What is a coronary stent?
How is coronary stenting performed?
How long does it take?
How safe is it?
Show me the results of a stent
Why are stents not used in all
cases of angioplasty?
What special treatment is needed
following a stent procedure?
What is a Coronary Artery
stent? A coronary stent is stainless tube
with slots. It is mounted on a balloon catheter in
a "crimped" or collapsed state. When the
balloon of is inflated, the stent expands or opens
up and pushes itself against the inner wall of the
coronary artery. This holds the artery open when the
balloon is deflated and removed. Coronary artery stents
were designed to overcome some of the short comings
of angioplasty. Angioplasty is a technique that is
used to dilate an area of arterial blockage with the
help of a catheter with an inflatable, small, sausage-shaped
balloon at its tip. Although introduced over two decades
ago, angioplasty continues to be the most frequently
employed procedure in the cardiac cath lab (either
by its self, or in conjunction with other procedures
such as coronary stenting).
However, coronary angioplasty has
two shortcomings. Firstly, the opening created by
the procedure is not very smooth because the balloon
does not evenly expand all areas that have different
degrees of hardness (atheroma is soft, plaques are
hard and mixture of the two have a medium and uneven
degree of hardness). This produces a channel with
an irregular shape and a rough surface that is covered
with superficial or deep cracks. The irregular surface
and the cracks on the inner lining of the artery increases
the risk of complete arterial blockage in a very small
number of patients. The picture on the left (below)
shows a blockage prior to angioplasty, while the picture
in the middle demonstrates the artists rendition of
the angioplasty results.
Secondly, some of
the compressed material tends to "spring back"
to some degree. This is known as "recoil."
Recoil causes the channel to become smaller shortly
after being enlarged by balloon expansion. Moreover,
the material within the expanded channel starts to
multiply after the channel is expanded. This causes
a gradual build-up of material. In 30-60% of cases,
the build-up of material can be large enough to cause
the blockage to return to its original (or worse)
severity. This occurs over a 6 week to 6 month duration
of time and is known as restenosis.
The picture on the left (above)
shows a cross-section of a coronary artery at the
level of a blockage or stenosis. The diagram on the
extreme right shows an increased opening after the
blockage was treated with a coronary stent. A stent
is a metal "mesh" that is mounted on an
angioplasty balloon. When the balloon is inflated,
it expands the stent and opens up the diseased segment
into a rounder, bigger and smoother opening (compared
to angioplasty, which is shown in the middle picture
as having a more "frayed" appearance), Stents
induce a more predictable and satisfactory result,
reduces the risk of the artery abruptly closing off
during the procedure and also decreases the chance
of restenosis (recurrence of the blockage) by nearly
50% (from 30-50% in cases of angiopalsty, down to
15-25% in cases of stents).
Like angioplasty, coronary stents
physically opens the channel of diseased arterial
segments, relieves the recurrence of chest pain, increases
the quality of life and reduces other complications
of the disease. Since it is performed through a little
needle hole in the groin (or sometimes the arm) it
is much less invasive than surgery and can be treated
with another needle or percutaneous procedure should
the patient develop disease in the same, or another,
artery in the future.
How is Coronary Artery
Stenting performed? Prior to performing stenting,
the location and type of blockage plus the shape and
size the coronary arteries have to be defined. This
helps the cardiologist decide whether it is appropriate
to proceed with angioplasty or to consider other treatment
options such angioplasty, atherectomy, medications
or surgery. Cardiac catheterization (cath) is a specialized
study of the heart during which a catheter or thin
hollow flexible tube is inserted into the artery of
the groin or arm. Under x-ray visualization, the tip
of the catheter is guided to the heart. Pressures
are measured and an x-ray angiogram (angio) or movie
of the heart and blood vessels is obtained while an
iodine- containing colorless "dye" or contrast
material is injected into the artery through a catheter.
The iodinated solution blocks the passage of x-rays
and causes the coronary arteries to be visualized
in the angios. In other words, coronary arteries are
not ordinarily visible on x-ray film. However, they
can be made temporarily seem by filling them with
a contrast solution that blocks x-ray.
As discussed in the cardiac
cath section, a sheath is introduced in the groin
(or occasionally in the arm). Through this sheath,
a long, flexible, soft plastic tube or guiding catheter
is advanced and the tip positioned into the opening
or mouth of the coronary artery. In the picture below,
the catheter tip is positioned in the mouth of the
left main coronary artery.
The tube measures 2 to 3 mm in diameter. The tip of
the catheter is directed or controlled when the cardiologist
gently advances and rotates the end of the catheter
that sits outside the patient.
Once the catheter tip is seated
within the opening of the coronary artery, x-ray movie
pictures are recorded during the injection of contrast
material or "dye."
After evaluating the x-ray
movie pictures, the cardiologist estimates the size
of the coronary artery and selects the type of balloon
catheter and guide wire that will be used during the
case. Heparin (a "blood thinner" or medicine
used to prevent the formation of clots is given. In
most cases, coronary stenting is preceded by angioplasty.
This is known as "pre-dilation." It helps
open up the blockage area, and makes it easier to
deliver the stent.
