Studies in thoracic aortic graft infections: The development of a porcine model and a comparison of collagen-impregnated Dacron grafts and cryopreserved allografts

Objective: A porcine model of thoracic aortic graft infection was created, and various anatomic sites and the timing of inoculation of the graft to in duce infection were investigated. Ultimately, the ability of cryopreserved allograft to resist infection was compared with that of collagen-impregnate d Dacron graft. Methods: Yorkshire pigs (n = 16) underwent placement of an expanded polytetrafluoroethylene patch graft in the ascending aorta and the left atrial appendage (phase I). Eight animals were immediately given a 50 -mL bolus (1 x 10(8) cfu/mL) of Staphylococcus aureus whereas the other 8 r eceived the infusion 24 hours later. Animals were put to death 8 weeks late r and the grafts were sterilely explanted and analyzed via microbiologic cu lture and standard histologic procedures for evidence of infection. The res ults displayed that the aortic graft and a delay of induced bacteremia of 2 4 hours were more reliable methods of producing infection. During phase II, 13 pigs were randomized to receive either a collagen-impregnated Dacron gr aft (n = 6) or a cryopreserved allograft (n = 7) in the ascending aortic po sition only and infusion of S aureus 24 hours after the operation. The expe riment then proceeded to completion. Results: Phase I results displayed tha t use of an aortic graft and induced bacteremia 24 hours after the operatio n was a more reliable and reproducible method of producing infection. In ph ase II, graft infection was present in 38.5% (5/13) of animals, with only 1 6.7% (1/6) in the collagen-impregnated Dacron graft group and 57.2% (4/7) i n the cryopreserved allograft group becoming infected. There was no signifi cant difference between the collagen-impregnate Dacron graft and cryopreser ved allograft groups in the incidences of thoracic aortic graft infections (P = .27, Fisher exact test). Conclusions: This novel porcine model of thor acic aortic graft infection is a reproducible method for the investigation of thoracic aortic graft infections. The phase I study investigated the tim ing of the induced bacteremia and the most susceptible position of a graft. Phase II demonstrated that collagen-impregnated Dacron grafts are equivale nt, if not superior, to cryopreserved allografts in resisting central vascu lar graft infections in the ascending aorta.