Expandable sheath for introducing an endovascular delivery device into a body
Embodiments of an expandable sheath can be used in conjunction with a catheter assembly to introduce a prosthetic device, such as a heart valve, into a patient. Such embodiments can minimize trauma to the vessel by allowing for temporary expansion of a portion of the introducer sheath to accommodate the delivery apparatus, followed by a return to the original diameter once the prosthetic device passes through. Some embodiments can include a sheath with inner and outer layers, where a folded portion of the inner layer extends through a slit in the outer layer and a portion of the outer layer overlaps the folded portion of the inner layer. Some embodiments include an elastic outer cover positioned outside the outer layer. Embodiments of the present expandable sheath can avoid the need for multiple insertions for the dilation of the vessel, thus offering advantages over prior art introducer sheaths.
1. A sheath for delivering a medical device, the sheath comprising:
an inner layer defining a lumen having a longitudinal axis and including a first fold and a second fold and an overlapping portion extending circumferentially between the first and second folds, the overlapping portion comprising overlap in a radial direction of at least two thicknesses of the inner layer; and
an outer layer extending at least partially around the inner layer and defining at least one elongate weakened portion generally aligned with the axis of the lumen, the weakened portion positioned adjacent to at least one of the folds;
wherein the first fold is configured to move closer to the second fold to shorten the overlapping portion at a local axial location during application of a radial outward force by passage of the medical device and wherein shortening of the overlapping portion corresponds with a local expansion of the lumen,
wherein the outer layer is at least partially adhered to a surface of the inner layer.
2. The sheath of claim 1 , wherein the weakened portion is a longitudinally extending discontinuity configured to facilitate radial expansion of the inner layer.
3. The sheath of claim 2 , wherein the outer layer comprises a first portion and a second portion defining the longitudinally extending discontinuity therebetween.
4. The sheath of claim 3 , wherein the first and second portions are configured to separate from one another into a gap as the first fold moves closer to the second fold.
5. The sheath of claim 4 , wherein the gap is configured to form over the overlapping portion as the first and second portions separate from one another.
6. The sheath of claim 5 , wherein the folds and overlapping portion are configured to expand into the gap.
7. The sheath of claim 6 , wherein the inner layer is configured to expand to a substantially cylindrical tube.
8. The sheath of claim 1 , wherein the outer layer overlaps only a portion of the at least one of the folds.
9. The sheath of claim 1 , further comprising a discontinuous intermediate layer between the inner layer and the outer layer, the discontinuous intermediate layer including a pattern of openings wherein each of the openings are at least partially defined by straight cut edges.
10. The sheath of claim 1 , further comprising a third fold, the third fold folding over an outside surface of the second fold.
11. The sheath of claim 10 , wherein the folds are folded regions.
12. The sheath of claim 1 , wherein the first and second folds are configured to meet and eliminate the overlapping portion at the local axial location.
13. The sheath of claim 12 , wherein the inner layer is configured to expand at the local axial location into a substantially tubular, unfolded cross-section.
14. The sheath of claim 13 , wherein the inner layer is configured to contract after passage of the medical device.
15. The sheath of claim 1 , further comprising:
a delivery apparatus, and
a prosthetic valve mountable onto the delivery apparatus for delivery through the sheath.
16. The sheath of claim 1 , wherein the weakened portion of the outer layer is configured to split from the radial outward force.
17. The sheath of claim 1 , further comprising third, fourth, fifth and sixth folds.
18. The sheath of claim 1 , wherein one of the folds moves closer to the weakened portion during application of the radial outward force.
19. The sheath of claim 1 , wherein the weakened portion is adjacent the first fold and wherein the first fold is configured to pass radially under the weakened portion as the first fold moves closer to the second fold.