Questions Surround Future of the Artificial Heart

Advances continue when it comes to artificial hearts. But count Karen May-Newman among the experts who wonder whether the artificial heart truly is the future.

Yes, there are innovations such as the beatless artificial heart pioneered by Billy Cohn, MD, a cardiovascular surgeon and device innovator at the Texas Heart Institute, and his mentor Bud Frazier, MD.

And just days after MPMN's interview with May-Newman, the French company Carmat announced implantation of its own artificial heart, which seeks to imitate the natural heart through size, the choice of structural materials, and innovative physiological functions.

But May-Newman, PhD, thinks much more needs to be done before artificially produced devices can truly imitate human tissues. Meanwhile, advances continue when it comes to growing human tissues and organs in the laboratory.

May-Newman has quite a bit of expertise in this area. She's director of the bioengineering program at San Diego State University, where she designs and runs transparent heart simulators that game out how left ventricular assist devices (LVADs) are changing the flow of blood through the heart and its valves.

Here's more of what May-Newman told MPMN:

MPMN: Cohn and Frazier have been pioneering ways to create a longer lasting heart through impeller technology (like a propeller, but inside a case) similar to what is used in the latest LVADs.

What do you think the prospects are for the beatless artificial heart?

May-Newman: There's potential for replacing the function of the heart. But I think there's more long-term interest in either rejuvenating the native heart by combining the use of LVADs with something that kind repair damaged tissues like stem cell therapy. ... I think a lot of therapies would work well with a device that helps take over the load from the heart as it rebuilds itself. ...

There is some other pretty exciting stuff with Doris Taylor [PhD, at the Texas Heart Institute, formerly of University of Minnesota]. She'll take a heart and dissolve all the cells away, but all the extracellular matrix will be left behind. That includes all the blood vessel structures, all the layers of the heart tissue, everything but cells. It also has the chemical tags and growth factors that encourage cells to grow correctly. ... The hope is you could take cells from a patient that are health, culture them with this matrix decellularized for a cadaver part, repopulate it and make it the patient's own part again for transplant.

There are these other strategies that are totally different that have just as much of a shot at it as the [beatless artificial heart]. There is generally something that the tissue can provide to your blood surface and your body [chemical signals, etc.] that a machine can't. It's more appealing to leave the tissue in there unless it is really diseased.

Leave the tissue in there and help it do its jobs by putting a device in there with it, rather than replace it.

MPMN: What are the major advances with LVADs? What are the design challenges with that?

May-Newman: One of the biggest advances with LVADs happened a few years ago, and that is the shift from pulsatile pumps that are designed like the heart to continuous flow pumps that are designed like mini-turbines.

The difference between those two is that the pulsatile pump usually has a large chamber that is getting bigger and smaller like the heart does. It has valves, one for inflow and one for outflow, that allows it to push in one direction when you're applying pressure. With those devices, the way the device function allows for the surface of the device that's contacted with the blood to be covered with a cell-like surface. ... It's the same type of remodeling the body does for blood vessel replacement. It tries to coat the surface with something that looks nonforeign. They were able to design a pulsatile device, but you had a completely covered blood contacting surface, which made it really nice and friendly to the blood. So the blood didn't form clots as much.

The new design is like a turbine. It has a rotor inside that spins. It has velocity. It's magnetically levitated, so there aren't a lot of obstruction to flow. But it requires that the surfaces remain clean. They don't get that tissue covering. This imparts a lot of the higher shear stress to the blood, which activates platelets to some degree. Plus, it has a highly foreign surface exposed to the blood which also activates platelets.  Generally speaking, these type of pumps ... require anticoagulant usage, while the pulsatile pumps didn't require them. With anticoagulants comes another challenge, which is bleeding. A lot of these patients with the non-pulsatile pumps develop GI bleeding or bleeding in other capillary beds.

There is this whole blood management required with these non-pulsatile pumps. But they're smaller. Certainly from an engineering standpoint they will last longer by the way they are designed. Their power consumption is lower. But they introduce this whole problem with your blood. ...

MPMN: Any chance this challenge could be overcome soon?

May-Newman:  People are trying different things. There is no clear path forward.

With blood contacting devices, it's complicated. Blood is a really complicated fluid that responds in ways we cannot always predict based on the tools we have.

It's one of the things that I think the FDA is really interested in right now, to figure out a way to predict blood clotting in the context of medical devices.

Chris Newmarker is senior editor of MPMN and Qmed. Follow him on Twitter at @newmarker and Google+.