The “safe-line” technique as theoretical additional attempt to mitigate spinal cord ischemia after urgent complete endovascular exclusion of a thoracoabdominal aortic aneurysm

We describe the feasibility of a technique for temporary aneurysm sac reperfusion after endovascular single-stage thoracoabdominal aortic aneurysm exclusion, to be used in the case of postoperative spinal cord ischemia. Two cases were treated for impending rupture of a thoracoabdominal aortic aneurysm. Before completion of sac exclusion, a supplementary buddy wire (V-18 control guidewire; Boston Scientific) was advanced in parallel fashion from the left percutaneous femoral access into the aneurysmal sac on the posterior aspect of the endograft. Distal aneurysm exclusion was completed using the main superstiff guidewire, and the femoral access was closed with a percutaneous closure device (ProGlide; Abbott) in standard fashion, leaving in place the sole V-18 guidewire, draped in sterile fashion. In the case of spinal cord ischemia, the “safe-line” can be rapidly used for spinal reperfusion after trans-sealing exchange with a 6F, 65-cm-long Destination sheath (Terumo) connected to a 6F introducer on the contralateral femoral artery.

Endovascular repair of thoracoabdominal aortic aneurysms (TAAAs) represents a valid treatment option, owing to its low 30-day mortality and complication rates. 1,2 Although endovascular treatment has evolved greatly, spinal cord ischemia (SCI) and consequent paraplegia or paraparesis continues to be a devastating complication for the patient, family, and surgeon. Large experience from different centers report a SCI rate ranging from 4% for multistage to #18% for single-stage endovascular repair. 3,4 SCI genesis is multifactorial, with arterial embolization, coverage of long aortic segments, hypotension, anemia, and/or insufficient collateral vessels the main predisposing factors. Over the years, several SCI preventive strategies have been developed. The most common consists of staging the procedure to allow for gradual spinal cord adaptation before sac exclusion. This can be obtained by two-step aortic coverage, temporary aneurysm sac perfusion (TASP), or minimally invasive segmental artery coil embolization. However, these approaches lack the possibility for allowing for spinal cord reperfusion in the case of SCI occurring after aneurysm exclusion. 5 In the present report, we aim to demonstrate the technical feasibility of maintaining a temporary guidewire into the aneurysm sac to be used as a rapid route for fast reperfusion in the case of SCI occurring #48 hours after complete endovascular TAAA exclusion.

TECHNIQUE
The technique is based on leaving a 0.018-in. guidewire (a "safe line") into the aneurysmal sac from femoral access. In the case of SCI occurring within 48 hours after complete exclusion, this guidewire can be rapidly exchanged for a 6F long sheath, which is advanced into the sac via a trans-sealing route and connected to contralateral femoral artery access for rapid sac reperfusion (Fig 1 and Supplementary Video, online only). We report two cases of symptomatic impending TAAA rupture treated endovascularly in an urgent setting with long-segment aortic coverage and a single-stage procedure. The patients provided written informed consent for the report of their case details and imaging studies.  In both cases, at the end of the endovascular procedure, the V-18 guidewire was wrapped in a sterile fashion and the patient monitored in the intensive care unit for 48 hours (Fig 4), with a continuous unfractionated heparin infusion and a target acti-

DISCUSSION
Surgical strategies to prevent SCI are based on staging the procedure through multiple steps of aortic coverage, TASP, or minimally invasive segmental artery coil embolization. 5,[7][8][9][10] In 2018, Gombert et al 11 reported an in vitro study on the use of a slowly occluding hydrogel-textile membrane that could be useful in the future.
However, once endovascular exclusion has been completed, none of these techniques allow for spinal cord reperfusion, and the only measures that can be used for SCI mitigation consist of spinal drainage and medical management (blood pressure and hemoglobin level optimization). One report described a dedicated branch for sac temporary perfusion based on delivering, as a final endovascular step, an Amplatzer plug into the branch for w4 hours, with complete detachment after this period if the patient has no signs of SCI. 12 However, maintenance of an Amplatzer plug in position for such a short period (4 hours) is a limitation because >65% of SCI cases can occur 24 hours after completion. 13 Also, the heparin infusion through the sheath side branch can prevent complete thrombosis of the plug and affect sac exclusion. Furthermore, all methods based on temporary sac perfusion carry the limitation that the large "intentional" leak could increase the risk of rupture and disseminated intravascular coagulopathy during the waiting time before the final step.
To the best of our knowledge, the "safe-line" method is the first reported technique that can eventually be used  as an ultimate attempt for fast sac reperfusion in the case of SCI occurring #48 to 72 hours after complete exclusion. This represents a simple and fast procedure that does not increase the complexity of surgery or the procedural time and, if needed, can guarantee fast sac reperfusion after symptom occurrence. To reduce the theoretical risk of iliacefemoral axis thrombosis in the early postoperative period, only the 0.018-in. guidewire is left in place, without any introducer sheath, via standard percutaneous access.
Furthermore, this technique does not require modification of the other standard SCI prevention methods. Also, in our protocol, it is used just as an adjunct to TASP and CSF drainage. If a spinal drain must be performed postoperatively because of SCI occurrence, 12 the heparin infusion can be stopped and the "safe-line" can be rapidly (within 1 hour) activated. During this time, the coagulation parameters can be adequately restored to an activated clotting time of <150 seconds. The continuous pulsatile flow in the circuit should guarantee a low risk of thrombosis, and the CSF drainage tube can be safely inserted. 14 If no clinical benefit is realized within 4 to 6 hours, we believe the system can be removed. If clinical improvement in SCI has occurred within 1 to 3 hours, the system can be maintained, with a low dose of heparin reintroduced 6 hours after drainage insertion. Within the limitations of our initial experience, we believe this technique can be applied to patients with elective type I, II, or III TAAAs undergoing the final step or treated in a single stage and all patients with urgent type I, II, or III TAAAs without frank rupture. Regarding the anatomic factors, the "safe-line" might be less useful in cases of extensive posterior chronic mural thrombus with no evidence of intercostal arteries on the preoperative computed tomography angiogram. However, for patients with patent large and multiple intercostal arteries, this technique can be considered. For postdissection TAAAs, we think that the "safe-line" role must be carefully evaluated. Placing the guidewire in the correct lumen from which the major collateral vessels arise could be cumbersome. Also, the pulsatile flow in a dissected area could result in a greater risk of sac complications. Regarding the level of the catheter into the sac, we believe it should be positioned in an area (abdominal infrarenal, paravisceral, or distal thoracic) where the major intercostal arteries have been identified on the preoperative computed tomography angiogram. If needed to evaluate SCI, an aneurysm sac angiogram can be performed to evaluate changes in the perfusion of the collateral vessels, with positioning of the catheter at the level of the remaining patent collateral arteries.
The limits of the described technique are primary that the safety and efficacy require further evaluation in additional and larger multicenter studies. Use of the "safe line" in the case of spinal cord ischemia (SCI). The guidewire is unwound (A), a 6F Destination introducer sheath is inserted directly into the aneurysm sac (B) and connected to the contralateral femoral percutaneous access via a three-way runner, reperfusing the aneurysmal sac (C). D, Intraoperative angiogram from the Destination sheath, confirming its correct position in the aneurysm sac (white arrow) with sac reperfusion.