or from something else, like the stillness in your chest. The actual stoppages didn’t last that long with me (obviously), but they were very memorable.
When I get a couple of ectopics in a row I already feel like I'm about to keel over, I imagine that even a few missed beats would be immediately obvious and dreadful. Blood pressure would start to drop super fast and I suspect your brain won't be too pleased with that. Well done on surviving that!
I guess if we find that a pulse is required it will be relatively easy to add a "pressure relieve" valve to the rotary design. Pressure builds up and gets released regularly, just like ye good 'ol pump.
Pulse is central to traditional Indian medicine (Ayurveda) [1]. Will be interesting to see what the science finds, although I wouldn’t personally volunteer to have a pumpless-heart. Sounds likely to have unintended consequences as you suggest.
The Carmat artificial heart was also developed as an end point, but it was easier for them to get it approved as a bridge to a transplant. One person had it at least for more than 2 years (it was in 2020 current fate is unknown).
This is not entirely correct. The default mode is pulse-less, but the bivacor can be spun up and down to simulate pulses (based on some articles I found looking at this a while back). I'm most curious about the auto rate adjustment. I'm assuming a built in oximeter? Also future revisions plan on a charge through skin internal battery. That'll be a killer (for lack of a better word) feature.
https://www.bivacor.com/ has a good explanation and video description of the system. It sounds really promising. The things I was most curious about are, it gets a charge from a battery you carry around on your person like a purse, and, it has a ten hour recharge time and comes with two batteries. I think I'd get a few more spares.
I would worry about something like the battery becoming disconnected when I sleep. Hopefully it has a very insistent alarm to alert the user. I'd also worry about getting mugged and having the mugger demand the battery from me.
One idea that seems cool is if you could manually control your blood flow rate. They say it does change but don't clarify if it's manual change or automatic. If it were manual, it would unlock some abilities. You could calm yourself by dialing down your heart rate or "warm up" by dialing it up.
Patients on those types of pumps (continuous flow LVADs) do actually have a pulse of their pump speed settings are properly set. The medical guidance is to set the pump speeds at a setting that allows the natural aortic valve to open once every few heartbeats. That makes it so the aortic valve doesn't calcify and get stuck shut. If they set the pump speed at that level the patients do still have a pulse, it's just a weak one.
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:
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
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
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.
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.
As a layman creating a reliable pump that runs on a battery seems like it would be a fairly easy job for with modern technology. Of course anything mechanical is going to require regular maintenance, but again I wouldn't expect this to be a difficult problem.
What are the complications here? Size? Preventing infection? Does it need to adjust flow rate based on oxygen requirements?
The challenge isn't in building a reliable pump. The challenge is in the connection between the pump and the human body. If we just put a highly polished titanium tube in the circulation there will be blood clots, hemolysis, and other blood damage. Over time these problems become the main hurdle in getting these types of devices to work.
Does anyone have information about the 'external power supply' of the heart in the linked article? I've found some info that is years out of date and I'm wondering how unobtrusive the unit is now.
Yes, typically they include circuitry/ICs for brushless motor controller to spin the thing, plus a few more "motor" controllers if they have active magnetics for bearings, or other reasons. This needs to all be redundant, or otherwise safe in the mission critical sense. Then they have batteries, and all the stuff that goes with connecting the two (power regulation, conditioning, etc) and alarms, etc.
> The Duke patient ... was referred to Duke in June after a sudden, unexpected diagnosis of heart failure. Moore and his wife, Rachel, recently adopted their two-year-old foster son, Marshall, and arrived at Duke expecting only to undergo heart bypass surgery.
39-year-old admitted to the hospital with unexpected heart failure? Is there more to this story? Is this possibly related to the myocarditis being reported with some mRNA reactions?
