Abstract:
A flexible, thin implantable electrode lead can maintain a desired portion of a lead body ( 14 ) in a desired shape conforming to a body portion. The lead body ( 14 ) includes a conductor coil ( 30 ) obtained by helically winding at least one insulation-coated electrical conduction conductor wire, an insulating sheath ( 32 ) made of an electrically insulating resin material and covering the outer surface of the conductor coil, and a flexible reinforcing tube ( 40 ) formed to deform into a desired shape in the cavity of the conductor coil.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an implantable electrode lead and, more particularly, to a technique for forming a predetermined portion of the lead body of an atrial lead into a desired shape such as a “J” shape in order to use the implantable electrode lead together with, e.g., a heart pacemaker or implantable defibrillator. 
     BACKGROUND OF THE INVENTION 
     Many conventional implantable electrode leads used together with heart pacemakers and implantable defibrillators are known. An implantable electrode lead is generally comprised of at least one electrode for supplying an electrical stimulation pulse or sensing an electrical evoked response of the heart, an electrical connector for connecting the electrode lead to a heart pacemaker or implantable defibrillator, and a lead body inserted between the electrode and the electrical connector and made up of a biocompatible insulating sheath and a conductor coil for transmitting an electrical signal between the electrode and the heart pacemaker or implantable defibrillator. 
     In an electrode lead for cervical vein, the distal-end electrode is indwelled in the heart via the vein, and the proximal-end electrode is connected to the connection housing of the heart pacemaker or implantable defibrillator. The implantable electrode leads are classified into atrial and ventricular leads. The ventricular lead electrode is generally indwelled in the apex of the right ventricle, while the atrial lead electrode is generally indwelled in the right atrial auricle. The atrial lead has a J-shaped portion near its distal end to facilitate indwelling of the electrode in the auricle. A general means for imparting the J shape to the atrial lead is comprised of an insulating sheath or conductor coil serving as a constituent element of the lead body. As a means for imparting the J shape to the atrial lead, a separate reinforcing member is disposed to impart the J shape or to hold the J shape in one or both of the insulating sheath and the conductor coil. The implantable electrode lead has a cavity for receiving a stylet. When the stylet reaches the J-shaped portion at the distal end of the atrial lead, the distal end of the atrial lead follows the shape of the distal end of the stylet. When the stylet is retracted to the proximal-end side, the distal end of the atrial lead restores the J shape. The atrial lead electrode is indwelled in the atrial auricle using such stylet movement. 
     Imparting a desired shape to the implantable electrode lead is not limited to the J shape of the atrial lead. Japanese Patent Laid-Open No. 5-49701 to Nakajima discloses a technique for forming a special shape such as a desired helical shape in the lead body. 
     SUMMARY OF THE INVENTION 
     As one of the state-of-the-art means for imparting the J shape to an atrial lead, the J shape is imparted to a constituent element of a lead body. To increase the rigidity of the insulating sheath or conductor coil, however, the outer diameter of the lead body increases, and flexibility of the whole lead body degrades. An increase in outer diameter of the lead body may cause hemostasis. The lack of flexibility of the lead body increases the mechanical stress inflicted on a living body by the lead body. 
     It is difficult to obtain a sufficient retaining force for maintaining the J shape in a thin flexible silicone atrial lead. It is therefore considerably difficult to indwell the electrode in the atrial auricle. According to the conventional method of imparting the J shape to a constituent element of a lead body, when a lead structure described in Japanese Patent Laid-Open No. 11-333000 proposed to improve the durability of the lead body is applied to an atrial lead, it is difficult to obtain a sufficient retaining force for maintaining the J shape. 
     For example, U.S. Pat. No. 4,454,888 discloses a case in which a metal wire is used as a separate reinforcing means to reinforce the J shape. According to this disclosure, when the metal wire breaks, the metal wire bores into the insulating sheath to the outside, thus posing problems as to safety and reliability. 
     The present invention has been made in consideration of the conventional problems described above, and has as its object to provide an implantable electrode lead which can have a small diameter with flexibility and can maintain a desired portion of a lead body to a desired shape conforming to a predetermined portion of a living body. 
     In order to solve the conventional problems described above and achieve the above object, according to the present invention, an implantable electrode lead having a lead body for performing at least one of transmission of an electrical stimulation pulse generated by an implantable device to a living body and transmission of an electrical signal from the living body to the implantable device, the lead body having at least one electrode at a distal end thereof, and connector for mechanically and electrically connecting a proximal position of the lead body to the implantable device, characterized in that the lead body comprises a conductor coil obtained by helically winding at least one insulation-coated electrical conduction conductor wire and an insulating sheath made of an electrically insulating resin material to cover an outer surface of the conductor coil, and a flexible reinforcing tube shaped to deform into a desired shape is disposed in a cavity of the conductor coil, thereby maintaining a predetermined portion of the lead body in the desired shape. 
     According to an aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the predetermined portion is located near a distal end of the lead body, and the desired shape is a substantially J shape. 
