A delivery system including a catheter and an accessory tool for engagement with the catheter, the catheter including a proximal section, a distal end and a lumen extending along a length of the catheter from the proximal section to the distal end; the proximal section of the catheter comprising: a proximal terminal end that defines a perimeter of a proximal opening into the lumen and includes an exposed sealing area, the proximal terminal end including a first portion and a second portion, the exposed sealing area forming the first portion; and a sidewall, more rigid than the exposed sealing area, surrounding the lumen, a sealing assembly configured to engage with the proximal section of the catheter, said sealing assembly comprising: a sidewall, the sidewall including an external engagement feature located in proximity to the second portion and on an opposite side of the proximal opening from the exposed sealing area; wherein the accessory tool comprises a slitter tool; wherein said slitter tool comprises a feature (636, 725) configured to interlock with the external engagement feature of the catheter; and the sidewall of the proximal section of the catheter further includes a wall section of reduced thickness relative to another section of the sidewall, that has a proximal edge forming at least a part of the second portion; the external engagement feature of the sidewall of the sealing assembly defines a gap that the relatively thin wall section spans and within which the feature of the accessory tool extends when the feature of the tool interlocks with the external engagement feature; wherein the slitter tool further comprises a blade that is aligned with the relatively thin wall section, when the feature of the tool interlocks with the external engagement feature. a proximal terminal end that defines a perimeter of a proximal opening into the lumen and includes an exposed sealing area, the proximal terminal end including a first portion and a second portion, the exposed sealing area forming the first portion; and a sidewall, more rigid than the exposed sealing area, surrounding the lumen, a sealing assembly configured to engage with the proximal section of the catheter, said sealing assembly comprising: a sidewall, the sidewall including an external engagement feature located in proximity to the second portion and on an opposite side of the proximal opening from the exposed sealing area; wherein the accessory tool comprises a slitter tool; wherein said slitter tool comprises a feature (636, 725) configured to interlock with the external engagement feature of the catheter; and the sidewall of the proximal section of the catheter further includes a wall section of reduced thickness relative to another section of the sidewall, that has a proximal edge forming at least a part of the second portion; the external engagement feature of the sidewall of the sealing assembly defines a gap that the relatively thin wall section spans and within which the feature of the accessory tool extends when the feature of the tool interlocks with the external engagement feature; wherein the slitter tool further comprises a blade that is aligned with the relatively thin wall section, when the feature of the tool interlocks with the external engagement feature. a sidewall, the sidewall including an external engagement feature located in proximity to the second portion and on an opposite side of the proximal opening from the exposed sealing area; wherein the accessory tool comprises a slitter tool; wherein said slitter tool comprises a feature (636, 725) configured to interlock with the external engagement feature of the catheter; and the sidewall of the proximal section of the catheter further includes a wall section of reduced thickness relative to another section of the sidewall, that has a proximal edge forming at least a part of the second portion; the external engagement feature of the sidewall of the sealing assembly defines a gap that the relatively thin wall section spans and within which the feature of the accessory tool extends when the feature of the tool interlocks with the external engagement feature; wherein the slitter tool further comprises a blade that is aligned with the relatively thin wall section, when the feature of the tool interlocks with the external engagement feature.