CARDIOVASCULAR STENTSBy Kris Fitzpatrick

The Heart

There are two types of blood vessels in the circulatory system of the body:

Arteries that carry oxygenated blood away from the heart to various parts of the body.

Veins that carry blood towards the heart for purification.

The heart is a muscle that pumps oxygen rich blood around the body using blood vessels.

Clinical Condition

Coronary heart disease (CHD) is when the arteries fail to supply the sufficient blood required, due to a build of a fatty plaque upon the artery walls. This problem is known as atherosclerosis.

Atherosclerosis

Potentially very serious as it restricts blood flow to the heart.

Can lead to heart attacks and heart failure, which can be fatal.

The cause of a high number of deaths across the globe

Medical Procedure Stent is introduced into

blood vessel that is suffering with atherosclerosis using a guide wire.

The stent is wrapped around an uninflated balloon.

The balloon is then inflated causing the stent to open up the artery, restoring blood flow.

The balloon is then deflated and removed, leaving the expanded stent within the artery.

Disadvantages

Risks

Bleeding from the site where the guide wire is inserted.

Can cause an irregular heart beat.

Damage to the blood vessel & on rare occasions a burst artery.

Infection

History of stentsThe origin of the word ‘stent’ comes from Charles Thomas Stent (1807-1885) an English dentist born in Brighton. Known for his work in

denture making.

Improved denture base compound making it practical for dental use and called it a ‘Stent’.

His achievements led to him being appointed as Dentist to the Royal Household in 1855.

The first coronary stent placed within a patient was in France 1986 by Jacques Puel.

Ulrich Sigwart from Switzerland is seen as the one who revolutionised modern day stenting.

OriginCoronary Stents

Manufacture Production process starts with the

winding of the wire on a jig to create the stent skeleton.

Stent then placed into a heating oven to imprint the shape memory into the metal.

Stent is then polished by rotating though abrasive particles. This specialised process reduces micro cracks and removes impurities and residue from the stent surface.

After polishing the metal surface is smooth and clean, resulting in a stronger and more durable wire.

Difference is evident in the change of colour. Before polishing the stent appears blue in appearance which changes to silver after polishing.

Different Designs Available Name Image FeaturesGianturco-Roubin Stent Flat wire coil attached to a single longitude strut.

Stainless steel. Approved in 1993. Considered outdated by many.

Palmaz-Schatz Stent Stainless steel. Balloon expandable. Regarded at the most successful design to date.

Jaguar Stent Nitinol Self-expanding. High elasticity matches perfectly the shape of the artery. Protects against migration. Very high radial force.

Drug-Eluting Stent Coated with a pharmacologic agent that suppresses restenosis. Balloon expandable. Stainless steel or cobalt-chromium alloy.

Esophageal e-PTFE Covered Stent

Self-expanding. Wire formed with woven construction. Double stepped shoulder design prevents stent migration. Membrane provides firm but flexible barrier.

Abbott Dissolving Stent Dissolves into harmless lactic acid in 2-3 years. Absorbed by the body after dissolved. Lower chest pain rate compared to other stents.

Future of StentsDissolvable Stents Made of biodegradable

plastic.

Starts to dissolve after 6 months, fully absorbed into body after 2-3 years.

Enables more natural recovery.

Removes threat of long term damage from a standard metal stent.

Dissolvable Stents

Clinical trails began in 2014 and approval is expected sometime in 2015.

Annual global market for stents exceeds £5 billion.

Dissolving stents expected to generate £1 billion by 2018.

Cardiologist Nicholas Burke states “If the dissolvable stent allows a patients artery to fully heal and return to its normal state, it could revolutionise patient care.”

Dissolvable stents

Concerns

More fragile then the metal stent.

Mesh needs to be thicker,

Not as flexible.

Cannot fit into the tiniest of blood vessels.

Cannot be stretched to fit better during implantation.

References

DEAN, R.T. and KELLY, D.T. (2000). Atherosclerosis: gene expression, cell interactions, and oxidation. Oxford: Oxford University Press. EUROPEAN ATHEROSCLEROSIS SOCIETY and INTERNATIONAL ATHEROSCLEROSIS SOCIETY, (1970). Atherosclerosis. IRANIAN SOCIETY OF ATHEROSCLEROSIS and ISFAHAN CARDIOVASCULAR RESEARCH CENTER, (2005). ARYA atherosclerosis. ABDELALI, M., REITER, S., MONGRAIN, R., BERTRAND, M., L’ALLIER, P.L., KRITIKOU, E.A. and TARDIF, J., 2014. Cap buckling as a potential mechanism of atherosclerotic plaque vulnerability. Journal of the Mechanical Behaviour of Biomedical Materials, 32(0), pp. 210-224. ANTRANIK (2012). “Anatomy Science”. National Heart, Lung and Body Institute. In-text – (Antranik, 2012). ALLY, DOLAN, PRENDERGRAST (2004). “Cardiovascular Stent Design and Vessel Stresses”. A Finite Element Analysis. MCGILL, MCHAHAN, HENDRICK, MALCOM, TRACY and STRONG (2000). “Origin of Atherosclerosis in Childhood and Adolescence, USA, the American Journal of Clinical Nutrition.  INSULL (2009). “The Pathology of Atherosclerosis” Plaque Responses to Medical Treatment. USA, the American Journal of Medicine.  HALWANI, ANDERSON, BROTT, ANAYIOTOS and LEMONS (2001). “The Role of Vascular Calcification in Inducing Fatigue and Fracture of Coronary Stents.” Res Part A. Pages 292-304.  MURPHY, SAVAGE, MCHUGH and QUINN (2003). “The Stress-Strain Behaviour of Coronary Stent Struts is Size Dependent.” Ireland, Biomedical Engineering Society. WONG, THAVORNPATTANAPONG, CHEUNG, SUN and TU (2012). “Effect of Calcification on the Mechanical Stability of Plaque Based on a Three-Dimensional Carotid Bifurcation Model.” BMC Cardiovascular Disorders. China.  SCHMIDT, BEHRENS, BEHREND and SCHMITZ (2001). “Fatigue Analysis of Coronary Stents.” University of Rostock, Institute for Biomedical Engineering, Rostock, Germany.

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