Jon Excell explains how new developments in artificial arteries offer alternative to vascular grafts and could help patients avoid amputations.
An artificial artery that recreates the swirling bloodflow of a natural vessel could help thousands of vascular disease sufferers avoid the misery of amputation, its Scottish developer has claimed.
While conventional vascular grafts and stents halt this swirling motion and raise the risk of vascular illness downstream of the device, Tayside Flow Technology’s (TFT) elegantly simple system uses a custom-designed structure inside the distal end (the end furthest away from the heart) to induce what it refers to as spiral laminar flow.
The device, which is nearly two years into an initial trial, is based on work carried out by Prof Peter Stonebridge, a vascular surgeon at the University of Dundee’s Ninewells hospital.
In the early 1990s Stonebridge was one of a number of researchers who identified the fact that vascular health is dependent on the characteristic swirling action of the blood. This action is initiated by the heart and perpetuated through the bloodstream by a range of factors, including the structure of the muscle and the shape of the arterial wall.
The trouble is that once blood leaves a conventional implant and returns to the arterial system the spiral flow isn’t reintroduced. ‘If you put a stent or graft into someone’s body you will lose spiral flow — even in a short stent — it’s not reintroduced,’ said David Lawrence, chief executive of TFT.
Deprived of the protective effects of helical flow — which among other things improves the transfer of oxygen and nutrients to the vessel wall — the potential for blockages and furring of arteries is increased. ‘If you lose spiral flow the rate and severity of disease progression is worsened,’ added Lawrence, ‘for instance, the endothelial cells at the join recognise there’s something wrong with the blood flow and send a signal to the smooth muscle walls and you get occlusions.’
For this reason, he said, surgeons frequently choose vein harvesting over existing graft technology: ‘The most patent and popular solution to bypass grafts is to harvest veins from other parts of the body — because this natural vein will, over time, start to support spiral flow again.’ But vein harvesting is far from ideal.
The procedure is lengthier and more expensive than artificial graft implantation and it exposes the patient to an increased risk of infection. Lawrence claimed that TFT’s technology will make this choice simpler: ‘Our clinical trials show that the patency of a device incorporating our spiral laminar flow technology is as good as natural vein.’
TFT’s first product is a vascular bypass graft for legs. ‘We’ve added a spiral inducer to the distal end [the end furthest away from the heart] that reintroduces blood flow,’ said Lawrence.
This inducer effectively consists of a purpose-designed ridge or vane on the inside of the distal end of the bypass graft. The effect it has on the blood-flow is, he added, analogous to the effect a bored rifle barrel has on a bullet; it imparts a spin on the blood, that reintroduces spiral flow.
The company already has nine European distributors signed up, and, according to Lawrence, is in the process of appointing a UK distributor that will attempt to get the NHS interested.
A number of patients from Greece, Belgium, Germany and Ireland have already been fitted with the firm’s grafts and the data generated by multi-centre trials clearly indicates the promise of the technology.
Although non-randomised, Lawrence said that these trials, which are being carried out in Belgium and the Netherlands, demonstrate the benefits of TFT’s approach. ‘For conventional below-the-knee bypass grafts up to 60 per cent will go down within two years and of those that go down 40 per cent will use all or part of a leg. Eighteen-month data from trials of our graft indicates patency of around 90 per cent below the knee and we are hoping to see that this holds up after two years.’
In the meantime, Lawrence’s team is looking at a number of future products, including an access graft for dialysis patients, as well as stents that incorporate the spiral laminar flow principle.
But TFT is not alone. Imperial College spin-out Veryan Medical is also working on the development of an implant that reintroduces swirling blood flow.
Based on research carried out by Prof Colin Caro from Imperial’s department of bioengineering, Veryan’s SwirlGraft device adopts a somewhat different approach, imparting spiral flow through its own helical structure rather than a single inducer.
Chas Taylor, chief executive of Veryan, claimed that its technology, which has been the subject of two clinical trials involving more than 200 patients and has regulatory approvals in the US and Europe, is more readily applicable to stents than TFT’s system.
‘TFT divert the flow using vanes,’ he added. ‘The trouble with doing that with a stent is that you reduce the lumen size and one of the most important things with a stent is the ability to get other gear [such as surgical devices] through. What you don’t want to do is put something in a patient that limits the treatment options later on — anything within the interior portion of the stent is a problem.’ He claimed the soon-to-be-published results of a recent study of more than 200 patients will indicate Veryan’s suitability for a new generation of stents.
Nevertheless, Lawrence remains confident that TFT will be able to grab a sizeable share in the global market for stents and grafts that is thought to be worth as much as £11bn.
Earlier this month, TFT secured £1.2m worth of investment from, among others, Kwik-Fit boss Sir Tom Farmer. This will be ploughed into further R&D.
Lawrence added that the estimated £9m injected into developing the technology is money well spent: ‘We have spent a lot of money developing the technology and we have got a higher cost of goods than existing products but we have also got a higher-performing product and we think that there are enormous advantages for healthcare providers and patients.’