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Bioabsorbable Coronary Stents – A New Frontier in Treating Heart Disease

Blocked heart arteries, also known as coronary artery disease, is a major problem in Asia and leads to symptoms of a heart attack and angina. Coronary angioplasty and stenting is a widely accepted procedure to effectively treat these blockages and involves the implantation of a permanent metallic tube called a stent in the artery which props the vessel open. A new generation of bioabsorbable stents is now available which disappears after two years, leaving the vessel in its restored natural state. This ‘vascular reparative therapy’ represents a new advancement in cardiology.

Coronary artery disease (CAD) is rampant in Asia. CAD leads to limited blood flow to the heart culminating in, at its worst, a heart attack in which a portion of the heart muscle permanently dies, but also symptoms of angina which can range from mild to limiting chest pain or shortness of breath on exertion.

A combination of increasing affluence leading to unhealthy dietary habits along with a general ageing of our population has made CAD a widely prevalent disease that affects not only longevity but also quality of life and productivity. Coronary angioplasty and stenting are widely accepted procedures to effectively treat blockages in the coronary arteries.

This article will highlight a recent advancement in the field and focus on the newest generation of biodegradable coronary stents.

Past CAD Invasive Treatments

A quick recap of how the invasive treatment of CAD has evolved over the last several decades is worthwhile.

 

Stents Renewed

“Studies with the leading bioabsorbable stent have shown that indeed, the stent is largely gone by two years and the vessel is restored to its original healthy functional state…” 

 

Dr Fahim H. Jafary

Dr Fahim H. Jafary is a Senior Consultant in the Department of Cardiology at Tan Tock Seng Hospital. He is a graduate of the Aga Khan University Medical College in Karachi. He was trained in Internal Medicine at the University of Texas Health Sciences Center in Houston and Cardiology at Tufts Medical Center in Boston. Dr Jafary is certified in Cardiology & Interventional Cardiology by the American Board of Internal Medicine, and Nuclear Cardiology & Cardiovascular CT by the Certification Boards of Nuclear Cardiology and Cardiovascular CT. Dr Jafary has been performing coronary angioplasty and stenting for close to 15 years.

This brings us to the most recent and exciting development in the field of angioplasty – the bioabsorbable stent. The basic concept behind having a temporary scaffold in place is quite simple.

Studies show that after balloon dilatation of a blockage you really need a stent to prop up the artery for 3-4 months after which the artery gets ‘set’ in its new, expanded shape. Therefore, if the stent could disappear after ‘doing its job’, the patient benefits from the implant and from not having a permanent presence in the artery. If this stent can elute the same drug as metallic drug-eluting stents, tissue regrowth and restenosis is prevented. Initial versions of bioabsorbable stents were made of magnesium which degraded very quickly, within a month or two and this rapid disappearance of the scaffold resulted in the blockage recurring in a large fraction of the patient’s heart due to recoil of the artery.

Another version of the bioabsorbable stent used poly-L-lactic acid (PLLA), a polymer similar in consistency to plastic. PLLA has a long history of safe use in medical implants (e.g. orthopedic screws, pins, soft tissue implants) and degrades into lactic acid which is then broken down by the body into water and carbon dioxide. This stent had a much slower degradation profile (12-24 months) and hence the scaffolding was retained for the critical first few months after stent implantation. The only problem was that the stent incited a similar tissue reaction as the bare metal stents leading to restenosis.

The next logical step was to impregnate the PLLA with the same drug that drug-eluting metallic stents use and the most recent generation of bioabsorbable stent is exactly that – a drug-eluting PLLA stent that combines the best of all worlds – a temporary scaffold that elutes a drug, expands the artery and then disappears.

Studies with the leading bioabsorbable stent have shown that indeed, the stent is largely gone by two years and the vessel is restored to its original healthy functional state, giving rise to the term ‘vascular reparative therapy’ for the current generation bioabsorbable stents.

A four-year follow-up of the current stent demonstrates excellent results with very low restenosis rates and no signs of a ‘late catch-up’ in terms of problems. The need for long-term blood thinners is significantly less. Furthermore, the bioabsorbable stent is substantially easier to image using non-invasive techniques like cardiac CT as compared to their metallic counterparts, an important and welcome benefit.

Drawbacks of Bioabsorbable Stent

While the bioabsorbable stent represents an important advancement in stent technology, at present there are a few limitations.

 

First, the stent has largely been tested in relatively simpler coronary lesions; more complicated blockages may not be suited to receive this stent and, hence, not everyone is a candidate.

Second, the stent is not as easily deliverable to the blockage as the metallic stents are – it is a bit more bulky and sometimes that may make getting the stent down the coronary artery a challenge particularly if the artery has a very curved course. Third, these stents are substantially more expensive than the metallic drug-eluting stents; this becomes particularly important if a patient requires multiple stents.

Finally, the long-term follow up is limited to 4-5 years. While we don’t know how these patients will behave years down the line, if the earlier studies with PLLA stents are any indication, there is no suggestion that these stents have any long-term adverse effects.

Bioabsorbable stents represent a new way forward and ‘vascular reparative therapy’ may indeed be the future. Patients should consider a bioabsorbable stent as an option preferably via the radial (wrist) approach. Patients should have an open discussion about the pros and cons with their physicians prior to undergoing coronary procedures.