THOUSANDS of people could avoid major bypass surgery on the body鈥檚 main artery thanks to a novel technique which uses plastic tubes to insert synthetic grafts into the blood vessel.
More than ten thousand people die in Britain every year after the aorta, the main artery carrying blood from the heart to the rest of the body, suddenly ruptures. The walls of the aorta become weaker in older people and can sometimes balloon out. When the diameter of the balloon reaches a critical size 鈥� usually about 6 centimetres 鈥� there is a risk that it will burst.
These weak spots, known as aneurysms, can be tackled with bypass surgery before they get to such a dangerous size. For people who are otherwise well, there is an excellent chance of surviving the operation, but the risks rise sharply when people are also unwell.
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The idea of using plastic tubes, or catheters, to insert a graft directly into the aorta is being developed at a number of centres in Britain, including Bath, Leicester and Nottingham. The procedure has the added advantage that it could eventually be carried out under local anaesthetic. The catheters are inserted into the body through a small incision in the groin.
Antony Fox, a vascular surgeon based at the University of Bath鈥檚 department of surgery, has produced a prototype which he says will be ready to test on people in a few months. The system at Bath is unique because the polyester graft is reinforced by a 鈥渟hape memory alloy鈥� called nitinol. Nitinol is a mixture of nickel and titanium. By varying the alloy鈥檚 composition, it can be pre-programmed to expand at a precise temperature 鈥� in this case the temperature of the patient鈥檚 blood.
The graft enters the patient inside the catheter. When the graft is sitting in the appropriate part of the aorta, the catheter is removed and the nitinol comes into direct contact with the blood. It then expands, pushing the ends of the graft against the wall of the aorta and anchoring it at the neck and cuff (see Diagram). As with other such operations, surgeons use X-rays to monitor the process.
If the aneurysm extends beyond where the aorta divides to pass blood to the legs, a 鈥渢rouser鈥� type graft is needed. Fox has designed a modular system to deal with this. The upper half of the graft is made from one module which has two channels at the bottom to allow for two further modules for the leg arteries.
鈥淭here are obvious advantages to developing modular systems, because over 90 per cent of people with aortic aneurysms need trouser grafts,鈥� says Peter Bell, professor of surgery at the University of Leicester. In Leicester, 16 people have had an operation using a catheter. But Bell warns that 鈥渁t the moment the risks of catheter surgery are greater than open surgery because the concept is still in its infancy鈥�.
There have been a number of teething problems. When surgeons insert the catheter, for example, they can cause small blood clots to break off from the aneurysm. These can pass into the kidneys or down into the legs, blocking the blood flow.
As screening for aortic aneurysms becomes more routine, more will be detected at an earlier stage. And as Fox explains, 鈥渢his system is faster and will probably be cheaper overall. It is also likely to become safer than conventional methods.鈥�
