Interventional catheter

0001This invention relates to an interventional catheter comprising a catheter tube having two superposed layers of materials secured together and with mechanical properties differing from one another, a guidewire lumen in said catheter tube for the sliding fit of a guidewire, and a balloon with a distal end sealingly surrounding said catheter tube, whereby the catheter tube has an inner layer forming the guidewire lumen and an outer layer forming an outer surface of the catheter tube.

0002Over the wire catheters have been widely used for interventions such as percutaneous transluminal cardiovascular angioplasty. A problem with these catheters is that the guidewire may clog into the guidewire lumen of the catheter, whereby the guidewire may follow the balloon upon withdrawal thereof after the inflation procedure, thereby making it necessary to re-insert the guidewire into the treated area of the blood vessel for re-positioning a balloon therein in case a second inflation is needed. A further problem is that the catheter has to achieve an acceptable compromise between the requirements of some stiffness to assure good pushability and some flexibility to assure kink resistance. In addition, the catheter has to permit safe attachment of the balloon to the catheter tube.

0003Monorail (Trade Mark) technology, which provides for an entry of the guidewire distal of the balloon and an exit for the guidewire distal of the proximal end of the catheter tube, substantially reduces the risk of guidewire clogging in the guidewire lumen because the length of frictional engagement between guidewire and guidewire lumen is strongly reduced. That is also of great help in the handling of balloon catheters for balloon exchange purposes. Though limited, the friction and clogging problem is, however, still existent.

0004<patcit id="pcit0001" dnum="WO9211893A"><text>WO 92/11893</text></patcit> describes an intraaortic balloon apparatus comprising a hollow catheter in which is located an elongated member forming a central lumen extending out of the catheter at the distal end thereof. An aortic pumping balloon is positioned over the elongated member; the distal end of the balloon is bonded to a tip affixed to the distal end of the elongated member, and its proximal end is bonded to the distal end of the catheter. In order to achieve a balance of flexibility and remains and to avoid kinking, the elongated member is formed of an inner layer comprised of a soft elastomeric material to impart flexibility to the tubing and the outer layer is comprised of a hard plastic material to impart structural support to the elongated member.This balloon apparatus cannot be loaded with a guidewire and moved into tortuous vessels with the guidewire loaded inside the elongated member as the friction between guidewire and elongated member increases distinctively when the elongated member is shaped into curves. There would be therefore the risk that a spiral wound guidewire could be captured in the soft elastomeric plastic material of the inner layer of the elongated member. Although the outer layer of the elongated member that is coextruded onto the inner layer is formed of nylon, a material which is expected to be directly weldable to a wide variety of materials, this balloon apparatus cannot be introduced into narrow vessels or narrow stenoses, nor can it be passed through narrow punctures to enter the blood vessels.This is because of the relatively large profile of the folded balloon, due to the distal fixture of the balloon to the elongated member. The balloon is bonded to an intermediate tip element which in turn is bonded to the elongated member.

0005The document <patcit id="pcit0002" dnum="EP0650740A1"><text>EP 0650740 A1</text></patcit> shows a catheter comprising a catheter tube having two superposed layers of materials secured in relation to one another and with mechanical properties differing from one another, a longitudinal lumen in the catheter tube for the sliding fit of a guidewire, and a balloon with a proximal end and a distal end, the distal end sealingly surrounding the catheter tube, whereby the catheter tube has an inner layer forming the longitudinal lumen and an outer layer forming the outer surface of the catheter tube. In this catheter, the inner layer is formed of a material with lower friction coefficient than the material forming the outer layer, whereby there is no more risk of having the guidewire clogging in the guidewire lumen of the catheter tube.

0006In terms of two layers catheter shafts, it has been observed that in practical use the adhesion of the two layers of material was not absolutely satisfactory. Although the coextrusion technology currently used for making such catheter shafts seems to involve close molecular interpenetration of the materials forming the superposed layers of the shaft, it has been possible to observe separation of the two layers, for example at the place of insertion of the shaft over the guidewire. Furthermore, tear test effected on such structures has shown that the two layers can separate under extreme conditions of stress on the shaft.

0007Further, <patcit id="pcit0003" dnum="WO9528982A"><text>WO 95/28982</text></patcit> discloses a differential stiffness tubing for a catheter. The tubing has a stiff section and a flexible section joined by a relatively short transition section in which the materials of the stiff and flexible sections are wedged into each other in a smooth gradual manner to produce an inseparable bond between the materials without abrupt joints. In one embodiment of <patcit id="pcit0004" dnum="WO9528982A"><text>WO 95/28982</text></patcit> (Fig. 1E), the stiffest material of a proximal section forms an interior layer, and the stiffest material extends into the transition section and is wedged into the less stiff material in portion of transition section. This less stiff material, in turn, is wedged into a softer material in portion of transition section, which, in turn, is wedged into the softest material in portion of transition section.

0008It is an object of this invention to propose an interventional balloon catheter which is versatile and which provides a fully controllable and easy to manufacture assembly. A further object of the invention is an interventional low profile balloon catheter that can be safely operated on a guidewire and moved into tortuous vessels and other extreme conditions.

