Three-dimensional printed templates to guide fenestrated endovascular aneurysm repair are not as straightforward as they appear

The current delay in receiving commercially available fenestrated endografts has proved fatal for some patients. In addition, efforts to reduce planning complexity and to increase fenestration location accuracy, thereby expediting the implantation procedure, are appreciated. Indeed, we agree that part of the reason for the relatively slow adoption of fenestrated endovascular aneurysm repair relates to case planning and procedural complexity.

A critical appraisal of the applicability of this technique requires understanding of how aortic angulation affects fenestration distance measurements and the limitations imposed by this anatomically accurate, rigid three-dimensional (3D) printed template.

Planning fenestrations in aortic anatomy with no or slight angulation is fairly straightforward, and results should be similar between conventional software planning and the plan generated by an anatomic reproduction of the patient's aorta. However, most juxtarenal patients have angulated visceral aortas, up to 60 degrees or more. We and others have learned that it is important to account for the interaction between the stiff wire and endograft delivery system and the angulated aorta.¹ Current understanding requires manually modifying the geometric centerline of flow to approximate the stiff wire path through the visceral aorta.2, 3, 4 This adjustment inevitably leads to a straighter path through the anatomy. Failure to make this centerline adjustment leads to significant errors in the distance measurements required to properly locate fenestrations and consequently leads to difficult branch vessel cannulations (or failures) during implant delivery.³

With little or no aortic angulation, no appreciable centerline adjustment is needed, and a conventional software plan looks much like one generated from a 3D printed template. The degree of angulation in the current patients appears small, and it is unclear whether centerline adjustments were made. If they were made, that could explain, in part, the fenestration discrepancies of 1 to 3 mm between the conventional plan and 3D printed template. Although it is tempting to print an exact replica of the visceral aorta for planning purposes, once aortic angulation is introduced, compensation for the delivery system path must be made in order for the fenestrations to properly align with the branch ostia during graft delivery.

Some of the potential friction issues between endograft/delivery system and 3D template have been overcome in this report because the authors printed only the anterior half of the aorta for fenestration planning purposes. In many patients, however, branch artery ostia are located on the posterior half of the aorta, which would require printing more of the circumference of the aorta, thus reintroducing the friction issues.

There is an ongoing need to more quickly deliver patient-specific fenestrated endografts that can be easily, accurately, and consistently planned. Automated fenestration planning software, which works as well in angulated aortic anatomy as in straight anatomy, coupled with more rapid turnaround from a graft manufacturer is an appealing avenue and is currently being pursued for elective patients.⁵ The physician-modified endovascular graft, with accurate planning, remains an attractive option for urgent and emergent patients and should be conducted within an investigational device exemption trial in the United States.