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Computer model gets to heart of blocked artery problem

Sun, 13th Dec 2009

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A new computer model promises to dramatically improve the outcomes when clogged heart arteries are unblocked and propped open with metal stents.

Angioplasty 3The process of treating heart disease like this, with angioplasty and stenting, known as PCI - percutaenous coronary intervention, has revolutionised the treatment of heart disease; patients now only rarely have to undergo risky open-heart arterial bypass procedures.

Instead, tubes are threaded into the coronary arteries via an artery in a patient's leg and dye is used to identify blockages.  The narrowed portions of the artery are then re-opened by briefly inflating a balloon inside the vessel before deploying a metal stent, which resembles a miniature cage, to ensure that the artery remains patent.

But when doctors first began to do this they discovered that new cells would grow around the stent, subsequently re-occluding it.  The problem was tackled by using stents impregnated with a drug (a so-called DES - drug eluting stent) to block this cell growth.  But unfortunately, whilst highly effective, in some cases these stents provoked blood clots and heart attacks in some patients.

Now a team in Harvard have worked out why and how to prevent the problem.

Writing in PLoS one, Vijaya Kolachalama and his colleagues have designed a computer algorithm that can predict how blood behaves downstream of stents and explains why, in some cases, patients have suffered repeat problems.  The model shows that when stents are plumbed into sections of arteries close to points where the vessels branch, the change in blood flow causes the drug to build up at certain points along the vessel wall, triggering damage.

According to study co-author Elazer Edelman, "by observing the arterial distribution patterns for various settings, we understood that drug released from the stent does not reach uniformly to all regions of the vessel and this non-uniformity depends on where the stent is placed in the artery as well as blood flow that is entering the vessel." This should make it much easier for doctors to position stents with greater safety in future and may help designers to develop novel stents capable of avoiding these problems. It may also herald the future arrival of individualised stents, bespoke built to match the specific demands of a patient's vasculature.

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