Coronary stent has been one of the therapeutic methods that has had the greatest impact on cardiovascular treatment. A stent is a tubular mesh structure that is introduced into the artery using a catheter and placed in an area of obstruction. The stent is inserted into the end of the catheter in a compressed position and expands in the area of arterial obstruction.
Coronary stent procedure
In the case of implantation of a stent in a narrowed area of a coronary artery, the catheter is inserted through an externally accessible artery, usually the femoral or radial artery. It is then advanced until it reaches the area of obstruction, which is dilated, and the stent is placed. This tubular mesh is then compressed against the inner wall of the artery, in the area where the narrowing occurred.
Before the use of stents, arterial blockages were only dilated with a catheter with an inflatable balloon at its tip (angioplasty). This procedure was quite effective, but had the disadvantage that in a significant percentage of cases the blockage recurred (restenosis). The introduction of stents made it possible to reduce the likelihood of restenosis.
When a stent is to be implanted, the narrowed arterial area is usually first dilated with one or more angioplasty balloons. The stent is mounted firmly on the angioplasty balloon, which is located near the distal end of the catheter. The catheter is advanced to the site of the blockage. Once the balloon with the stent is properly positioned in the center of the arterial narrowing, the angioplasty balloon is inflated to expand the stent and implant it on the inner wall of the artery.
The balloon is then deflated and removed, leaving the stent permanently in place. The purpose of a coronary stent is to prevent the narrowing from occurring again. This is not always successful. The coronary stent implantation procedure is quite common and is used as an alternative to coronary artery bypass grafting. This was the only way to bypass coronary blockages in the past. However, angioplasty is not always possible, and certain characteristics of the blockage must be assessed to determine whether a stent is appropriate, such as the size of the artery and the location of the blockage.
Types of coronary stents
The classic stent is a tubular stainless steel mesh. Many stents have been designed using different materials, structures, designs, and placement methods. Thus, stents have been made from tantalum, nitinol, platinum, cobalt alloys and others. The structures have been in the form of a fenestrated tube, multicellular mesh, spirals, and others. In terms of placement methods, there are not only balloon-expandable stents, but also self-expandable ones. In more recent years, stents have been developed using absorbable materials, which are polymers that disappear when they dissolve over time.
On the other hand, the most commonly used stents today are the so-called drug-eluting stents, which are coated with an agent that inhibits cell proliferation and therefore reduces the incidence of restenosis. The cytostatic drugs used have been diverse, such as sirolimus, everolimus, zotarolimus, tacrolimus, paclitaxel, etc.
The drug is slowly released into the artery over approximately 30 days after implantation. Its effect is to inhibit cell division and growth, and the activation and proliferation of T cells. These are the cells that initiate the inflammatory response that commonly follows implantation and which can lead to restenosis. With uncoated stents, restenosis occurs in 15% to 25% of patients. The rate of restenosis in patients receiving a drug-eluting stent is less than 5%.
Indications
Currently, a stent is implanted in most cases where a coronary stenosis is dilated, since it significantly reduces the likelihood of restenosis. In very few cases, angioplasty without a stent is performed. A stent is indicated in patients with angina or myocardial infarction. In patients with stable angina that is not adequately controlled with medication, coronary angiography is recommended. If severe lesions amenable to angioplasty are found, one or more stents are placed.
In patients with unstable angina, coronary angiography and implantation of one or more stents in severe lesions is usually performed. In the case of acute myocardial infarction, stent implantation is also common. In all situations, the lesions must be located in arteries of sufficient caliber, in more or less straight areas (not in bends or bifurcations) and must be susceptible to dilation, since in older chronic obstructions, it is generally not feasible to open them. Dilating the artery improves blood flow in the corresponding area of the myocardium and thus relieves the patient’s symptoms and, in some cases, even improves the prognosis.
Stent risks
The most important initial problem after stent implantation is the risk of thrombosis in the implantation area, since the stent is a foreign material that remains in contact with the blood and, therefore, tends to form a thrombus. This would lead to unstable angina or acute myocardial infarction during the same procedure or shortly after.
Therefore, patients undergoing stent implantation are initially treated with heparin and two antiplatelet agents. After discharge from hospital, the patient must continue with dual antiplatelet therapy for a period of time, which may be 3 to 6 months, although it is usually recommended for a year. Stent thrombosis after one year of stent implantation is very unlikely. The other major issue with stents is restenosis, which occurs more slowly than thrombosis, and can occur shortly after the procedure or years later.
People who have a stent implanted can lead a completely normal life, with the logical limitations imposed by their illness, but not by the stent in particular. Although there were initially doubts about the influence of magnetic resonance on the stent, it has been shown that patients with one or more stents can undergo magnetic resonance in complete safety. However, some advise against it during the first 6 to 8 weeks to avoid the small possibility of the stent moving. Likewise, the patient does not have to take any precautions if they have to go through a metal detector, such as at airports, since these devices do not affect the stent.