Effectiveness of a prolapsed bird's nest filter

Area of Science:

• Vascular Surgery
• Medical Device Engineering
• Interventional Radiology

Background:

• Inferior Vena Cava (IVC) filters are used to prevent pulmonary embolism.
• The Bird's Nest filter is a commonly deployed IVC filter.
• Variability in filter deployment, such as wire prolapse, may affect its performance.

Purpose of the Study:

• To evaluate the clinical deployment variability of the Bird's Nest filter.
• To analyze the impact of filter prolapse on clot-trapping efficiency using an in vitro model.

Main Methods:

• Measured cephalic filter wire length in 20 clinical filter placements.
• Used a variable-rate pump to simulate IVC flow and respiration.
• Tested four clot sizes (5x20, 5x40, 10x20, 10x40 mm) with four prolapse configurations (2-12 cm wire length).
• Evaluated filter performance in horizontal and vertical positions.

Main Results:

• Clinical filter wire length averaged 5.4 cm (range, 1.2-9.0 cm).
• In vitro, filter prolapse did not significantly reduce trapping efficiency except for the smallest clots (5x20 mm) in maximum prolapse (horizontal position).
• Slower, constant flow rates improved filter efficiency compared to variable rates, particularly in maximum prolapse (horizontal).

Conclusions:

• The Bird's Nest filter demonstrates effective clot-trapping in clinical use, even with varying degrees of prolapse.
• Filter performance is minimally impacted by prolapse for larger clot sizes.
• Clinical deployment variations do not significantly compromise the filter's overall efficacy for most clot types.