Commentary: The Zenith t-Branch Endograft

Intraoperative Measures for Prevention of Spinal Cord Ischemia

Spinal cord ischemia (SCI) remains one of the most frequent and severe complications after endovascular treatment of TAAAs. The incidence varies between 10% and 20%, and a clear pathogenic mechanism (ischemia, embolization, steal phenomenon) has still to be defined. ⁹ It remains unclear as to which adjuvant measure is the most optimal to prevent SCI. We advocate staging the procedure in 2 or even 3 sessions, but in high-urgent patients, this option is not realistic.^6,9 Our current policy in urgent cases is to deploy completely all aortic endografts, including the t-Branch, and restore perfusion of both limbs prior to the transaxillary delivery of the bridging endografts. Thereby, we try to avoid prolonged occlusion of the limbs and the hypogastric arteries. In addition, we perform sac angiography through the last open branch (mostly this is the celiac trunk) in order to identify relevant intercostal or lumbar arteries that might send branches to the anterior spinal artery. If the angiogram clearly demonstrates such arteries and the aneurysm is not symptomatic or ruptured, the branch remains open and is connected to the target vessel 6 to 8 weeks later. Up to now, we did not face any aneurysm rupture between the stages, but such ruptures have been described. ¹⁰ In this context, addition of adjuvant measures, such as near-infrared spectroscopy and motor/sensory-evoked potentials, might detect in a safe manner which patient might benefit from staging.^11,12

Bridging Endograft

At present, there is no dedicated bridging stent-graft for multibranched endografting. Quite the contrary, none of the well-known bridging endografts has been manufactured for this indication. Especially in case of the t-Branch endograft, where the branches do not always perfectly fit to the origin of the target vessels, the choice of the bridging endograft is essential for a good outcome.

During the past 3 years, we have changed our policy as to the type of bridging endografts. For the SMA and celiac trunk, we use balloon-expandable stent-grafts (iCAST/Advanta V12; Atrium Maquet Getinge Group, Hudson, NH, USA; Figure 1B), and we typically reline them with an additional self-expanding stent [SMART (Cordis Corporation, Bridgewater, NJ, USA), Complete (Medtronic, Minneapolis, MN, USA), or Zilver (Cook Medical)], aiming for a smooth transition across the vessel wall. However, the most challenging target vessel in the t-Branch endograft is the renal artery. Main anatomic issues are the cephalad orientation of the vessel, any proximal stenosis of the origin, the early branching of the vessel, and sometimes the long distance (>50 mm) between the end of the branch and the origin of the target vessel. After assessment of the midterm performance of our branches, we observed that additional relining of the renal vessels was a risk factor for branch occlusion. ⁸ Thus, we recommend additional relining of the renal arteries only when this seems necessary (kinking, compression of the bridging endograft between the aortic wall and stent-graft, tortuosity, etc). We advocate the self-expanding and very flexible Viabahn endoprosthesis (W.L. Gore & Associates, Flagstaff, AZ, USA; Figure 1C) for long distances between branch and target vessel, as well as for renal arteries with cephalad orientation. Of note, the fluoroscopic visualization of the Viabahn endograft remains suboptimal, and the endograft may be too floppy during implantation. Thus, we recommend controlled deployment by slowly retracting the sheath and opening the stent-graft (Figure 1C).

Alternative Designs May Be Necessary

At present, though technical success with the t-Branch endograft is excellent in our experience, its implantation sometimes requires adjunctive measures (proximal extension, carotid-subclavian bypass) or unnecessary coverage of the proximal thoracic and distal abdominal aorta. This could lead to unnecessary additional morbidity for the patients. For instance, thoracic aortic coverage was the most relevant risk factor for SCI in our TAAA series [predicted SCI risk = e^{(0.032 × percent of thoracic aortic coverage)}]. ⁹

Based on our experience with the planning of custom-made endografts, we have suggested an alternative option, having a proximal diameter of 38 mm (instead of 34 mm in the current version) to avoid additional proximal extension. By changing only the proximal diameter, the primary suitability (ie, without any adjunctive measures) of the device would rise automatically by 60% in patients treated previously with custom-made endografts. Additionally, some patients having type IV TAAAs may benefit from a modified shorter proximal part of the device (2 instead of 3 sealing stents) in terms of less aortic coverage.

Last but not least, the company provides a universal distal bifurcated endograft with a proximal diameter of 22 mm. However, in patients with type I TAAAs or with TAAA after previous infrarenal Y-prosthesis, a universal reversed tapered distal tube (22 mm proximal) could facilitate the procedure without the need of bilateral femoral access and extension of the stent-graft to both common iliac arteries (less coverage of the distal abdominal aorta) or use of abdominal tubes from other companies.

Implantation of the t-Branch Outside the Suitability Criteria

The availability of the t-Branch endograft remains its great advantage. However, this characteristic could also be a great challenge for the endograft; a number of surgeons will surely challenge the limits of the device outside the instructions for use, particularly in multimorbid patients with no other endovascular treatment options. Of note, chronically occluded target vessels are not an exclusion criterion for the implantation of the t-Branch, since the respective branch can be safely closed by combining a balloon-expandable stent-graft and an Amplatzer plug (St. Jude Medical, St. Paul, MN, USA; Figure 2).

OPEN IN VIEWER

Figure 2.

(A) Fluoroscopic image and (B) 3-dimensional reconstruction after computed tomography angiography of plug occlusion of the branch to a chronically occluded right renal artery.

In this context, Khanafer et al ¹³ present the outcomes of just such a challenging case and have to be congratulated for the excellent outcome. They report for the first time the implantation of the t-Branch endograft in a multimorbid patient to treat a type Ia endoleak. Our main concern regarding such an implantation would be the 26-mm aortic diameter at the level of the renovisceral segment and the extensive aortic coverage. However, both issues caused no adverse events in this patient. Alternatively, use of the chimney technique could be a different approach, but we would agree that that the gutter-associated endoleaks is an issue that should be taken into consideration in a 10-cm growing juxtarenal aneurysm. In any case, a new outside-the-IFU application of the device is demonstrated in the report by Khanafer et al, ¹³ highlighting the urgent need for off-the-shelf endografts to treat juxta- and pararenal aortic aneurysms and the great challenges that interventionists are facing in real-world scenarios.