0009To this effect, the interventional catheter according to the invention complies with the definitions given in the claims.

0010Accordingly, where the catheter comprises mediator layer means arranged between said inner layer and said outer layer for the adhesive anchorage of said layers thereto, securing of the inner layer and outer layer is strongly enhanced independently of their intrinsic capacity of adhesion to one another. The risk of a poor adhesion or the risk of a failure in the adhesion of the two layers to one another is eliminated. The inner and outer layers may be chosen for their most appropriate mechanical characteristics rather than for their capacity to adhere to one another. Because of the adhesive anchorage of the inner and outer layers on the mediator layer means, the risk of separation of the two layers upon insertion of the catheter tube over a guidewire is minimized. And the assembly of inner and outer layers is under control and the possibilities of changing the flexibility of the assembly are improved; due to the adhesive anchorage on the mediator layer means, rigidity of the assembly is enhanced with the same basic inner and outer layers, whereas flexibility of the assembly may be mastered by safely acting on the thickness of the inner and outer layers, with the resulting reduction in the profile of the catheter. As a result of the adhesive anchorage of the inner and outer layers on the mediator layer means the assembly behaves like a unit; accordingly, the assembly may be safely grabbed by the outer layer and tear tests are thus facilitated.

0011The inner and outer layers and said mediator layer means are congruent in length, so that the catheter shaft can be produced in long tubes which may be cut at will to the appropriate length. Accordingly, a catheter tube is formed in a continuous process avoiding the need of using a core in the inner layer.

0012Where said inner and outer layers are substantially transparent and said mediator layer means are contrasted with respect to said substantially transparent inner and outer layers, a visual control of the assembly is readily available to further improve the manufacture.

0013Where the mediator layer means have mechanical properties differing from the mechanical properties of the inner and outer layers a further step is achieved in the possibility of changing the lengthwise flexibility properties of the catheter.

0014When the inner layer is formed of a material with lower friction coefficient than the material forming the outer layer, there is no more risk of having the guidewire clogging or being captured in the guidewire lumen of the catheter tube. Withdrawal and re-positioning of the balloon catheter on a guidewire left in place at the site of treatment in the vessel system is rapid, safe and precise. Furthermore, the choice can be made for materials for the inner and outer layers having the most appropriate friction and kink resistance coefficients, while safe attachment of the balloon may be made at will on the outer layer which is chosen without being influenced by the friction properties of the inner layer.

0015The mediator layer means is formed on the basis of a low density polyethylene to offer superior adhesion performance in a wide variety of configurations of the inner and outer layers and ease of processing on conventional fabrication equipment.

0016In a preferred form of the invention, the inner layer is made of a polyethylene or of a high density polyethylene, both of which assure an extremely low friction coefficient and an appropriate kink resistance coefficient. In another preferred form or the invention, the outer layer is made of a polyamid to assure easy welding of the balloon and a good stiffness at that level.

0017These and other objects, features and advantages of the invention will become readily apparent from the following description with reference to the accompanying drawings which show, diagrammatically and by way of example only, preferred but still illustrative embodiments of the invention. <dl id="dl0001"><dt><b>Figure 1</b></dt><dd>is a longitudinal cut of an over the wire balloon catheter embodying the in- vention.</dd><dt><b>Figure 2</b></dt><dd>is a longitudinal cut of a Monorail (Trade Mark) balloon catheter embodying the invention.</dd><dt><b>Figure 3</b></dt><dd>is an enlarged detail of a variant.</dd></dl>

0018The interventional catheter shown in <figref idref="f0001"><b>Figure 1</b></figref> comprises a catheter tube <b>1</b> formed of two superposed tubular layers of materials <b>2</b> and <b>3</b> with a tubular mediator layer <b>4</b> arranged therebetween for the adhesive anchorage of said layers <b>2</b> and <b>3</b> onto the mediator layer <b>4.</b>

0019The tubular layers <b>2, 3</b> and <b>4</b> extend all over the length of catheter tube <b>1,</b> being thus congruent in length, and the assembly of layers forming the catheter tube <b>1</b> is obtained by the known co-extrusion technology, i.e., by extruding simultaneously the inner layer <b>2</b> with the mediator layer <b>4</b> and with the outer layer <b>3</b> thereover. Layers <b>2</b> and <b>3</b> have mechanical properties differing from one another and, preferably, mediator layer <b>4</b> also has mechanical properties differing from the mechanical properties of inner and outer layers <b>2</b> and <b>3.</b>

0020Preferably, the inner layer <b>2</b> is formed of a material with lower friction coefficient than the material forming the outer layer <b>3.</b> For example, the inner layer <b>2</b> may be formed of a polyethylene, preferably a high density polyethylene, whereas the outer layer <b>3</b> may be formed of a polyamid. The mediator layer 4 is formed on the basis of a low density polyethylene.

