Catheter shaft and associated devices, systems, and methods

1. A catheter comprising:

an elongated shaft having a proximal portion, a distal portion, and an intermediate portion therebetween, wherein the distal portion terminates distally at an opening;

wherein:

the intermediate portion has a proximal region, an overlapping region, and a distal region, the overlapping region being between the proximal and distal regions;

the proximal region extends from the proximal portion of the shaft to the overlapping region;

the proximal region includes an inner polymer structure, an outer polymer structure, an inner braid, and an outer braid surrounding the inner braid;

the outer polymer structure is disposed in and around the inner braid and the outer braid;

the inner braid comprises a first plurality of interwoven wires;

the outer braid comprises a second plurality of interwoven wires;

the overlapping region extends from the proximal region to the distal region;

the overlapping region includes: (a) the inner polymer structure, (b) the outer polymer structure, (c) a coil wound around the inner polymer structure and positioned within the outer polymer structure, and (d) the outer braid;

a proximal terminus of the coil is at a border between the proximal region and the overlapping region;

a distal terminus of the inner braid is at the border between the proximal region and the overlapping region;

a distal terminus of the outer braid is at a border between the overlapping region and the distal region;

the distal region extends from the overlapping region to the distal portion;

the distal region includes the inner polymer structure, the outer polymer structure, and the coil wound around at least a portion of the inner polymer structure and does not include the inner braid or the outer braid;

a pitch of the coil is less at a distal region of the coil than at a proximal region of the coil.

2. The catheter of claim 1 , wherein a stiffness of the inner polymer structure decreases in a distal direction.

3. The catheter of claim 1 , wherein a stiffness of the outer polymer structure decreases in a distal direction.

4. The catheter of claim 1 , wherein the outer polymer structure has a first section having a first stiffness and a second section distal to the first section having a second stiffness less than the first stiffness.

5. The catheter of claim 1 , wherein an outer diameter of the shaft at the distal region is less than an outer diameter of the shaft at the overlapping region.

6. The catheter of claim 1 , wherein the outer polymer structure is composed of two different polymers.

7. The catheter of claim 1 , wherein the outer polymer structure is composed of three different polymers.

8. The catheter of claim 1 , wherein the outer polymer structure is composed of four different polymers.

9. The catheter of claim 1 , further comprising a handle coupled to the proximal portion of the shaft.

10. The catheter of claim 1 , further comprising a liner that coats an inner surface of the inner polymer structure.

11. The catheter of claim 1 , further comprising a radiopaque marker positioned along the distal portion distal of a distal terminus of the coil.

12. The catheter of claim 1 , wherein the pitch of the coil varies along a length of the coil.

13. The catheter of claim 1 , wherein the inner braid has an inner braid pitch, and wherein the inner braid pitch is constant along a length of the inner braid.

14. The catheter of claim 1 , wherein the outer braid has an outer braid pitch, and wherein the outer braid pitch is constant along a length of the outer braid.

15. The catheter of claim 1 , wherein the inner braid, the outer braid, and the coil are embedded in the outer polymer structure.

16. The catheter of claim 1 , wherein the inner polymer structure comprises a first layer and a second layer surrounding the first layer.

17. The catheter of claim 16 , wherein the second layer ends proximal of a distal terminus of the coil.