Self-expandable spindle for transcatheter vascular occlusion: in vivo experiments. Work in progress

The square stent-based large vessel occluder: an experimental pilot study

PURPOSE

The purpose of this study is in vitro and in vivo experimental evaluation of a square stent-based vascular occlusion device for large vessels.

MATERIALS AND METHODS

Square stent-based large vessel occluders (LVO) 5 mm-50 mm in size were constructed from stainless-steel square stents covered by porcine small intestine submucosa (SIS). The LVOs with two back-side barbs were delivered through a guiding catheter. The LVOs with two back-side barbs and two frontal barbs were front-loaded and delivered coaxially. A pusher with a retention mechanism at its end was used for deployment. In vitro testing for competency was performed with use of a flow model with pressure increases. In an experimental pilot study in seven pigs and five dogs, 16 LVOs were placed into the aorta (n = 4), common iliac artery (n = 2), pulmonary artery (n = 4), and medial sacral artery (n = 6). Four animals received two LVOs in different locations. Angiography was performed before and after placement of each LVO. Animals were followed for as long as 3 months with use of angiography and were then killed for gross and histologic evaluation.

RESULTS

In vitro LVOs with two and four barbs were easily collapsed and pushed through or front-loaded into guiding catheters (6-F for a 5-mm occluder, 10-F for a 50-mm occluder). A 20-mm LVO adapted to tubular structures 10-15 mm in diameter, forming polygons 17-18.5 mm in length. In the flow model, LVOs endured pressure increases to 300 mm Hg. In vivo, the LVOs self-expanded and adapted to the vessel without migration in all cases. The locking pusher allowed precise LVO placement and engagement of its barbs into the vessel wall before complete deployment, preventing dislodgment by blood flow. Complete arterial occlusion occurred within 10-20 minutes and arteries remained occluded until the animal was killed in all cases. After 2 months, histologic evaluation revealed replacement of SIS by host tissue and its remodeling with variable fibrocytes, fibroblasts, and some inflammatory cells. Complete endothelialization was seen on both sides of the LVO.

CONCLUSION

The SIS LVO is effective and reliable for acute and chronic occlusion in a high flow model in an experimental animal.

Preliminary results with a new vascular basket occluder in swine

PURPOSE

To experimentally evaluate a new self-anchoring vascular occlusion device suitable for use in large, high-flow vessels.

MATERIALS AND METHODS

A basket-shaped occluding device consisting of a nitinol frame (with or without polyester threads) covered with Dacron was evaluated in the common iliac arteries and abdominal aortae of normal pigs. One occluder was placed in each recipient vessel. Angiography was performed before and after placement of each occluder.

RESULTS

Precise placement of the device was achieved in all cases. Mechanically, all but one occluder worked dependably. Angiographically, devices without polyester threads produced only partial occlusion. Devices with threads produced complete occlusion in all but one abdominal aorta, in which partial occlusion occurred because the occluder opened asymmetrically. Complete iliac arterial occlusion occurred within 2-8 minutes of placement and aortic occlusion was achieved within 8-20 minutes. At necropsy, all devices were found to be securely anchored against the vascular wall.

CONCLUSION

Preliminary results indicate that this vascular basket occluder containing polyester threads is easy to place precisely, produces rapid embolization, and demonstrates good self-anchoring ability in a high-flow arterial model.

Repositionable vascular occluder: experimental comparison with standard Gianturco coils

PURPOSE

To evaluate the efficacy and recanalization rates of a newly designed vascular occlusion device.

MATERIALS AND METHODS

The self-expanding vascular occluder was braided from fine nitinol wires and filled with polyester fibers. The device was delivered through a 6-F polyethylene introducing sheath with use of a delivery cable with a microscrew adaptor. Comparison was made between one occlusion plug and two Gianturco coils placed in the corresponding contralateral arterial segment in nine dogs and six pigs. The mean diameter of the targeted vessels was 4.8 mm +/- 0.8. Two animals were killed immediately after occlusion, and the remaining 13 animals underwent follow-up angiography at 1 week and/or 1 month, after which the animals were killed and the vessels were explanted for gross and histopathologic examination.

RESULTS

Significantly shorter time-to-occlusion was achieved with the nitinol plug compared with two Gianturco coils (1.73 minutes +/- 1.28 vs 5.73 minutes +/- 6.18; P = .021). The recanalization rate at 1 month was also significantly lower (36.4% vs 81.8%, P = .027). The occlusion time was strongly dependent on the target artery diameter with Gianturco coils (R = .79, P = .0007), and not with the nitinol plug.

CONCLUSION

The nitinol vascular occluder appears highly effective and reliable, with one plug resulting in significantly faster and longer lasting occlusions compared with two Gianturco coils. The new device can be repositioned prior to release, therefore allowing optimal positioning.

Experimental nonsurgical female sterilization: transcervical implantation of microspindles in fallopian tubes

PURPOSE

A nonsurgical method of female sterilization was investigated in rabbits.

MATERIALS AND METHODS

A self-expanding microspindle (length 9-18 mm, diameter 1.5-2.0 mm) made from tubular metal mesh was implanted in a single fallopian tube of 12 rabbits via catheterization of a single uterus. The contralateral fallopian tube and uterus served as controls. Each rabbit was scheduled to undergo three cycles of breeding. Before delivery, absence of pregnancy on the side with the microspindle was verified with hysterography.

RESULTS

Eight rabbits completed three cycles of breeding and pregnancy. Two rabbits had one pregnancy. Two rabbits did not conceive. Spindles were placed correctly in 11 rabbits. Successful contraception was achieved in nine rabbits, who had 25 gestations on the nonspindle side and no gestation on the spindle side. One rabbit, which received the shortest spindle, was bilaterally pregnant, indicating a failure of contraception on the spindle side. No spindles dislocated. Histologic study showed all spindles firmly embedded in the tubal wall without signs of inflammation.

CONCLUSION

Microspindles of a certain minimum length have potential as a transcervically implantable, permanent intratubal contraceptive device.