A catheter, comprising: an elongated shaft (106, 206) having a proximal portion and a distal portion (106b, 300, 400, 500, 600, 700, 800), wherein an inner surface of the elongated shaft defines a lumen that extends distally from the proximal portion to an opening (118, 318, 518, 618, 718, 818) at a distal terminus of the distal portion; wherein the distal portion includes: an inner polymer structure (114, 314, 414, 514, 614, 714, 814) having a first portion (319, 419) and a second portion (320, 420) positioned distal of the first portion along the length of the inner polymer structure, wherein the first portion has a first stiffness and the second portion has a second stiffness less than the first stiffness; an outer polymer structure (116, 316, 416, 516, 616, 716, 816) disposed around the inner polymer structure; and a coil (170, 370, 470, 570, 670, 770, 870) wound around the inner polymer structure and disposed within the outer polymer structure, characterised in that, a portion of the coil within the distal portion includes a first region, a second region distal to the first region, and a third region distal to the second region, wherein the first and third regions each have a tighter pitch than the second region. an elongated shaft (106, 206) having a proximal portion and a distal portion (106b, 300, 400, 500, 600, 700, 800), wherein an inner surface of the elongated shaft defines a lumen that extends distally from the proximal portion to an opening (118, 318, 518, 618, 718, 818) at a distal terminus of the distal portion; wherein the distal portion includes: an inner polymer structure (114, 314, 414, 514, 614, 714, 814) having a first portion (319, 419) and a second portion (320, 420) positioned distal of the first portion along the length of the inner polymer structure, wherein the first portion has a first stiffness and the second portion has a second stiffness less than the first stiffness; an outer polymer structure (116, 316, 416, 516, 616, 716, 816) disposed around the inner polymer structure; and a coil (170, 370, 470, 570, 670, 770, 870) wound around the inner polymer structure and disposed within the outer polymer structure, characterised in that, a portion of the coil within the distal portion includes a first region, a second region distal to the first region, and a third region distal to the second region, wherein the first and third regions each have a tighter pitch than the second region. an inner polymer structure (114, 314, 414, 514, 614, 714, 814) having a first portion (319, 419) and a second portion (320, 420) positioned distal of the first portion along the length of the inner polymer structure, wherein the first portion has a first stiffness and the second portion has a second stiffness less than the first stiffness; an outer polymer structure (116, 316, 416, 516, 616, 716, 816) disposed around the inner polymer structure; and a coil (170, 370, 470, 570, 670, 770, 870) wound around the inner polymer structure and disposed within the outer polymer structure, characterised in that, a portion of the coil within the distal portion includes a first region, a second region distal to the first region, and a third region distal to the second region, wherein the first and third regions each have a tighter pitch than the second region.