Development and in-vitro characterization of a novel fetal vesicoamniotic shunt - the Vortex Shunt
Kunj R. Sheth, MD, Enrico Danzer, MD, Eric Johnson, MS, James K. Wall, MD, Yair J. Blumenfeld, MD.
Stanford School of Medicine, Palo Alto, CA, USA.
BACKGROUND: Fetal vesicoamniotic shunting (VAS) for severe lower urinary tract obstruction (LUTO) improves survival. However, the risk for perioperative complications with a 50-80% dislodgement rate of currently available shunts is significant and the effect on long-term renal morbidity remains limited. We aimed to develop and test a novel VAS to treat fetal LUTO. Our primary design objectives were to decrease dislodgement and optimize shunt deployment in-vitro. METHODS: The limitations of existing shunts characterized through user interviews and early benchtop testing were used to outline desired VAS performance components. The key design objectives included: 1) robust and atraumatic fixation elements, 2) kink resistant conduit to adjust to fetal movement and growth, 3) one-way pressure valve to facilitate in-utero intermittent bladder cycling, and 4) echogenic visualization aids to facilitate deployment. After a working prototype was developed, the force to dislodge the novel Vortex, Harrison and Rocket shunts (existing commercially available shunts) was characterized using a bench model of porcine bladder tissue mounted in a frame. Sonographic echogenicity of the Vortex shunt was evaluated with ultrasound-guided deployment, and the shunt valve opening pressure was measured. RESULTS: To achieve desired performance specifications, a prototype novel Vortex shunt was developed using braided nitinol “umbrella-type” ends with a kink-resistant stem incorporating an internal one-way valve. Using the anchor pull-out force porcine bladder model, an average peak force of 0.74±0.13 lbf was required to dislodge the Vortex shunt, significantly higher than the average force required to dislodge both the Harrison shunt (0.05±0.00 lbf) and the Rocket shunt (0.33±0.08 lbf) (p<0.01, n=3). The Vortex shunt was successfully deployed using ultrasound guidance, with the umbrella-type ends allowing for sonographic confirmation of appropriate proximal and distal shunt deployment. Following deployment, the Vortex shunt had brisk drainage with complete decompression of the inflated porcine bladder. Kink radius testing, in which each shunt was manually deflected 180° resulted in both the Harrsion and Rocket shunts kinking and occluding the lumen, whereas the coil-reinforced Vortex conduit did not kink and a patent lumen was maintained. The average measured opening pressure of the one-way valve, using the open manometer test fixture, was 20.60 cm H2O (±0.96 cm H2O, n=5) with a steady stream of drips visualized upon valve opening.
CONCLUSIONS: In-vitro testing shows that the Vortex shunt facilitates deployment, improves sonographic visualization, improves kink resistance, and allows for dynamic size adjustment compared to currently available fetal shunts. In-vitro valve gauge pressure testing mirrored bladder pressures in human LUTO cases. Validation in preclinical animal models are warranted and currently underway to assess effectiveness, reliability, and safety of the Vortex shunt prior to clinical application.
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