Goal

A list of unresolved issues and a compilation of test concepts that
could potentially address these issues.

### 

Table 6

The following table lists unresolved issues and test concepts that may
need to be developed to address these critical parameters/failure modes.
These comments were provided by participants in response to the work
assignment and were discussed during the workshop. Comments generated at
the workshop are highlighted in the table.

##  

**Table 6 Additional Testing Needs**

+----------------------------+-----------------------------------------+
| **[Unresolved              | **[Test concept]{.smallcaps}**          |
| issue]{.smallcaps}**       |                                         |
+============================+=========================================+
| [Metal fractures, fabric   |                                         |
| erosion, wear              |                                         |
| holes]{.smallcaps}         |                                         |
+----------------------------+-----------------------------------------+
| 1.  Mechanical failures    | Incorporate design-dependent effects of |
|     (metal fracture,       | angulation and tortuosity into tests.   |
|     fabric erosion).       | May not need new test concepts, just    |
|                            | new protocols that recognize these      |
|                            | effects (on both loads and device       |
|                            | response).                              |
+----------------------------+-----------------------------------------+
| 2.  Evaluation of effects  | **[Workshop comments:]{.underline}**    |
|     of predicted failure   |                                         |
|     locations (fixation    | -   **Same as for number 6.**           |
|     modes), for example    |                                         |
|     barbs or support bars. |                                         |
+----------------------------+-----------------------------------------+
| ######### Graft wear holes | New test that simulates movement        |
|                            | between the graft material and wireform |
|                            | in a simulated AAA model. Also to be    |
|                            | assessed is the functional significance |
|                            | of any wear holes observed. In other    |
|                            | words, if wear holes are generated,     |
|                            | what is their impact on WEP, IWP, etc.? |
|                            | Given the porosity of Dacron fabrics,   |
|                            | it is not unrealistic to expect that    |
|                            | wear holes below a certain size will    |
|                            | have minimal adverse impact on the      |
|                            | device's ability to exclude an aneurysm |
|                            | (i.e., there is probably some tolerance |
|                            | around allowable minimal type III       |
|                            | endoleak rate).                         |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **This is relevant to all graft     |
|                            |     materials, not just textiles.**     |
|                            |                                         |
|                            | -   **There is a need to model the      |
|                            |     attachment sites and the part of    |
|                            |     the graft that is in the sac, and   |
|                            |     at interaction points (junctions),  |
|                            |     in an *appropriate* model.**        |
+----------------------------+-----------------------------------------+
| 3.  Clinically-significant | **[Workshop comments:]{.underline}**    |
|     hole size              |                                         |
|                            | -   **Captured in number 3.**           |
|                            |                                         |
|                            | -   **Characterization of hole size     |
|                            |     (any hole), and holes identified in |
|                            |     number 3 is important.**            |
|                            |                                         |
|                            | -   **Need to consider distortion in    |
|                            |     weave as a sign of hole             |
|                            |     development.**                      |
+----------------------------+-----------------------------------------+
| 4.  Stent fracture         | Transition zones & flexion site forces. |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **See earlier discussion.**         |
+----------------------------+-----------------------------------------+
| 5.  Effects of Fractured   | Evaluate the impact of stent-wire       |
|     Stent Element(s) on    | fracture(s) on the mechanical           |
|     Mechanical Integrity   | attributes of the deployed / implanted  |
|                            | endoprosthesis (e.g., hoop strength,    |
|                            | migration resistance, sealing           |
|                            | efficiency, etc.) to answer the         |
|                            | question- Does stent-wire fracture      |
|                            | necessarily constitute a device         |
|                            | failure? The location and number of     |
|                            | fractures could be identified from the  |
|                            | high strain regions identified by the   |
|                            | FEA analysis, anticipated to be         |
|                            | 'weak-spots'. If it could be            |
|                            | demonstrated that the mechanical        |
|                            | attributes of an endoprosthesis are not |
|                            | significantly compromised by wire       |
|                            | fracture(s), this information could be  |
|                            | a strong mitigator of our               |
|                            | interpretation of the mechanical        |
|                            | significance of fatigue fracture of the |
|                            | stent.                                  |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **This is a form of prospective     |
|                            |     failure analysis.**                 |
|                            |                                         |
|                            | ```{=html}                              |
