WO2012095349A2

WO2012095349A2 - Needles and catheters

Info

Publication number: WO2012095349A2
Application number: PCT/EP2012/050131
Authority: WO
Inventors: Glyn Thomas
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-01-14
Filing date: 2012-01-05
Publication date: 2012-07-19
Anticipated expiration: 2013-07-14
Also published as: WO2012095349A3; GB201100581D0; GB2487527A

Abstract

A set comprises a needle (10) and a needle configuring catheter (18). The needle (10) has a hollow needle body (12) having a puncturing end (16). The needle body (12) is resiliently flexible so that in a relaxed state the needle body (12) tends to assume a straight configuration. The catheter (18) has a hollow catheter body (20) having a distal opening (24) and a portion (26) spaced from the distal opening (24) towards a proximal end of the catheter body (20). The catheter body (20) is resiliently flexible so that in a relaxed state the spaced portion (26) tends to assume a straight orientation having an axis and the distal opening (24) tends to assume a position offset from the axis of the spaced portion (26). The needle body (12) is insertable into the catheter body (20) such that an end portion (32) of the needle body (12) including the puncturing end (16) projects outwardly from the distal opening (24) of the catheter body (20). When the needle body (12) is inserted in this way, the catheter body (20) bends the needle body into a configuration in which the projecting end portion (32) of the needle body (12) extends in a direction that has a radial component relative to the axis of the spaced portion (26) of the catheter body (20). A splittable catheter (34) comprises an elongate annular wall (36). The annular wall (36) is provided with a longitudinally extending line of weakness (42) for splitting of the annular wall (36) along the line of weakness (42). The catheter (32) also includes a structure (40) that is distensible and which when distended extends radially outwardly of the annular wall (36) and circumferentially partially around the annular wall (36). The structure (40) does not extend over the line of weakness (42). The splittable catheter (34) can be used independently of the set. However, alternatively, the catheter body (20) of the configuring catheter (18) is insertable into the annular wall (36) of the splittable catheter (34). When the catheter body (20) is inserted in this way, the annular wall of the splittable catheter (34) constrains the catheter body (20) so as to reduce or eliminate the offset of the distal opening (24) of the catheter body (20) from the axis of the spaced portion of the catheter body (26).

Description

Needles and Catheters

The invention relates to a set comprising a needle and a needle configuring catheter, and also to a splittable catheter.

As used herein, in relation to needles and catheters, the term "distal" is used to refer to the end which is inserted into a human or animal patient's body and the term "proximal" is used to refer to the opposite end which generally remains outside of the patient's body.

It is often desirable to be able to pass a needle from the lumen of a blood vessel or other elongate body space through the wall of the blood vessel or body space into an adjacent body space. In order to do this, it is known to use a set comprising a needle and a catheter. The needle has a hollow needle body with a puncturing tip. The needle body is resiliently flexible so that in a relaxed state the needle assumes a curved configuration. The catheter has a hollow catheter body having a distal opening. The catheter body is resiliently flexible so that in a relaxed configuration the catheter body assumes a straight configuration. The needle body is insertable into the catheter body. The catheter body is stiffer than the needle body so that any portion of the needle body located within the catheter body is constrained into a generally straight configuration. As the puncturing tip of the needle body is extended out of the distal opening of the catheter body, the protruding section of the needle body tends to assume a curved configuration.

In use, the needle body is inserted into the catheter body so that the puncturing tip of the needle body lies within the catheter body. The catheter body is then introduced into the blood vessel or elongate body space so that the length of the catheter body lies generally parallel with the length of the blood vessel or elongate body space. The catheter body, with the needle body inside, is still sufficiently flexible to conform to the shape of the blood vessel/space, to allow advancement of the catheter body through the blood vessel/space. The needle body is constrained to the shape adopted by the catheter body and prevented from assuming its natural curved shape. When the distal end of the catheter body is in the desired position, the needle body is then extended out of the catheter body whereupon the protruding section assumes a curved configuration. This causes the tip to move in a direction which includes a radial (or lateral) component, relative to the longitudinal axis of the catheter body. In this way the tip can penetrate the wall of the blood vessel or elongate space and pass across the intervening tissue to an adjacent body space.

