Experimental Study of Staged Increase in Shunt Flow for Systemic to Pulmonary Arterial Shunts using vascular grafts

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We experimented with a new technique in which the vascular graft was stenosed by an absorbable material and the shunt flow was decreased to prevent excessive flow in the acute postoperative stage for systemic to pulmonary arterial shunts using vascular grafts.Left modified Blalock-Taussig shunts using 5-mm expanded polytetrafluoroethylene (ePTFE) tubes were created in 9 beagle dogs. The shunt was pinched by polydioxanone absorbable clips and the shunt flow was decreased. At 4 weeks after the operation, the dogs whose shunts had been patent were classified into group A or B.In group A,the pinched site was dilated by means of balloon angioplasty. At 12 weeks after the shunt operation, the dogs were sacrificed and the grafts were removed. In group B,the dogs were sacrificed and the grafts were removed. In addition to these groups, in group C (n=3), the shunt was not pinched at the shunt operation. The dogs were sacrificed and the grafts were removed at 12 weeks after the shunt operation.A … More t 4 weeks after the shunt operation, three dog's shunts whose flow had been decreased of 30.1,40.7 and 44.6% were occluded. But six dog's shunts whose flow had been decreased of 66.8 to 85.4% were patent. Three of the six dogs were classified into group A.In group A,when the shunts were pinched by clips, a rate of decrease in the shunt flow were 30.1,40.7 and 44.6%, respectively. Balloon angioplasty dilated the pinched sites completely and a rate of increase in the shunt flow were 54.1,33.2 and 30.7%, respectively. In group A,light microscopic examination of the grafts showed that the lumens were covered with a pseudointima organized by fibrin and cellulofibrous tissues. In group B,these sites were covered with a fibrin layr with leukocytes at the pinched sites. In group C,the lumens were covered with a pseudointima organized by cellulofibrous tissues in the middle of each graft. The extent of pseudointimal thickening was greater in groups A and B than in group C.In conclusion, a staged increase in shunt flow is feasible using this technique and prevents excessive shunt flow after systemic to pulmonary arterial shunts using vascular grafts. However, further investigation is needed to prevent pseudointimal hyperplasia and a delay in healing mechanism of vascular grafts. Less