Data, gathered in a study on the impact of aortic neck dilation after fenestrated endovascular aortic aneurysm repair (FEVAR), show that the process does indeed occur after the procedure—but with minimal clinical implications.
For principal evidence, the researchers pointed out, look to the lack of a type 1a endoleak in the entire series covered in their investigation.
The findings were presented at the Critical Issues America (CIA) annual meeting (7–8 February, Miami, USA) during a session on renal and mesenteric concerns by Benjamin W Starnes, the professor and chief of vascular surgery at the University of Washington School of Medicine in Seattle, USA.
Before delving into the data, Starnes set the scene by referring to a case report from his institution, published in the Journal of Vascular Surgery—“Long- term durability of a physician-modified endograft.”
“We had an 82-year-old gentleman about 10 years ago who entered our study, was treated, completed the study after five years and then, seven years after his implantation at the age of 88, he was driving in Halfway, Oregon, and was in a car accident,” explained Starnes. “He always told his wife that ‘When I die, I want you to return my aorta to Dr Starnes.’
“I got a call from a mortician, who asked me what I wanted—and they put the retroperitoneum in a box and mailed it to me,” he continued. “We did a lot of analysis of this, and it was a pretty rare event. You can see on the CT slices at the level of the SMA (superior mesenteric artery) from preop all the way out to five years, we have complete stability of this graft. When we did vivisection and dissection of this graft and digested the tissue, the graft was in perfect condition compared with the preoperative—or day-of-surgery—photographs.”
This finding raises the whole concept of effective seal zone, said Starnes. “The effective seal zone length of a FEVAR is the circumferential graft seal zone length plus the infrarenal neck length.”
With the research team’s mid-term results now published, the proximal seal zone length has been revealed as an average of 41mm.
“When you look at the results compared to other registries that are published, our rate of type 1a endoleak is zero. That is with a final seal zone length of 41mm,” Starnes said. “So aortic neck dilatation occurs at a reported rate of 0.7±2.1mm in the first year after standard EVAR.”
Starnes et al have already reported and published on aortic neck dilatation, specifically the infrarenal neck associated with fenestrated EVAR, and found “that the infrarenal aortic neck expands over time; it dilates over time, but only to the nominal diameter of a stent graft that you put in.” They measured the infrarenal neck diameter at the lowest renal artery, defining aortic neck dilatation as ≥3mm.
“We posed this question specifically for this meeting: In our prospectively collected IDE (investigational device exemption), with all of this data that we have, does aortic dilation occur in the paravisceral segment and to what degree?” Starnes said.
Further questions followed: If aortic dilation does occur, what are the clinical implications of this? “We already know that we have had no type 1a endoleaks, so the clinical implications are few.” He further posed: “How does degree of oversizing affect aortic dilation? What impact, if any, does device selection have on aortic dilation? And does graft diameter have any influence on aortic dilation?”
In a near decade-long study—since April 2011— patients were selectively recruited based on a neck length of at least 2mm, requiring a “good” paravisceral segment. In addition to measuring aortic diameter at the lowest renal artery, the investigators also did the same at the mid-SMA level.
“We looked at preop, 30 days, six months and annually out to five years,” Starnes explained. “We analysed the overall cohort and we completed subgroup analysis to look at the degree of oversizing. We divided these into quartiles: less than 10% oversizing, 10–15% oversizing, 15–20% and greater than 20%.”
Three different devices were implanted in their IDE—the Cook Zenith, the Medtronic Endurant and Bolton Treovance. Furthermore, graft diameters were divided into small, medium and large categories.
The results showed that of 166 patients enrolled, 101 underwent at least one year of follow-up, while 73, 56, 38 and 21 patients received two, three, four and five years of follow-up, respectively. Oversizing for the entire cohort registered at a mean 14.1%. Results by graft type were revealed as 50 for the Cook Zenith device, 13 for the Medtronic Endurant and 38 for the Bolton Treovance with at least one- year follow-up.
With regards to aortic dilation at the SMA with one year of follow-up, “the mean aortic increase in our series was 1±2.2mm for a 5% increase,” Starnes said, recalling a 1998 study on standard EVAR that reported a dilation of 0.7±2.1mm. “So very, very similar results,” he added.
“At two years, we were up to 2.2±2.4mm, and this is where the dilation stops. This is where it peaks: at two years. Because at three years, we drop down to 6.9%—mean aortic increase of 3mm. At four years, we are down to 6.7%, and out to five years we are down to 4.1% aortic neck dilation.”
What about oversizing? “When we divide these patients based on their oversizing, if you look at those patients who had less than 10% oversizing, their aortic dilation over three years was 1%; 10–15%, it was 4.6%; 15–20%, it was 7%; and greater than 20% oversizing, it was up to 15.4% aortic neck dilation. So it increases with increasing degrees of oversizing.”
Device selection yielded interesting findings. Starnes continued: “With the Medtronic Endurant graft, out to three years, average oversizing was 8.5% and the aortic neck at the region of the SMA dilated to 8.3%, so to the nominal diameter of the Endurant graft. If we look at the Bolton Treovance, the oversizing was an average of 12.9% and the aortic neck dilatation that occurred was 11.7%. Again, the aortic neck is dilating to the nominal diameter of
the stent graft. However, with the Cook graft, which is a different platform—the Bolton and Medtronic are nitinol-based frames and the Cook Zenith is a stainless-steel frame—there was 17.5% oversizing, and yet only a 7% increase in aortic neck dilatation.”
Starnes next turned to graft diameters. “This was interesting,” he mused. “I thought for sure that if we were treating patients with large diameter grafts [36mm], that means we’re treating diseased large necks, and that those patients would dilate more. Actually, we didn’t find that. What we found was very similar among all three graft sizes. So if you had a 22–26mm graft, you dilated at 7%; 28–30mm, 8.6%; 32–36mm, you only dilated up to 6%.”
Concluding, Starnes expanded on his chief finding of minimal clinical implications of dilation after FEVAR. “Aortic dilation seems to plateau at two years and then gradually abate over time,” he said. “Graft size has no influence on aortic dilation at all. And there is a difference between nitinol- and stainless steel-based platforms.
“We can also say from this dataset that increased oversizing increases aortic dilation, and so it calls into question how to design a fenestrated endograft if you knew you could get an average seal zone length of not 15mm, but 40mm of effective seal every single time.
“That’s a 167% increase in seal zone length based on the standard IFU requirement of 15mm. So if you could guarantee that long a length of seal, would we have to oversize as much as we do? Maybe we can treat these patients with just 10% or less of oversizing.”