Abstract:
An improved guidewire for assisting in implantation of a cardiac lead includes three sections. The most distal zone is sufficiently floppy to prevent trauma to the vessel walls through which the guidewire and lead are inserted. An intermediate zone is generally stiffer and has a cross-section less than or equal to the cross-section of the distal zone. The third zone is stiffer yet and is joined to the intermediate zone by a shoulder. The shoulder cooperates with protrusions on the lead to transfer forces between the guidewire and lead. A removal wire having temporary locking device to lock the removal wire to the lead is employed to remove the guide catheter without moving the lead from its desired location. Lubricious coatings are also provided to reduce friction between the lead and guidewire.

Description:
CROSS REFERENCE TO THE RELATED APPLICATION 
     This patent application is a continuation of application Ser. No. 09/466,266, filed Dec. 17, 1999, which is a continuation-in-part of application Ser. No. 09/164,891 filed Oct. 1, 1998 now abandonded, which was a continuation-in-part of application Ser. No. 09/097,101, filed Jun. 12, 1998, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The invention relates to the implantation and placement of cardiac leads used in combination with cardiac rhythm management devices, e.g., heart pacemakers or defibrillators, to monitor and control the rhythm of the heart. This invention is more particularly directed toward a guidewire/pacing lead configuration adapted to assist in the implantation and placement of a cardiac lead having one or more electrodes that are to reside in the distal branches of the coronary venous system, the great cardiac vein, or coronary sinus. The invention also encompasses the use of a guide catheter along with a guidewire and removal wire configurations useful in removing guide catheters without dislodging the implanted leads. 
     II. Discussion of the Prior Art 
     Placement of cardiac leads in the distal branches of the coronary venous system, the great cardiac vein, or the coronary sinus is a difficult task. Often when deploying the lead there comes a point at which the lead cannot be advanced further into the vascular system using standard techniques and equipment. All too often this point is not the optimal position for the lead&#39;s electrode, either for sensing cardiac electrical activity or delivering pacing therapy to the heart. 
     There are several reasons which make proper placement of the lead difficult. These include (1) friction between the vasculature and the lead; (2) partial obstruction of the vasculature; (3) unusually shaped bifurcations in the vasculature; and (4) accumulative friction between lead, guide catheter and guidewire. Prior efforts to resolve such problems included the use of a stiffer guidewire. While stiffer guidewires offer additional support, they may impede advancement due to their relative size with respect to the lumen of the lead. Additionally, when proper placement of the lead is achieved, problems arise during guide catheter or guidewire extraction. All too often, the act of extracting the guide catheter and/or guidewire causes the lead to be dislodged from the implanted position. Standard guidewires and stylets are not suitable for maintaining position while the guide catheter is removed due to insufficient stiffness, lack of appropriate force transmission features, and friction between the guidewire and lumen wall of the coronary vein lead. A means must be provided which will hold the lead and its corresponding electrodes in place while allowing the guide catheter and guidewire to be removed. 
     The present invention is deemed to be an improvement over conventional prior art guidewires. It is more effective in properly placing the lead and it is also less likely to cause a properly placed lead to become dislodged during extraction of the guide catheter and the guidewire itself. 
     SUMMARY Of THE INVENTION 
     In cases where the over-the-wire lead is to be implanted without the aid of a guide catheter, the guidewire may be of a uniform stiffness along its length except at a distal end portion where there is attached a floppy segment comprising a coiled wire helix having a very thin, flexible core member extending through the center of the helix and with the distal end of the core wire affixed to an atraumatic tip. The stiffness of the guidewire is designed to be less than the stiffness of the lead with which it is used. The lead is of the type having an elongated, flexible, polymeric lead body with a lumen extending the full length thereof from a proximal end to a distal end and of a cross-section allowing the guidewire to extend therethrough as the lead body is advanced over the guidewire in placing the lead&#39;s electrode(s) at a desired location within the patient&#39;s vasculature. 
     Because the lead has a somewhat greater stiffness property than its associated guidewire, there are greater frictional forces between the lead and the vessel in which it is placed than between the guidewire and the wall of the lead body defining the lead&#39;s lumen. Hence, the guidewire can be removed from the lead without dragging the lead with it. 
     In instances where a guide catheter is first advanced through a blood vessel and into the ostium of the coronary sinus before the guidewire is inserted and the lead advanced over the guidewire, it may become necessary to utilize a removal wire to hold the lead against movement as the surrounding guide catheter is removed subsequent to removal of the guidewire. The removal wire includes an element for engaging the lead and holding it stationary as the guide catheter is stripped free of the pacing lead body. 