However, the angle of the puncturing tip relative to the catheter body is dependent on the length of the section of the needle body which protrudes from the distal end of the catheter body. This is undesirable because the length of protruding needle body needed to reach the wall may vary in an uncontrollable manner, whereas it is desirable to be able to control the angle of puncture.

According to a first aspect of the invention, there is provided a set comprising a needle and a needle configuring catheter. The needle has a hollow needle body having a puncturing end. The needle body is resiliently flexible so that in a relaxed state the needle body tends to assume a straight configuration. The catheter has a hollow catheter body having a distal opening and a portion spaced from the distal opening towards a proximal end of the catheter body. The catheter body is resiliently flexible so that in a relaxed state the spaced portion tends to assume a straight orientation having an axis and the distal opening tends to assume a position offset from the axis of the spaced portion. The needle body is insertable into the catheter body such that an end portion of the needle body including the puncturing end projects outwardly from the distal opening of the catheter body. When the needle body is inserted in this way, the catheter body bends the needle body into a configuration in which the projecting end portion of the needle body extends in a direction that has a radial component relative to the axis of the spaced portion of the catheter body.

Preferably, the end portion of the needle body has an axis and this axis (when extended beyond the end portion) will tend to cross or pass near the axis of the spaced portion of the catheter body (when the latter axis is extended beyond the spaced portion) with an angle between the two axes. The angle is preferably obtuse, and may be between about 90° and about 160°, more preferably between about 1 10° and about 150°, an most preferably between about 130° and about 140°.

Preferably the set also includes a constraining catheter. The constraining catheter has an elongate annular wall. The catheter body of the configuring catheter is insertable into the annular wall of the constraining catheter. When the catheter body is inserted in this way, the annular wall of the constraining catheter constrains the catheter body so as to reduce or eliminate the offset of the distal opening of the catheter body from the axis of the spaced portion of the catheter body.

Preferably, the annular wall of the constraining catheter is provided with a longitudinally extending line of weakness for splitting of the annular wall along the line of weakness.

Preferably, the constraining catheter includes a structure that is distensible and which when distended extends radially outwardly of the annular wall and circumferentially part of the way around the annular wall. The distensible structure does not extend over the line of weakness so as not to interfere with splitting of the annular wall along the line of weakness.

Preferably, the catheter body of the configuring catheter has, between the distal opening and the spaced portion, an end portion adjacent the distal opening and an intermediate portion between the end portion and the spaced portion. The end portion tends to assume a straight configuration and the intermediate portion tends to assume a curved orientation, such that in a relaxed state the end portion extends in a direction that includes a radial component relative to the axis of the spaced portion of the catheter body.

Preferably, the end portion of the catheter body has an axis and this axis (when extended beyond the end portion) will tend to cross or pass near the axis of the spaced portion of the catheter body (when the latter axis is extended beyond the spaced portion) with an angle between the two axes. The angle is preferably obtuse, and may be between about 90° and about 160°, more preferably between about 110° and about 150°, an most preferably between about 130° and about 140°.

The end portion of the catheter body may have a length between about 2mm and about 10mm, preferably between about 3mm and about 7mm, and most preferably between about 4mm and about 6mm.

The needle preferably includes a fitting, such as a needle hub, provided at a proximal end of the needle body and the configuring catheter preferably includes a fitting, such as a catheter hub, provided at a proximal end of the catheter body. The needle fitting contacts the catheter fitting to limit the insertion of the needle body into the catheter body. Preferably, the needle body is made of a superelastic alloy. A suitable superelastic alloy is Nitinol. Nitinol is highly flexible and a Nitinol needle can be bent through sharp radii while returning to its relaxed state when the bending force is removed. Nitinol is also suitable for the formation of a needle tip which can penetrate tissues. Other materials having these properties may be used for the manufacture of the needle body.

According to a second aspect of the invention, there is provided a splittable catheter comprising an elongate annular wall. The annular wall is provided with a longitudinally extending line of weakness for splitting of the annular wall along the line of weakness. The catheter also includes a structure that is distensible and which when distended extends radially outwardly of the annular wall and circumferentially partially around the annular wal! . The structure does not extend over the line of weakness.

