Tissue Storage Ex Vivo Significantly Increases Vascular Fusion Bursting Pressure

James D Cezo, PhD, Eric A Kramer, MS, Jonathan A Schoen, MD, Virginia L Ferguson, PhD, Mark E Rentschler, PhD. University of Colorado at Boulder.

Introduction: Harvested biological tissue is a common medium for surgical device assessment in a laboratory setting; this study aims to differentiate between surgical device performance in the clinical and laboratory environments. Vascular tissue fusion devices are particularly sensitive to environmental changes due to a reliance on tissue-device temperature gradients, tissue water content and ionic concentrations, each of which can vary following ex vivo tissue storage. In this study, we aim to standardize the methods by which bursting pressure, the industry standard in fusion strength measurement, is collected in order to reduce extrinsic testing variance and facilitate comparisons of device performance. To assess the impact of tissue storage on the efficacy of vascular fusions, bursting pressures were measured for porcine venous tissues that were fused in vivo and compared to adjacent tissues that were harvested, stored, and then fused ex vivo.

Methods: Epigastric veins (in 5cm increments) from seven porcine models were subject to identical bursting pressure protocols after fusion. One half of each vein was fused in vivo, harvested and immediately analyzed for burst pressure, the remainder was stored (0.9 % Phosphate Buffered Saline, 24 h, 4°C) and then subjected to identical fusion and burst pressure testing ex vivo. Histological slides were prepared for qualitative analysis of in versus ex vivo fusions (n = 2 sections / sample).

Results: Bursting pressures were significantly different between vessels fused in vivo (310 ± 127.7 mmHg) and those fused ex vivo (514.7 ± 187.0 mmHg, p = 2.06 E-10). While the ex vivo samples displayed a greater variance between animals, they were consistent with a marked increase in bursting pressure (?BP = 216.7 ± 124.0 mmHg, a 70% increase). Histological imaging of venous axial cross-sections indicated the lamination of adventitia and media layers in ex vivo fusions, whereas the media was compressed and buckled away from the fusion region in in vivo samples.

Conclusions: These findings suggest that the fusion of porcine venous tissue ex vivo may overestimate the clinical performance of fusion devices. We have previously demonstrated that increased tissue hydration and the lamination of tissue layers both positively affect the bursting pressure of arterial fusions. The bursting pressure increase observed in this study may therefore be due to added tissue hydration during storage, structural variations between live and stored tissues, or alterations in the fusion process due to tissue-device temperature gradients. While harvested tissue provides an accessible medium for comparative study, the fusion of vascular tissue in vivo may avoid the biomechanical alterations induced by ex vivo tissue storage, and is likely a better indicator of fusion device performance in a clinical setting.