     In accordance with a second embodiment of the present invention, there is provided a guidewire comprised of at least three zones. Each zone differs from the other two in terms of its stiffness and flexibility. Each zone also has geometric characteristics which assist in proper placement of the lead and further assist in preventing dislodgement of the lead as the guide catheter is extracted and as the guidewire itself is extracted. 
     Specifically, the first and most distal zone is intended to be very floppy to prevent trauma to the surrounding vessel walls when the guidewire is being advanced beyond the distal end of a guide catheter when deploying a coronary vein lead. This distal zone may include a spiral wound portion surrounding a thin, solid ribbon core and a spherical tip. The second zone is relatively more stiff than its adjacent distal section and may comprise a solid wire or spiral wound wire having a cross-sectional diameter that does not exceed the cross-sectional diameter of the first zone. The second and most proximal zone is preferably of a larger diameter and is somewhat stiffer than the first zone but not as stiff and flexible as the lead body in which it is inserted. The second zone comprises a wire or hypo tube which can be manipulated to apply advancement forces during deployment of the lead and stabilizing forces to a lead during extraction of the guide catheter. A diametric transition between the first and second zones is abrupt and ideally corresponds to a matching feature in the lead so that this transition is the point where most of the advancement forces and counter forces are transmitted to the lead. 
     In a third embodiment, a removal wire is provided which has a squared end for engaging a portion of the lead to hold it in place during guide catheter removal. The guide catheter easily disengages from the lead for withdrawal of the removal wire. 
     In yet another embodiment a three zone removal wire is used which extends beyond the length of the guide catheter, but does not exit the lead to frictionally hold the lead in place while removing the guide catheter. 
     In still another embodiment the three zone removal wire is provided with a temporary locking means to hold the lead in place while removing the guide catheter. The temporary locking means can be proximal, distal or both. The temporary locking means can also be along the length of the removal wire or in the lumen of the lead. 
     In a further embodiment the removal wire with the temporary locking means can be modified to have only one zone. 
     Other improvements also exist. For example, the improved guidewire (or portions thereof) can be provided with a hydrophilic coating to produce a highly lubricious surface. The presence of such a surface reduces friction between the lumen wall of the lead and the guidewire thereby reducing the risk that the lead will be dislodged during extraction of the guidewire. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The foregoing features, objects and advantages of the present invention will become more clear to those skilled in the art from the following detailed description of a preferred embodiment, particularly when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts. 
     FIG. 1 is a view showing an intravenous cardiac lead having an electrode positioned in a coronary vein, a segment of a guide catheter, a removal wire and a proximal end locking means; 
     FIG. 1A is a fragmentary view showing an alternative locking mechanism; 
     FIG. 1B is a fragmentary view showing a further alternative locking mechanism; 
     FIG. 2 is a perspective view of a preferred embodiment of a guidewire of the present invention; 
     FIG. 3 is a cross-sectional view of a cardiac lead with a guidewire of FIG. 2 positioned within the lumen of the lead; 
     FIG. 4 is a plan view of an embodiment of a removal wire made in accordance with the present invention; 
     FIG. 5 is a cross-sectional view of a cardiac lead surrounded by a guide catheter and with a removal wire of the type shown in FIG. 4 positioned within the lumen of the lead; 
     FIG. 6 is a cross-section of the distal zone of the guidewire shown in FIG. 1; 
     FIG. 7 is a cross-section of a guide catheter, lead and removal wire with a spherical tip and a temporary locking mechanism in the proximal zone; 
     FIG. 8 is a fragmentary side view of a removal wire with a bullet tip and a temporary locking mechanism in the intermediate zone; 
     FIG. 9 is a fragmentary side view of a removal wire with a tapered tip and a temporary locking mechanism in the distal zone; and 
     FIG. 10 is a partial side view of a removal wire having a proximal zone and a distal zone with a bullet tip and an expandable element as a temporary locking mechanism on a large portion of the length of the proximal zone of the removal wire. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a human heart  1  with a coronary lead  10  passing through the superior vena cava  2 , the right atrium  3 , and the coronary sinus  4  into the great vein  5  of the heart  1  so that an electrode  12  on the lead  10  is properly positioned in a branch of the coronary vein on the left sides of the heart. When positioned as shown, the electrode  12  can be used to either sense the electrical activity of the heart or to apply stimulating pulses to the left ventricle  7  without the electrode being positioned within the left ventricular chamber. A portion of a guide catheter  8  is used to insert the lead into the heart  1 . The present invention is concerned with guidewires and/or removal wires useful for placing leads  10  and their electrodes in the vasculature and for removing the associated guide catheter  8  and a guidewire  20  without dislodging the leads  10  and its electrode(s)  12 . As used herein, the term “guidewires” includes both the guidewires used to install the leads and “removal wires” also known as “removal wires” used for removing the guide catheter without moving the leads. In some embodiments disclosed herein the guidewires also function as removal wires and in others, a separate guidewire and removal wire is employed. 
