Wednesday, March 29, 2006

Drug Eluting Stents

We've been talking about stents a fair bit on this blog. Perhaps it's time we focused a series on drug eluting stents. This topic is closely related to angioplasty. Stents were, after all, introduced in the early 1980s to lessen the risk of heart artery reblockage (re-narrowing) following balloon angioplasty. It also, incidentally, made balloon angioplasty safer as it also acted as a metal scaffolding after the balloon had caused pressure trauma on the heart artery wall. It also reduces acute blockage of the heart artery. So the indication for stents has been to reduce chronic reblockage and also acute blockages following angioplasty. The initial kinds of stents used were bare metal stents (BMS) made of surgical grade stainless steel. Since we had the BMS, why was there a need for the special Drug Eluting Stent?

Understand first that angioplasty is done to reduce blockage. Hoever, after angioplasty there was a 30-60% risk of reblockage. Whether a patient was on the 30 or 60 end of the probability would depend on diverse factors such as diabetes, the size of the vessel,the length of the lesions and whether the blockage was at aretery junctions. Each factor would add to the risk of rebloackage.

With the bare metal stents (BMS), the risk of acute closure of heart artery following angioplasty was abolished. Emergency bypass surgery following failed angioplasty became a thing of the past. However, the risk of chronic re-blockage of the heart artery following angioplasty was still not acceptable. Compared with plain old balloon angioplasty (POBA), the risk of chronic re-blockage was halved using the BMS(from 30-60% following POBA to 15-25% following BMS).
Interventional cardiologist found those risk of re-blockage following BMS still too high. A way had to be found to further reduce the re-blockage rate. Initially, oral drugs were given at time of angioplasty, to try and reduce scar tissue formation at the stented site. Many different drugs and compounds were tried. There were some investigators who tried injecting the drugs at the site of the angioplasty. All these attempts failed.

Then X-ray radiation was used to lessen scar tissue at the angioplasty site. This was like using a cannon to kill a fly. The cumbersome nature of the radiation machine and method put paid to the technique. It is still used in some centers who have already invested in the machines. By and large this technique have fallen out of favour. Fortunately, no center in Malaysia invested in these machines so we never used it here. We waited and watched the scene unfold. As all these were going on, investigators in Brazil and Europe were working on the on the new drug coated stent. A new era had arrived.

Over the next couple of days we will be going deeper into the whole topic of DES. At the end of the series we will probably have a post to answer any questions that come in about this topic in the meantime.

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