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Monthly Archives: April 2017

A dear friend and colleague, Dr Vivek Baliga has written this very informative article about heart attack on his blog.

Here’s the link:

http://heartsense.in/chest-pain-and-heart-attacks-what-to-do/

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Coronary Stents
Coronary stents have been around for a few decades. They are used to treat narrowed arteries of the heart to alleviate cardiac chest pain, termed angina, and during a heart attack while performing life saving coronary angioplasties. Nearly all of the coronary stents are made of metal and crudely resemble a spring inside your ballpoint pen. The best long-term results are seen with drug eluting stents (DES) that are essentially the metallic stents coated with special medicines to improve performance.
Downside of metallic stents
Metallic stents including DES, have a few perceived drawbacks. The main ones are:
1. A metal is left behind after an angioplasty. Some patients are conscious that they are carrying a foreign object. This is perhaps the least of the concerns.
2. Very late stent failure (>1 year after implantation) and Very very late stent failure (>5 years after implantation) are known to occur. These are related to presence of the metal or the adhesive that binds the metal to the drug.
3. Coronary arteries have dynamic physical properties. For example, expansion of calibre when more flow of blood is needed termed vasodilation. They also possess biochemical properties such as secretion of local hormones that are beneficial. The metal from the DES cages the artery from inside this preventing it from demonstrating these properties.
4. If long segments of coronary arteries are treated with metallic DES, in the event of a subsequent Bypass surgery, the cardiac surgeon has difficulty finding a place to stick the grafts.
Case for Stents that dissolve after their job is over!
 A stent that would stay for 3-6 months after implantation and disappear after that would be an ideal foil to address these problems. This was the premise with which scientists invented Absorbable Stents. The basic material used to build absorbable stents could be either metal (magnesium, zinc) or polymer (Poly-L-lactic acid, PLLA) that has appropriate degradation characteristics.
Absorb™ BVS
The absorbable stent that has shown the best performance is the Abbott’s Bioresorbable Vascular Scaffold (BVS), Absorb™. Absorb is the only fully dissolvable stent system approved for clinical use (also received FDA approval in July 2016). The clinical evidence for its efficiency and safety comes from a series of clinical research trials called as the ABSORB trials.
In ABSORB trial 29 of the 30 patients who underwent implantation of the BVS, first reported in 2011), continued to​ do well at 5 years. The comparative study of the BVS with Abbott’s own best performing metallic DES, Xience™ called ABSORB II showed that as late as 2 years on, the two stents were more or less similar in efficacy and safety. The patients with the BVS had similar relief from symptoms and somewhat similar, low failure rates. But it was really the results of the ABSORB III a large enough study for doctors to generalise conclusions from that really proved that the BVS performed as well as the DES. The abrupt and gradual failures​ of the BVS were seen in a few patients more than with the DES but the statistical analysis suggested that it was due to chance rather than a true difference between the stents. With these results, and the USFDA approval, the BVS was ready to go places. In India and some European countries the Absorb BVS was already popular even before the USFDA approval.
Is there an issue now?
While superficially the promise seems to hold, of late some mixed signals are emerging with the use of Absorb BVS. The 3-year results from ABSORB II trial showed a higher rate of heart attack and stent failure with the BVS compared to the metallic DES. The difference was so striking that the trial’s lead investigator, Dr Patrick Serruys termed these results as unexpected and disappointing. The setback seemed more alarming because it happened in patients who were not expected to have these complications. In fact, these were the patients who were being regularly followed up and had shown no warning signs of problems!
Are there signals from ABSORB lll?
The ongoing trial ABSORB III has also shown some issues when the BVS is implanted in coronary arteries of smaller calibre. The lead investigator of that trial, Dr Stephen Ellis has cautioned against the use of BVS in smaller vessels. The manufacturer Abbott Vascular seems to endorse this view, at least partially.
What happens now?
Experts acknowledge that there are some niggling issues with the current iteration of the absorbable stent. Clearly, they cannot be used in all types of arteries from all types of patients. So over enthusiastic implantation regardless of patient type just because of patient’s request or affordability is a definite no!
Secondly, Absorbable Stent technology is a definite breakthrough. Further research from scientists will certainly iron out the issues faced by the first generation of dissolvable stent systems. Until then, bioabsorbable stents are meant for very select individuals in carefully monitored environments such as research trials and registries.
Cardiac doctors have been very perceptive and careful in examining and reporting even minor failures. It is this culture of scientific temperament that has lead to tremendous advances in cardiology. We look forward to great times ahead.