A person dies of cardiovascular disease-related causes every
33 seconds. While the overall rate of heart disease in the US has
shown a promising decline in recent years, one type of heart disease,
heart failure, is on the increase. Patients with milder forms can
be treated with a number of potent medications. However, patients
with more advanced disease have few options. They must either receive
a new human heart from a brain-dead donor or die. The outlook for
these patients is now improving, as temporary implantable pumps
called ventricular assist devices keep patients alive for longer
periods as they await a heart transplant. Perhaps most promising
of all, a new artificial heart is now ready for human trials. I
asked noted transplant authority Dr. Mehmet Oz to provide an update
on this exciting field of medical research.
Thank you for joining us Dr. Oz. To begin with, please review
the status of heart transplantation today in order to help us understand
why we need artificial hearts and ventricular assist devices.
A: One of the problems we have faced as we have improved
the management of patients who would have died of heart disease
is that these surviving patients develop heart failure, which is
now the leading cause of death in this country. As these patients
develop heart failure, we have to replace their hearts. The best
biologic solution has been transplantation. But for the estimated
40-50,000 people per year who might need a heart transplant, we
only have about 2,200 donors. You might ask why we don't push harder
to get people to donate organs, . We do have about 7,000 potential
donors per year. These are often tragic instances where young men
and women have died in car accidents or from gun shot wounds and
the parents aren't ready to make the decision, so it is understandable
that we only get about one third of the potential candidates to
provide their organs. So we have a big gap and the desire to fill
that gap has led us to investigate mechanical solutions for pumping
Let's begin with ventricular assist devices or VADs. What is
a VAD? How does it work and when is it used?
A: A VAD is a ventricular assist device. LVADs assist the
pumping on the left side of the heart, and RVADs assist pumping
on the right side. Most patients are dying of left heart failure,
the thicker chamber that pumps blood to the entire body. When the
heart is unable to pump blood to the head, kidney, arms and legs,
we find the muscle can be replaced best by leaving the heart in
place and putting in a kind of piggy back heart, an assist device
that can perform this role of the heart, without having to remove
LVAD use has become a fairly common procedure. Can you tell
us how these devices have evolved?
A: One of the issues we have had to cope with as VADs were developed
was that we knew we would not manage to create a perfect device
the first time out. Remember, if these devices fail suddenly, you
would have about five seconds to fix it. So we developed a model
that works reproducibly well for months and years. We elected to
keep part of the pump (the cable) that connects the pump to the
power supply (either battery or wall socket) outside the body. It
is also important for us to have access to the pump if we have to
deal with an emergency. So all of these pumps have both electrical
and air connections. If necessary, we can connect to a port and
manually pump air through the device. There have been cases where
a patient is literally pumping the device by hand en route to the
hospital in order to keep the blood flowing.
Haven't newer VAD designs managed to get away from the need
for external power and air venting?
A: Yes, there have been exciting advances in mechanical
heart support devices. In a way it is very similar to the evolution
of the automotive industry at the turn of the century. There are
many parallels between replacing a heart and building an automobile.
For example, both had competitors that were biologically based.
With hearts you have the natural heart or a xenograft (animal) heart.
For the car it was the horse. At first glance the heart and the
horse seemed like better solutions. But they are limited in power.
Ultimately the ability to reproducibly make a device that can save
someone's life is easier to do with a pump than a biological organ.
So these newer devices are based on lessons we've learned from the
first generation devices. We have just started to implant these
in humans in the past year. They are much smaller, about the size
of your thumb. They work more like jet engines than propellers.
The new heart pump devices are based on the use of something called
an axial flow pump. These can swirl the blood forward at very high
speeds. They still require electrical support, but cables are smaller
and the battery packs are smaller.
The axial flow pumps are unusual in that the blood flow is continuous.
Does this mean the patients do not have a pulse?
A: Yes. One of the big challenges we are going to have with
these axial flow pumps is trying to figure out what happens to the
human body when you loose the heartbeat. There are all kinds of
romantic reasons why you want to have a heartbeat- you can tell
if you are nervous or not, and so can the person you are with. The
study of the heart has focused on this internal cadence or metronome.
Yet it may be that we can more efficiently pump blood using these
axial flow pumps. The problem for the medical staff is we don't
know what your blood pressure is. We measure blood pressure by looking
at pulsations. If you don't have a pulse you don't have blood pressure,
so I don't even know if the device is pumping blood or not. You
could be walking around feeling fine, and I would have no way to
identify how your blood is flowing unless I put in a catheter, which
I don't really want to do. So these devices monitor themselves and
give us feedback so we can make intelligent decisions.
