The Jarvik-2000 is gettIng close to human trials.
O. H. Frazier
Part 2 | Back to Part 1
NOVA: What are the advantages of continuous rather than pulsatile (pulse-like) flow?
Frazier: With continuous flow, there isn't a pulse. Without a pulse,
it is not necessary to have volume compensation for the heart. If volume compensation
isn't needed, then we don't have to penetrate the skin. If we don't have to penetrate
the skin, then we can do away with what I think is the most important problem with
long-term devices being used now—infection.
So, continuous flow has many advantages, although it wasn't widely considered until recently
because we didn't know whether patients could live without a pulse. Maybe complications would
result from pulseless flow. Maybe nature intended for us to have a pulse. How do you feed
the pump that pumps the blood (and nutrients) to the rest of the body? The only way to
do that is to give the heart a rest. So, we have a pulse to allow the heart to get its
rest and renewed energy. It's a remarkable organ in that regard.
NOVA: Do you think the AbioCor total artificial heart [which is slated to begin human
trials in the year 2000] is ready for use in human patients?
Frazier: We're very anxious to use this technology because we will be able
to help patients who aren't being helped now. I think we've validated this concept
biologically more than adequately. We have studied more than 100 animals with the
AbioCor heart, some for more than 100 days, and the pump has worked very well.
If it lasts that long in animals, it will work in humans. Reliability testing and
further wear testing are ongoing.
NOVA: What are the specific advantages of the AbioCor heart?
Frazier: What we need is a solution for heart failure that will allow patients
to leave the hospital, go back to what they were doing before, and lead meaningful
lives. The HeartMate [an LVAD that has been implanted in over 1,500 patients to date]
does this to some degree now. Some of our LVAD patients have been able to return to
work. But the device is large and loud, and it is powered from outside the body, so
it needs to be improved upon.
trials soon, the AbioCor total artificial heart will be entirely enclosed within the chest.
The AbioCor artificial heart is small, and it was designed for the human heart.
The first artificial hearts were designed more for the calf, and the first patients
who received those devices were large people. Barney Clark, for instance, was a huge
man. He weighed more than 300 pounds, and he was well over 6'4" tall. But the AbioCor
pump is designed for the average-sized adult. It's still too big for small adults,
but it will fit in most of the U.S. adult population.
Another advantage is that the AbioCor pumps alternately right to left. So it doesn't
pump both to the lungs and the body at the same time, like the normal heart, but it
pumps side to side. This is an important advantage, because the bulk of the volume
compensation that a pulsatile pump needs can be adjusted by using alternating
ventricles. So when the left side is pumping, the right side is a volume chamber, and vice versa.
NOVA: Why is that important?
Frazier: Well, the right heart and the left heart don't pump the same amount
of blood; the left heart pumps more. So there has to be some way of compensating for
that variance between the two sides of the heart and the amount of blood pumped. This
has been done in a very ingenious way by the engineers who developed the AbioCor
heart—a really outstanding engineering accomplishment. They designed a small
compensation chamber, which acts in a way to allow the right side of the heart
to sense whether it needs to pump more blood or less blood. It automatically adjusts
internally according to changes within this little chamber.
It also has a beautiful advantage that I think will make it much less thrombogenic
(that is, it will have a very low problem with blood clots or strokes). As in normal
human circulation, the blood never stops in this pump. Whenever blood stops,
it has a tendency to form clots, and patients need aggressive thinning of the
blood. But in the AbioCor, the blood is always moving, either on the right or
left side. So, I think that patients will not need as much blood thinning
medication with this device, and the incidence of strokes will be lower.
Frazier believes that the new AbioCor heart will most benefit patients who would otherwise die within a few days after a heart attack or open-heart surgery.
NOVA: Which patients do you think the AbioCor will benefit most?
Frazier: The bulk of patients who die within a few days after a heart attack
or after open-heart surgery could benefit from these pumps, because they need both
ventricles. Artificial hearts are like transplants except they can't be rejected,
and they can also be produced in unlimited quantities.
NOVA: And the AbioCor will be totally enclosed within the body?
Frazier: Yes. The technology to transmit energy across the skin—that is,
without going through the skin—has been available for years. Remember the high
school experiment in which you lit an electrical bulb by bringing an electrical
field close to the bulb? It's the same principle. A small coil inside the body can
be supplied with energy from a small coil on the outside of the body during day-to-day
activities. The pump will also have a small internal battery that will supply energy
for short periods of time when power needs to be completely internal, like when a
patient is taking a shower.
And it's totally quiet. Because of that, I think patients will be able to go
back to work easily. Patients with these hearts will look like
anyone else—with no tubes or wires to be seen. These patients will be able to
work and live in much the same way as a normal person does.
NOVA: Will we still need LVADs and other heart-assist devices?
Frazier: I think it's important for surgeons to have a variety of options,
because patients have so many variables, beginning with their size and including
things as complicated as the amount of resistance within the lungs and whether
the patient needs a total heart or a partial heart. There are many different
causes of heart failure, and a technology is needed that best addresses that
cause. For example, if you thInk the patient's heart wIll recover with a few
months of rest, then a small pump that can be put in with very few
complications would be best. You don't want to take the whole heart
out and put in an artificial heart if all the patient needs is a small
LVAD has been one of the more successful of the left ventricular assist devices.
When we first started using the HeartMate in 1986, we used it in very few patients.
Last year, more than 500 patients in the United States who would have died had this
pump implanted. But the need is still much greater than that, because the number of
patients dying prematurely of heart disease is far in excess of what we should accept.
I think that all of the very different technologies we have discussed will
play a big role in the treatment of heart disease. To have all of these varying
technologies available off the shelf is our goal. I'm not sure if it will take
two years or 20 years, but I think it will be achieved.
Photos: (1,2) NOVA/WGBH; (3) WGBH; (4) courtesy of Richard Wampler; (5,7,8) Texas Heart Institute.
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