     FIG. 2 shows a first preferred embodiment of a guidewire  20  advantageously used to position the coronary lead  10  as shown in FIG.  1  and retain the coronary lead in that position as the guide catheter  8  is removed. Guidewire  20  in FIG. 2 has three zones, a distal zone  22 , intermediate zone  24 , and a proximal zone  26 . As will be later described, a two zone guidewire can also be employed in the practice of the invention. 
     With continued reference to FIG. 2, the distal zone  22 , as best seen in FIG. 6, preferably may be about 1 to 1.5 inches long. The distal zone  22  is circular in cross-section and may have a cross-sectional diameter of approximately 0.014 inches. The distal zone  22  comprises an internal shapeable ribbon core member  28  (FIG.  6 ), a spiral winding  30  and a spherical tip  32 . The internal ribbon core member  28 , as it extends distally, may taper from about 0.005 inches to about 0.001 inches. This construction is sufficiently floppy such that there is no trauma induced by the guidewire to a surrounding vessel wall as the guidewire is advanced through the vasculature. This construction also allows it to be capable of being biased so as to aid in steering through the vasculature. 
     The intermediate zone  24  is generally slightly stiffer than the distal zone  22 . The intermediate zone may comprise a solid wire having a circular cross-section. The cross-sectional diameter of the wire can vary depending upon the performance needs, but should not exceed the cross-sectional diameter of distal zone  22 . The length of intermediate zone  24  can also vary, but preferably will be one to four inches long. 
     The proximal zone  26  is made of a wire or tubing and is the stiffest and longest section of the guidewire  20 . The proximal zone  26 , being the stiffest and most proximal, is the portion handled and used by the medical professional to apply forces during deployment and guide catheter extraction. Preferably, the overall length of the guidewire  20  will be in the range of four to five feet. The cross-sectional diameter of the proximal zone  26  is larger than the cross-sectional diameter of the distal zone  22  and the intermediate zone  24 . For example, if the distal and intermediate zones have a diameter of approximately 0.014 inches, the proximal zone could have a diameter of approximately 0.022 inches. The diametrical transition between the proximal and intermediate zones taper, though abruptly, from about 0.022 inches to about 0.014 inches. As discussed below, this diametrical transition constitutes a shoulder  34  through which most of the advancement and stabilizing forces are transmitted between the lead  10  and guidewire  20  during insertion of the guidewire  10  and extraction of the guide catheter  8 . The dimensions set out herein are intended to be illustrative, but not limitive. 
     FIG. 3 shows the guidewire  20  of FIG. 2 positioned within a lumen  14  of the coronary lead  10 . The lumen  14  preferably has a transition  16  which corresponds to the shoulder  34  of the guidewire  20 . When the shoulder  34  engages the transition  16 , advancement forces applied to the guidewire  20  during insertion of the guidewire  20  are transferred to the lead  10  through the shoulder  34  and transition  16  which is a reduction in lumen diameter. Similarly when the guide catheter  8 , FIG. 1, is extracted from the lead  20 , transition  16  is held in place by shoulder  34  the guidewire  20 . 
