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An innovative stent that modulates blood flow has shown early promise for treating aortic aneurysms. But the technology needs technical refinement and longer-term follow-up before it is ready to be tested against established endovascular and open repair strategies, according to findings from a small series published in the June 2013 issue of the Journal of Endovascular Therapy.

Sherif Sultan, MD, of Galway University Hospital, and Niamh Hynes, MD, of Galway Clinic (both Galway, Ireland), looked at periprocedural and 1-year outcomes of the first 55 patients with aortic aneurysm or dissection who received the Multilayer Flow Modulator (MFM) stent (Cardiatis, Isnes, Belgium) as part of a worldwide registry.

The novel technology consists of a flexible self-expanding mesh of interconnected cobalt alloy wires in 5 layers. The device’s low porosity configuration channels blood to native side branches and slows flow, creating a nonturbulent pattern within the aneurysm. The stent has CE mark approval in Europe but remains experimental in the United States.

Periprocedural Results Excellent

Technical success was achieved in all but 1 patient (98.2%). The mean number of side branches covered per case was 3.7 ± 1.3, and the mean number of stents used was 1.96 ± 1.09. No patients required conversion to open repair or admission to the ICU. In addition, no cases of perioperative paraplegia or visceral or renal insult occurred. There was no major blood loss or indication for blood transfusion, and all patients survived to 30 days.

Mean follow-up was 8.2 months, with just over half of patients (50.9%) available for 12-month follow-up. At 1 year, overall survival was 84.8%, while rupture-free survival was 93.7%.

Four cases of bleeding were observed; 2 patients died of hemorrhagic stroke, while another died after refusing transfusion for gastrointestinal bleeding. The fourth patient presented with hematuria and bleeding from the ear, which resolved. In 2 of the bleeding cases, hemorrhage was attributed to stent implantation.

One-year intervention-free survival was 92.4%. Reintervention was needed in 4 patients due to stent foreshortening with retraction of the stent into the aneurysm sac. All involved deployment of a second MFM stent, without complications.

After an initial increase in the median maximum sac diameter from baseline at 3 months, the median diameter fell at 6 months and remained reduced at 12 months. The mean absolute volume of the aneurysm increased over time, as did that of thrombus, with the largest increases occurring between 6 and 12 months. The mean flow volume changed little over 12 months. The ratio of thrombus to total volume remained almost constant over 12 months, while the ratio of flow to total volume declined over the same period.

At 6 months, the mean rate of sac volume increase was 0.36% per month, resulting in a mean volume increase of 2.14%. At 12 months, the rate of increase had slowed to 0.28% per month, resulting in a total average increase of 3.26%. However, the rate reduction was not significant (P = 0.460).

According to the authors, current endovascular technologies have several drawbacks. Acceptable outcomes are only achievable in high-volume, specialty centers, and off-the-shelf branched and fenestrated endografts have limited application given the diversity of aneurysm morphology. The main concern, however, is that the devices provoke systemic inflammatory reactions, they add.

More generally, Drs. Sultan and Hynes say, the exclusion of the aneurysm sac with a relatively stiff covered endograft tends to reduce aortic wall compliance and increase pressure within the aneurysm sac. These effects, in turn, increase the risk of rupture and compromise spinal artery perfusion, they add.

New Stent Discourages Rupture

In contrast, the authors say, the new stent "curtails the odds of aneurysmal rupture through dissipation of wall stress by permitting an organized thrombus to develop, initiating laminar flow in the aortic sac and maintaining vital branches." They note that the slight increase in sac volume in the first 6 months "offers a more controlled manipulation of the body’s innate physiological potential for auto repair than the abrupt and unnatural exclusion of the sac by covered endografts." Moreover, because flow does not occur within a closed space, as with conventional covered endografts, pressure buildup is not an issue, and attempts to repair endoleak after implantation would do more harm than good.

The investigators caution that operators need to be alert to the potential for significant stent foreshortening after deployment. If the device is not properly positioned, the target zone may not be completely covered. As a result, the stent will not realign the flow and the sac may rupture, they explain. The situation can be remedied by deployment of a second stent, they add. In addition, they advise, any side-branch stenosis should be treated before stent deployment to avoid inhibiting target-organ perfusion.

Antiplatelet therapy is needed to preserve side-branch patency, the authors observe, and patients should receive at least 1 antiplatelet drug for a minimum of 12 weeks. However, they add, because the remodeling of the aneurysm sac consumes platelets, clinicians should be attentive to the possibility of excessive platelet loss with the attendant risk of serious bleeding.

Promising but Not Ready for Prime Time

In conclusion, the investigators acknowledge that the current version of the MFM stent has many technical shortcomings and more long-term data are needed to assess the lifelong risk of rupture.

In an accompanying editorial, Andreas M. Lazaris, MD, and colleagues from the University of Athens (Athens, Greece) say that "flow-diverting stents are an appealing innovative technology for treating aortic pathologies."

However, they note, the fact that the aneurysm sac continues to grow after stent implantation, albeit more slowly with time, is worrisome. More basic and clinical research is needed before the strategy is considered a viable alternative to current treatments, they say. Among the questions to be answered are:

However, according to Dr. Lazaris and colleagues, if flow-diverting stents do achieve aortic aneurysm remodeling, their use in small, early-stage aneurysms could alter the degenerative process, leading to ‘healing’ of the aorta.

Study Details

Patients’ mean age was 64.5 ± 18 years. The majority (80%) were American Society of Anesthesiologists (ASA) class IV, while 14.5% were ASA class III. The pathologies included 31 thoracoabdominal aortic aneurysms, 7 arch aneurysms, 3 infrarenal abdominal aortic aneurysms, 8 suprarenal aortic aneurysms, and 6 type B dissections. In the aneurysm cases, the indications for intervention were aneurysm diameter greater than 5.5 cm, unless the aneurysm was saccular, embolizing, and/or tender (20.4%).

1. Sultan S, Hynes N. One-year results of the Multilayer Flow Modulator stent in the management of thoracoabdominal aortic aneurysms and type B dissections. J Endovasc Ther. 2013;20:366-377.

2. Lazaris AM, Charalampopoulos A, Maheras AN, Vasdekis SN. Flow-diverting multilayer stents: A promising but questionable solution for aortic pathologies [editorial]. J Endovasc Ther. 2013;20:378-380.

Disclosures:

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