Commentary: Endovascular Aneurysm Sealing for Ruptured Abdominal Aortic Aneurysms

Although the (r)evolution of endovascular aneurysm sealing (EVAS) for elective abdominal aortic aneurysm (AAA) repair has just started, the avant-garde of this exciting new technique already are exploring new horizons. While a substantial part of the endovascular world is still questioning the working mechanism and durability of EVAS, these early enthusiasts are inserting the Nellix Endovascular Aneurysm Sealing System (Endologix Inc, Irvine, CA, USA) in aortic anatomies that were previously considered totally unsuitable for endovascular repair.^1,2 Although the instructions for use (IFU) of the Nellix system have restrictions that are largely similar to standard stent-grafts, this device in particular seems to seduce vascular surgeons to go outside the IFU.

The essential difference between EVAS and standard endovascular aneurysm repair (EVAR) is that the endobags are used to provide anatomical fixation in the aneurysm sac with complete elimination of the sac lumen and seal of side branch flow, as well as providing a proximal and distal seal in, respectively, the aortic neck and iliac arteries.^3–5 The main question that is raised is whether this sac-anchoring system provides a true seal of the aneurysm sac, in which case a seal in the aortic neck and iliac arteries would seem less important, or provides some sort of fixation in the sac only. Probably the main reason to use the Nellix device outside of IFU, with treatment of short necks or even no-necks, conical necks, large neck angulations, and wide necks, is the belief that the seal in the aneurysm sac is enough for a successful and durable aortic repair.

Recently, 2 large EVAS studies were published. In the single-center study of Brownrigg et al, ⁶ which reported 30-day outcomes of EVAS in 105 patients with non-ruptured AAAs, 69% of patients had adverse neck morphology. Technical success was achieved in 97% and 30-day mortality was 1%. The incidence of type I endoleaks within 30 days was 4%, all successfully treated with transcatheter embolization. There was no type II or III endoleak. Angioplasty and adjunctive stenting were performed for postoperative limb stenosis in 3% of the patients. In the large multicenter study of Böckler et al, ⁷ 171 patients were treated with EVAS, 169 with intact AAAs and 2 with ruptured aneurysms. Anatomic measurements were outside the IFU in 33% of the patients. Technical success was 99%, and 30-day mortality was 0% in 130 patients with completed 30-day follow-up. Device occlusions occurred in 5% of the patients. Type Ia, type Ib, and type II endoleaks were reported in 3%, 2%, and 4% of the patients, respectively; there were no type III endoleaks. Both studies concluded that the Nellix EVAS system appears to have a reasonable short-term outcome and that patient selection and procedural evolution will further enhance outcome. However, definite conclusions regarding the utility of EVAS will be defined by the durability of the device in long-term follow-up.

Compared with regular abdominal aortic stent-grafts, the Nellix system would be a particularly attractive alternative for the treatment of ruptured AAAs (RAAA). Sizing is fast and easy and basically requires only length measurements; as a result, only a small inventory of devices is needed. There is no time-consuming contralateral limb cannulation, and early hemostasis can be achieved through endobag inflation with saline (the “prefill”), while maintaining limb perfusion. Furthermore, patients with unsuitable aortic anatomy for treatment with currently available stent-grafts might be successfully treated with Nellix as shown by the 2 studies mentioned above.^6,7 A minor drawback of the Nellix system, however, especially when used outside office hours, is the need for 2 experienced operators, one to hold the deployed stent-grafts at the desired position and another to fill the endobags. ⁸

At present, 3 case reports are published about EVAS for RAAA, excluding the 2 patients with RAAA in the study by Böckler et al ⁷ of 171 patients. Coppi et al ⁹ described one patient with infrarenal RAAA and adverse anatomy successfully treated with EVAS, and Truijers et al ¹⁰ described one patient with a pararenal RAAA successfully treated with EVAS and chimney grafts. The “largest” published series is by de Bruin et al, ¹¹ who reported on EVAS for infrarenal RAAA in 5 patients, all with aortic morphology outside the IFU for standard EVAR (mainly due to infrarenal neck angulation). Interestingly enough, 4 of these 5 patients had aortic morphology outside the IFU for Nellix as well. All 3 reports showed that EVAS for RAA is feasible, but there is most likely bias toward reporting good results, as failures of EVAS for RAAA, and I am pretty sure there are some, will not be submitted for publication.

In this issue of the JEVT, a case report by Antoniou et al ¹² on EVAS for RAAA addresses, in my opinion, the most important issue, that is, can we seal an aneurysm sac with a torn wall? As shown in this article and by previous reports, the answer might be yes, at least for a short period of time.^9–11 The danger of using pressurized endobags in RAAAs, however, is enlarging the size of the rupture or tearing of the aorta. Truijers et al ¹⁰ mentioned that this is not likely to occur when the endobags are filled to an intended transducer pressure of 180 mm Hg. However, Antoniou and colleagues ¹² showed quite nicely that further disruption of an already damaged aortic wall can happen even at a pressure of 180 mm Hg. Probably further tearing of the aneurysm sac might also depend on the initial size of the tear, which unfortunately is impossible to detect on preoperative computed tomographic angiography. In addition, EVAS might fail to seal the ruptured aneurysm sac due to an inability to generate the required pressure, as the aorta might give way during endobag filling. Interestingly, in the study of de Bruin et al, ¹¹ endobag fill pressures up to 230 mm Hg were applied, and no further tearing of the sac was found. One patient, however, was reoperated for continuous bleeding due to reperfusion of the sac because of a type I endoleak.

Enlarging of the aneurysm rupture during endobag filling might be detected when a prefill is applied with a small amount of contrast in the saline. In the Nellix IFU, the use of contrast in the prefill is not advocated, but in the case of a RAAA (or even in elective cases), it might help to observe the behavior of the endobags throughout the filling process. ¹⁰ In this way, bulging of the endobags through the aortic tear might be instantly detected, although it is unclear what the best operative strategy would be in such a case. No further increase of the prefill would seem logical, but in the event of further rupture, removing the prefill from the endobags might result in severe hemorrhage. Polymerization of the endobags, with enough polymer thawed, should then be performed really quickly to save the patient’s life, if at all possible.

This is why the authors of the present case report, based on their experience with this specific patient, recommend that intraoperative endobag saline prefill should be avoided in RAAA to minimize the risk of aortic wall disruption. This is in contrast to the recommendation of Truijers et al, ¹⁰ who advocate the use of a prefill, but, importantly, with the addition of contrast to the saline to observe potential bulging of the endobags. de Bruin et al ¹¹ performed a pure saline prefill in their 5 cases of RAAA, but they did question the need for it. Additionally, they stated that a refined protocol is needed for target polymer fill pressures and for the identification of specific morphological parameters that predict success or failure.

EVAS for RAAA is still in its infancy and probably the most important, and the obvious lesson that can be learned from these case reports is that larger series are needed to judge the true merit of EVAS for RAAA. Surgeons who use the Nellix device for RAAA should be encouraged to publish not only their successes, but most important, to report their failures too, what they learned from them, and how they adjusted their specific surgical strategy and protocols.