Steep-taper flared stents and apparatus and methods for delivering them
A stent includes a first flaring portion including first and second sets of cells that flare outwardly when the stent is expanded from a contracted to a flared condition, and a second main portion connected to the first flaring portion. During use, the stent is introduced into a main vessel in the contracted condition and positioned with the first portion adjacent an ostium. The first portion is flared, causing first struts of the first set of cells to move from an axial towards a radial and partial circumferential orientation and causing second struts of the second set of cells to move from an axial towards a radial orientation. The second portion resists expansion when the first portion is flared. The stent is expanded further such that the second portion expands within the branch body lumen, and the first and second struts move towards a more circumferential orientation.
1. An apparatus for treating an ostium communicating between a main body lumen and a branch body lumen, comprising:
an elongate member comprising a proximal end, a distal end sized for introduction into the main body lumen and the branch body lumen;
a first expandable member formed from substantially compliant material on the distal end, the first expandable member being expandable from a collapsed configuration to a substantially spherical expanded configuration;
a second expandable member formed from substantially non-compliant material on the distal end adjacent the first expandable member, the second expandable member being expandable from a collapsed configuration to a substantially cylindrical expanded configuration; and
a stent on the distal end over the first and second expandable members, the stent comprising a first flaring portion overlying a portion of the first expandable member, and a second main portion comprising a distal main portion overlying the second expandable member, and a proximal main portion connecting the first flaring portion to the distal main portion, the proximal main portion overlying a transition between the first and second expandable members;
the first and second expandable members being independently expandable such that, when the first expandable member is expanded, the first flaring portion of the stent is expanded to a flared condition while the second expandable member remains in the collapsed configuration, and when the second expandable member is subsequently expanded, the second main portion is expanded radially outwardly and the first flaring portion is further expanded radially outwardly,
wherein the first flaring portion of the stent comprises:
a first set of cells disposed at the first end;
a second set of cells including first ends coupled to the first set of cells and second ends opposite the first ends, and
a plurality of flexible connectors coupled to the second ends of the second set of cells to connect the second set of cells to the second portion of the stent,
wherein the second set of cells comprises struts connected to curved segments, the curved segments having a lower yield strength than the struts.
2. The apparatus of claim 1 , wherein the proximal main portion has a greater stiffness than the first flaring portion such that the proximal main portion resists expansion when the first expandable member is expanded.
3. The apparatus of claim 1 , wherein the proximal main portion has a greater radial strength than the distal main portion, and the distal main portion has a greater radial strength than the first flaring portion.
4. The apparatus of claim 1 , wherein the first and second expandable members require respective inflation pressures to expand to the expanded configuration, and wherein the inflation pressure of the first expandable member is less than the inflation pressure of the second expandable member.
5. The apparatus of claim 1 , wherein the first expandable member is expandable independently of the second expandable member using an inflation pressure that is less than an inflation pressure necessary to expand the second expandable member.
6. The apparatus of claim 1 , wherein the struts are directed from a generally axial orientation towards a generally radially outward orientation when the first expandable member is expanded.
7. The apparatus of claim 1 , wherein the struts are directed from the generally radially outward orientation in the flared condition towards a circumferential orientation when the second expandable member is expanded.
8. The apparatus of claim 1 , the first set of cells comprising struts that extend substantially axially when the stent is in a contracted condition, the first end portion flaring such that the struts are directed towards a circumferential orientation in the flared condition.
9. The apparatus of claim 1 , wherein the connectors comprise curvilinear segments having a thickness and a width, at least one of the thickness and the width being thinner than segments comprising the first end portion.
10. The apparatus of claim 1 , further comprising a source of inflation media communicating with an interior of the first expandable member for delivering first and second predetermined volumes into the first expandable member to partially and fully expand the first expandable member, respectively.
11. The apparatus of claim 10 , wherein the source of inflation media comprises a syringe comprising a barrel including inflation media therein and a plunger, the barrel comprising first and second markers such that, when the plunger is depressed successively to the first and second markers, the first and second predetermined volumes are delivered into the interior of the first expandable member, respectively.
12. The apparatus of claim 1 , wherein the first expandable member comprises a distal portion that extends distally from a substantially spherical portion at least partially over the second expandable member.
13. The apparatus of claim 3 , wherein the radial strength of the second main portion decreases from the proximal main portion to the distal main portion.