     According to another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the reinforcing tube is made of a predetermined resin material containing polyimide. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that rigidity of the reinforcing tube is higher than rigidity of a combination of the coil and the insulating sheath. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the reinforcing tube is formed into the desired shape beforehand prior to assembly. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that after the reinforcing tube is disposed in the cavity of the coil in a straight state, the reinforcing tube is shaped to obtain the desired shape. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the distal end of the reinforcing tube is connected to the electrode, and a proximal end of the reinforcing tube is connected to the connector. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the lead body has a size of not more than 2 mm, the insulating sheath is made of an electrically insulating, flexible resin material having a Shore hardness of less than 80 A, and the conductor coil has a spring index D/d (average diameter of coil/diameter of conductor wire) of more than 7.8. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the conductor coil comprises a multi-wire coil obtained by winding a plurality of insulation-coated conductor wires in the same average diameter. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the conductor wire comprises a multi-wire coil and the electrode is divided into a plurality of electrode portions such that one of wires of the multi-wire coil transmits one electrical signal and remaining ones of the multi-wire coil transmit remaining electrical signals. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that an insulation coating of the conductor coil is made of fluoroplastic. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the conductor wire has a composite or cladding structure of a first metal material having a low resistivity and a second metal material excellent in corrosion resistance and mechanical characteristics. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that a cavity for receiving a straight stylet is formed in the reinforcing tube, the stylet is inserted into the cavity to deform the desired shape of the predetermined portion of the lead body into a linear shape, and the desired shape is then restored by removing the stylet. 
     According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the implantable electrode lead is applicable to the implantable electrode lead described in Japanese Patent Laid-Open No. 11-333000, and a flexible reinforcing tube formed into a desired shape is disposed in the cavity of the coil to form the predetermined portion of the lead body in the desired shape. 
     With the above arrangements, a flexible, thin implantable electrode lead can provide reinforcing means for forming the predetermined portion of the lead body into a desired shape. Since the reinforcing means is comprised of a tube and disposed in the cavity of the coil, a danger of the reinforcing means boring into the insulating sheath to the outside can be prevented. In addition, when the reinforcing means is imparted with, e.g., the J shape of an atrial lead, the atrial lead can have better operability. Movement and removal of the electrode upon surgical operation can be prevented. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a state in which an implantable electrode lead (atrial lead) is indwelled in the atrium; 
     FIG. 2 is a view showing the outer appearance of an atrial lead according to the first embodiment; 
     FIG. 3 is a sectional view taken along the line A—A of FIG. 2; 
     FIG. 4 is a front view showing a state in which a portion B in FIG. 2 is removed; 
     FIG. 5 is a front view of a flexible reinforcing tube; and 
     FIG. 6 is a view showing the outer appearance of an implantable electrode lead according to the second embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     [First Embodiment] 
     This embodiment exemplifies a case in which the structure of an implantable electrode lead of the present invention is applied to the J shape generally formed near the distal end of an atrial lead. The present invention is not limited to this. An arbitrary shape can be set in any portion. 
     FIG. 1 shows a state in which an atrial lead  10  as the implantable electrode lead is indwelled in the atrium. As shown in FIG. 1, a tip electrode  16  of the atrial lead  10  is indwelled in a right atrial auricle  2 . 
     FIG. 2 is a front view showing the entire outer appearance of an atrial bipolar lead. Referring to FIG. 2, the atrial lead  10  is mainly comprised of a connector  12 , lead body  14 , tip electrode  16 , and ring electrode  17 . A fixing tool  20  is attached near the tip electrode  16  to fix the lead on the endocardium. 
     A sutural sleeve  22  is attached to the lead body  14  at an illustrated position. To fix the lead body  14  to tissue, the lead body  14  is not directly sutured to the tissue, but the outer surface of the sutural sleeve  22  is sutured to the tissue to protect the lead body  14 . A predetermined section near the distal end of the lead body has a J shape, as shown in FIG.  2 . 
     FIG. 3 is a sectional view taken along the line A—A in FIG.  2 . The lead body  14  has an insulating parallel winding structure comprised of a coil  30  and an insulating sheath  32  covering the outer surface of the coil and having electrical insulating properties. The coil  30  is formed by helically winding two-layered conductor wires  33   a  and  33   b  covered with an insulating coating  31 . A flexible reinforcing tube  40  having a cavity  40   a  for receiving a stylet (to be described later) is fitted in the cavity of the coil  30 . 
     The outer diameter of the lead body  14  is 2 mm or less, and the insulating sheath  32  is made of a flexible, electrically insulating resin material having a Shore hardness of less than 80 A. A spring index D/d (average diameter of coil/diameter of conductor wire) of the coil  30  is preferably set to be larger than 7.8, thereby greatly improving the bending durability of the lead body  14  and at the same time advantageously assuring a large cavity. 
     The lead body in the conventional bipolar lead generally has a coaxial structure in which the insulating sheath and conductor coil are arranged coaxially. Note that the coaxial structure, however, makes it difficult to form a desired shape when a flexible reinforcing tube is inserted in the cavity (stylet cavity) because the rigidity of the lead body itself is lower than that of the flexible reinforcing tube. 