     FIGS. 4 and 5 show another embodiment of a guidewire  120 . This type of guidewire  120  is referred to herein as a removal wire or removal wire. It is ideally suited for use during removal of a guide catheter  8  to prevent lead displacement. After a guidewire is used to insert the lead, the guidewire is first withdrawn and replaced by a removal wire  120  that is inserted to retain the lead  10  in place during extraction of the surrounding guide catheter  8 . Again, the removal wire  120  of this embodiment may comprise three zones—a distal zone  122 , an intermediate zone  124 , and a proximal zone  126 . The removal wire  120  shown in FIGS. 4 and 5 is dimensioned somewhat in a fashion similar to the guidewire shown in FIGS. 2 and 3. The primary difference between the removal wire shown in FIGS. 4 and 5 and the guidewire shown in FIGS. 2 and 3 is that the distal tip  132  in FIGS. 4 and 5 are not attached to the core  128  by a solder joint. Also, the distal tip  132  of this embodiment is not intended to exit the distal end of the lead  10 , thus it is not shapeable or steerable in the vasculature nor is an atraumatic spherical tip required. Finishing wire  120  may be used to lock into the lead  10  and transmit force to the lead tip, but is only used in conjunction with the lead  10  during removal of the guide catheter  8 . The spiral wound wire in the intermediate zone  124  may be secured to the proximal zone  126  by a solder joint or by crimping. The direction of the winding  124  will preferably be opposite that of any winding  11  of the elongated conductor of lead  10  itself. This allows for better tracking through the central lumen  14  of the lead  10 . The distal zone  122  is a continuation of the spiral winding of the intermediate zone  124 . However, the diameter of the winding increases to form the distal zone  122 . The distal tip  132  of the coil which forms the intermediate end distal zones is cut square and not attached to a core wire or the like. Thus, as the guide catheter  8  is withdrawn, the square cut of tip  132  seats in the taper of the coil  11  of the lead  10  preventing the lead from withdrawing as the guide catheter  8  is pulled free. Furthermore, as the removal wire  20  is pulled free from the lead  10 , the square, unattached coil tip  132  slightly distends and easily frees itself from the tapered coil section  11  of the lead  10 . This feature allows for easy, predictable removal of the removal wire  120  from the lead  10 , thus preventing loss of purchase of the lead upon its withdrawal. 
     In other embodiments, a removal wire  220 ,  320  and  420 , as shown in FIGS. 7,  8 , and  9 , respectively, may be used to extract the guide catheter  8  while leaving the lead  10  and its electrodes in place. As shown in FIG. 7, the removal wire  220  is inserted into the lead  10  and extends some distance past the distal end of the guide catheter  8 , but short of the end of the lead  10 . Although FIG. 7 is shown with the catheter guide  8 , lead  10  and removal wire  220  in a concentric, collinear relation, when, inside of the heart, they really have a curved tortuous path. The catheter guide  8 , lead  10  and removal wire  220  will be in frictional contact with each other over a curved path. The lead  10  will be in frictional contact with the guide catheter  8  making it difficult to withdraw the guide catheter  8  without applying a force to the lead  10  that tends to withdraw the lead. It is desired to leave the lead in its originally placed position to maintain the optimal placement of the electrodes. The removal wire  220  is used to maintain the lead  10  in place while withdrawing the guide catheter  8 . Since the removal wire  220  extends beyond the length of the guiding catheter  8  the total frictional contact area between the removal wire  220  and the lead  10  will be greater than the frictional contact area between the guide catheter  8  and the lead  10 , thus the lead  10  will tend to stay in place as the guide catheter  8  is withdrawn, particularly if the removal wire  220  extends substantially past the end of the guide catheter  8  and is maintained stationary. Following removal of the guide catheter, the removal wire can be removed by extracting it from the lumen  14  of the lead  10  by simply pulling it out while holding the proximal end of the lead to prevent it from being dislodged from the position it had been placed in. 
     As shown in FIG. 7 the removal wire  220  has a spherical tip  50  for ease of inserting and withdrawing the removal wire  220  over the length of lead  10 . FIG. 8 shows a removal wire  320  having a bullet shaped tip  51  for ease of inserting and withdrawing the removal wire  320  in the lead  10 . FIG. 9 shows another embodiment of the removal wire  420  with a tapered tip  52 . The tips  50 ,  51  and  52  on the removal wires  220 ,  320  and  420  should be atraumatic tips to avoid punctures of the leads  10  and the veins in case the removal wire is allowed to exit the distal end of lead  10 . 
     In other embodiments the spherical tip  50 , the bullet tip  51  and the tapered tip  52  may be made to frictionally contact lead  10  to help hold the lead in place. 