How are patients doing?
A: The majority of patients who have received these devices
are still alive and most are doing quite well. Only recently have
they been implanted in reasonable numbers. In US in particular,
FDA approval is only now happening. You will hear more about these
devices as they become more common.
One of the problems with early devices was that patients had
wires coming out of their chest that needed to be plugged into a
battery or other power source. Can you describe how the newer devices
overcome this limitation?
A: We now have mechanisms for providing transcutaneous power
transfer. We have a battery inside the body that can be charged
externally, so the power supply never touches the pump. The benefit
is that we avoid infection, the problem that has been the Achilles
heel of the technology.
The earlier devices also had to equalize the air pressure by
use of external venting tubes. How has the problem of venting been
A: Venting has been a major concern for us. By venting we
mean you have to place a reservoir in the body, because when the
pump fills with blood, the air that was in the pump is displaced
and has to go somewhere, either to the outside atmosphere as in
first generation systems, or to reservoir inside the body. Those
reservoirs unfortunately calcify and fibrose over time and become
rigid and can no longer receive the air as they should, so the pumps
lose efficiency. The virtue of the axial flow pump is that it does
not require air transfer, so we are able to jump that big hurdle.
At the moment, VADs are used either until a patient's heart
recovers from a temporary problem, or in other cases, until a donor
can be found. What are the prospects for using these devices for
longer periods, if not permanently?
A: We have been favorably impressed by the number of patients
who can survive for a number of years with LVADs. To study this
we embarked on large study called REMATCH trial, a $7.5 million
NIH trial comparing how a group of patients with LVADs do in the
long term compared to a matched group receiving optimal medical
management. That trial is in its final stages. Enough patients are
alive that there is considerable interest in following this approach.
We may eventually evolve to a point where if you are younger than
the age of 55 and you need a mechanical heart to keep you alive,
you will receive one as a bridge for weeks or years. Ultimately
you will be offered a transplant. But if you are over the age of
65 or whatever the cutoff will be, you will not be offered a transplant.
Rather, if you require an LVAD, you will get an LVAD.
Another riddle you are dealing with is that some patients hearts
recover sufficiently to let them get off the LVAD? Is there any
way to predict who these patients might be?
A: It is fascinating to those of us who see heart failure
every day to observe that there are patients whose hearts should
be dead and should get mechanical heart support to stay alive, that
somehow recover miraculously to near normal heart function. The
problem is we can't predict whom that will happen with. More importantly,
we cannot predict the duration of that recovery. We are not really
interested in running a windsprint, we want a marathon running heart.
If the heart recovers but only lasts another six months, I should
have transplanted you. That is holding us back. On the other hand
it has opened a huge vista for us. Now we have a model for predicting
heart that should have been dead that are now being kept alive so
we can study them meticulously to determine what happened at a chemical
and hormonal level, but also at a genetic level, at the protein
creation level in individual myocytes that have made this heart
fail. When we tease these issues apart we may be able to offer genetic
solutions to patients dying of heart failure.
Click here to continue to page 2
for a discussion with Dr. Oz of the Abiocor fully implantable
artificial heart and related issues. You will also find extensive
links to multimeda education resources on this topic.
This interview was conducted by Sean Henahan on February 27,
Dr. Mehmet Oz
"So Oz brought a pair of tinsmith's
shears and cut a small, square hole in the left side of
the Tin Woodman's breast. Then, going to a chest of drawers,
he took out a pretty heart, made entirely of silk and stuffed
with sawdust." "Isn't it a beauty?" he asked"
L Frank Baum
The Wizard of Oz
A normally functioning heart pumps about 3 ounces of blood
with each beat, or about 5 or more quarts per minute.
Source- Mayo Clinic
New Window Will Open
LVAD in Action
(Image courtesy Abiomed)
A US First
February 28, 2001, Walter Pae, Jr., M.D. and colleagues
(pictured above) completed the first United States human
implant of the LionHeart™ fully implantable Left Ventricular
Assist System. The procedure was done at Penn State Milton
S. Hershey Medical Center in Hershey, PA.
Axial Flow Pump,
click image to enlarge
Your heart pumps blood through a network of 60,000 miles
Source- Mayo Clinic
a Discussion Forum on Artificial Hearts and LVADs