Evaluation of the Characteristics of Venous Occlusion After Placement of an Ameroid Constrictor in Dogs

Objectives— To evaluate the mechanism of vascular occlusion after placement of an ameroid constrictor (AC) on a large intra-abdominal vein and document changes in blood flow. Study Design— Experimental study. Animals— Six adult dogs. Methods— Six 6.5 mm ACs were digitally scanned to measure area and circumference of the ameroid and inner lumen before surgery. ACs were surgically positioned around the left common iliac vein (CIV) in each dog. Peri-vascular ultrasonic flow probes were positioned on the left CIV cranial to the AC, and on the right CIV as an internal control. Blood flow measurements were recorded daily until there was no, or prolonged minimal, blood flow, at which time the dogs were euthanatized. Left and right CIVs were removed for histologic evaluation, and the ACs re-scanned to evaluate degree and direction of expansion of the ameroid. Results— Reduction in blood flow occurred within 10 days in all dogs. Three dogs had complete occlusion by day 10 from thrombus formation. One dog damaged the flow probes at 13 days when blood flow was approximately 50% of intra-operative values; the dog was euthanatized at 37 days; there was partial occlusion from thrombosis. Two dogs had persistent low blood flow and occlusion from thrombus formation when euthanatized at 59 and 98 days. There was a significant increase in total AC area and outer circumference, and decrease in luminal area and inner circumference when presurgical and postocclusion measurements were compared. Conclusions— Vascular occlusion after placement of an AC on a large intra-abdominal vein occurred from thrombus formation. Clinical Relevance— A similar pattern of venous occlusion may occur after placement of an AC on a portosystemic shunt, which may lead to both short- and long-term complications associated with portal hypertension.