Roshan
Pakistan : Health Issues : ARTIFICIAL
HEART
..
Your heart is the
engine inside your body that keeps everything running. Basically,
the heart is a muscular pump that maintains oxygen and blood
circulation through your lungs and body. In a day, your heart
pumps about 2,000 gallons of blood. Like any engine, if the heart
is not well taken care of it can break down and pump less
efficiently, a condition called heart failure.
The AbioCor is the first artificial heart to be used in
nearly two decades.
Until recently, the
only option for many severe heart failure patients has been heart
transplants. However, there are only slightly more than 2,000
heart transplants performed in the United States annually, meaning
that tens of thousands of people die waiting for a donor heart. On
July 2, 2001, heart failure patients were given new hope as
surgeons at Jewish Hospital in Louisville, Kentucky, performed the
first artificial heart transplant in nearly two decades. The AbioCor
Implantable Replacement Heart is the first completely
self-contained artificial heart and is expected to at least double
the life expectancy of heart patients.
The average adult human heart pumps
blood at a rate of 60 to 100 beats per minute.
In the first
stage, the right and left atria contract at the same
time, pumping blood to the right and left ventricles.
In the second
stage, the ventricles contract together to propel blood
out of the heart.
The heart muscle then
relaxes before the next heartbeat. This allows blood to fill up the
heart again.
Chambers of a natural heart
Patients with an
implanted AbioCor heart will still have atria that beat at the same
time, but the artificial heart, which replaces both ventricles, can
only force blood out one ventricle at a time. So, it will
alternately send blood to the lungs and then to the body, instead of
both at the same time as a natural heart does. The AbioCor is able
to pump more than 10 liters per minute, which is enough for
everyday activities.
Diagram of the AbioCor heart
The AbioCor,
developed by Abiomed, is a very sophisticated medical device, but
the core mechanism of the device is the hydraulic pump that shuttles
hydraulic fluid from side to side. To understand how it works, let's
look at the various components of the system:
Hydraulic pump
- The basic idea with this device is similar to the hydraulic
pumps used in heavy equipment. Force that is applied at one
point is transmitted to another point using an incompressible
fluid. A gear inside the pump spins at 10,000 revolutions per
minute (rpm) to create pressure.
Porting valve
- This valve opens and closes to let the hydraulic fluid flow
from one side of the artificial heart to the other. When the
fluid moves to the right, blood gets pumped to the lungs through
an artificial ventricle. When the fluid moves to the left, blood
gets pumped to the rest of the body.
Wireless
energy-transfer system - Also called the Transcutaneous
Energy Transfer (TET), this system consists of two coils,
one internal and one external, that transmit power via magnetic
force from an external battery across the skin without piercing
the surface. The internal coil receives the power and sends it
to the internal battery and controller device.
Internal
battery - A rechargeable battery is implanted inside the
patient's abdomen. This gives a patient 30 to 40 minutes to
perform certain activities, such as showering, while
disconnected from the main battery pack.
External
battery - This battery is worn on a Velcro-belt pack around
the patient's waist. Each rechargeable battery offers about four
to five hours of power.
Controller
- This small electronic device is implanted in the patient's
abdominal wall. It monitors and controls the pumping speed of
the heart.
The AbioCor heart,
which is composed of titanium and plastic, connects to four
locations:
The surgery to implant a AbioCor
artificial heart is extremely delicate. Not only are the surgeons
cutting off and extracting the natural heart's right and left
ventricles, but they are also placing a foreign object into the
patient's chest. The patient must be placed on, and later removed
from, a heart-lung machine. The surgery requires hundreds of stitches,
to properly secure the heart to artificial ventricles, and grafts
to connect the AbioCor to remaining parts of the natural heart.
Grafts are a kind of synthetic tissue used to connect the artificial
device to the patient's natural tissue.
Surgeons implanting the AbioCor heart
Due to the complexity
of the surgery, there are lots of medical personnel on-hand during
the operation. The surgery on July 2, 2001, which was the first of
its kind in the world, included a team of the two lead surgeons, 14
nurses, perfusionists, anesthesiologists and other support staff.
