Kinky bypass grafts last longer

GET kinky. Go with the flow. This is not a lifestyle recommendation, it’s the latest advice to vascular surgeons. Evidence is mounting that bypass grafts work much better, and last much longer, if they have helical twists.

When surgeons make a graft to bypass a blockage in a blood vessel they often have to use prosthetic tubes because suitable arteries and veins are hard to come by. Similarly, when patients with renal disease have dialysis, a loop of tubing may be fitted between a vein and an artery, usually in the arm. This loop, made from polytetrafluoroethylene (PTFE), is called a shunt.The problem with this is that blood flow in these prosthetic tubes is different from in natural blood vessels. Arteries naturally twist like a corkscrew and this 3D structure makes the blood swirl as it flows, which stops it stagnating. In contrast, blood flows through an artificial tube like water in a river, leading to areas of faster and slower flow, and stagnant zones, resembling the inside of river bends where sand builds up (New Scientist, 6 February 1999, p 32).”Stagnation is bad news for blood vessels,” says Colin Caro, a bioengineer at Imperial College London. It increases cell death in the blood vessel wall, and more platelets are formed. This leads to coagulation and causes a disease called intimal hyperplasia (IH), a thickening of the blood vessels, which is the most common reason for the failure of shunts and bypass grafts.And many shunts and grafts do fail. More than 300,000 people have renal shunts fitted per year, and about two-thirds fail and have to be replaced within the first 12 months. Of the more than half a million bypass grafts fitted annually, about half fail in the first year.The solution is to make blood flow in grafts and shunts mimic natural arteries. To do this, Caro makes PTFE tubes with helical twists, dubbed SwirlGrafts. Fluids flow through the twisty tubes and beyond in swirls.Now Caro, working with Nick Cheshire, a vascular surgeon at St Mary’s Hospital, London, has fitted lab pigs with SwirlGrafts to test their effectiveness in live animals. Each test animal had both a SwirlGraft and a conventional, non-twisting shunt fitted. When the grafts were examined eight weeks later, the results were clear cut: the conventional shunts were thickened and clogged with coagulated blood while the SwirlGrafts looked almost brand new.European regulatory authorities have given their approval for SwirlGrafts to be used in people and clinical trials have begun in seven renal patients in the University Medical Centre, Utrecht, and nearby hospitals in the Netherlands. “Two patients have had a SwirlGraft fitted for about six months, and are going well,” says Caro. If SwirlGrafts live up to their promise, the improvement in patient welfare, not to mention the financial savings, will be dramatic. “We’re talking millions of dollars,” says Caro.(Source: New Scientist: Issue 2503: 11 June 2005, p 28: Journal of the Royal Society Interface, DOI: 10.1098/rsif.2005.0044)