New challenger has entered the arena: bioengineered vascular conduit, autologous vein, and prosthetic graft in extremity vascular trauma

The authors here present an investigation of a novel vascular conduit, the Symvess acellular tissue-engineered vessel, that recently received FDA approval for use in vascular injury.¹

Manufacture of Symvess involves the culture of human aortic smooth muscle cells in a ‘bioreactor’ to form a vessel. The living cells are then removed, leaving an acellular conduit composed of extracellular matrix. In vivo studies show this matrix, once implanted, repopulates with the patient’s vascular smooth muscle and endothelial cells.²

Two prior studies have examined the use of Symvess as conduit in vascular repair after trauma. These data were used in combination with historical benchmarks to compare efficacy and complications of Symvess to prosthetic graft.³ The results favored the tissue-engineered conduit over prosthetic in several domains. The performance of Symvess relative to autologous vein was not investigated, leaving some questions as to where the conduit falls in comparison to the accepted gold standard.

The authors attempt to address this by propensity matching the clinical trial subjects and historical comparator data taken from the largest registry of vascular trauma in existence, the Prospective Observational Vascular Injury Trial (PROOVIT) database. Matching was performed between Symvess and those PROOVIT subjects who underwent repair with autologous vein conduit. Outcomes included patency, amputation, infection, reintervention, conduit complication, and death. There were no significant differences found between Symvess and autologous vein in any outcome measure.

The authors are careful to specify that their study is underpowered for the detection of non-inferiority. Nevertheless, the hypothesis—‘that there are no significant differences…between autologous vein and the ATEV…’ is, inasmuch as it is a null hypothesis, definitive of a non-inferiority trial.⁴ If the hypothesis were to be restated appropriately, the authors have actually demonstrated that autologous conduit is not superior to Symvess, a conclusion of arguably greater import.

The need for an optimal non-autologous conduit is clear. Investigators for the recent BEST-CLI trial found that less than 15% of patients undergoing distal bypass for peripheral arterial disease had suitable saphenous vein in either leg for use as conduit.⁵ Vein diameter of less than 3.5 mm is associated with a 1.5-fold risk of graft failure; under 3 mm, that risk increases to 2.4-fold.⁶ The authors of this study have, perhaps unintentionally, raised the possibility that Symvess may be preferable to autologous conduit of marginally suitable diameter, a question that is certainly worth further investigation.