Most
of the 150,000 Americans with severe coronary artery disease
(CAD) have some degree of angina. Angina
is a recurring pain or discomfort in the chest that occurs when
the heart's need for oxygen increases beyond the oxygen available
from the blood nourishing the heart. It is a common symptom
of CAD (also called coronary heart disease [CHD]), which occurs
when vessels that carry blood to the heart become narrowed and
blocked due to atherosclerosis.
Some
people have such severe and frequent chest pain (angina) that
have a very limited lifestyle. A small number of people who
have chest pain that cannot be adequately controlled by medications
or effectively treated by balloon angioplasty or other surgical
methods may now be able to benefit from new laser surgeries.
What
are the surgeries?
Transmyocardial
laser revascularization
In
transmyocardial laser revascularization (TMR) a high-powered
CO2 (carbon dioxide) laser beam is used to make a series of
holes, the size of toothpicks, in the wall of the heart. The
laser is synchronized with the beating heart, so a heart bypass
machine does not have to be used. Approximately 40 holes are
made 1 cm apart, from the epicardium to the endocardium, the
"outside - in" of the heart.
This
forms a network of channels allows oxygen rich blood to diffuse
from the heart chamber to the outer parts of heart muscle, similar
to how a reptilian's heart receives it's blood. TMR requires
only a 4-inch incision on the left side of the chest, avoiding
a thoracotomy, a long incision down the middle of the chest,
which is needed for heart
bypass surgery.
Percutaneous
myocardial revascularization
Percutaneous myocardial revascularization (PMR) similar to TMR,
is a minimally invasive surgical procedure. A catheter with
an optical fiber which delivers the laser energy is threaded
into the leg through the femoral artery, then guided into the
heart chamber. In percutaneous myocardial revascularization
(PMR) the laser is applied from the "inside - out". In this
procedure the channels do not completely go through the heart
muscle.
How
do the lasers work?
Exactly
how the lasers works in these procedures is not fully understood,
but may be due to a reduction in the perception of pain, formation
of new small blood vessels, or increased blood flow to the heart
muscle. Initially it was thought that the channels remained
open over a long period of time, and continued to supply blood
to ischemic areas of the heart.
However,
when looking at autopsies of the human hearts that had undergone
the procedure, most of TMR channels did not remain open. It
is possible that creating the channels somehow stimulates the
growth of new blood vessels (angiogenesis), which bypassed the
blocked arteries.
Alternatively,
it has been shown that in making the channels, nerves are destroyed
in the myocardium. It may be that all of these factors: angiogenesis,
cutting nerves, and having a few channels remain open play a
roll in the success of TMR. Lastly, the placebo effect may also
play a role in the success of these procedures.
Who
benefits from these procedures?
Most
patients treated with the laser procedure experience considerable
relief from angina, an effect that has been shown to last up
to one year. The laser treatment does not slow the progression
of coronary artery disease.
This
is not a life-saving procedure, and it does not eliminate the
pain completely, but it can provide significant relief of severe
angina and improve the quality of life for a group of patients
for whom there was previously no effective treatment.
Many
of these patients had already had at least one bypass surgery,
and re-operation would have posed a high risk. And some patients
were not able to undergo surgery or angioplasty because of other
medical problems.
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