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Dr Wesley S. Moore (Los Angeles, Calif). This was an excellent presentation and superbly analyzed; however, I'm still not totally convinced that the adverse effect of migration is related to the oversizing of the prosthesis. It is more likely related to the reasons that oversizing was selected to begin with.

You mentioned two possible reasons, including short neck or extreme angulation; perhaps there are more. These reasons for oversizing reflect the adverse effect based on patient selection rather than the generic consequence of oversizing per se. Clearly, there is no reason that one would want to excessively oversize unless you were trying to compensate for some particular adverse anatomic problem. Clearly there was a trend toward shorter necks in your series. Even though this trend wasn't statistically significant in your analysis, that may be a sample size problem and a type II error. Would you like to comment?

Dr Charles Sternbergh III. Thank you for those comments, and I couldn't agree more. We looked very hard for anatomic characteristics that might explain the correlation between >30% device oversizing and adverse events. As shown in this presentation, we could not identify any statistically significant associations; aortic neck length did trend shorter, although the differences were not statistically significant. The rate of endoleak was half of that in the patients who were oversized less than 30% than in the patients who were oversized greater than 30%, but this too was not statistically significant. Increased endoleak rates have correlated with a decrease in the chance of aneurysm shrinkage; but again, those trends were not significant.

Dr Jacob Buth (Eindhoven, The Netherlands). I also would like to congratulate Dr Sternbergh for an excellent paper. My question is this: How did you get to the threshold of 30%? Was this handpicked or was there any graphical or mathematical method used, like a ROC curve?

Dr Sternbergh. That's an excellent question. No, there were not ROC curves developed for this study. Thirty percent was chosen because it was double the size of the recommended maximum oversizing, which was 10% to 15%.

Dr David C. Brewster (Boston, Mass). Dr. Sternbergh, I'm a little surprised about migration with suprarenal hooks. I can understand where oversizing of a device without such fixation might be associated with a higher incidence of migration, but wouldn't one expect that suprarenal hook fixation would prevent that? And secondly, as a participant in the Zenith trial, the device selection was pretty tightly controlled, as I remember, by the sponsor, so why would 30% oversizing occur in certain patients if that wasn't desirable?

Dr Sternbergh. I'll start with your first question. I agree that any incidence of migration, frankly, was somewhat surprising based on the suprarenal barb fixation. But the data do suggest a small chance of migration (>25 mm) despite the suprarenal fixation.

In regard to the choice of oversizing, I, too, was surprised to find that a number of the patients had this excessive oversizing. And while I too recall that there was some significant oversight in terms of sizing of these devices, it was ultimately left to the discretion of the investigator.

Dr Piergiorgio Cao (Perugia, Italy). You report low incidence of migration, which is quite different from our experience. We had a higher incidence of migration with a different kind of endograft: the highest peak migration was after 2 years. You reported the results after 1 year. Do you have any other data after this interval?

And the second question is this: since you couldn't find any correlation between migration and neck dilatation, can you speculate where this migration is coming from? What is the cause since, you have no

Dr Sternbergh. I very much agree with you that migration is a time-dependent phenomenon and 12 months is fairly early. I don't have any available data yet on more long-term migration, but certainly that's going to be an important thing to keep an eye on. Your last question really is another question of why are these migrating. And the bottom line is that we don't know. We looked very hard for other anatomic characteristics that perhaps were the causative factor(s), and the >30% oversizing was simply a surrogate, but we could not find them.