Coronary Stent
Huma Abdul Rauf
Maria Gonzalez
BMED 101-04, Fall 2011
Wentworth Institute of Technology
Dr. Douglas Dow
Dr. Shankar Krishnan
Abdul Rauf and Gonzalez
BMED 101-04
Table of Content
Introduction……………………………………………………………………………………..3
Objective ………………………………………………………………………………....…. 4-5
Background History ………………………………………………………………………….5-6
Principles …………………………………………………………………………….………6-8
Current Application/ Future Work ……………………………………………………….....8-11
Conclusion…………………………………………………………………………………….12
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Introduction
Over decades, technology has evolved drastically and knowledge in science has increased
rapidly. Thus, when technology has increased rapidly many questions has been answered prior to
health problems and cures for disease. Atherosclerosis which is known as blockage or hardening
of arteries, has been around for decades and increased the risk of heart attack, stroke and angina.
Cardiovascular disease is the number one leading cause of death in United States. Majority of
these cardiovascular diseases are caused by atherosclerosis also coronary arteries disease.
Therefore, the discovery of coronary stents has decreased rate of deaths that are caused by
cardiovascular diseases.
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Objective
The objective of the following research project is to overview the effects of stents and benefits
on society. This project mainly focuses on coronary arteries and how they have evolved over
time and the future work that is being researched.
Atherosclerosis and Coronary Stent
Atherosclerotic Peripheral Vascular Disease, hardening of arteries, which primarily
affects the arteries. Atherosclerosis can affect any party of the body. Atherosclerosis of coronary
arteries is generally limited to the large superficial epicardial vessels before they give off
branches that bring blood to the heart muscle. Developed atherosclerotic plaques consist of a
central core of lipid and cholesterol crystals and cells such as macrophages, smooth muscle cells
and foam cells along with necrotic debris, proteins and collapsing blood elements. This central
core is separated from the lumen by a fibrous cap in collagen. The major complications of
atherosclerosis result from progressive obstruction of a vascular lumen, disruption of a plaque
followed by thrombus formation and also destruction of the primary vascular wall.
Figure 1: Atherosclerosis is caused by buildup of plaques in the walls of arteries. People with
high level cholesterol and are obese are at high risk and higher chance of getting coronary disease.
The most important complication is myocardial infarction, which is permanent injury to
heart muscle initiated by complete thrombotic occlusion following rupture of an atherosclerotic
plaque that previously was only partially obstructive. The natural history of athermanous plaque
and the effectiveness and safety of interventional therapies depend in part on relative plaque
composition, the spatial distribution of the constituents and the integrity of the fibrous cap, which
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largely determines plaque stability. Risk factors for atherosclerosis and coronary artery disease
include diabetes, systemic arterial hypertension, high levels of cholesterol, and smoking.
Angioplasty is used in patients with stable angina, unstable angina, or acute myocardial
infarction to restore blood flow through a diseased portion of the coronary circulation obstructed
by atherosclerotic plaque and thrombotic deposits. A deflated balloon is passed over a guide wire
to a site of stenosis, where the balloon is inflated using progressive and substantial expansible
force. Enlargement of the lumen and increased blood flow occurs by plaque reduction through
compression or rearrangement of the plaque contents and by overall mechanical expansion of the
vessel wall.
Figure 2: Procedure of angioplasty and a stent is inserted to keep the arteries open.
http://www.youtube.com/watch?v=3Srimon14CY&feature=related
Background History
In 1964, Charles Theodore dotter and Melvin P. Judkings described the first angioplasty.
And in 1974, Andreas Gruentzig tested using balloons on animals to test the procedure to open
an artery. Angioplasty was a innovative treatment that led to the beginning of a great advanced in
the cardiovascular field of medicine. Since the beginnings of stents and angioplasty many
discoveries has been developed and like mentioned later great plans are in the table for the future
of stent and angioplasty procedure. Today angioplasty is the most frequently performed medical
procedures in clinical practice today.
