Stent grafts must be designed to move with the arteries through the cardiac cycle, as revealed by modern dynamic imaging techniques, according to Frans Moll, Universitair Medisch Centrum, Utrecht, The Netherlands.
Moll presented results of a study measuring arterial movement to delegates at the International Congress on Endovascular Interventions, Scottsdale, USA, in February 2009.
His team in Utrecht used electrocardiographically-triggered multislice computed tomography and electrocardiographically-gated magnetic resonance imaging to measure shape changes of the thoracic and abdominal aorta in healthy individuals and patients with aneurysm.
They found significant pulsatory changes of around 10%.
These changes were not distributed evenly along the arch, as he demonstrated with dynamic scans of pulsating aorta. “You tell me what size of diameter I should choose for my thoracic stent graft?” he asked the audience. “How much do I have to over-size my device?”
“With computed tomography scans you normally get you get somewhere in the middle – a kind of mean of the diameter.”
He showed results of a thoracic stenting – with a device no longer in use – in which, two years after implantation, the movement of the aorta had caused the stent to collapse. “We learned from these dynamics that we need more substantial support in the proximal end to prevent this kind of collapse in this dynamic environment.”
Further examples of stent damage caused by cardiac pulsation were presented from cases in the renal, iliac, and innominate arteries. Movements in three dimensions caused erosion leading to perforation of the graft tissue, and, in one case, simply broke the stent in two.
“These forces,” he warned, “are not to be underestimated.”
“If you want to adapt to this asymmetric pulsatility, you can probably can handle it with Z-shaped stents, or wave-form stents, and the amplitude should not be too high.
“However, if you use rings, it is different. It will work for the first couple of years – that has already been proven – but does it also work in the long term? It’s not very likely.”
Moll’s team wanted to see whether stents restricted the movement of the arteries, and found – in measurements of the renal arteries – a significant reduction in distensibility post-procedure.
He warned that movement in the renal arteries is caused not only by cardiac pulsation, but also by respiration; if the lungs go up and down, then the kidneys will also go up and down.
He urged that studies of artery movement are taken into account when designing new stent grafts, but admitted, “This talk probably will leave you with more problems than solutions.”
Don’t miss the CX Symposium (4-7 April 2009), inlcuding Ian Loftus, Hence Verhagen, Krassi Ivancev, and Florian Dick on imaging for endovascular aortic repair, and Frans Moll on the role of European biobanks. Register Now!