Acute Clot-Trapping Efficiency in Dogs with Compacted versus Elongated Wires in Bird's Nest Filters

The clot-trapping efficiency of the Bird's Nest filter was studied in dogs with the stainless steel wires in a compacted versus fully elongated configuration. Bird's Nest filters were placed infrarenally with the wires compacted in 10 dogs and with the wires elongated in an additional 10 dogs. The dogs were separated into two groups, five dogs with each wire configuration in each group. In group 1, 10 unlabeled 6 × 30-mm blood clots were injected into the inferior vena cava. In group 2, six 6 × 10-mm, four 6 × 15-mm, and four 6 × 30-mm labeled clots were introduced. In group 1, clot-trapping efficiencies were 82% for the compacted versus 86% for the elongated configuration, as seen on serial cavograms and pulmonary angiograms. In group 2, clot-trapping efficiencies were 90% for the compacted versus 97% for the elongated configuration, as seen at fluoroscopy. Clot size did not affect trapping efficiency. Acute clot-trapping efficiency of Bird's Nest filters did not differ when the wires were in a compacted versus elongated configuration. This study suggests that placement of a Bird's Nest filter in the elongated configuration may be satisfactory and may not indicate placement of a second filter.