The splittable catheter of the second aspect of the invention can be used independently of the needle and configuring catheter of the first aspect of the invention.

In both the first and second aspects of the invention, the line of weakness in the annular wall may be a line of reduced thickness. For example, a line of reduced thickness might be formed by removing material from an external surface of the annular wall. Alternatively a line of reduced thickness may be produced by extrusion in an appropriate configuration. As an alternative to a line of reduced thickness, the line of weakness may be produced by forming the annular wall from two different materials so that a line of weakness is formed by a strip of weaker material, or at a junction between two different materials, as described in WO 00/15289.

In both the first and second aspects of the invention, the distensible structure preferably extends circumferentially at least 180° around the annular wall, more preferably at least 225° around the annular wall, and most preferably at least 250° around the annular wall.

In both the first and second aspects of the invention, the distensible structure may comprise an elastic wall which expands to allow distension. Alternatively, the distensible structure may comprise a foldable wall which unfolds to allow distension. As another alternative, the distensible structure may comprise both a foldable wall and an elastic wall. In a preferred embodiment, the distensible structure is formed partially by the annular wall and partially by an elastic wall located radially outwardly of the annular wall.

In both the first and second aspects of the invention, the distensible structure is preferably located at or near a distal end of the annular wall.

The following is a more detailed description of embodiments of the invention, by way of example, reference being made to the appended schematic drawings in which:

Figure 1 shows a needle;

Figure 2 shows a constraining catheter for use with the needle in Figure 1 ;

Figure 3 shows the needle of Figure 1 partially inserted into the catheter of Figure 2;

Figure 4 shows the needle of Figure 1 fully inserted into the catheter of Figure 2;

Figure 5 shows a constraining catheter for use with the needle of Figure 1 and with the configuring catheter of Figure 2;

Figure 6 shows a first cross-sectional view through the constraining catheter of Figure 5:

Figure 7 is an enlarged, second cross-sectional view through the constraining catheter of Figure 5;

Figure 8 shows the constraining catheter of Figure 5 in use;

Figures 9, 10, 11 , 12 and 13 show various stages in a first method for delivering a wire into the pericardial space, making use of the needle of Figure 1, the configuring catheter of Figure 2 and the constraining catheter of Figure 5; and

Figures 14, 15 and 16 show stages in a second method for delivering a wire into the pericardial space, making use of the needle of Figure 1, the configuring catheter of Figure 2 and the constraining catheter of Figure 5.

The needle 10 that is shown in Figure 1 consists of an elongate hollow needle body 12 and a needle hub 14. The needle hub 14 is annular and is fixed to a proximal end of the needle body 12 such that an interior space (not shown) of the needle hub 14 communicates with the interior of the needle body 12. The needle body 12 has a distal end that is shaped to form a puncturing tip 16.

The needle body 12 is formed from a superelastic alloy, such as Nitinol. When the needle body 12 is in its relaxed state, as shown in Figure 1, the needle body 12 has a straight configuration. The resilient nature of the needle body 12 allows the needle body 12 to be bent through tight radii and still return to its original shape.

The needle body 12 may be any suitable length. By way of example, the needle body 12 may be 705mm long.

Referring to Figure 2, the configuring catheter 18 consists of an elongate, hollow catheter body 20 and a catheter hub 22. The catheter hub 22 is annular and is fitted to a proximal end of the catheter body 20 so that an interior space (not shown) of the catheter hub 22 is in communication with interior of the catheter body 20. The catheter body 20 has an opening 24 at the distal end of the catheter body 20.

The catheter body 20 is resiliently flexible and, in its relaxed state, assumes a configuration in which the catheter body 20 has a straight main portion 26 which extends from the catheter hub 22 to a curved portion 28, and finally a straight end portion 30 which extends from the curved portion 26 to the distal opening 24 of the catheter body 20. The curvature of the curved portion 28 is such that the end portion 30 extends at about 135° from the main portion 26. This configuration is shown in Figure 2.

