By Alex O’Brien in Discover Magazine
The need to mend broken hearts has
never been greater. In the USA alone, around 610,000 people die of heart
disease each year. A significant number of those deaths could potentially have
been prevented with a heart transplant but, unfortunately, there are simply too
few hearts available.
In 1967 the South African surgeon
Christiaan Barnard performed the world’s first human heart transplant in Cape
Town. It seemed like a starting gun had gone off; soon doctors all around the
world were transplanting hearts.
The problem was that every single
recipient died within a year of the operation. The patients’ immune systems
were rejecting the foreign tissue. To overcome this, patients were given drugs
to suppress their immune system. But, in a way, these early immunosuppressants
were too effective: they weakened the immune system so much that the patients
would eventually die of an infection. It seemed like medicine was back to
square one.
Early
Mechanisms
One solution that researchers have
pursued since the late 1960s is an artificial heart. Perhaps the most
influential device was kick-started by Willem Kolff, the physician-inventor who
produced the first kidney dialysis machine. Kolff invited a fellow medical
engineer, one Robert Jarvik, to work with him at the University of Utah, and
the result was the Jarvik-7. Made up of two pumps, two air hoses and four
valves, the Jarvik-7 was more than twice as big as a normal human heart and
could only be implanted in the biggest patients – mainly adult men. It had
wheels, was as big and heavy (although not as tall) as a standard household
refrigerator, and was normally connected to sources of compressed air,
vacuum and electricity.
In 1982, Jarvik and Kolff won
approval from the US Food and Drug Administration to use it in human patients
and implanted it that same year. Their first patient was a 61-year-old dentist
called Barney Clark, who lived on the Jarvik-7 for 112 days. A second patient
was implanted in 1984 and died after 620 days. History records a total of five
patients implanted with the Jarvik-7 for permanent use, all of whom died within
18 months of the surgery from infections or strokes.
The device has been tweaked and
renamed many times; at the time of writing, it was the world’s only
FDA-approved total-replacement artificial heart device used as a
bridge-to-transplant for patients. Another widely used artificial heart, a
direct descendent of the Jarvik-7, is the SynCardia. And in the early 2000s, Massachusetts-based company Abiomed unveiled a new heart that (unlike the SynCardia) was
designed to be permanent – a total replacement heart for end-stage heart
failure patients who were not candidates for transplant and couldn’t be helped
by any other available treatment.
But all these versions of artificial
heart devices, whether they are meant to support the heart or replace it
completely, are trying to copy the functions of the heart, mimicking the
natural blood flow. The result is what’s called a pulsatile pump, the flow of
blood going into the body like a native heart, at the average of 80 spurts a
minute needed to sustain life. That’s the cause of the gentle movement you feel
when you put your fingers to your wrist or your chest – your pulse, which
corresponds with the beating of your heart.
Today, scientists are working on a
new wave of artificial hearts with one crucial difference: they don’t beat.
Pulseless
Hearts
The Archimedes’ screw was an ancient
apparatus used to raise water against gravity. Essentially, it is a screw in a
hollow pipe; by placing the lower end in water and turning it, water is raised
to the top. In 1976, during voluntary medical mission work in Egypt,
cardiologist Dr. Richard K. Wampler saw men using one such device to pump water
up a river bank. He was inspired. Perhaps, he thought, this principle could be
applied to pumping blood.
The result was the Hemopump, a
device as big as a pencil eraser. When the screw inside the pump spun, blood
was pumped from the heart to the rest of the body. It was the world’s first
‘continuous flow’ pump: Rapidly spinning turbines create a flow like water
running through a garden hose, meaning the blood flow is continuous from moment
to moment.
Because of this, there is no
ejection of the blood in spurts. There is no ‘heartbeat’. The patient’s own
heart is still beating but the continuous flow from the device masks their
pulse, meaning it is often undetectable at the wrist or neck.
And the Hemopump lives on in spirit
of newer devices. Abiomed’s newest heart prototype, Impella, uses similar technology boosted by
leaps in modern engineering. It has a motor so small it sits inside the device
at the end of the catheter, rather than outside of the body. The Impella is the
smallest heart pump in use today – it’s not much bigger than a pencil – and as
of March 2015 has been approved by the FDA for clinical use, supporting the
heart for up to six hours in cardiac surgeries.
Meanwhile, at the Texas Heart
Institute, the HeartMate II is
being developed. Like the Hemopump, it doesn’t replace the heart but rather
works like a pair of crutches for it. About the size and weight of a small
avocado, the HeartMate II is suitable for a wider range of patients than the
SynCardia and has, on paper, a significantly longer lifespan – up to ten years.
Since its FDA approval in January 2010, close to 20,000 people – including
former US Vice President Dick Cheney – have received a HeartMate II, 20 of whom
have been living with the device for more than eight years. All with an almost undetectable
pulse.
The
Future of Heart Transplants
I try to imagine a world full of
people with no pulse. How, in such a future, would we determine if a person
were alive or dead? “That is very easy,” says William (Billy) Cohn, a surgeon
at the Texas Heart Institute, bringing my existential philosophizing to a halt.
“When we pinch our thumb and it goes from pink to white and immediately back to
pink, this means blood is flowing through the body. You can also tell if
someone is still alive if they are still breathing.”
He admits that once more of these
devices are implanted into patients we will need a standard method of
determining such a person’s vitals. Cohn imagines them wearing bracelets or
even having tattoos to alert people to their pulseless state.
I wonder how people will take to
hearts that literally don’t beat. Perhaps it will be the same as when patients
were offered the first heart transplants: resistance, followed by acceptance
due to overwhelming need.
“Any new procedure is going to have
critics,” says surgeon Denton Cooley. “On the day that Christiaan Barnard did
the first heart transplant, the critics were almost as strong, or stronger,
than the proponents of [artificial] heart transplantation,” he says. “A lot of
mystery goes with the heart, and its function. But most of the critics, I
thought, were ignorant, uninformed or just superstitious.”
Cooley performed the first US heart
transplant in May 1968. And at 94 years old he still treasures the memory of
the day, in 1969, when he implanted the first artificial heart into Haskell
Karp and the “satisfaction that came from seeing that heart supporting that
man’s life.”
“I had always thought that the heart
has only one function, and that is to pump blood,” he says. “It’s a very simple
organ in that regard.”
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