P160: A simple intra-aortic shunt restores hemodynamics and prevents paralysis in an ovine model to test tissue engineered vascular patches

Abstract

Introduction: Recent advances in the engineering of novel tissues for vascular patches and heart valves require pre-clinical in-vivo testing. Although many animal models are available, the United States Food and Drug Administration highly suggests testing cardiovascular tissue in sheep as an accelerated model of calcification. However, sheep are particularly prone to spinal cord ischemia and subsequent paralysis during aortic cross clamping, which is often required for the implantation procedure. We report the use and hemodynamic effects of a simple intra-aortic shunt to facilitate the implantation of tissue engineered vascular patches in the descending thoracic aorta of sheep. Methods: After clamping the descending thoracic aorta, a 6cm longitudinal aortotomy was made at the level of the 6th intercostal space. A shunt consisting of a 9 cm long heparin bonded 6.35 mm (internal diameter) polyvinyl tube was inserted through the aortotomy into the aorta to provide blood flow across the operative site. Blood pressure and flow in the distal aorta were measured continuously with an indwelling femoral artery catheter and a Triton ultrasonic aortic flow probe. The hemodynamic effects were measured in seven 45 - 55 kg Suffolk sheep. This shunt was then used to implant decellularized pulmonary artery patches into 25 animals. Multiple means were compared by ANOVA with Scheffe post hoc analysis. Results: The mean aortic pressure distal to the shunt prior to clamping the aorta was 86.4 ± 4.6 mmHg. Occlusion of the aorta reduced the distal mean aortic pressure to 1.79 ± 0.4 mmHg (p < 0.001) and opening the intra-aortic shunt restored the distal mean aortic pressure to 67.9 ± 7.3 mmHg (p = 0.053). Blood flow in the distal aorta was 2.35 ± 0.37 L/minutes at baseline and was reduced to -0.01 ± 0.01 L/minutes (p < 0.001) with the aorta cross clamped. When the shunt was opened, distal aortic flow returned to 2.49 ± 0.36 L/minute (p = 0.945). Prior to instituting this shunt, 2 of 2 sheep developed immediate paralysis of the hind legs following the implantation of a vascular patch in the descending thoracic aorta. Use of this shunt prevented hind leg paralysis in all 24 animals surviving the procedure. Early in this series, one animal died intraoperatively from an aortic injury related to removing the shunt. Ten animals were survived for 4 weeks and 13 were survived for 6 months without complication. A single animal died 61 days after surgery from a ruptured mycotic aneurysm. Conclusions: A simple intra-aortic shunt was effective in restoring blood pressure and flow in the aorta distal to the operative site and prevented hind leg paralysis associated with aortic clamping. Moreover, this shunt was easy to insert and remove and does not require additional aortotomies.