NEW YORK — While stent grafting of thoracic aortic aneurysm has become more routine, the procedure still has a number of limitations, Martin Malina, Ph.D., said at the Veith symposium on vascular medicine sponsored by the Cleveland Clinic.
Currently-available thoracic endografts are limited by issues of access, hostile neck, deployment, and durability. Dr. Malina, a consultant vascular surgeon at Malmö (Sweden) University Hospital, offered thoughts on these limitations and tips for overcoming them.
▸ Access. “We do have many quite simple tricks to get around this problem,” of access said Dr. Malina.
He recommends using an ultra-stiff guidewire. And don't push the graft in. “The more you push, the more the wire buckles,” he said. To avoid this, use a brachial wire to pull the graft by placing a clamp at the lower end of the wire. “This way, the more you pull, the more the wire will get straightened out.”
Iliac stenosis poses an access problem. One alternative is to make an incision in the groin and to advance the sheath outside of and parallel to the external iliac artery, inserting the graft at a more favorable angle.
▸ The neck. “Very often there is no neck,” said Dr. Malina. One option in these cases is to push the stent graft further around the arch, covering the left subclavian artery. Contraindications to this technique include right vertebral stenosis, aberrant right subclavian artery lusoria, and left internal mammary artery coronary bypass.
“In these cases, you still can cover the left subclavian, if you do it first,” said Dr. Malina. This can be followed by transposition of the subclavian or carotid-subclavian bypass.
▸ Deployment. “It is actually very hard to assess where the stent graft will be deployed,” said Dr. Malina. Whether the carotid artery will be covered is of particular concern, even after the stent has been deployed. Some projections used to view the stent may give the appearance that the carotid artery is not covered, when in fact it is or vice versa. “You have to find the ideal projection … to really prove that you have not covered the vessel,” he said.
▸ Durability. When the stent is deployed at the vertex of an elongated aortic arch, “the blood will hit the upper surface of the stent-graft and you will end up having a flapping motion,” which contributes to material fatigue and possibly stent collapse, leading to occlusion or migration and high risk of death. said Dr. Malina. “Also this flapping motion may erode the arch and cause immediate rupture and hemorrhage.”
Motion also should be avoided when telescoping the various components, or the stent-graft can disintegrate. Also, without sufficient overlap, the stent can migrate upward. “So wherever you place the stent-graft, you must make sure that you have enough overlap and secure the position of the stent-graft without any motion,” said Dr. Malina, who disclosed that he had no conflicts of interest.