0021Preferably, the inner and outer layers <b>2</b> and <b>3</b> are substantially transparent, whereas the mediator layer <b>4</b> is contrasted with respect to said substantially transparent inner and outer layers <b>2</b> and <b>3.</b>

0022The catheter tube <b>1</b> has thus a longitudinal lumen <b>5</b> for the sliding fit of a guidewire exemplified by dotted line <b>6,</b> which lumen <b>5</b> has a very low friction coefficient, lower than that of the outer layer <b>3,</b> and a non kinking capacity while the outer layer <b>3</b> forms an outer surface of the catheter tube <b>1</b> and is easily weldable to the materials commonly used for making balloons for angioplasty purposes and the like. And therebetween the mediator layer <b>4</b> assures the best adhesive anchorage of inner and outer layers <b>2</b> and <b>3</b> thereto, the catheter tube <b>1</b> thus behaving as a unitary element with differentiating properties at its inner and outer levels.

0023Over the distal portion of the catheter tube <b>1</b> is positioned a balloon <b>7</b> the distal end <b>8</b> of which sealingly surrounds the outer layer <b>3</b> of catheter tube <b>1,</b> for example by welding.

0024A tube 9 is arranged over the catheter tube <b>1,</b> at a radial distance thereof, thus defining an inflation lumen <b>10</b> for the balloon <b>7.</b> The proximal end <b>11</b> of the balloon <b>7</b> is welded onto the distal end of tube <b>9.</b>

0025The interventional catheter shown in <figref idref="f0001"><b>Figure 2</b></figref> also comprises a catheter tube <b>12</b> having two superposed tubular layers of materials <b>13</b> and <b>14</b> with a tubular mediator layer <b>15</b> arranged therebetween for adhesive anchorage of said layers <b>13</b> and <b>14</b> onto the mediator layer <b>15.</b>

0026The tubular layers <b>13, 14</b> and <b>15</b> extend all over the catheter tube <b>12</b> and the assembly of layers forming the catheter tube <b>12</b> are obtained by the known co-extrusion technology whereby inner tubular layer <b>13</b> is extruded simultaneously with the mediator layer <b>15</b> and the outer layer <b>14</b> thereover. Layers <b>13</b> and <b>14</b> have mechanical properties differing from one another and, preferably, mediator layer <b>15</b> also has mechanical properties differing from the mechanical properties of inner and outer layers <b>13</b> and <b>14.</b>

0027Preferably the inner layer <b>13</b> is made of a material with lower friction coefficient than the material forming the outer layer <b>14.</b> For example, inner layer <b>13</b> may be formed of a polyethylene, preferably a high density polyethylene, whereas the outer layer <b>14</b> may be made of a polyamid. The mediator layer <b>15</b> is formed on the basis of a low density polyethylene.

0028Preferably the inner and outer layers <b>13</b> and <b>14</b> are substantially transparent and the mediator layer <b>15</b> is contrasted with respect to said substantially transparent inner and outer layers <b>13</b> and <b>14.</b>

0029The catheter tube <b>12</b> has thus a longitudinal lumen <b>16</b> for the sliding fit of a guidewire exemplified by dotted line <b>17,</b> which lumen <b>16</b> has a very low friction coefficient, lower than that of the outer layer <b>14</b> and with a non kinking capacity, whereas outer layer <b>14</b> forms an outer surface of the catheter tube <b>12</b> and is easily weldable to the materials currently used for making angioplasty balloons. And therebetween, the mediator layer <b>15</b> also assures superior adhesive anchorage for inner and outer layers <b>13</b> and <b>14,</b> the catheter tube <b>12</b> acting as a unit with different properties at its inner and outer levels.

0030A tube <b>18</b> is affixed, for example welded, in parallel relationship to the proximal portion of catheter tube <b>12,</b> and this tube <b>18</b> extends proximally of the catheter tube <b>12.</b> The tube <b>18</b> defines an inflation lumen <b>19</b> for a balloon <b>20</b> the distal end <b>21</b> of which sealingly surrounds the outer layer <b>14</b> of catheter tube <b>12,</b> for example by welding. The proximal end <b>22</b> of balloon <b>20</b> sealingly surrounds a proximal portion of the catheter tube <b>12</b> and a distal portion of tube <b>18,</b> whereby the proximal portion of catheter tube <b>12</b> extends proximally out of the balloon <b>20</b> and the distal portion of tube <b>18</b> extends within the balloon <b>20.</b>

0031Variants are readily available. For example, the mediator layer may be made of two superposed tubular layers of materials which differ from one another in order to respectively provide superior adhesive anchorage for the inner and outer layers while assuring total adhesive anchorage between them. This configuration is advantageous for example to match particular flexibility requirements for the catheter tube or to assume adhesive anchorage conditions which would be otherwise difficult for the inner and outer layers.

0032<figref idref="f0001"><b>Figure 3</b></figref> shows such a configuration where the catheter tube <b>23</b> is formed of two superposed tubular layers of materials <b>24</b> and <b>25</b> with a tubular mediator layer <b>26</b> arranged therebetween and formed of two superposed adhesively anchored tubular layers <b>27</b> and <b>28,</b> layer <b>27</b> being for adhesive anchorage of inner layer <b>24</b> and layer <b>28</b> for adhesive anchorage of outer layer <b>25.</b> Within inner layer <b>24</b> is the guidewire lumen <b>29</b> for the sliding fit of a guidewire exemplified by dotted line <b>30.</b>