14 It has been proposed that acute kinking of the shunt vessel after ARC placement could account for increased morbidity and mortality rates in a manner similar to acute suture ligation of the shunt vessel, especially in smaller patients. 14 A mortality rate of 9% was also reported. In a retrospective study by Mehl et al, 14 80% of owners reported an excellent outcome despite 21% of the dogs being diagnosed with persistent shunting in patients in which an ARC was used for shunt attenuation. 5,13ĭespite the benefits associated with ARC use, compared with acute, complete ligation, the use of ARCs is not entirely benign. 5 This has been documented via measurement of shunt fraction by use of transcolonic portal scintigraphy. 12 Total luminal obliteration of a portosystemic shunt with these devices takes 4 to 5 weeks. 7 More recently, the rate of constriction has been shown to be influenced by the protein concentration of the surrounding fluid. 5,9 Factors including size, shape, encasement of the ameroid ring, and the type and temperature of the surrounding fluid modify the expansion pattern. Occlusion likely results from a combination of the following 3 mechanisms: reduction in external vessel diameter caused by centripetal swelling of the ameroid, fibroblastic response within the vascular wall at the site of application, and ultimate formation of intraluminal thrombi arising concentrically from the intima. 4–11 The ameroid core is surrounded by an outer stainless steel ring. Ameroid is a casein derivative that undergoes rapid volumetric expansion that plateaus in 60 days. One of the most commonly used methods for gradual attenuation is the use of an ARC. 5 Various methods have been described to achieve gradual attenuation and ultimate closure of the shunt vessel. This reduces the risk of developing acute portal hypertension or perioperative seizures. 3,4 Gradual occlusion of the aberrant vessel is preferred, thereby allowing the cardiovascular and nervous systems to adapt to changes in portal blood flow. Up to 68% of dogs with congenital portosystemic shunts will develop portal hypertension when surgically treated with acute shunt ligation. 1,2 Congenital, single, extrahepatic portosystemic shunts are the most common category in dogs and cats with a high incidence in certain breeds of dogs. Portosystemic shunts are vascular anomalies that divert portal blood away from the liver and into the systemic circulation. Results of this study indicated that the outer stainless steel ring of an ARC may not be necessary for attenuation and closure of some single extrahepatic portosystemic shunts. The inner diameter and luminal area of the R-group constructs did not change significantly, while the inner diameter, outer diameter, luminal area, and height of N-group constructs all significantly increased over the course of the study.Ĭonclusions and Clinical Relevance-R-group constructs had insignificant centripetal swelling without ring closure, whereas N-group constructs had significant generalized centrifugal expansion. Results-The inner diameter, outer diameter, and luminal area were significantly different between the 2 groups over the course of 34 days. Volume and weight of rings were obtained at the start and completion of the study. Inner diameter, outer diameter, luminal area, and height were measured for each time point. The ARCs were digitally imaged at day 0, daily for the first 10 days, then on days 14, 20, 27, and 34. Procedures-6 ARCs were immersed in canine plasma baths for 34 days without the stainless steel outer ring in place (group N), and 6 ARCs were immersed in canine plasma baths with the stainless steel outer ring in place (group R). Sample Population-12 ARCs (5.0-mm diameter). ![]() Objective-To evaluate and quantify in vitro dimensional changes of ameroid ring constrictors (ARCs) with and without the outer stainless steel ring in place over time.
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