The guide wire which is
an extremely thin wire with a flexible tip is inserted
into the catheter. The tip of the wire is then guided
across the blockage and advanced beyond it. This wire
now serves as a "guide" or rail over which
the balloon catheter is passed. The tip of the stent
balloon catheter is then positioned across the lesion.
The balloon is situated on the tip of the catheter
shaft and is inflated by connecting it to a special
hand-held syringe pump. A mixture of saline and contrast
material is used to inflate the balloon. The balloon
catheter has metallic markers (at either side of the
balloon). The unexpanded stent is mounted just inside
these visible metallic markers that helps the cardiologist
know the location of the otherwise poorly visible
Inflation is initially carried
out at a pressure of 1 - 2 times that of the atmosphere
and then increased to 8 - 12 and sometimes as high
as 20 atmospheres, depending upon the type of stent
that is used. The handheld inflation syringe has markers
that are used to determine the pressure. The balloon
is kept inflated for 30 to 60 seconds and then deflated.
The expanded stent is embedded into the wall of the
diseased artery, holding it open. If not satisfied
by the results, the cardiologist will further expand
the stent using another balloon (frequently it is
the same balloon catheter that was used for "pre-dilation.".
Results of coronary
The video on the left (above)
shows a 95% blockage in the proximal portion of the
left anterior descending coronary artery (arrow). The video to its
right shows no remaining blockage after the patient
was treated with a coronary artery stent.
The patient remains awake
throughout the procedure and mild sedation is used
to ensure relaxation and comfort. The deflated balloon
and wire are withdrawn when the cardiologist is satisfied
with the results.
The sheath is secured to the
groin and the patient is sent to his or her room.
The sheath is removed when the effect of Heparin wears
off. This is determined by obtaining blood tests at
specified intervals. Pressure is applied to the groin
with a clamp. Once it is confirmed that there is no
bleeding, a sandbag or ice bag is placed over the
After approximately 6 hours,
the patient is ambulated or allowed to walk with assistance
and is usually discharged the following morning. A
Band-Aid or small dressing is applied over the tiny
needle hole. Slight bruising around the site is not
In some labs, a sealant device is applied in the cath
lab after removal of the sheath.
For a description of the equipment,
preparation and experiences during the procedure,
please review the cardiac
cath section. It is not uncommon for patients
to experience chest discomfort while the balloon is
inflated. This usually resolves when the balloon is
deflated. Patients who are uncomfortable can be given
intravenous medication to alleviate this problem.
How long does the procedure
take? It can take anywhere from 30 minutes
to an hour to perform the entire case. The duration
is dependent upon the technical difficulty of the
case and the number of balloon catheters that have
to be employed.
How safe is the procedure?
In the hands of experienced cardiologists, and with
availability of modern day technology, it is estimated
that the risk of death is during a stent procedure
is usually less than 1%, while the chance of requiring
emergency bypass surgery is around 2% or less. It
is a relatively safe procedure and is carried out
all over the world. An "out patient" or
an inpatient uncomplicated stent case usually require
23 hours or less of hospitalization after the procedure.
The risk of a other serious complication
is estimated to be less than 4 and probably around
1 to 2 per thousand, and similar to that described
for cardiac cath. The risk of a heart attack and bleeding
that requires a blood transfusion is increased when
compared to cardiac cath. However, the risks are relatively
low and acceptable in most cases when one balances
the potential benefit against the expected risk (risk-benefit
The aggravation of kidney
function (particularly in diabetics and those with
prior kidney disease) is higher than that expected
with cardiac cath because of the larger amount of
contrast material that is usually required. In such
cases, the cardiologist takes extra precautions to
prevent this possible complication.
The stent is completely covered
by natural tissue in a matter of 4 - 6 weeks.and the
risk of clot formation is nearly absent by that time.
In very few cases (1 chance out of 200) a clot may
form during the first two weeks after a stent procedure).
Such patients develop symptoms of a heart attack.
With prompt treatment, the majority of these stents
can be reopened.
If coronary artery stenting
is superior to angioplasty, why is it not used in
every single case? Good question! If stents
could be delivered to every lesion, and if it had
the same good short and long term results in every
case, it would be used in 100% cases of angioplasty.
However, this is not the case. Stents are difficult
to deliver across tight bends in blood vessels (particularly
if they have a lot of calcium deposits in the wall)
and are not usable in very small blood vessels. There
are other types of technical considerations that also
come into play. Today, it is estimated that stents
are employed in nearly 50-75% of cases.
What special treatment
is needed after a coronary stent procedure?
Coronary artery stents are foreign metallic objects
that are left inside the coronary artery. Special
precautions have to be taken to prevent them from
being covered with clot. Medications that make platelets
less active has been found to be extremely effective
in preventing clots. A combination of soluble aspirin
(Bayer Aspirin* is an example) and Plavix* is very
popular in the USA. (* = Trade Names of the manufacturers).
The medications are started either before or during
the procedure. Aspirin is continued indefinitely if
the patient is not allergic to the medication and
does not develop any problems with it. Plavix* is
usually stopped in 4 - 6 weeks because the stent is
usually completely covered by natural tissue during
that period and the risk of clot formation is nearly
absent by that time.
If patients are allergic
to aspirin or Plavix(R) or are unable to take medication
because of bleeding or other problems, the cardiologist
may employ alternative medications (depending upon
the problem) and even delay or avoid the use of a