Here is the
procedure, as described by University of Louisville surgeon
Robert Dowling:
Surgeons implant
the energy-transfer coil in the abdomen.
The breast bone
is opened and the patient is placed on a heart-lung machine.
Surgeons remove
the right and left ventricles of the native heart. They leave in
the right and left atria, the aorta and the pulmonary artery.
This part of the surgery alone takes two to three hours.
Atrial cuffs are
sewn to the native heart's right and left atria.
A plastic model
is placed in the chest to determine the proper placement and fit
of the heart in the patient.
Grafts are cut to
an appropriate length and sewn to the aorta and pulmonary
artery.
The AbioCor is
placed in the chest. Surgeons use "quick connects" --
sort of like little snaps -- to connect the heart to the
pulmonary artery, aorta and left and right atria.
All of the air in
the device is removed.
The patient is
taken off the heart-lung machine.
The surgical team
ensures that the heart is working properly.
Abiomed officials
have cautioned against overly-optimistic results for the first
patients to receive a transplant. While doctors hope for more, the
device is only designed to double life expectancy for
patients who had only about 30 days to live prior to the operation.
The most optimistic predictions are that a patient could currently
live up to six months with the AbioCor heart.
Robert Tools,
the patient who received the heart transplant on July 2, 2001, at
Jewish Hospital in Louisville, remains hospitalized. Doctors have
not said when or if the patient will be able to return home.
The U.S. Food and
Drug Administration (FDA) has cleared Abiomed to perform five
initial implants. The surgery to implant these hearts will take
place at medical centers in Houston, Los Angeles, Boston and
Philadelphia. Dates or candidates for the operation are still
unknown as of July 23, 2001. The FDA will review the results of
these transplants on a case-by-case basis to determine the future of
the AbioCor device. If the $70,000 to $100,000 device is successful,
meaning it can prolong the life of a patient without complications,
it could be approved for use in more heart centers around the United
States.
Laman Gray said that
initial candidates for the heart will be the "sickest of the
sick." FDA and Abiomed officials have laid a few parameters for
who can become one of the initial recipients of the artificial
heart. The patient must fit the following profile:
Have end-stage
heart failure
Have a
life-expectancy of less than 30 days
Is not a
candidate for a natural heart transplant
Have no other
viable treatment option
Another requirement
is that the grapefruit-sized device must fit inside the patient's
chest. To determine the fit of the device, the patient must undergo
a CAT scan and chest X -ray. Then, using a computer-aided design
(CAD) program, the natural heart is virtually removed and the
AbioCor heart is virtually placed in the patient's chest. If the
computer program shows that the device will fit, doctors can proceed
with the operation to implant the artificial heart.
X-ray of the AbioCor device implanted in a patient
For nearly two months
following the surgery, hospital and AbioMed officials kept the name
of the first recipient a secret. However, on August 21, 2001,
it was revealed that Robert Tools, a Kentucky resident and
former telephone company employee, was the history-making patient.
Although Tools has battled an infection and needed a ventilator
following his surgery, his doctors report that the mechanical heart
continues to function without problems.
Patient Robert Tools with Dr. Laman Gray (left) and Dr.
Robert Dowling (right)
Here is what was
known about Tools prior to his surgery:
He suffered from
class IV heart failure.
He had severe
bi-ventricular failure.
He was turned
down by a heart transplant center.
He has undergone
previous coronary bypass surgery.
He has had
multiple heart attacks.
He has diabetes.
Currently, there are
between 2 million and 3 million Americans living with heart failure,
and 400,000 new cases are diagnosed annually. Heart failure causes 39,000
deaths per year, according to the National Heart, Lung,
and Blood Institute (NHLBI). Most people diagnosed with heart
failure can expect to live about five years, and will usually need
to have a heart transplant to extend their life.
In the United States
alone, 2,184 heart transplants were performed in 1999, and 2,340
were performed in 1998. However, thousands of potential recipients
die annually while waiting for a heart transplant. Doctors still
encourage the public to become organ donors, but the AbioCor may
save many of those who don't have the option of a natural transplant
or of waiting for an available heart.
