Misalignment of the SMA with ZFen and resultant complications have been a concern and previously investigated for both scallops and large fenestrations (Oderich et al. 2014b). There is some variation in practice and in the literature. Motta et al. evaluated outcomes of selective SMA stenting for scallops in 39 patients, with criteria for alignment stent use including concern for misalignment with SMA “balloon testing” and SMA stenosis. With strict criteria and rigorous follow up, there were no adverse events with selective SMA stenting at a mean follow-up of 22 months (Motta et al. 2019a). Ullery and colleagues examined the postoperative occurrence of “shuttering” or partial coverage of the SMA in unstented scallops. No patients presented with symptoms of mesenteric ischemia during the mean follow-up of 11 months. However, 50% of patients had some degree of SMA shuttering, ranging between 12% and 40%. The majority of patients had at least 21% shuttering, and while no acute or chronic mesenteric ischemia was noted, the mean follow-up period was only 11 months (Ullery et al. 2014). Conversely, in Lala’s series of 47 patients that compared the use of stent to no stent in large fenestrations and scallops, more MAEs were attributed to misalignment in the unstented group, with no misalignment occurring in the stented cohort. One patient developed SMA stenosis distal to the bridging stent that was remedied with angioplasty, similar to the case described in this report (Lala et al. 2016).
These studies only provide short-term data. There is a paucity of data looking at whether there is progression of partial SMA shuttering with scallops or fenestrations, and the long-term effects of partial shuttering on SMA patency and mesenteric ischemia. However, several observational studies have reported change in anatomy of target vessels after fenestrated repair. Kalder and colleagues demonstrated significant shift of target-vessel origin compared to the main device, independent of device and bridging stent used (Kalder et al. 2014). Furthermore, leaving arguably the most important visceral artery (SMA) partially covered by fabric is unsettling for most vascular surgeons.
The current ZFen configuration was conceived in 1999. Since then, significant knowledge has been gained and lessons have been learned thanks to results from physician-sponsored (PS) investigational device exemption (IDE) studies and industry-sponsored trials. Currently, none of the devices used in trials have struts spanning any target vessels. In fact, routine bridging of all target vessels with covered stents is now the norm rather than an exception. This is perhaps best evidenced by the Zenith p-Branch®, developed after the ZFen as an off-the-shelf option for juxtarenal aneurysms, with a strut free SMA fenestration for bridging stent placement (Kitagawa et al. 2013). This is also the case for most physician-modified fenestrated stent grafts (Tenorio et al. 2019a, b; Mirza et al. 2020; Oderich et al. 2017b; Motta et al. 2019b; Sveinsson et al. 2015). Therefore, we believe that performing a minor modification of ZFen device by displacing struts of the large fenestration to the side in order to bridge the SMA fenestration with a covered stent is prudent, logical and safe. This is particularly reasonable since doing so allows for an unobstructed flow to the SMA, eliminates the possibility of shuttering, makes re-intervention on target vessel easier, and does not compromise the long-term integrity of the device as demonstrated by our results. The issue of spanning struts across SMA fenestration has been eliminated in Europe, where subsequent device designs have incorporated the use of strut-free 8-mm fenestrations in additional to the traditional two small fenestrations utilized for the renal arteries. However, in cases where custom manufactured and off-the-shelf devices are not suitable, such as emergent presentations, PMEGs are a valuable option. In these cases, patient anatomy will often dictate that the SMA fenestration be made in a location where there is a crossing strut. This study demonstrates the safety and feasibility of strut relocaton, without detrimental effects.
While placement of bridging stents in visceral arteries ensures excellent perfusion, vessel catheterization carries an inherent risk of dissection, embolization, and small branch perforation that can sometimes be fatal. However, Motta et al. reported no increase in complications with placement of bridging stents in CA and SMA (Motta et al. 2019b). Starnes et al. described SMA incorporation with PMEGs using large fenestrations without routine use of SMA bridging stents (Starnes et al. 2016, 2017, 2018; Starnes 2012). On evaluation of their learning curve over an 8-year period with 136 cases there was one case of transient bowel ischemia that “resolved with medical management,” and another case of mesenteric ischemia, “unrelated to the implant or procedure,” that was treated with a celiac stent 4 years postoperatively (Starnes 2012). While the reasoning for stenting the celiac artery rather than the SMA in patient with mesenteric ischemia was not explained, one can infer that struts spanning the SMA fenestration made it difficult, if not impossible to stent the SMA (Starnes et al. 2017). This was certainly the case in our experience, where trying to stent an SMA that had struts spanning it resulted in a dissection of this critical vessel and conversion to an open bypass.
Starnes et al. also reported on the use of automated planning software to determine fenestration location, using algorithms that account for angulated aortic anatomy. The 97% rate of target-vessel incorporation demonstrates the importance of preoperative planning for FEVAR in accurate placement of fenestrations adjacent to the intended vessels (Starnes et al. 2018). However, we maintain our preference for SMA stenting due to uncontrollable variables such as tortuosity and angulation that can exert variable degrees of rotational force on the endograft and result in fenestration misalignment unless each target vessel is stented. This is partially exemplified by the reports on shuttering mentioned previously (Ullery et al. 2014). Additionally, while the rate of mesenteric ischemia is low with complex endovascular repair of TAAA and PRA (Oderich et al. 2017b), in our experience an SMA bridging stent facilitated endovascular rescue.
There were two (1.7%) deaths in our series, one in each arm. The first death occurred in a frail 91 year-old male in the NR group with a juxtarenal aortic aneurysm repaired using a three-fenestration device. Unfortunately, the patient developed postoperative paraplegia that improved after cerebrospinal fluid drainage and increased mean arterial pressures. Due to respiratory failure with ventilator dependence and the patient’s frail state, the family decided to withdraw care and she expired on post-operative day three. The second patient underwent successful exclusion of the aneurysm and stenting of all target vessels, including the SMA with excellent angiographic result but developed abdominal pain on postoperative day one with elevated lactic acid. On exploratory laparotomy, he was found to have diffuse and scattered ischemia of the small and large intestines. After multiple trips to the operating room for bowel resection, it was determined that short gut syndrome was likely and the family decided to withdraw care. In both cases, mortality was due to microembolization that likely occurred during attempts to align the device with fenestration. The first patient embolized to the lumbar and internal iliac arteries and the second patient embolized to the SMA and branches.
Study limitations
The limitations of this study reside in the fact our group has a good experience with PMEG, having trained at a facility that routinely performed these procedures prior to obtaining an PS-IDE. For this reason, deploying the graft on the sterile back table, performing this minor modification and sheathing is very safe and does not take more than 15 min. This process, however, can be challenging for people with limited experience with back table device modifications. One needs to practice with demonstration devices, carefully examine fenestrations extracorporially under fluoroscopy, to ascertain there is no twisting or kinking before introducing the device in to the patient.