By way of example, the overall length of the catheter body 20 may be about 700mm and the end portion 30 may have a length of about 5mm. The material and the wall thickness of the catheter body 20 are such that the catheter body 20 is stiff er than the needle body 12. A suitable material for the catheter body 20 is polyether block amide, for example the polyether block amide sold under the trade mark Pebax.

As shown in Figures 3 and 4, the needle body 12 can be inserted into the catheter body 20 by passing the puncturing tip 16 of the needle body 12 through the interior space of the catheter hub 22 and through the proximal end of the catheter body 20.

As seen in Figures 3 and 4, in view of the highly flexible nature of the needle body 12 together with the stiffer characteristic of the catheter body 20, the needle body 12 conforms itself to the shape of the catheter body 20, taking on a curvature corresponding to the curved portion 28, and the configuration of the catheter body 20 remains substantially the same as the relaxed configuration shown in Figure 2. The needle body 12 is longer than the catheter body 20 and so, when the needle body 12 is pushed fully into the catheter body 20, so that the needle hub 14 contacts the catheter hub 22, an end portion 32 of the needle body 12 extends outwardly from the distal end opening 24 of the catheter body 20. Clearly, the length of the end portion 32 can be determined by adjusting the length of the needle body 12 relative to that of the catheter body 20. In the current example, the length of the end portion 32 extending from the catheter body 20 is 5mm.

Given the highly resilient nature of the needle body 12, the end portion 32 assumes a straight configuration and, as shown in Figure 4, the end portion 32 of the needle body 12 is angled from the axis of the main portion 26 of the catheter body 20 by the angle imparted by the curved portion 28 of the catheter body 20, In this specific example, the axis of the end portion 32 of the needle body 12 crosses the axis of the main portion 26 of the catheter body 20 at an angle of about 135°.

Figures 5 to 8 show the constraining catheter 34 that can be used with the needle 10 and the configuring catheter 18. The constraining catheter 34 consists of an elongate annular wall 36, a fitting 38 provided at a proximal end of the annular wall 36 and an distensible structure 40 provided at a distal end of the annular wall 36.

As seen in Figures 5, 7 and 8, the annular wall 36 is provided with a line of reduced thickness 42 which extends longitudinally along the whole length of the annular wall 36. The line of reduced thickness 42 can be produced by cutting material from the exterior of the annular wall 36. Alternatively, the annular wall 36 can be extruded so as to have the line of reduced thickness formed therein 42.

The annular wall 36 is also provided with a duct 44 foraied internally in the body of the annular wall 36. The duct 44 extends longitudinally along the annular wall 36 from adjacent the proximal end of the annular wall 36 to near the distal end of the wall 36.

The catheter fitting 38 consists of a first fitting tab 46 and a second fitting tab 48. The two fitting tabs 46 and 48 are connected, respectively, to opposite sides of the annular wall 36 at the proximal end of the annular wall 36. The line of reduced thickness 42 passes between the two tabs 46. 48. The first fitting tab 46 is provided with a port (not shown) that is in fluid communication with the duct 44 provided in the annular wall 36. The port in the first fitting tab 46 is sized so as to be connectable to a syringe, so as to allow liquid to be pumped into the port and into the duct 44.

As best seen in Figure 6, the distensible structure 40 is formed partially from the annular wall 36 and partially from an elastic wall 50 which is bonded in an air-tight manner to an exterior surface of the annular wall 36. The duct 44 opens into the space between the annular wall 36 and the elastic wall 50. Hence, the distensible structure 40 can be distended by introducing liquid into the port in the first fitting tab 46 such that the liquid passes through the duct 44 into the space between the annular wall 36 and the elastic wall 50. The distensible structure 40 is shown in its distended state in Figures 5 and 6 and in its collapsed state in Figure 8.

As best seen in Figures 5 and 6, the distensible structure 40 extends in a circumferential direction, by about 270°, around the annular wall 36. The distensible structure 40 does not extend over the region of the annular wall 36 provided with the line of reduced thickness 42.

