In vitro comparison of initial lumen diameter on closure rates of ameroid ring constrictors

Ameroid ring constrictors (ARC) are used in veterinary medicine to provide gradual occlusion of portosystemic shunts. To date, ARCs with an inner lumen diameter of 3.5-mm are the smallest that have been studied. Smaller sizes are available but there is evidence from previous studies to indicate that suggest closure dynamics may vary with ARC size. This study compared the closure dynamics of smaller ARCs with previously evaluated larger sizes. Twenty four ARCs, six of each size: 2.5-mm, 3.0-mm, 3.5-mm and 5.0-mm were incubated in canine plasma for 28 days and were digitally imaged prior to the start of study and then on days 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, 20, 24, and 28. The inner lumen diameter was compared for rate and percent of closure over time. No ARC evaluated had completely closed by 28 days. Smaller ring sizes closed faster and to a greater extent than larger ring sizes. There was a significant difference in time to achieve 50% closure with post hoc testing showing that time to achieve 50% closure was faster for 2.5-mm and 3.0-mm rings vs 3.5-mm rings and 3.0-mm vs 5.0-mm rings. In conclusion, the rate and proportion of lumen closure was greater with ARCs with smaller initial lumen size. Clinicians should be aware that use of these smaller sized ARCs will likely result in a more rapid and more complete closure in comparison to larger size constrictors.