|                            | <!-- -->                                |
|                            | ```                                     |
|                            | -   **The question is: is this device   |
|                            |     failure amenable to corrective      |
|                            |     intervention?**                     |
|                            |                                         |
|                            | -   **The presence of hooks or barbs    |
|                            |     represents a new source of          |
|                            |     metal-against-fabric wear.**        |
|                            |                                         |
|                            | ```{=html}                              |
|                            | <!-- -->                                |
|                            | ```                                     |
|                            | -   **A risk analysis for failure modes |
|                            |     and the potential for failure of    |
|                            |     components should be conducted.**   |
|                            |                                         |
|                            | -   **The potential need for repair     |
|                            |     versus surgical conversion should   |
|                            |     be considered.**                    |
+----------------------------+-----------------------------------------+
| 6.  Testing of device to   | New test or new vessel model that       |
|     vessel wall attachment | accounts for simulation of actions upon |
|     components such as     | the attachment component of the device. |
|     barbs. May also apply  |                                         |
|     to device to device    | **[Workshop comments:]{.underline}**    |
|     attachment components  |                                         |
|     for multi-component    | -   **It may be possible to group this  |
|     devices.               |     with number 5.**                    |
|                            |                                         |
|                            | ```{=html}                              |
|                            | <!-- -->                                |
|                            | ```                                     |
|                            | -   **This concern is covered by other  |
|                            |     tests, e.g., pull tests for modular |
|                            |     components, tensile tests,          |
|                            |     durability test.**                  |
|                            |                                         |
|                            | -   **In response to a question of the  |
|                            |     definition of a hook versus a barb, |
|                            |     one definition was that a hook is   |
|                            |     curved and a barb is straight.**    |
|                            |                                         |
|                            | -   **For all components of the device, |
|                            |     there is a need to evaluate the     |
|                            |     loads and justify why the           |
|                            |     components (e.g., stents, anchoring |
|                            |     systems) will not fail.**           |
+----------------------------+-----------------------------------------+
| 7.  Effects of Fractured   | Evaluate the impact of stent-wire       |
|     Stent Element(s) on    | fracture(s) on the integrity of the     |
|     Graft Integrity        | deployed / implanted endoprosthesis     |
|                            | (e.g., Bond/peel strength, delamination |
|                            | propagation, WEP, IWP, etc.) to answer  |
|                            | the question- Does stent-wire fracture  |
|                            | necessarily constitute a device         |
|                            | failure? The location and number of     |
|                            | fractures could be identified from the  |
|                            | high strain regions identified by the   |
|                            | FEA analysis, anticipated to be         |
|                            | 'weak-spots'. If it could be            |
|                            | demonstrated that the graft integrity   |
|                            | of an endoprosthesis is not             |
|                            | significantly compromised by wire       |
|                            | fracture(s), this information could be  |
|                            | a strong mitigator of our               |
|                            | interpretation of the mechanical        |
|                            | significance of fatigue fracture of the |
|                            | stent.                                  |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Same comments as for number 6.**  |
+----------------------------+-----------------------------------------+
| 9.  Effects of Fractured   | Evaluate the impact of stent-wire       |
|     Stent Element(s) on    | fracture(s) on the biological response  |
|     Biological Response    | to a deployed / implanted               |
|                            | endoprosthesis (e.g., fistula           |
|                            | formation, vessel wall erosion, failure |
|                            | propagation by redistribution of loads, |
|                            | inflammatory response, etc.) to answer  |
|                            | the question- Does stent-wire fracture  |
|                            | necessarily constitute a device         |
|                            | failure? The location and number of     |
|                            | fractures could be identified from the  |
|                            | high strain regions identified by the   |
|                            | FEA analysis, anticipated to be         |
|                            | 'weak-spots'. If it could be            |
|                            | demonstrated that the biological        |
|                            | response of an endoprosthesis is not    |
|                            | significantly compromised by wire       |
|                            | fracture(s), this information could be  |
|                            | a strong mitigator of our               |
|                            | interpretation of the mechanical        |
|                            | significance of fatigue fracture of the |