As seen in Figures 11 to 13, the annular wall 36 is sized so that the catheter body 20 of the configuring catheter 18 can be inserted into the annular wall 36. In addition, the annular wall 36 is sufficiently stiff so that, when the curved portion 28 and the end portion 30 of the catheter body 20 lie within the annular wall 36, the catheter body 20 is constrained into a relatively straight configuration with the end portion 30 lying generally in line with the main portion 26 of the catheter body 20. The annular wall 36 is, however, sufficiently flexible so as to allow the constraining catheter 34 to be inserted into and guided through the vasculature of a patient.

Figures 9 to 13 show various steps in a first surgical procedure for inserting a wire into the pericardial space 52 of a human patient, the surgical procedure utilising the needle 10, the configuring catheter 18 and the constraining catheter 34 described above.

Firstly, the needle body 12 of the needle 10 is inserted into the catheter body 20 of the configuring catheter 18 such that the puncturing tip 16 of the needle body 12 is positioned just short of the distal end opening 24 of the catheter body 20. Hence, the needle 10 and the configuring catheter 18 are in the relative positions shown in Figure 3 and the needle hub 14 is spaced from the catheter hub 22. The catheter body 20 (with the needle body 12 positioned within the catheter body 20 as described above) is then inserted into the proximal end of the annular wall 36 of the constraining catheter 34 and pushed into the annular wall 36 such that the distal end opening 24 of the catheter body 20 lies just short of the distal end of the annular wall 36. As discussed above, the relative stiffness of the annular wall 36 constrains the catheter body 20 into a generally straight orientation.

The distal end of the annular wall 36 (with the catheter body 20 and the needle body 12 inserted into the annular wall 36 as described above) is then introduced, in a known manner, into the vasculature of a human patient at the femoral site. The annular wall 36 of the constraining catheter (together with the catheter body 20 and the needle body 12) are then advanced through the vasculature of the patient, in a known manner, so that the distal end of the annular wall 36 becomes positioned in the coronary sinus 54 as shown in Figure 9. During this process, the end portion 30 and the curved portion 28 of the catheter body 20 are constrained by the annular wall 36 so that the end portion 30 lies generally in line with the main portion 26 of the catheter body 20. This assists in the process of advancing the assembly into the coronary sinus 54, because without such constraint the end portion 30 would lie at an angle of approximately 135° to the main portion 26 which could cause snagging and prevent advancement through the vasculature.

Figure 10 shows the distal end of the annular wall 36 located in position in the coronary sinus 54. Figure 10 also shows the spatial relationship between the coronary sinus 54 and the pericardial space 52. As will be appreciated, in order to deliver a wire into the pericardial space 52, it is necessary to puncture and pass through a section 56 of heart tissue. This requires a force to be applied, and movement, in a direction relative to the annular wall 36 which includes a radial component. In order to achieve this, the annular wall 36 is retracted a short distance while the catheter body 20 and the needle body 12 remain in place in coronary sinus 54. As seen in Figure 1 1, the extent of retraction of the annular wall 36 is sufficient so that the end portion 30 and the curved portion 28 of the catheter body 20 protmde outwardly from the distal end of the annular wall 36.

The retraction of the annular wall 36 of the constraining catheter 34 is achieved by the process illustrated in Figure 8. As shown in Figure 8, the annular wall 36 is split along the line of reduced thickness 42, starting at the proximal end of the annular wall 36. The line of reduced thickness 42 acts as a line of weakness and it is possible to split the annular wall 36 cleanly along this line. Once the annular wall 36 has been split along a portion of its length, starting from the proximal end, the annular wall 36 can be retracted relative to the catheter body 20 without retraction being blocked by the catheter hub 22 of the configuring catheter 18.

If desired, the annular wall 36 can be removed completely from the patients body, and also be removed from the catheter body 20, by splitting the annular wall 36 along the full length of the line of reduced thickness 42.

However, for the current purposes, only partial retraction of the annular wall 36 is desired, so as to leave the end portion 30 of the catheter body 20 in the angled configuration shown in Figure 11.

It will be appreciated that, splitting and retraction of the annular wall 36, as described above may be avoided if the catheter body 20 and the needle body 12 are longer than the annular wall 36. In this case, the catheter body 20 and the needle body 12 would be pushed further into the annular wall 36 so that the end portion 30 and the curved portion 28 of the catheter body 20 extend out of the distal end of the annular wall 36.

