LE NUOVE ENDOPROTESI AORTICHE

DI CARLO SETACCI

 

"La nuova generazione di endoprotesi aortiche consente di ottenere eccellenti risultati non solo a breve termine ma anche a medio e lungo termine.
Il riuscire a non esercitare forza radiale sul colletto prossimale evita una dilatazione che è causa di continua sollecitazione sulla parete aortica con conseguenti, inevitabili complicanze."-
Di seguito una sintesi della presentazione che ho illustrato nel corso del congresso LINC 2017 a Lipsia, successivamente pubblicato su VASCULAR NEWS.

Prof. Setacci’s talk at LINC 2017
The evolution of the aortic neck after EVAR


Summary

A continuous aortic enlargement at the level of infrarenal aortic neck has been reported after endovascular repair (EVAR) of abdominal aortic aneurysm (AAA).  Current concepts regarding the reason for this phenomenon remain poorly understood, although it is known that the amount of proximal device oversizing with self-expanding stent grafts (SESG) influences neck progression.  Once deployed, SESG continue to expand until the nominal diameter is reached, unless tissue resistance limits its expansion. It has been reported that when aortic neck dilatation occurs it is related to adverse mid-term outcomes.
The beginning of the endovascular aortic repair  era was characterized by endografts that essentially consisted of a tubular fabric graft attached at both ends by a large balloon-expandable stent graft (BESG), such as the home-made Parodi Endograft and the Montefiore Endograft System. Not surprisingly, because of the lack of a chronic outward force at the level of proximal neck, these devices were not associated with neck dilatation over time, even though stent migration and endograft collapse into the aneurysmal sac were possible complications. With the advent of SESG, BES had been rapidly disappearing from the market for several years.

Traditional SESGs require an infrarenal non-aneurysmal segment - so called aortic neck - to adequately seal the aneurysm sac from chronic circulatory pressures. Sealing is obtained by oversizing the stent (from 10 to 30%) prospecting that the chronic radial force exerted longitudinally against the aortic wall will circumferentially prevent any leakage.

For a long time, the only available technology for sealing had been based on the application of self-expanding forces to a portion of healthy proximal aortic neck.   The recent appearance on the market of the Ovation endograft represents a valid alternative to chronic outward forces for an appropriate sealing.

The Ovation endograft [Endologix(™), Santa Rosa – CA], with its new concept of sealing by non-expansive circumferential apposition of polymer-filled rings to aortic wall, creates no chronic outward force at infrarenal aortic level.

The Ovation technology is based on a new sealing concept that redefines the idea of aortic neck length. The polymer-filled sealing ring provides uniform, nonexpansive, continuous wall apposition that aims to isolate the aortic neck from circulatory pressures.
The sealing is not longitudinal and related to neck length, but circumferential and based on the apposition of the polymer-filled ring to the aortic wall at 13 mm below the lower renal artery. This makes the Ovation system the only stent graft approved by the US Food and Drug Administration (FDA)  for EVAR that is not restricted by the conventional measurement of aortic neck length. Actually, the FDA criteria for the use of the Ovation endograft is the presence of an inner wall diameter ≥16 mm and ≤30 mm at 13 mm below the inferior renal artery to allow correct apposition of rings to the aortic wall.

This sealing mechanism, which is completely different from that obtained by SESG, promises to isolate the aortic neck from blood pressure, thus preventing aortic neck evolution over time.

We reported for the first time in literature mid-term clinical outcomes from a series of patients treated with this new sealing technology, describing really encouraging data (assisted primary clinical success rate at 2 years of 100%, estimated freedom from type I endoleak at 3 years of 98%).
With a core lab analysis of morphological changes, our research evaluated aortic neck evolution at 2 years after EVAR by endograft with no chronic outward force, revealing that no aortic neck dilatation. This may suggests that aortic neck evolution is not associated with EVAR at mid-term follow-up when an endograft with no chronic outward radial force is implanted.

Aortic neck can definitely maintain its diameter when the radial force applied by the stent graft is lower than the recoil force of the elastic aortic wall.  Nowadays, while BESG, have been removed from the market, the sealing technology of the TriVascular Ovation (™), which does not apply chronic outward force, may guarantee a similar phenomenon as suggested by the absence of neck dilatation and migration in our study.

In a recent sub-analysis of our registry we have further investigated the behavior of the Ovation technology in the absence of a suitable neck length of 7 mm, revealing that it was not associated with poor outcomes in the midterm period. This data showed that the use of the Ovation system for the treatment of infrarenal abdominal aortic aneurysms is not restricted by the conventional measurement of aortic neck length, as confirmed by clarified FDA indication statement recently.  Our data confirm that the Ovation sealing ring creates uniform continuous wall apposition, and provides circumferential non-expansive seal at mid-term follow-up, independently of aortic necklength. This means that the Ovation system may be used in all aneurysmal necks when the inner wall diameter is the range of compatibility with the polymer-filled rings (16-30 mm).


Prof. Carlo Setacci, MD

Chief
Vascular and Endovascular Surgery Unit
Department of Medicine, Surgery and Neuroscience
University of Siena
Past-President of European Society for Vascular Surgery
Past-President of Italian Society for Vascular and Endovascular Surgery