Safer cardiac ablation

A robotic guidance system that eliminates patient exposure to radiation during cardiac ablation is being developed by researchers at King’s College London.

The work is part of a four-year project being undertaken by the university’s Medical Engineering Centre and builds on research into the use of force sensing and magnetic resonance imaging (MRI) for robotic medical systems.

The university’s latest project aims to develop MR-compatible steering and sensing tools to guide a catheter through a blood vessel and to the site of a cardiac arrhythmia. The condition, which affects more than a million over 40s in the UK, causes irregular heartbeats that can result in a stroke, heart failure or sudden death.

Diagnosis and treatment of an arrhythmia is currently performed under X-ray guidance. However, the procedure takes several hours and exposes the patient and the doctor to ionising radiation, leading to long-term health risks. Unlike MRI techniques, it doesn’t offer any 3D information, temperature detail or soft tissue contrast, which can reduce the precision of the operation.

Dr Kaspar Althoefer, a researcher at King’s College, said that hospitals continued to use X-ray imaging despite the health risks, as existing sensing and steering tools contained metal parts that would interfere with MRI scanners. To overcome this, the team at King’s has been working on replacing these metal components with fibre-optic material that prevents disruption to the images and are safe to use within the body.

Althoefer explained that these components will form a sensor that will be used on the tip of the catheter to provide performance feedback to the surgeon. ‘You have to keep in mind that these are only 3-4mm in diameter,’ he said. ‘Miniaturising the sensors will be our biggest challenge, however once installed, they will give the doctor the opportunity to see a visual representation of the forces involved in the procedure to prevent damage to the tissue.’

As well as scaling down the sensor and developing new material, Althoefer claims that introduction of the MRI technology will prove challenging. ‘Measuring the forces accurately will be one of the problems we have to overcome. This is a remote-sensing technique and if you consider that the catheter is around 1.5 to 2m long, then there could be accuracy issues when you send the results back to the screen,’ he added. ‘Another disadvantage is that the patient has to be in a tube [the MRI scanner], which can restrict the surgeon’s movement.’

However, Althoefer is confident that once these technical challenges are resolved, MRI will soon replace X-ray imaging in cardiac procedures. ‘At the moment, experienced doctors are carrying out these operations and they have built up a feel for the forces that are on the catheter,’ he said. ‘The problem is they don’t only feel the forces at the tip, but the forces at the side of the catheter as they move through these arteries and push against the wall. It’s difficult to distinguish between these two forces and you need experience in order to do it properly, which can take a long time.

‘MR-compatible tip-force sensing and robotic catheter steering techniques can provide a shortcut to doing this and is, I believe, the future for cardiac ablation technology.’

The team is currently engaged in a further area of research that will develop steering techniques to move the catheter in a restricted space with greater precision. This research is expected to benefit from input by industrial partners Hansen Medical and Philips Healthcare, who earlier this year signed a joint cooperation agreement to co-develop robotics products that would simplify cardiac procedures.

Under the agreement Philips will combine its X-ray imaging technology with Hansen Medical’s Sensei system. This allows physicians to place catheters in the heart by translating a surgeon’s movements at a work station to the robotic device. Steffen Weiss, a researcher at Philips’ Technical Systems division, claims that it won’t be long before projects such as this one will lead to the replacement of X-ray imaging with MRI technology in minimally invasive ablation procedures.

‘I can see this happening within the next decade,’ he said. ‘MRI has technical challenges but also significant benefits over X-rays, which are harmful to a patient. It is an area that Philips and other healthcare providers are very interested in. As well as providing better visual imaging, MRI can see areas that already have ablated tissue and avoid critical structure. This will be significant to future cardiac procedures.’

Ellie Zolfagharifard