|                            | stent.                                  |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Same comments as for number 6.**  |
+----------------------------+-----------------------------------------+
| 10. Device damage          | Test forced dilation and over-dilation  |
|                            | in narrow segments.                     |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Need to evaluate tolerance to     |
|                            |     balloon dilatation due to           |
|                            |     re-intervention or treatment of     |
|                            |     occlusions.**                       |
|                            |                                         |
|                            | ```{=html}                              |
|                            | <!-- -->                                |
|                            | ```                                     |
|                            | -   **This includes more than stent and |
|                            |     suture breaks, that is, it includes |
|                            |     any and all device damage.**        |
+----------------------------+-----------------------------------------+
| [Separation of Modular     |                                         |
| Components]{.smallcaps}    |                                         |
+----------------------------+-----------------------------------------+
| 11. Modular component      | Evaluate effects of remodeling and      |
|     joints.                | other anatomic changes (longitudinal    |
|                            | shrinkage, changes in angulation and    |
|                            | tortuosity). These changes may produce  |
|                            | tension, compression, or bending loads  |
|                            | on joints.                              |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Qualitative assessment of modular |
|                            |     separations under worst-case        |
|                            |     conditions (i.e., extreme           |
|                            |     angulation and tortuosity) is       |
|                            |     needed.**                           |
|                            |                                         |
|                            | -   **Possible bending or kinking of    |
|                            |     the device due to changes post      |
|                            |     implant should be assessed.**       |
+----------------------------+-----------------------------------------+
| 12. Axial dislocations,    | New test that simulates axial loads on  |
|     separations.           | the implant-- if determined to be       |
|                            | significant. These may be found to have |
|                            | several causes such as vessel motion    |
|                            | and hemodynamic components (shear).     |
+----------------------------+-----------------------------------------+
| 13. Separation of          | Unidirectional flow in durability       |
|     overlapping component  | tester.                                 |
|     in supported and       |                                         |
|     unsupported region.    |                                         |
+----------------------------+-----------------------------------------+
| 14. Reproduction of        | Reproduction of anatomical conditions   |
|     kinking of grafts,     | including development of synthetic      |
|     suture break,          | material to resemble natural artery.    |
|     endoleak, endotension. |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Delete based upon discussion.**   |
|                            |                                         |
|                            | ```{=html}                              |
|                            | <!-- -->                                |
|                            | ```                                     |
|                            | -   **Covered under other tests.**      |
+----------------------------+-----------------------------------------+
| [Aneurysm remodeling       |                                         |
| effects]{.smallcaps}       |                                         |
+----------------------------+-----------------------------------------+
| 15. AAA remodeling         | A relevant, realistic test does not     |
|                            | exist; perhaps only clinical trials     |
|                            | with good long-term follow-up will      |
|                            | enable understanding of device          |
|                            | response.                               |
+----------------------------+-----------------------------------------+
| 16. Iliac leg kinking.     | Evaluate aneurysm longitudinal          |
|                            | shrinkage effects on implant.           |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Delete based upon discussion.**   |
+----------------------------+-----------------------------------------+
| 17. How the grafts null    |                                         |
|     adapt to morphologic   |                                         |
|     changes -- i.e.        |                                         |
|     fatigue testing in     |                                         |
|     multiple or changing   |                                         |
|     conditions.            |                                         |
+----------------------------+-----------------------------------------+
| 18. Stent/device           | Angles & flexion sites with changing    |
|     \_\_\_\_\_\_\_\_\_     | morphology.                             |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Delete based upon discussion.**   |
+----------------------------+-----------------------------------------+
| 19. Failure resulting from | New type of durability test             |
|     changes in aneurysm    |                                         |
|     over time              | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Delete based upon discussion.**   |
+----------------------------+-----------------------------------------+
| 20. Fixation post-neck     | Wall contact evaluation in growing neck |
|     dilation               | model at various minimum and maximum    |
|                            | oversizings and engagement lengths (can |
|                            | use tensile loads as well for migration |
|                            | resistance).                            |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Delete based upon discussion.**   |