The story I was told was that president Lyndon Johnson was having heart trouble. Coming right out of the Apollo age, the powers that be said "we can send a person to the moon, why can't we build an artificial heart". They thought it would be a relatively simple problem to solve. At that time the battery technology wasn't there, so the only way to make something work was nuclear power. They came up with an implanted sterling engine, powered by a nuclear thermopile with the cold side of the heat flow being the human body. In that case, the limiting factor for how much power could be generated was how much heat could we dump into the human body without causing things like internal burns and necrosis. They actually built several prototypes, tested them in animals, but never in humans. These devices were enormous, they typically had a large thermopile/sterling engine portion connected by a shaft or hydraulic connection to the pumping portion of the device. Both needed to be implanted in the body, and the devices were entirely mechanical, no electronics needed. The thermopile drove the sterling cycle engine, which then either acted on hydraulic working fluid to actuate the blood pump, or used a shaft or similar to actuate the blood pump from the sterling engine.
I have a feeling there isn’t enough power in nuclear at the scale that would fit inside the body with sufficient shielding. Nuclear is surely for low power devices, but human hearts would actually use a great deal of power (estimate 50-100W). It won’t last for years like you’d expect.
Even if you _can_ package it, still needs batteries for redundancy and clearly those don’t fit inside either. Patients with batteries carry around massive backpacks.
Brings a new meaning to ‘having a meltdown’ though. Overheating nuclear heart would literally boil your blood.
That may be because of the difference between output power and input power needed to produce it. One citation there says the mechanical efficiency of the heart is about 20%.
Exactly, the human heart is a marvel of design and performance.
Typically these devices use between 10-30 watts of power for each side of the heart (in the LVAD case). For an artificial heart (which is two LVADs, basically a LVAD and a RVAD) it's more like 30-60 watts of continuous power.
It’s pretty easy to calculate if we knew how long the battery lasts. We can estimate the size of the battery from the weight of the backpack (6kg) and use the time to flat to estimate the power draw - that’s the actual electrical energy usage of the heart.
My estimation was based on a value that is a fraction of the smallest brushless automotive water pump that I work with, which is smaller than a heart and barely suits a go kart.
Last I read there were a few folks with them still implanted to this day.
It's interesting, one of the major development challenges for these devices was making them safe so that if the patient were to be cremated they didn't create a small dirty bomb.
I just want something like this for my next kidney transplant, I'm so sick of the meds, yes I'm blessed to be alive and living a really good life, but man the 2nd kidney is starting to give me anxiety. Context: Transplant isn't a cure to my autoimmune disease, it will slowly pick away at the graft and have me needing another. Love reading about this kind of stuff.
Lots. The old gen, the only approved one, is actually the continuation of the Jarvik 7 made famous by the Barney Clark case. They've been making and using it all this time. It's now called Syncardia. It's pneumatic and the patients have to carry around a bit pneumatic driver that makes quite a bit of noise during every heartbeat. Patients have large air lines running in and out of their chest to carry the air in and out to drive the diaphragm based pump. It works, bit is not ideal in many ways.
I really feel for those that receive these implants and live with it for a few days more. The first such implant receiver lived for 3 months only. The next one maybe 1.5 years.
Personally I would have preferred to die rather than put a battery and pump inside my body as a heart.
Implanting an artificial heart is, like most surgical operations, a risky endeavor, especially for the first persons who are taking the most risks (and also helping the most to develop our knowledge).
The people choosing to have a new heart implanted do so with full knowledge of the risks, and potential reward (more time alive, helping to develop a new life saving technology/procedure, etc...).
If I get a serious disease that requires me to have a dangerous operation, I would love to have the choice to do so, instead of having to endure the disease with no choice.
I understand 'feeling' for people that have cardiac issues, but I cannot understand 'feeling' specifically for people that have cardiac issues and choose to undergo a risky and potentially saving surgery.
There are people with Heartmate II's (LVADS not artificial hearts, so a bit different) that have lived 10+ years on the devices, with a very high quality of life. That's worth it in my view.
One of the inventors behind Bivacor is Dr. Billy Cohn, an elite heart surgeon with a strong bent toward innovation. He would have an idea, hit his garage to cut up some plastic mesh, seal it, sterilize it, and be trying it in a patient in a few days. He jokes about Home Depot being his best source of medical equipment. In fact, he tells a hilarious Home Depot story in the middle of his standard talk on medical innovation.[1]
[0] https://www.bizjournals.com/houston/news/2021/05/19/bivacor-...
[1] https://youtu.be/iHTVTU8PPGk?t=623