Artificial Heart Inventor Turns Focus to Heart-Assist Devices
Robert Jarvik, the inventor of the first successful permanent artificial heart has had a change of heart. He tells IEEE Spectrum that diseased hearts should only rarely be replaced with mechanical ones. Instead, most just need some help pumping until they can recover. He has developed a new pump to do just that, and it's barely a tenth the weight of competing products. He expects such heart-assist devices to become as commonplace as pacemakers.
Jarvik's company, New York City-based Jarvik Heart Inc., is now gearing up for a U.S. Food and Drug Administration trial of its ventricular-assist device, the Jarvik 2000 Flowmaker. Implanted in one of the two ventricles of the heart—compartments that pump blood out of the heart—a ventricular-assist device helps a patient's natural heart pump blood. In the United States they are used as temporary implants until a donor heart can be found, although they've been used as permanent implants in Europe. In fact, the first person to get the Jarvik 2000 implant, now the longest-surviving patient supported by any type of artificial heart, will have had the implant five years in June. More important for patients, the Jarvik 2000 is light as a feather compared with competitors. It's the size of a C battery and weighs just 90 grams, as opposed to its rivals, which weigh at least 1000 grams. Spectrum's Prachi Patel Predd recently spoke with Jarvik about his new device and about the state of artificial heart technology in the United States.
SPECTRUM: What was your goal when you designed the Jarvik 2000?
JARVIK: It was designed to treat the symptoms of heart failure and the physiologic problems of heart failure, by boosting the blood flow of the natural heart. And we wanted it to be used in patients that needed permanent support as well as those that needed short-term support, like the bridge to transplant situation. Our goal was to create a very miniaturized, effective mechanical heart device that would become common like a pacemaker and be available widely to everybody that needed it.
Does the device ever need to be replaced?
Well, you know, presently the longest-living patient with the Jarvik 2000 has lived just a little bit less than five years. In June, it'll be five years, and this is the longest that any patient in the world has lived with any heart-assist device without replacing it. Typically, the currently used device called the HeartMate breaks down in one to two years and doctors have to go in to operate and replace it. With the Jarvik 2000, so far we haven't had a broken blood pump in more than a hundred patients. So far the reliability of our implant is extremely high, and we hope that it will be reliable for more than 10 years with the present model and for much longer than that with improved models.
Does the Jarvik 2000 work like the other devices? If it does, how did you achieve similar results with such a small, lightweight design?
That depends on what you compare it to. A full approval has been given to the HeartMate and Novacor for long-term pump implant, and only HeartMate is approved for permanent use in patients who cannot have a transplant. Now, HeartMate and Novacor are pusher-plate-type pumps [a device where a plate acts as a piston, moving between two sides of a chamber], so they have inflow and outflow valves, resulting in a big heavy mechanism.
The Jarvik 2000 is a rotary blood pump that uses a miniature high-speed axial flow pump [like a spinning coin-size propeller that pushes the blood along]. One of the ways you achieve such extreme miniaturization is by using a very tiny pump that's properly matched to a very tiny motor.
The physics of getting power out of a motor essentially says that the higher the speed you run the motor at, the more power you can get out. Of the different types of rotary pumps the axial-flow pump has what's called the highest specific speed, meaning that it creates the most flow for a certain pump size. Matching an axial flow pump with the proper electric motor and having the right engineering balance of the two so that both of them are working near their maximum efficiency point is what gives a good miniaturized artificial heart at this point.
Do you think that artificial heart technology is where you envisioned it to be when you designed the first artificial heart almost thirty years ago?
No, not at all. [The Jarvik 7, now called the CardioWest heart] has been approved as a temporary heart for bridge-to-transplant and they're working on portable power systems for it, but I really don't believe anymore that it's very wise to remove a diseased natural heart. We're learning that many hearts that had seemed to be hopelessly damaged by heart disease are recoverable. They may not become well enough to take over immediately, but they get better. So I think that it's a rare circumstance that it's best to remove a natural heart and replace it with a mechanical heart.
I think that tiny blood pumps like the Jarvik 2000 will be much better than the types of total replacement hearts that the Jarvik 7 is. I'm not saying the old technology doesn't have usefulness. The CardioWest is doing very well and it's saving lives, but I think that if you want to make a long-term treatment for someone with otherwise incurable heart disease, you should treat them sooner; you don't want to take their natural heart out, you want to assist it to get better.
And the technology for these two options is drastically different. The miniature rotary blood pumps are totally silent; they're very simple, very small, and highly reliable. The only thing they have in common is the result that blood gets pumped, but the way it all works is much better than it used to be. So I think there should be much more research focused on better ventricular-assist devices like the Jarvik 2000.
What direction do you think the research should take in the future?
I think that there are a lot of ways to apply miniature blood pumps, and there are many different patient circumstances. For example, there are patients with congenital heart disease, which means malformation of the heart that they're born with, and those kinds of conditions are going to be able to be treated with small blood pumps that can save children. So there's a lot of potential for different applications, and I think the important thing is to really understand how to make this kind of pump work and how to power it and control it so that there will be more and more designs for different sizes and varieties of applications.
We're working on about four or five different types of miniature pumps right now and there will be quite a few kinds of applications. For example, in addition to the children's version of Jarvik 2000, there's one for infants and one that's for temporary support of the heart in patients that won't need a permanent pump for the rest of their lives.
Of all your accomplishments, which are you most proud of?
The Jarvik 2000, which was developed in part with a National Institutes of Health contract. The goal of the program was to create a heart that would be suitable for five years of high quality of life. What I'm very proud of is the fact that the very first patient in whom we implanted it for permanent use is now at five years of survival. It's very difficult to do this at all but to do it well enough that it actually achieved its goal in the very first patient is unusual, and it's nice that it happened that way.
What's the most challenging part of artificial-heart research?
I think the most challenging task is to find a solution that meets all the diverse needs. You have to find a solution that's suitable in so many numerous ways you know, ethical, medical, engineering, that's the hard part.