+----------------------------+-----------------------------------------+
| 21. The effect of the      | **[Workshop comments:]{.underline}**    |
|     biologic milieu on the |                                         |
|     materials (corrosion,  | -   **Delete based upon discussion.**   |
|     etc).                  |                                         |
+----------------------------+-----------------------------------------+
| [Other]{.smallcaps}        |                                         |
+----------------------------+-----------------------------------------+
| 22. Endotension / aneurysm | Flow simulation of active versus        |
|     sac reduction          | passive diffusion.                      |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Delete based upon discussion.**   |
+----------------------------+-----------------------------------------+
| 23. Type IV endoleak       | Determine integral water leakage        |
|                            | specification using pure water that     |
|                            | correlates to no Type IV endoleaks *in  |
|                            | vivo*.                                  |
+----------------------------+-----------------------------------------+
| 24. Proximal seal in short | Pulsatile dye penetration in            |
|     neck                   | progressively angled necks.             |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Delete based upon discussion.**   |
|                            |                                         |
|                            | -   **Hopkinson's testing is a useful   |
|                            |     reference.**                        |
|                            |                                         |
|                            | -   **Covered under vessel wall         |
|                            |     attachment.**                       |
+----------------------------+-----------------------------------------+
| 25. Migration              | Unidirectional flow model.              |
+----------------------------+-----------------------------------------+
| ######### Columnar St      | Harris (1999) showed that aneurysmal    |
| rength / Buckle Resistance | shrinkage leading to endoprosthesis     |
|                            | buckling is a significant source of     |
|                            | early and late-term complications. A    |
|                            | number of authors (Carpenter, 20001;    |
|                            | Resch, 2000; Kalliafas, 2000) have      |
|                            | demonstrated that kinking, buckling, or |
|                            | twisting of the deployed endoprosthesis |
|                            | subsequent to device migration,         |
|                            | hemodynamic forces, or aneurysmal       |
|                            | shrinkage constitutes a significant     |
|                            | failure mode necessitating              |
|                            | reintervention. Characterization of the |
|                            | columnar strength /buckle resistance of |
|                            | the deployed device to in response to   |
|                            | anticipated hemodynamic forces and/or   |
|                            | longitudinal displacements may be a way |
|                            | to gain understanding with this         |
|                            | clinical problem.                       |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Numbers 26, 27 and 28 are of      |
|                            |     academic interest.**                |
+----------------------------+-----------------------------------------+
| ######                     | Given the relatively high rate (26.6%)  |
| ### Revision Methodologies | of reintervention reported for AAA      |
|                            | endoprostheses (Holzenbien, 2001), the  |
|                            | compatibility of the deployed           |
|                            | endoprostheses with convention revision |
|                            | techniques (e.g., adjunctive stenting,  |
|                            | coil embolization, balloon dilatation,  |
|                            | etc.) should be established empirically |
|                            | or through rationales.                  |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Numbers 26, 27 and 28 are of      |
|                            |     academic interest.**                |
+----------------------------+-----------------------------------------+
| ######### Ruptur           | Are the consequences of aneurysm        |
| e failure mode consequence | rupture as severe when an endovascular  |
|                            | prosthesis is implanted (containing the |
|                            | rupture) as when a rupture occurs       |
|                            | without the device?                     |
|                            |                                         |
|                            | **[Workshop comments:]{.underline}**    |
|                            |                                         |
|                            | -   **Numbers 26, 27 and 28 are of      |
|                            |     academic interest.**                |
|                            |                                         |
|                            | ```{=html}                              |
|                            | <!-- -->                                |
|                            | ```                                     |
|                            | -   **This may be relevant in defining  |
|                            |     successful clinical outcomes.**     |
+----------------------------+-----------------------------------------+
| #######                    | **[Workshop comments[:                  |
| ## Aneurysm size and shape | ]{.smallcaps}]{.underline}**            |
|                            |                                         |
|                            | -   **A standard size and shape of      |
|                            |     aneurysm is difficult to define for |
|                            |     *in vitro* testing purposes, yet    |
|                            |     can have impact on test relevance   |
|                            |     and outcome.**                      |
+----------------------------+-----------------------------------------+

## References / Abstracts

Carpenter (2001)

Harris (1999)

Holzenbien (2001)

Kalliafas (2000)

Resch (2000)