     In the embodiments of FIGS. 7,  8  and  9  the removal wires  220 ,  320 , and  420  may have additional means  60  for temporarily locking to the lead  10  at the distal end of the lead  10  such that the guide catheter  8  can be removed without the lead  10  being dislodged. Any number of means for temporarily locking the lead  10  at the distal end of the removal wire may be employed. For example, in U.S. Pat. No. 5,011,482 to Goode et al., FIGS. 10 to  19  disclose expandable balloons, and radially expanding projections, such as deformable strips, radially expanding barbs, expanding sleeves, and off center (eccentric) cylinders on the removal wire for temporarily locking the removal wire onto the lead and holding the lead in place while a guide catheter is removed. In Goode et al U.S. Pat. No. 5,013,310 a wire is radially unwound for engaging the lead and locking the lead in place. In Pearson et al. U.S. Pat. No. 5,769,858 the distal end of the removal wire is bent into a J-shape hook at the distal end for engaging the lead and holding it in place while the guide catheter is removed. These patents show some means, but not the only means, for temporarily locking the distal end of the removal wire to the lead. U.S. Pat. Nos. 5,769,858, 5,013,310 and 5,011,482 are hereby incorporated herein by reference. 
     Alternatively, the removal wires  20 ,  120 ,  220 ,  320 , and  420  in the several embodiments may have a means of temporarily locking to the lead  10  at the proximal end of the lead, as at locking connection  80  shown in FIG. 1 abutting the proximal end of the terminal pin  70 , such that the lead  10  will be held in place while the guide catheter  8  is removed by slipping it back over the locking connection  80 . In another embodiment shown in FIG. 1A, the locking connection  80 ′ comprises a suture  81  where the suture affixed to the removal wire  20  is made to abut the proximal end of the leads terminal pin  70  to hold the lead in place as the guide catheter  8  is removed. In another embodiment, the locking connection  80  can be achieved by slipping a short length of hypo tubing over the removal wire and bonding or welding the two together, such that he distal end of the hypo tube  80 ′ creates a shoulder that abuts the free end of terminal pin  70 . See FIG.  1 B. In still other embodiments the terminal pin  70  may have a collet or other temporary locking device for engaging and holding the lead  10  in place on the removal wire. The locking element must be sufficiently small in size to allow the guide catheter to strip over it. In some embodiments, both the distal temporary locking mechanism  60  and the proximal temporary locking mechanism  80  can be used simultaneously. 
     Although the removal wires  20 ,  120 ,  220 ,  320  and  420  shown in the various figures may be of the three-zone design, they need not necessarily have a distal zone  22  which is designed to be very flexible since the removal wire need not exit the distal end of the lead. Similarly the removal wires may not need an intermediate zone  24  since the flexibility inside of the lead is not as much of an issue as when the guidewire and the lead were in the vein without a guide catheter. However, the removal wires have to be flexible enough to snake their way through the lead  10  without damaging the lead or exiting the lead and damaging the vein in which the lead is located. The removal wire may have one continuous zone for this purpose. The distal tips may be of the spherical, bullet or tapered designs. Such removal wires may have just a single zone, or both a proximal zone and a flexible distal zone, or a proximal zone, an intermediate zone, and a flexible distal zone. 
     For removal wires  20 ,  120 ,  220 ,  320 ,  420  with a distal zone  22 , a intermediate zone  24  and a proximal zone  26  a temporary locking means  60  is preferably used in the proximal zone  26  for greatest locking stability and stiffness. However the temporary locking means  60  may be in the distal zone  22  or the intermediate zone  24 . 
     In another embodiment shown in FIG. 10, the entire length or a predetermined portion of the removal wire  20  within the lead can be expanded, such as with a braided element  90 , to temporarily lock the removal wire  20  securely to the lead. The element  90  acts like so-called “Chinese handcuffs”. It expands by contracting the braided wire mesh material along its length by moving the edge  95  thereof in direction  97 . The radius of the braided element thereby increases to provide a large surface contact area and, thus, firm grip on the lead  10 . The braided element  90  is radially retracted by pulling the braided element at the edge of the element  95  in direction  96 . In this manner the removal wire is unlocked from the lead. A braided element  90  may be of a shorter length and be used as the temporary locking means  60  in the embodiments of FIGS. 7,  8 , and  9 . 
     In all of the embodiments, a hydrophilic coating can be applied to create a surface  21  (FIG. 3) on the guidewire  20  that is highly lubricious. Alternatively, all surfaces of guidewire  20  can be coated with a hydrophilic coating, of polytetrafluoroethylene (PTFE), or some other dry lubricious material, i.e. silicone film. This serves to reduce friction between the guidewire  20  and lead lumen  14  of the lead thereby reducing the risk that the lead  10  will be dislodged from its proper position as the guidewire  20  is extracted.