Pig specific vascular anatomy allows acute infrarenal aortic occlusion without hind limb ischemia and stepwise occlusion without clinical signs

Abstract

Objective: In a porcine, aortic graft model we found 5 animals to develop and survive unnoticed, complete infrarenal aortic occlusion and 2 pigs with an acute occlusion but rather unspecific clinical symptoms. We investigated the pigs' vascular system to classify the anatomic capabilities to compensate for an acute abdominal aortic occlusion. Design of study: Retrospective analysis of CT scans and clinical data to specify unexpected results in a case series of infrarenal occlusion in a porcine model. Setting: Collaborative study of experimental and clinical departments. Subjects: Fifteen healthy female minipigs. Interventions: All pigs underwent an infrarenal aortic graft intervention. Anesthesia and perioperative management of the animals were preformed along the standard operating procedures of the local Department of Experimental Medicine. All animals received perioperative antibiotics, ASS, and carprofen for postoperative analgesia. Arterial pressure, heart rate, body temperature, and diuresis were monitored during surgery and therapeutic interventions. Main outcome measures: Contrast media based computed tomography (CT) with total body scans were performed at 1, 4, 10, 12 weeks after surgery. Comparable scans of cardiovascular healthy subjects (humans and pigs) and patients with a Leriche's syndrome were analyzed. Results: Neither acute (within the first 12 h after surgery) nor stepwise total aortic occlusion show unmistakable clinical signs. In pigs, the epigastric artery (EGA) – which is in connection with suprarenal lumbal arteries, subclavian and external iliac artery – is highly developed associated to the high number of mammary glands of about 7 on one side. In humans, the ratio of aortic to EGA-diameter is 1 : 0.15. In minipigs we found a ratio of 1 : 0.43 which changed during aortic occlusion resulting in a ratio of 1 : 0.58. Pigs with a slowly developing occlusion demonstrated an enlargement of the ureteric artery of about 210% completing a sufficient collateral system. Conclusion: While in the human Leriche's syndrome months are needed to enlarge the EGAs for a partial collateral support of an infrarenal aortic occlusion the pig's EGA is a naturally sufficient collateral system capable to cover immediately for an acute infrarenal aortic occlusion. Further collateral enlargement even provides a permanent, sufficient hind limb perfusion in pigs. As the sufficient collateral system probably reduce pressure and shear rates in the infrarenal aortic segment after cross clamping, pigs might have a higher predisposition to produce early thrombosis related graft occlusions tan humans.