Once the catheter body 20 is in the position shown in Figure 11 , the needle body 12 is then extended out of the catheter body 20 by pushing the needle hub 14 into contact with the catheter hub 22 as shown in Figure 4 and in Figure 12. The length of the needle body 12 that extends beyond the distal end opening 24 of the catheter body 20 will depend on the relative length of the needle body 12 and the catheter body 20 and this distance will be predetermined so that the length of protruding needle body 12 is sufficient to pass through the section 56 of heart tissue into the pericardial space 52, without contacting the pericardium 58. As seen in Figure 12, the tip 16 of the needle body 12 now lies within the pericardial space 52.

At this stage, a wire 60 can be passed through the needle body 12 into the pericardial space 52, as shown in Figure 13.

In the first procedure described above, the distensible structure 40 of the constraining catheter 34 is not used. A second surgical procedure in which the distensible structure 40 of the constraining catheter 34 is used is described below. In this second procedure, the distensible structure 40 allows a guide wire to be positioned at different points within the pericardial space 52,

In the section procedure, the annular wall 36, the needle body 12 and the catheter body 20 are positioned in the coronary sinus 54 as discussed above. The end portion 30 and the curved portion 28 of the catheter body 20 are then revealed, either by retracting the annular wall 36 or by pushing the catheter body 20 further into the annular wall 36, again as described above. Finally, the puncturing tip 16 of the needle body 1 2 penetrates through the section 56 of heart tissue into the pericardial space 52 as described above.

At this stage, the annular wall 36 of the constraining catheter 34 is then advanced over the catheter body 20 and the needle body 12 while the needle body 12 extends through the heart tissue 56. During this process, the annular wall 36 is guided by the catheter body 20 and the needle body 12 so that the distal end of the annular wall 36 enters into the pericardial space 52. Penetration of the annular wall 36 through the section 56 of heart tissue is facilitated as the heart tissue 56 has already been punctured by the needle body 12.

Once the distensible structure 40 lies within the pericardial space 52, the distensible structure 40 is distended, as shown in Figure 9. This is achieved by introducing liquid from a syringe into the port in the first fitting tab 46 such that the liquid passes through the duct 44 into the space between the annular wall 36 and the elastic wall 50.

Once distended, the distensible structure 40 becomes jammed between the pericardium 58 and the section 56 of heart tissue so as to hold the distal end of the annular wall 36 firmly in place in the pericardial space 52.

At this point, the catheter body 20 may then be advanced through the annular wall 36 so that a portion of the catheter body 20 extends outwardly from the distal end of the annular wall 36, into the pericardial space 52. This is shown in Figures 15 and 16.

As the distensible structure 40 is jammed within the pericardial space 52, the distensible statcture 40 acts as a pivoting point. Figure 15 shows that by gently pulling the annular wall 36 the protruding section of the catheter body 20 can be advanced, while Figure 16 shows that by gently pushing the annular wall 36, the protruding section of the catheter body 20 can be moved in the opposite direction in the pericardial space 52.

In this manner, by adjusting the position of the catheter body 20 within the pericardial space 52, a wire can be placed at a number of different positions within the pericardial space 52.

A number of advantages arise from the features of the apparatus described above.

Firstly, the needle 10 and the configuring catheter 18 allow the puncturing end of the needle body 12 to be advanced towards the wall of the coronary sinus 54 at a predetermined angle relative to the main portion 26 of the catheter body 20, independently of the length of the needle body 12 that is advanced out of the catheter body 20. This is advantageous as it facilitates positioning of the needle tip 16. The principle can be applied to other surgical procedures and other areas of the body.

The features of the constraining catheter 34 provide a balloon catheter that can be retracted completely by splitting.

