Introduction
Over the last two decades, endovascular aortic repair (EVAR) has become the preferred treatment with regard to aortic pathologies and is an alternative treatment for patients who do not qualify for open surgery. Although EVAR has been shown to have significantly fewer complications when compared with open surgery, it is associated with complications that can lead to severe morbidity or even mortality. Complication rates after EVAR are as high as 30%, with a 2%–3% rate of late complications requiring intervention. From this, the Streamliner Multilayer Flow Modulator (SMFM; Cardiatis, Isnes, Belgium) technology has evolved. However, many studies involving the SMFM device have described patients who have developed complications, often fatal, after treatment.
The SMFM is an endovascular bare-metal stent for use in aortic, peripheral, visceral, and intracranial aneurysms. Its design comprises multiple interlocked layers of cobalt-alloy metal wire, braided together to create a mesh. Unlike conventional aortic endografts, the SMFM uses the innate physiological response of the human body to remodel the aneurysm sac, rather than excluding it from the circulation, which is the current traditional method. The design permits blood flow to perfuse through the mesh. In this way, it preserves collateral branches, negating the need for surgical branches or fenestrations. Flow within the device is modulated and decreases over time within the surrounding aortic aneurysm sac, theoretically leading to gradual thrombosis of the sac.
When the SMFM technology was first introduced, the Conformité Européenne (CE) labeling was granted without proper compulsion to inform and to train physicians in the new technology. Surgeons used the technology according to their judgment and discretion on a compassionate and trial-and-error basis. As with all new technologies in ill-informed hands, the consequences were disastrous. When the SMFM was first launched, preliminary instructions for use (IFU) were issued to guide physicians’ understanding and correct use of the flow modulator technology. Nonetheless, various studies have shown that not all physicians adhered to these instructions, continuing to treat on a compassionate basis patients who were not eligible for other forms of surgery. This, coupled with the surprising lack of awareness of the evolving IFU, has resulted in mortality and unnecessary complications for patients who were already suffering from significant comorbidities.
The SMFM was a relatively new technology, which received CE marking in 2010. Its introduction has been fraught with complication, not only because of its unconventional nature, but also because of lack or ardent operator knowledge, as discussed. This chapter aims to identify the complications in relation to the SMFM, discuss probable causes for these complications, and suggest ways these complications can be avoided in the future.
The Global Registry
The SMFM was a disruptive technology, representing a new concept in the management of aortic disease. The mode of action of this device is completely different from that of conventional aortic devices, which caused much skepticism among the vascular community worldwide. Negative clinical outcomes have forced a more thorough analysis of this new device, and the team at the MFM Global Registry has been undertaking this investigative task. The aim of the Registry is to collect data from surgeons and interventionalists around the world who have used this device, to treat thoracoabdominal aortic pathologies. The experienced team then objectively analyzes the clinical outcomes and engages in biomedical testing of the device. The Registry has, to date, published more than 20 articles on the SMFM and presented its results in over 40 national and international presentations.
Surgical Technique
Preoperative computed tomography angiography (CTA) with contrast should be carried out to assess aortic vessel and aneurysm/dissection size, including any angulation, proximal/distal landing zones, and femoral access. Accurate measurements are crucial in SMFM size selection and should be assessed using EndoSize virtual deployment software (Therenva SAS, Rennes, France). This software predicts the behavior of the stent through the vessel center-line and anticipates possible foreshortening.
Aneurysm Repair Technique
In aneurysm repair, especially thoracoabdominal, coverage of visceral and spinal branches is inevitable, which is a major downfall of currently available commercial endografts. The SMFM can be deployed across these vessels, without fear of compromised perfusion. This is because of its specific mesh design, which allows flow through the device.
The SMFM can cover visceral arteries because of its mesh design.
Preoperatively, the common femoral artery (CFA) is exposed using standard methods. Landing zones, previously identified on CTA, are visualized using intraoperative fluoroscopy. The appropriately sized SMFM (oversized by 25%–30%) is then introduced through a 20-French introducer sheath.
The diameter of SMFM should be 25%–30% of the diameter of the target vessel.
Visceral vessels to be covered by the SMFM should be surveyed for stenosis, thrombus, or calcification preoperatively.
When deploying multiple SMFM, overlap should be 6 cm, with 8 cm recommended in regions of high tortuosity.
An overlapping region of 6 cm between devices is recommended, with 8 cm in areas of tortuosity. In addition, the SMFM should be deployed at a rate of 1 cm/min to enhance aortic wall apposition and further prevent foreshortening, in a method known as “endoquilting.” Endoquilting allows accurate conformability to the aortic wall during deployment. All guidewires and delivery sheaths should then be removed and wound closure carried out using standard methods.
If the proximal or distal ends of the SMFM are to be molded, it is recommended that the UnBalloon (LeMaitre, Massachusetts), a mesh-type balloon, be used, because the SMFM wires will inevitably rupture a conventional balloon.
Dissection Repair Technique
The SMFM size should be selected similar to the methods described. In aortic dissection, visceral branches may arise from the false lumen. In these cases, the operator should use a process known as endovascular scissoring ( Fig. 24.1 ). Two 12×60 mm balloons should be advanced into both the true and false lumens and concomitantly inflated at the level of the aortic bifurcation. These should then be pulled caudally to cut the septum. Alternatively, a 12-French sheath with two superstiff wires, one in each of the true and false lumens, can be used to divide the septum. The ultimate aim of dividing the septum between the true and false lumens is to equalize the pressure between them.