Coronary stents used in angioplasty where first develop in the 1980’s. and approved by
the FDA in the USA in the mid 1990’s their placement is made through a balloon angioplasty to
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treat coronary artery blockages. After balloon angioplasty reduces the narrowing of the artery
stent is placed immediately leaving a residual stenosis of 10% or less of the original stenosis of
the artery. In addition to treating coronary artery stents are used during angioplasty of any other
arteries of the body, for example, is commonly used in kidney arteries, arteries of the lower
limbs mainly in the iliac and has now been demonstrated effectiveness and safety of angioplasty
for the treatment of blockages of the carotid arteries. This Coronary angioplasty improves the
circulation to provide important benefits to society like lower chest pain, decreased the
possibilities for stroke , heart attacks and decrease pain in leg arteries. Stents are not all alike,
come with different textures, plasticity, elasticity, radial strength, diameter and other
properties. Stents are essentially permanent devices become a part of the cardiovascular
system. Stents have the risk of two long-term complications. First there is the possibility of
recurrence in narrowing it at the site of stent placement (restenosis), the risk of restenosis is
approximately 20% within the first 6 months of opposing the risk placed 30 - 40 restenosis
following made only to Balloon Angioplasty.
coronary artery: insertion of a stent into a coronary artery. Photograph.Encyclopædia Britannica
Online.
Principles
Stents were first developed in the 1980s to address the problems and side effects of
balloon angioplasty. Most patients who received balloon angioplasty would have a case of
restenosis. Thus, most patients who undergo angioplasty also receive stents. Stents are
expandable tubes of metallic wire and were designed to be flexible. Stents preserve luminal
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patency and provide a larger and more regular lumen by acting as a support to the disrupted
vascular wall. Stents were also introduced to minimize thrombus formation following
angioplasty and thereby reduce the impact of post angioplasty restenosis. Stent technologies have
rapidly increased. The majority of stents in use today are composed of balloon expandable 316L
stainless steel or nitinol mesh tubes that range from 8 to 38 mm and from 2.5 to 4.0 mm in
diameter. Current stents that are in use today are follows: Cordis Palmaz-Schatz stent, the Cordis
Crossflex stent and Medtronic stent. Development has focused on permitting stents to become
more flexible and more easily delivered and deployed. The choice of stent is based on several
factors, including the characteristics of a given plaque, such as its diameter, length, and location
within the coronary structure, and the experience of the interventional cardiologist with a
particular stent.
Figure 3: The size of a stent relative to the hand.
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Figure 4: Stents have been are special designed such as having wider peaks, shorter segments and
nested peaks that avoid contact with each other which helps keep the arteries open.
Thus, stents are mainly composed of metal alloys or compound materials which vary in shapes
and sizes depending on the manufacturer and the organ that is being placed in.
Current Application/ Future Work
Every day more and more solutions are being research to solve the future problems
derivate from the implantation of coronary stents. Improvements have been happening from the
90’s purely mechanical improvements but to pharm logics points of views.
Drug- Eluting Stents
Current research project are being held on stents that prevent restenosis, one of the main
discoveries so far is the idea of finding drugs that inhibit biological processes that causes
restenosis. The stent are coated with these drugs, sometimes wrapped in a layer thin of thin
polymer that retards their action.
From the year 2002 two systems were found that have had good results in this field. An
immunosuppressive drug called Sirolimus manufactured by Wyeth-Ayerst, which Johnson and
Johnson and Cordis have used before in the past to cover their stent CYPHER. The results after 8
months of testing were very positive, was reduction in presence of restenosis raging between 3.2
and 91%. Today in 2012 CYPHER is considered the first of an advanced generation of hearth
Stents Called drug coated or “drug eluting” stents. Cypher has been used to open blocked arteries
for more than 3 million people. The CYPHER stent has been evaluated in more than 45,000
people in over 75 clinical studies.
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The second System that has had great results like cypher is the research done for 6
months at the Boston Scientific TAXUS II. TaxusII is a research based on a stent by Boston
scientific. The research consisted on using the stent and covered it with a polymer that delivers
the paclitaxel drug fabricated in Canada by a company named Angiotech. Pactixel is a principle
find in a drug called TAxol. Paclixatel has been used in the passed
Currently in the market DES (Drug-eluting stents) has two models that have been
approved by the FDA (Food Administration) each stents is about $2500 a piece but also many
stents are in current medical in medical trial. The approved stents are made of 316L of stainless
steel with a polymer containing a specific drug to prevent restenosis. The polymers control the
rate which with the medicine goes into the body.