Claims

1 . A set comprising a needle and a needle configuring catheter: the needle comprising a hollow needle body having a puncturing end, the needle body being resiliently flexible so that in a relaxed state the needle body tends to assume a straight configuration; the catheter comprising a hollow catheter body having a distal opening and a portion spaced from the distal opening towards a proximal end of the catheter body, the catheter body being resiliently flexible so that in a relaxed state the spaced portion tends to assume a straight orientation having an axis and the distal opening tends to assume a position offset from the axis of the spaced portion; the needle body being insertable into the catheter body such that an end portion of the needle body including the puncturing end projects outwardly from the distal opening of the catheter body, and, when the needle body is so inserted, the catheter body bends the needle body into a configuration in which the end portion of the needle body extends in a direction that has a radial component relative to the axis of the spaced portion of the catheter body.

2. A set according to claim 1, including a constraining catheter, the constraining catheter comprising an elongate annular wall, the catheter body of the configuring catheter being insertable into the annular wall of the constraining catheter, and when the catheter body is so inserted, the annular wall constrains the catheter body so as to reduce or eliminate the offset of the distal opening of the catheter body from the axis of the spaced portion of the catheter body.

3. A set according to claim 2, wherein the annular wall of the constraining catheter is provided with a longitudinally extending line of weakness for splitting of the annular wall along the line of weakness.

4. A set according to claim 3, wherein the constraining catiieter includes a stnicture that is distensible and which when distended extends radially outwardly of the annular wall and circumferentially partially around the annular wall, and wherein the structure does not extend over the line of weakness.

5. A set according to claim 4, wherein the distensible structure extends circumferentially at least 180° around the annular wall.

6. A set according to claim 5, wherein the distensible structure extends circumferentially at least 225° around the annular wall.

7. A set according to claim 6. wherein the distensible structure extends circumferentially at least 250° around the annular wall.

8. A set according to any one of claims 4 to 7, wherein the distensible structure is formed partially by die annular wall and partially by an elastic wall located radially outwardly of the annular wall.

9. A set according to any one of claims 4 to 8, wherein the distensible structure is located at or near a distal end of the annular wall.

10. A set according to any preceding claim, wherein the catheter body of the configuring catheter has, between the distal opening and the spaced portion, an end portion adjacent the distal opening and an intermediate portion between the end portion and the spaced portion, the end portion tending to assume a straight configuration and the intermediate portion tending to assume a curved orientation, such that in a relaxed state the end portion extends in a direction that has a radial component relative to the axis of the spaced portion.

11. A set according to claim 10, wherein the end portion of the catheter body has an axis which tends to cross or pass near the axis of the spaced portion of the catheter body with an angle between the two axes.

12. A set according to claim 1 1, wherein the angle is obtuse, preferably between about 90° and about 160°, more preferably between about 110° and about 150°, an most preferably between about 130° and about 140°.

13. A set according to any one of claims 10 to 12, wherein the end portion of the catheter body has a length between 2mm and 10mm, preferably between 3mm and 7mm, and most preferably between 4mm and 6mm.

14. A set according to any preceding claim, wherein the needle includes a fitting provided at a proximal end of the needle body and the configuring catheter includes a fitting provided at a proximal end of the catheter body, the needle fitting contacting the catheter fitting to limit the insertion of the needle body into the catheter body.

15. A set according to any preceding claim, wherein the needle body is made of a superelastic alloy.

16. A splittable catheter comprising an elongate annular wall, the annular wall being provided with a longitudinally extending line of weakness for splitting of the annular wall along the line of weakness, the catheter including a structure that is distensible and which when distended extends radially outwardly of the annular wall and circumferentially partially around the annular wall, and wherein the structure does not extend over the line of weakness.

17. A catheter according to claim 16, wherein the distensible structure extends circumferentially at least 180° around the annular wall.

18. A catheter according to claim 17, wherein the distensible structure extends circumferentially at least 225° around the annular wall.

19. A catheter according to claim 18, wherein the distensible structure extends circumferentially at least 250° around the annular wall.

20. A catheter according to any one of claims 13 to 16, wherein the distensible structure is formed partially by the annular wall and partially by an elastic wall located radially outwardly of the annular wall.

21. A catheter according to any one of claims 16 to 20, wherein the distensible staicture is located at or near a distal end of the annular wall.

22. A splittable catheter, substantially as hereinbefore described with reference to the drawings.

23. A set comprising a needle and a needle configuring catheter, substantially as hereinbefore described with reference to the drawings.