Medical device anchor and delivery system

#Recent advances in medical technology have resulted in the development of a variety of medical devices for permanent or temporary implantation in the human body. Effective positioning of such devices can prove to be a very difficult task, and maintaining an implanted device in a desired position for an extended period of time is often more difficult. This is particularly true if the implanted device is to remain only temporarily and is designed to facilitate subsequent removal.

#A number of medical implant devices are designed to collapse for insertion within a catheter or other delivery unit and to expand to a predetermined shape when ejected after delivery. Many of these self expanding devices rely primarily upon the contact between the device and the wall of a body vessel or passageway to maintain the device in position after the delivery unit is removed. Unfortunately, changes in the dimensions of the body vessel or passageway or variations in the flow of blood or other fluids there through can cause the medical implant to migrate and change position.

#It is extremely important that a medical implant device be properly positioned and oriented, and that this position and orientation be maintained. Otherwise, effective performance of such therapeutic devices will not be achieved. It is often very difficult to move such a device into position with the desired orientation, and once this is achieved, it is critical that no further motion occur.

#FIG. 1 is a sectional view showing a blood clot filter with anchors formed in accordance with the present invention mounted within a catheter;

#FIG. 2 is a perspective view showing the anchor support hub and leg retention sleeve of FIG. 1;

#FIG. 3 is a perspective view showing the locking sleeve for the leg retention sleeve of FIG. 2;

#Referring to FIGS. 1-2, a blood clot filter which includes anchors in accordance with the present invention is illustrated generally at 10. This filter, shown for illustration as a vena cava filter, is formed with a plurality of elongate legs 12 which are secured to, and extend outwardly from a leg retention sleeve 14. The elongate legs are formed by small, open ended tubes each having a first open end 16 which opens at the leg retention sleeve. A plurality of long anchor shafts 18 are attached at a distal end to an anchor support hub 20 which is spaced from the leg retention sleeve when the vena cava filter is collapsed within a catheter or delivery tube 22. Each shaft 18 extends from the anchor support hub 20 into the first open end 16 of a tubular leg 12 and through the leg to a distal end 24 at a point adjacent to a second open end 26 of the tubular leg. An anchor 28 is formed at the distal end of each shaft 18 in a manner to be described.

#The elongate legs 12 and the long anchor shafts 18 are formed of a material which will permit them to be compressed toward the longitudinal axis of the filter 10 for delivery by a catheter 22. Once the filter is ejected from the catheter, the legs 12 and the shafts 18 are designed to expand outwardly from the filter longitudinal axis as shown in FIG. 6 to bring the legs into contact with the wall of a blood vessel. Although spring metal and suitable plastics can be used to form the legs 12 and/or the shafts 18, it is preferable to form the anchor shafts 18 and in most cases the legs 12 of a suitable shape memory material. If a temperature responsive shape memory material such as nitinol is used, transition between the martensitic and austenitic states of the material can be achieved by temperature transitions relative to a transition temperature. In the martensitic state, the material softens, thereby permitting a filter formed thereof to be compressed and loaded into a catheter. If the transition temperature of the material is set at, or near to normal body temperature, then the filter legs will pass to the austenitic state when the filter is ejected from the catheter and expand to regain a memorized shape.

#For delivery through the catheter 22, the leg retention sleeve 14 is locked to the anchor support hub 20 by a locking sleeve 30 which surrounds both the anchor support hub and the leg retention sleeve when in the locking position as shown in FIG. 1. In the unlocked position, the locking sleeve is moved longitudinally back away from the leg retention sleeve as shown in FIG. 3. Two spring arms 32 are connected at one end to a housing 34 behind the anchor support hub and extend outwardly over opposite sides of the leg retention sleeve. The free end of each of the spring arms is curved to form an arcuate latch member 36 which overlies and, in the locking position of FIG. 1, engages a locking projection 38 formed on the leg retention sleeve. When the locking sleeve 30 moves toward the locking position over the leg retention sleeve 14, it forces the spring arms 32 and 34 together and the arcuate latch members engage the locking projections. As the locking sleeve reaches the full locking position of FIG. 1, the arcuate latch members slide into slots 40 in the locking sleeve and the leg retention sleeve is positively locked to the anchor support hub. However, as the locking sleeve is moved longitudinally away from the leg retention sleeve, the arcuate configuration of the latch members 36 permits them to slip out of the slots 40, and as the locking sleeve moves further, the spring arms 32 move outwardly causing the arcuate latch members to disengage the locking projections 38.