Expandable sheath with elastomeric cross sectional portions
An expandable introducer sheath for passage of implant delivery catheters, such as catheters for delivery of prosthetic heart valves. The expandable sheath balances the amounts, shapes and positions of various stiff and elastic structures in the sheath to selectively program the expandability and buckling stiffness of the sheath. The expandable sheath can include, for example, an expandable tubular layer that includes alternating stiff and elastic wall portions of a single radial thickness. The combination of stiff and elastic wall portions allow for torque and push strength to advance the expandable sheath while at the same time accommodating temporary expansion. The expandable sheath can also be reinforced with a tubular layer of braided fibers or a stent structure for additional strength. Other embodiments include selective use of slots or gaps at the distal end of a stiff wall portion to enhance expandability and distribute strain.
1. A sheath comprising:
a stiff wall portion extending generally parallel to and partially around an elongate axis of the sheath and defining at least two edges, the two edges extending generally parallel to the elongate axis and between an inner surface and outer surface of the stiff wall portion; and
an elastic wall portion extending generally parallel to and partially around the elongate axis, the elastic wall portion extending between and abutting the edges of the stiff wall portion so as to define an expandable tubular layer;
wherein the expandable tubular layer has a starting profile smaller than an implant and defines a lumen and wherein the expandable tubular layer is configured to temporarily expand at least at the elastic wall portion to allow passage of the implant through the lumen and then return to approximate the starting profile after passage of the implant through the lumen;
wherein the elastic wall portion is 45 degrees to 90 degrees of an axial cross-section of the expandable tubular layer and at least one elongate rod is coupled to an inner surface of the elastic wall portion and extends generally parallel to the elongate axis.
2. The sheath of claim 1 , wherein the stiff wall portion and the elongate rod have a lubricious inner surface configured to facilitate passage of the implant.
3. The sheath of claim 1 , wherein the elastic wall portion is part of an outer elastic tubular layer and the stiff wall portion is embedded in the outer elastic tubular layer.
4. The sheath of claim 3 , wherein the lumen of the expandable tubular layer has a larger radius where defined by the elastic wall portion than where defined by the stiff wall portion.
5. A sheath comprising:
a stiff wall portion extending generally parallel to and partially around an elongate axis of the sheath and defining at least two edges, the two edges extending generally parallel to the elongate axis and between an inner surface and outer surface of the stiff wall portion; and
an elastic wall portion extending generally parallel to and partially around the elongate axis, the elastic wall portion extending between and abutting the edges of the stiff wall portion so as to define an expandable tubular layer;
wherein the expandable tubular layer has a starting profile smaller than an implant and defines a lumen and wherein the expandable tubular layer is configured to temporarily expand at least at the elastic wall portion to allow passage of the implant through the lumen and then return to approximate the starting profile after passage of the implant through the lumen;
wherein the elastic wall portion is 45 degrees to 90 degrees of an axial cross-section of the expandable tubular layer; and a plurality of elongate rods coupled to an inner surface of the elastic wall portion and the inner surface of the stiff wall portion, the elongate rods extending generally parallel to the elongate axis and inward into the lumen.
6. The sheath of claim 5 , wherein the elongate rods are spaced circumferentially apart around the lumen of the expandable tubular layer.