Coronary Stents

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.

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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.