A recent meta-analysis of patients with cAAA treated with PMEG show that the procedure has a technical success, 30-day mortality, and branched patency at 14.8 months ranging from 96.35 to 100%, 0% to 8%, and 96.3 to 100%, respectively. However, this study revealed several discrepancies between centers with regard to the type of stent used, device modification techniques, and the lack of reporting outcomes based on aneurysm types. For instance, for abdominal aortic pathologies, the stent graft used was reported in 273 (60%) cases, a strikingly low percentage. (Canonge et al., 2021) In a matched cohort of 82 patients with cAAA treated with either CMD or PMEG, Dossabhoy et al. reported no difference in perioperative complications, hospital length of stay, type I or III endoleak, or survival between the two devices. The only difference noted involved total fluoroscopy time, contrast volume used, and operative time. (Dossabhoy et al., 2018) Certainly, PMEG will continue to play an important role in the management of patients with cAAA for years to come. Unfortunately, the lack of a standardized protocol with regard of stent graft modification steps, sizing and type of bridging stent used by various centers performing these procedures make it impossible to perform a pooled or meta-analysis to help prove the long-term efficacy of this technique. Furthermore, the technique is not widely embraced owing to the lack of training and complexity of these operations.
While other devices have been successfully modified, the Cook Zenith remains our platform of choice for PMEG for several reasons. First, the devices are easily constrainable using one of the three nitinol wires located in the inner cannula of all Cook Zenith endografts, reducing the size and allowing device rotation in-situ to ensure fenestration alignment with target vessels. Second, the availability of straight and tapered devices of various sizes and lengths accommodates variable anatomy easily. Third, modification steps are similar for all devices.
In patients with tortuous vessels large enough to accommodate it, delivery of the PMEG through a previously placed Gore Dryseal sheath helps eliminate friction and ensures proper fenestration/target vessel alignment. This is also the case with failed EVAR being rescued with a PMEG. For this reason, we favor thoracic devices (Zenith TX2 TAA Endovascular Graft with Pro-Form or Alpha Thoracic Endovascular Endograft) for four vessels cases or for failed previous repair requiring 3 or more vessels incorporation due to the long delivery system. The Zenith Flex AAA bifurcated device is suitable for patients requiring one to three vessels repairs (Fig. 5) as the shorter delivery system makes it challenging to reach the celiac artery, especially in taller patients.
For patients requiring repair extension to the iliac arteries, we prefer the combination of a tapered Zenith thoracic device and Gore Excluder AAA Endoprosthesis or Iliac Branched Endoprosthesis (IBE) owing to their lack of suprarenal fixation struts that can crush bridging renal stents. We prefer to build our repair from the top down – the fenestrated cuff is placed first, followed by a bifurcated device. While acceptable, we often avoid a one-to-one size match between devices and allow for a minimum of two stents overlap between devices.
As illustrated by our carefully selected four cases, PMEG is indicated for a variety of patients with CAA, including those with infrarenal non amenable to currently approved devices, patients with juxtarenal, paravisceral, thoracoabdominal, certain patients with arch aneurysms and those with failed previous endovascular repair (failed EVAR). The technique is particularly useful in emergent or urgent situations, in patients who are poor candidates for open repair or those whose anatomy excludes them from being treated with currently approved CMD or off-the-shelf devices. However, not every patient is a candidate for PMEG; this includes patients with small and/or multiple renal arteries as well as those with excessive target vessels calcification. Furthermore, excessive aortic thrombus around target vessels may result in embolization to these vessels or lumbar arteries during device manipulation leading to renal impairment, bowel ischemia, or even paralysis. For this reason, careful patient selection is imperative.
Modification time is certainly an issue in emergent cases. The average device modification time for our four cases was 89 min, though considerably longer (109.7 min) for devices requiring posterior constraining and fenestration creation. For this reason, in situ fenestration is a reasonable approach in patients with frank rupture, though fenestrations are not reinforced. However, in our experience, back table modification operative metrics and mid-term outcomes are similar to patients treated with CMD in an elective setting.
From sizing to implantation, treating patients with cAAA with PMEG can be challenging. First, not an insignificant number of vascular specialists lack the training and expertise to expeditiously size a patient and obtain required measurements from software such as TeraRecon or 3mensio. Yet, we feel this critical skillset can be easily acquired by asking for a tutorial from software representatives. This step is key, and one should not attempt offering PMEG to patients without mastering it. Second, if not carefully planned, it is easy to find that the area where one of the four fenestrations needs to be created is not ideal due to the presence of a strut. For this reason, we mark, with a marking pen, the location of all fenestrations prior to starting burning fabric with an ophthalmologic cautery. There are instances when struts cannot be avoided. In this case, struts can be gently bent with a curved or straight hemostat prior to reinforcing the fenestration with a snare and Ethibond suture. Third, the Cook Alpha thoracic endograft has laser cut barbs in the proximal stent graft that prevent resheathing of the device. In this case, once can either cut these barbs with hemostat or can transition the modified device through a series of peel away dilators prior to resheathing it completely. The detailed steps of this technique have been previously described by Manunga. (Manunga, 2018) With careful planning and expert execution, PMEGs provide an important repair option in the treatment of cAAAs.