IN-VITRO EVALUATION OF COILS FOR ENDOVASCULAR THERAPY

PURPOSE: To evaluate the physical characteristics and behavior of coil s for endovascular therapy. METHODS: Mechanically detachable coils wer e constructed with simple helical (4 mm x 10 cm and 8 mm x 30 cm) and pretzel shapes (4 mm x 5 cm) made from three metals using 0.003- and 0 .004-in wire. Stiffness or pliability, frictional resistance, shape me mory, and coil stability were evaluated in vitro. RESULTS: The 0.004-i n wire stock coils proved significantly stiffer when compared with the 0.003-in coils. Tungsten coils proved least pliable; platinum coils w ere intermediate in stiffness; and nitinol coils were softest. Frictio nal resistance in the catheter was greatest for stiffer coils. The 5-c m pretzel coil consistently created more frictional force than the 10- or 30-cm simple helical coils. Despite a shorter length, the 4-mm sim ple helical coil exerted more frictional force than the 8-mm coil. Sti ffer metal coils constructed of larger-diameter wire (0.004 in) were m ore stable than softer coils. CONCLUSION: Stiffer coils exert greater frictional forces within the catheter and a greater resistive force du ring bending but are more stable after placement. Frictional forces al so depended on the complex three-dimensional shape of the coil and the diameter of the turns in that shape rather than coil length. These da ta suggest that a family of coils of different metals is optimal for v aried intravascular needs.