IN-VITRO EVALUATION OF A NEW TEMPORARY VENOUS FILTER - THE SPRING FILTER

Purpose: To evaluate in vitro the functional efficacy of a new variabl e-sized, temporary venous filter, the Spring filter (SF). Methods: The SF was tested in a flow phantom, using flexible, thin-walled polyethy lene tubes 12, 14, and 16 mm in diameter to simulate veins, Clots of t hree sizes were used: 6 x 10 mm, 6 x 20 mm, 9 x 20 mm. Filter deployme nt was performed, ensuring that its functional diameter after placemen t was a predetermined multiple of the radius 'r' of the tube: 3.0r, 2. 8r, 2.6r, 2.4r. The terminal coil was visually examined for changes in configuration. Clot retention by the filter for a period of 3 min was recorded as a success. The baseline intraluminal pressure and the max imum pressure reached after clot introduction were recorded. The trapp ing ability was calculated from the results for 10 clots. The effect o f the following parameters on filter function were studied: size of em bolus, caliber of simulated vein, and functional diameter of filter. R esults: The filter configuration was stable. Not a single instance of axial tilting occurred on deployment. Functional diameter was the majo r determinant of filter function. One hundred percent of clots were tr apped irrespective of clot size and tube caliber when the functional d iameter was 3.0r. Only 73% (95% confidence interval (CI): 57%-88%) and 77% (95% CI: 61%-92%) of small emboli were held up by the filter when the functional diameters were 2.6r and 2.4r, respectively (p = 0.0001 ). A significant reduction in clot trapping was encountered even with medium clots when the functional diameter was 2.4r (p = 0.02). Conclus ion: Against the background of available data on retrievable vena cava l filters, the current model of SF warrants further investigation.