Stents treated with ionic Implementation
Another technique applied to treat the surface of
cardiovascular stents is the ion implantation. The ions
penetrate to an area near the surface, this process does not
form any new layer so that no problems adhesiveness.
Using this technique it is possible to enrich the surface up
to 91% of foreign ions so if you make a good choice of
these can be clearly improve the biocompatibility of the
material. The introduction of C and ion strange displaces
nickel into the substrate. In addition, the depth of
penetration of ions is low (about 20Mn) so are not altered
mechanical properties of the substrate material
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Stents with Radiation.
Stent with radiation is another technique that is being investigated which includes the use
radioactivity as a measure to prevent the occurrence of restenosis in patients. Patents have been
written in which the application of this technique and the introduction of drugs are key to a good
patients responses to the cardiovascular stent placement. The invention consists in a coating
containing a radiation source emitting β or γ radiating to the tissues and prevents the proliferation
of cells in the wound response in angioplasty. This coating has a second layer deposited on top
substance containing anticoagulant that radiation never is in direct contact with the patient’s
body. All these new techniques involving the superposition of layers with different focus
functions all research in this field since the main goal is find the combination of techniques able
to eliminate the problem of training clotting and restenosis.
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Porous stents introduction of drugs
Another method being investigated to improve the problem of restenosis is manufacture
of porous stents. As shown in the figure layouts can be varied as needed. In the figure a) can be
seen that the size of pores is higher inside than outside. This provides high capacity
drug storage inside and a much lower expulsion rate. This treatment may last longer. In the case
of Figure b) there are two parts separated by a central solid. Both the top and bottom are
porous so that you can enter drugs. Moreover, since there are communicated with each other can
be introduced different drugs. These are specific to the area to be in touch with the
material, the wall of the vein or blood. There are many other combinations in other cases you can
do playing with pore size distribution. For its versatility this is a line of research that is taking a
lot of strength.
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Conclusion
The use of cardiovascular stents has been a great advance in medicine and biomedical
engineering. Stents have helped to the lower risk for humans to suffer from severe cardiac
disease. The risk of Restenosis has been highly reduced in a 33% with respect to the process of
traditional angioplasty.
Currently in the market the presence of various Biomedical Engineering companies have
permitted that we can have more than 100 different types of stents being fabricated. This has
permitted doctors around the world to have more options when choosing the right stent for
different patients.
On the other hand, the great advances in the drug-eluting stents are currently being every
day more and more successful showing a bright future for stent technology. The risk for
restenosis is less and less day by day by combining different drugs depending on the condition of
the patient.
Different investigations have been made about the surface of treating stents like the ionic
implementation to eliminate the contact of the body with the damaging ions like Ni. During this
research another idea has been brought to the table. The project consists in coloring the stainless
steel creating a barrier with the ions enabling researchers to evaluate the behavior of the ions
with the blood. This method of coloration is a cheaper solution for stent technology and would
be a huge impact on stent price.
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References:
(1)Garg, Scot, and Patrick W. Serruys. "Coronary Stents." Journal of the American College of
Cardiology 56.10 (2010): S1-S42. Health Reference Center Academic. Web. 7 Dec. 2011.
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San Diego, California: 1996, p.
(3) MICHAELS, ANDREW D.; CHATTERJEE, KANU. Angioplasty versus Bypass surgery
for coronary disease. Cardiology Patient Page. 2002. Vol. 106, p.187-190.
http://www.circulationaha.org
(4) "Stent Review - Cath Tech.com." Home - Cath Tech.com. Web. 07 Dec. 2011.
http://www.cathtech.com/content/view/17/1/
(5) Ratner, Buddy D.; Hoffman, Allan S.; Schoen, Frederick J.; Lemons, Jack E. (2004).
Biomaterials Science - An Introduction to Materials in Medicine (2nd Edition).. Elsevier.
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(6)Hacker, Andrew, and Claudia Dreifus. "Are Colleges Worth the Price of Admission? Commentary - The Chronicle of Higher Education." Home - The Chronicle of Higher Education.
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(7) Lim, Issel Anne. Biocompatibilty. MIT. Web. <http://web.mit.edu/murj/www/v11/v11Features/v11-f5.pdf>.
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