Where all side branches arise from the true lumen, a 4-French pigtail catheter is used to access the true lumen through an advanced torsion technique. Approximately 2–3 mL of 50% diluted dye should be simultaneously injected to visualize the catheter up to the coronary sinus. Impedance of the catheter at this time should denote entry of the catheter into the false lumen. Where the SMFM is deployed over the aortic arch (for example in a Stanford Type A dissection), the initial 10 cm should be deployed in 20 seconds, during rapid pacing or adenosine-induced cardiac arrest. Endoquilting should then be used for the remainder of the deployment. Similarly, an UnBalloon should be used to inflate the SMFM where necessary. Analogous to the previous technique, all guidewires and delivery sheaths should then be removed and wound closure carried out using standard methods.
SMFM Complications
In preceding years, there has been a slow but nonetheless encouraging learning curve among physicians with regard to the usage of the multilayer technology. This is a direct reflection of the quantity and quality of published literature. So far, there have been a handful of studies and reviews of patient cases from registries, which have shed light on the practical application of the SMFM in patient populations. These studies have included patients who have had complications after implantation of the SMFM and, as will be evident, these are largely a result of noncompliance with the available IFU.
Preoperative Planning and Complications
The Global Registry has previously documented 38 cases in which the SMFM was implanted outside of IFU in patients for treatment of thoracoabdominal aortic aneurysms (TAAA) or Stanford Type B aortic dissection. In all of these cases, zero technical success was achieved, although there were no incidents of death, paraplegia, stroke or renovisceral compromise during the initial hospital stay. Thirteen patients had chronic Stanford Type B dissection with aneurysm dilatation of more than 6 cm. There were also 4 saccular and 6 mycotic aneurysms along with 15 primary TAAA. There was failure to land the device in the normal aorta in 31 (81.6%) cases with 12 inadequate stent overlaps and 11 cases where a smaller SMFM was deployed inside a larger one. Suboptimal sizing of two or more devices relative to each other and to the patient anatomy led to Failure Mode II, which is equivalent to an endoleak Type III, i.e., a leak between overlapping stents.
Ten patients suffered aneurysm ruptures and 23 had previous open or thoracic endovascular repair (TEVAR). Five of the nine cases resulted in a failure mode I (Type I endoleak), in which an undersized device was used. There were eight visceral branch complications. In total, 14 secondary endovascular interventions were required in 11 patients for endoleak or device foreshortening. In those with Stanford Type B dissection, no false lumen was completely thrombosed in the dissecting aneurysms. Follow-up at 10.0±6.9 months showed that all-cause mortality was 89.5%, of which 27 (71.1%) were aneurysm-related deaths. Overall survival, freedom from aneurysm related death, and rupture-free survival estimates were 17.5%, 25.0%, and 31.5%, respectively, at 18 months.
A number of technical failures were recorded in this cohort, such as foreshortening, migration, device collapse, and device undersizing. The authors have reviewed the current manufacturer’s IFU and made recommendations for their revision, based on their experience.
Aneurysm Size
The authors have found that in patients with large diameter aneurysms, greater than 6.5 cm, the aneurysm fails to remodel over time, when compared with those with smaller diameters. Lack of aortic remodeling is thought to be caused by adventitial elastolysis, where the structural integrity of the artery wall is lost because of reduction of adventitial elastin. This begins in the aortic wall, restricting remodeling of the aneurysmal sac, which in these cases is larger in diameter ( Fig. 24.2 ). Additionally, a computational study by the authors of six aneurysmal aortic cases found that one patient treated for a TAAA had an extensive aneurysm length. This in turn generated a large volume of flow that could not be modulated by the SMFM devices. This observation led to the conclusion that the SMFM device has no benefit if the sac volume exceeds 400 mL. Therefore, to avoid potentially fatal complications, the authors now recommend against using the SMFM in patients with aneurysmal disease of diameter greater than 6.5 cm and/or volume greater than 400 mL.
The SMFM is not recommended in aneurysm >6.5 cm maximum aneurysm diameter.
The SMFM is not recommended in TAAA >20 cm maximum aneurysm length.
The SMFM is not recommended in aneurysms with >400 mL total aneurysm volume.
Infectious Aneurysms
Based on current IFU, it is contraindicated to implant the SMFM in mycotic/infectious aneurysms because the infection drastically increases postoperative complications. Interestingly, previous studies have illustrated the successful use of the SMFM in patients with infection. Benjelloun et al. reported the case of a 16-year-old girl treated 4 years previously for a ruptured AAA of tuberculous origin. Three SMFM stents were successively implanted despite being contraindicated in infectious aneurysms. Flis et al. described their experience with treating a primary infected juxtarenal aortic aneurysm with the SMFM. Follow-up imaging showed persistent aneurysm shrinkage of the sac until complete regression to a normal aortic configuration was seen at 1 year.
Reijnen et al. reported their successful treatment of an infected 56-mm saccular aneurysm of the aorta, located at the level of the superior mesenteric artery (SMA), with both renal arteries located within the aneurysm. At 18-month follow-up, the aneurysm was stable and mostly thrombosed, with adequate perfusion of the side branches and no signs of persistent infection.
However, the authors disagree regarding placing the SMFM in any patient with evidence of infection, based on experience with patients with multiple recurrent aortic aneurysms, which subsequently resulted in fatal aneurysm rupture ( Fig. 24.3 ).
