[Editors] MIT: Building better stents with computer models

[Teresa Herbert]

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MIT model predicts how to build a better stent
--Work could help reduce blood clot risk in stent recipients
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For Immediate Release
MONDAY, JAN. 5, 2009

Contact: Teresa Herbert, MIT News Office
E: therbert at mit.edu, T: 617-258-5403


CAMBRIDGE, Mass. -- Researchers have been puzzled in recent years by  
observations that drug-releasing stents (mesh-like tubes implanted to  
hold patients’ coronary arteries open) can increase the likelihood of  
blood clots and heart attacks. Now, a mathematical model developed by  
MIT engineers can predict whether particular types of stents are  
likely to cause life-threatening side effects.

The model “helps explain why some stents are better than others, and  
could predict which stents are predisposed to cause clotting,” said  
Elazer Edelman, the Thomas D. and Virginia W. Cabot Professor of  
Health Science and Technology (HST) and senior author of a paper on  
the work appearing as the cover story of the Jan. 5 issue of the  
Journal of Controlled Release.

Edelman and HST postdoctoral associates Vijaya Kolachalama and Abraham  
Tzafriri designed the model to predict how the size and shape of a  
stent affects blood flow and drug distribution.

Drug-releasing stents are used in more than a million patients per  
year in the United States. The drugs, including paclitaxel and  
rapamycin, are intended to prevent tissue from growing inside the  
artery after it is inflated during angioplasty.

However, drug-releasing stents have been proven a “double-edged  
sword,” Edelman said. The drugs successfully block tissue growth that  
could impede blood flow, but can have the unforeseen side effect of  
increasing the risk of blood clots and heart attacks.

This paper explains why: Stents affect the fluid dynamics of blood  
flowing past them and cause drugs to accumulate in certain areas. Too  
much drug buildup promotes clot formation.

The MIT model shows that the dynamics of blood flowing around a stent  
is similar to whitewater rapids, said Edelman. When water in a river  
flows over a boulder, some of the water strikes the base of the  
boulder, flies up in the air and comes back down, instead of flowing  
over the rock. This water continuously recirculates in the same area.

The same thing happens when blood flows across a stent: Drugs tend to  
accumulate and spin around in the recirculation zone. This is most  
likely to happen with stents that protrude further into the artery.  
“Until now, the degree to which recirculation zones impact the  
distribution of drugs was not appreciated,” said Edelman.

This is the first time that a mathematical model has successfully  
predicted stent performance based on changes in arterial blood flow  
and design, and the researchers hope the model and concepts it  
establishes could aid efforts to design stents that allow drugs to be  
more evenly distributed throughout the area.

The model could also help the FDA in its approval processes, by  
helping regulators figure out which stents are most likely to be safe  
or harmful, based on their size and shape, which controls how they  
will affect blood flow.

Davis Arifin, a graduate student in the MIT-Singapore Alliance, is  
also an author of the paper.

This research was funded by the National Institutes of Health.

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Written by Anne Trafton, MIT News Office
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