Story of the vanishing stent
Bioabsorbable Coronary Stents are the latest innovation in treating blockages in the heart.
Coronary artery disease is the commonest cause of death worldwide. A number of advances have taken place in managing this disease in the recent times. Advances in medical treatment,coronary angioplasty and coronary artery bypass surgery are the main therapeutic measures to manage this scourge.
At present,over 2 million angioplasties with stenting are being done across the world. In India is the number is approximately 100,000.
Over the last four decades,four revolutions in the non-surgical method of opening blocked arteries have dominated the cardiac surgery scene.
Balloon Angioplasty
The first balloon angioplasty was done in Europe in November 1977 by Dr Andreas Gruentzig. The balloon era continued till 1995.
The main problems associated with this were the requirement of emergency bypass surgery in 2 to 3 per cent of patients. Also among approximately one-third patients,blockages recurred within 3 to 4 months,and they needed another procedure or bypass surgery.
Bare Metal Stent
The advent of coronary stent a metal mesh which is deployed at the site of balloon dilatation. The mesh prevents acute closure of the blood vessel,making the procedure of angioplasty very predictable and nearly eliminating the need for emergency bypass surgery.
These bare metal stents also reduced the problem of blockage recurrence from 30 per cent to approximately 20 per cent. As a result,the angioplasty technique was expanded to deal with more complex blocks. The problem of restenosis repeated narrowing of the coronary artery after treatment,however,continued especially in diabetics,in case of smaller vessels and more complex lesion subsets branching arteries where multiple stents may be required.
Drug Eluting Stent
The problems of bare metal stents in terms of recurrence of blockages was finally addressed by coating the stent with drugs. The drugs were released slowly into the walls of the blood vessel to slow down the healing process,and thus reducing recurrence of blockade to very small figures of five to six per cent.
It,however,meant extending the period for administering drugs like aspirin and clopidogrel for at least one year.
These stents coated by polymers which release the drug Sirolimus,Everolimus or Paclitaxel also brought in a new problem: very late stent thrombosis caused by the polymer and the stent scaffold,which stay on as permanent parts of the blood vessel.
In addition,the drug polymer combination leads to endothelial dysfunction malfunctioning of endothelium,the inner lining of blood vessels,making the blood vessel cord-like and performing a repeat procedure like CABG coronary artery bypass graft surgery difficult.
There was always a need to overcome these issues and have a stent system which will dissolve in the system after completing its function of providing a scaffold to the opened vessel.
Fully Bioabsorbable Drug Eluting Stent or Vascular Restoration Therapy
This concept has been there for more than a decade and after in vitro work,a system made of polymer polylactic acid PLA of the same design and shape as the stainless steel or chromium cobalt stent has been made. This scaffold is coated with the same PLA polymer which is mixed with drug everolimus. This stent is mounted on a balloon catheter and used in the same way as a current coronary stent.The stent gets completely absorbed in the system within a year and the vessel becomes completely normal. Initial studies have proven the safety of this device.So far,around 250 such stents have been used worldwide. India is one of the several countries included in a prestigious International study Absorb Extend.We at the Fortis Escorts Institute and Research Centre have used the stent on two patients last week. These were the first Asian patients to receive this dream stent and the primary results have been excellent and very gratifying. Six more Indian centres will be participating in this study MMM Hospital in Chennai,SAL Heart Center,Ahmedabad,Sanjay Gandhi Research Centre,Lucknow,Apollo Hospital,Chennai and CARE Hospital,Hyderabad.The advantages of this stent are that there is no foreign body left in the arteries after a year,the artery resumes its normal state and the patients can undergo investigations like MRI without a problem. The need for blood thinners will not be critical after a few months and the chances of very late stent thrombosis will not be there,since the stent dissolves after a year.The Absorb Extend study is expected to recruit 1,000 patients in a years time and it is hoped that this product will be available for commercial use by first quarter of 2013.
The author is Executive Director and Dean,Fortis Escorts Heart Institute and Research Centre amp; Fortis Hospital,Vasant Kunj,New Delhi
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