     The conductor wire preferably has a composite or cladding structure made up of a first metal material  33   a  having a low electrical resistivity and a second metal material  33   b  excellent in corrosion resistance and mechanical characteristics. Examples of this wire structure are DFT (Drawn Filed Tubing) and DSB (Drawn Brazed Strand). It is preferable that silver be used as the first metal material, and a cobalt-based alloy such as MP35N be used as the second metal material. 
     FIG. 4 is a detailed view showing a state in which a portion B in FIG. 2 is partially removed. Referring to FIG. 4, the flexible reinforcing tube formed into a J shape is disposed in the cavity of the coil  30 . This allows maintaining the J shape of the lead body  14  and increasing the retaining force for the J shape. 
     The material of the flexible reinforcing tube  40  is preferably a relatively hard resin material. Polyimide is selected as the material of the flexible reinforcing tube  40 . A stylet  50  can be inserted into the cavity of the flexible reinforcing tube  40 . In implanting the lead, the stylet  50  is inserted to the distal end of the lead body  14  to deform the lead body  14  into a straight shape, as indicated by the dotted line in FIG.  4 . The stylet  50  is retracted toward the proximal end side upon indwelling the fixing tool  20  in a desired portion, so that the lead body  14  restores the original J shape. 
     The flexible reinforcing tube  40  has a cavity and disposed in the cavity of the coil  30 . There is a very low possibility of the end face of the flexible reinforcing tube  40  boring into the lead body  14  to the outside through the coil  30  and insulating sheath  32 . 
     FIG. 5 is a front view of the flexible reinforcing tube  40 . As shown in FIG. 5, the flexible reinforcing tube  40  is made up of a straight portion  42  indicated by an arrow  42   a  starting from the distal end, a straight portion  44  indicated by a proximal-end arrow  44   a , and an arcuate portion  46  indicated by an arrow  46   a  located between the distal end and proximal end, thereby forming a J shape. The straight portion  42  preferably has a length within the range of 0 mm to 50 mm; and the straight portion  44 , 10 mm to 100 mm. The arcuate portion  46  preferably has a radius within the range of 2 mm to 20 mm. The curvature of the arcuate portion  46  may continuously or discontinuously change. 
     The distal end of the flexible reinforcing tube  40  can be connected to the distal end of the lead body  14 , and the proximal end of the flexible reinforcing tube  40  may be connected to the end of the lead body  14 . In this manner, the flexible reinforcing tube  40  can extend throughout the lead body  14 . This increases the rigidity of the entire lead body. Since the rigidity of the lead body is uniformly distributed, the stylet can be very easily guided to the portion having a desired shape. 
     In a state prior to assembly of the implantable electrode lead of this embodiment, the shape of the flexible reinforcing tube  40  is not necessarily the same as the desired shape required for the finished product. That is, the flexible reinforcing tube  40  may be combined with the insulating sheath  32  and coil  30 , and the resultant structure may be formed into a desired shape. 
     The bending rigidity of the insulating sheath  32  and coil  30  is determined to be much lower than that of the flexible reinforcing tube  40  to easily obtain a desired shape of the lead body  14 . That is, unlike the conventional case, the insulating sheath  32  and coil need not be formed into a desired shape beforehand. Alternatively, the insulating sheath  32  and coil  30  are formed into a desired shape at a portion where the flexible reinforcing tube  40  is located. This can increase the shape-retaining force. 
     Since the flexible reinforcing tube  40  is made of a resin, its rigidity inevitably decreases upon receiving long-term bending stress in the living body. However, no problem is posed even with a decrease in rigidity due to the following reason. The implantable electrode lead implanted in the living body for a long period of time is covered with tissue around the fixing tool  20 , and movement and removal of the electrode can be prevented accordingly. 
     The flexible reinforcing tube  40  can be made of a thermoplastic resin material. In this case, in the assembly process, the flexible reinforcing tube  40  is set in the coil  30  in a straight state. In one or both of during and after the assembly, the thermoplastic reinforcing tube can be heat-treated to impart a desired shape to the lead body. 
     [Second Embodiment] 
     As in the first embodiment, a desired shape can be formed intermediate portion along a lead body  14 , as shown in the front view of FIG.  6 . This can facilitate contact between the electrode and the cardiac muscle in a single lead or the like. 
     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. 
     As described above, according to the present invention, a desired portion of the lead body of a flexible, thin implantable electrode lead can be formed into a desired shape. The reinforcing tube serving as the reinforcing means is comprised of a flexible tube and disposed in the cavity of the coil. The flexible tube can be prevented from boring into the insulating sheath to the outside. The reinforcing tube is formed into a J shape for an atrial lead. This can improve operability of the atrial lead and prevent movement and removal of the electrode upon surgical operation. 
     As has been described above, according to the present invention, there can be provided a flexible, thin implantable electrode lead capable of maintaining a desired portion of the lead body in a desired shape.