Latest Advances in Coronary Stenting
PROF UPENDRA KAUL
Bioresorbable Coronary Stents ( Vanishing Stents) are the latest innovations in treating the blockages in the heart. These stents after undergoing rigrous studies are now commercially available in our country.
Coronary artery disease is the commonest cause of death worldwide. A number of advances have taken place in management of 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 source.
At present, over 2 million angioplasties with stenting are being done across the world. In india is the number is approximately 150,000. Over last four decades, four revolutions in non-surgical method of opening blocked arteries have dominated cardiac surgery scene.
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 2-3 percent of patients. Also among approximately one third patients blockages recurred within 3-4 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 stent also reduced the problem of blockage recurrence from 3o percent 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 percent.
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 the endothelium, the inner lining of the 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 Bioresorbable 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 the device.
The pivotal study to evaluate these stents in a 1000 patient cohort included 1oo patients from India and it included Fortis Escorts Hospital, New Delhi with me as one of the investigators. Based upon this study the vanishing stent is now available for commercial use in selected cities in our country.
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 and CT angio to look at the stented artery without a problem and with clarity. The need for blood thinners will not be critical after few months and the chances of very late stent thrombosis will not be there, since the stent dissolves after a year.
High cost is going to be an issue in the beginning but with the expected competition from other companies improvement in the design and lowering of the cost is bound to be there. It certainly is the future of coronary stenting in the years to come.
Lastupdate on : Tue, 1 Jan 2013 21:30:00 Makkah time
Lastupdate on : Tue, 1 Jan 2013 18:30:00 GMT
Lastupdate on : Wed, 2 Jan 2013 00:00:00 IST
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