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Coronary Stents A stent is a small screen made out of stainless steel in a tubular shape that holds the artery open. The procedure is the same as a balloon angioplasty. After the blockage has been opened to some extent with a balloon, a second balloon with a small crimped stent is positioned at the place of the blockage and expanded. The expanded stent stays in the artery. The healing that occurs in the first 4-6 months will cover the stent, which then has become part of the arterial wall. Stents have been shown to reduce the likelihood of re-blockage. Frequently, new and better stents become available making this procedure easier, allowing our cardiologists to treat some blockages that could not possibly be treated 1 or 2 years ago. A stent is used in about 70-80% of angioplasties today. A stent cannot be used in some patients for a variety of reasons. Sometimes the artery is too small or too weak. Possibly the blockage can’t be reached in the vessel or involves an important side branch, etc. In addition to aspirin, the patients are given medication for 2-4 weeks after the procedure to prevent clotting of the stent. What
is a Coronary Stent? 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).
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 degress
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 and is known as
"recoil." Recoil causes the channel to become smaller shortly
after being enlarged by balloon expansion. The smaller channel produced
by angioplasty causes the blockage to return to its original (or worse)
severity in 30 to 50% of cases. This occurs over a 6 week to 6 month
duration of time and is known as restinosis.
The picture on the right (above) 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), This results in a much more predictable result, reduces
the risk of the artery abruptly closing off during the procedure and
decreases the chance of restinosis by nearly 50% (from 30-50% in cases
of angioplasty, down to 15-25% in cases of stents).
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.
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."
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 "predilation." 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 ballon 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 stent.
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. Th expanded stent is embedded
into the wall of th ediseased 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 artery stenting:
The video on the far left shows a 95% blockage in the proximal portion of the circumflex 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.
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 uncommon. 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 ratio). 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* 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 stent.
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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.