Patent Publication Number: US-8532791-B2

Title: Medical pacing wires

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/451,104, entitled Medical Pacing Wires, filed Mar. 9, 2011, which is hereby incorporated herein in its entirety. 
    
    
     BACKGROUND 
     Cardiac surgical procedures have become very common worldwide. By some estimates, 700,000 are performed annually in the USA. Despite their complexities, the risk associated with these procedures has steadily declined over the years. However, the temporary pacing wires that are placed on essentially every heart at the completion of the procedure have not improved their safety profile in close to two decades. As a matter of fact, surgeons continue to use temporary pacing wires that were designed in 1992. These temporary pacing wires/leads, when removed several days post-operatively, continue to pose a significant risk of bleeding to the patient. Such bleeding could lead, in about 1% of cases, to tamponade and even death. These devices are so hazardous that some surgeons prefer to refrain from using them rather than expose the patient to the bleeding risks. 
     Several different prior art pacing wires will now be discussed for background purposes. In various prior art pacing wires, a distal end of the pacing wire is secured to the heart with a suture. A few days later, the pacing wire is removed by pulling on the proximal end of the wire, which is outside the patient&#39;s chest, in essence tearing the tissue attached to the distal end and pulling it through the chest wall. The major complication of such a system is the potential bleeding complications that may ensue by ripping a portion of the heart tissue in order to dislodge the sutured distal end of the device. Another minor, yet annoying, feature of this prior art pacing wire is encountered if the surgeon decides to lift the heart and inspect it after securing the pacing wire in place. In such cases, he or she will often dislodge/rip the distal end of the pacing wire off of the patient&#39;s heart, and must then reattach the device to the heart. This may lead to intraoperative bleeding that can make the surgery more difficult to complete. Another shortcoming of this device is that, when securing the distal electrode to the heart with a suture, bleeding may occur from the suture itself as the suture passes into the heart tissue. In such cases, additional sutures may be required to stop the bleeding. 
     In other prior art pacing wires, the pacing wire&#39;s distal pacing electrode is driven into, rather than sutured to, the heart tissue. In such pacing wires, the distal electrode is attached to a helical suture that has a curved needle at one end. The curved needle is driven into the heart and pulled through until the distal electrode is embedded within the heart tissue. The curved needle and a portion of the helical suture are then cut leaving the distal electrode positioned inside the heart tissue. A few days later, the pacing wire is removed, by pulling on the proximal end of the wire/lead that is outside the patient&#39;s chest. In this case, instead of tearing the tissue that is attached to the distal end of the pacing wire, and pulling the distal electrode through the chest wall, the distal electrode slips out of the myocardium/tissue of the heart and is removed. Unfortunately, however, bleeding can still occur from the tract evacuated by the electrode and attached wire with all of the associated morbid consequences including death. Furthermore, this arrangement is also subject to all of the other shortcomings that plague the prior art arrangement discussed above in terms of dislodgement and bleeding associated with resecuring the electrode to the heart. 
     Yet another prior art pacing wire arrangement calls for securing a permanent clip to the heart that has an antenna (in the form of two parallel rabbit ears), or a round receptacle through which a pacing wire may be introduced. The problems with this design are multifold. First, since the electrode and pacing wire are loosely attached together, the potential for the wire to dislodge from the electrode antenna in such a way as to stop pacing is very high as a result of: (1) the beating of the patient&#39;s heart; (2) the patient&#39;s movements; or (3) the patient&#39;s respiratory fluctuations. Also, the permanent electrode is disadvantageously left on the heart permanently. In addition, securing the electrode to the heart poses the risk of causing bleeding as described above in regard to the arrangements of  FIGS. 1 and 2 . Lastly, disengaging the wire from the permanent electrode could potentially be hazardous. 
     In brief, currently known cardiac pacing wires continue to present significant hazards to patients. Accordingly, there is a need for improved, safer cardiac pacing wires. 
     SUMMARY 
     A medical pacing wire according to various embodiments comprises: (1) an elongated flexible conductor (e.g., an insulated wire with two stripped ends that serve as electrodes, or any other suitable conductor); (2) a clamp attached to the flexible conductor&#39;s distal end; and (3) a needle (e.g., a Keith needle) that is attached to the flexible conductor&#39;s proximal end. In particular embodiments, the Keith needle is scored for easy removal. 
     In various embodiments, the clamp includes first and second opposing clamp members and a grip portion that may be used to move the clamp between: (1) an open position in which the first and second clamp members are spaced a first distance apart from each other; and (2) a closed position in which the first and second clamp members are spaced a second distance apart from each other, the second distance being shorter than the first distance. The medical pacing wire may be adapted to allow a user to attach an electrode to a living tissue by: (1) moving the clamp into the open position; (2) positioning the clamp so that the living tissue is positioned between the clamp&#39;s first and second opposing clamp portions; (3) closing the clamp until the first and second clamp portions are in the closed position and exert opposing compressive forces on opposite sides of the living tissue and thereby maintain the electrode in engagement with the living tissue. 
     In various embodiments, the clamp is adapted to allow a user to remotely cause the clamp to at least substantially release the living tissue without substantially damaging the tissue. For example, the clamp may be made of a material, such as a metal shape alloy, that is configured to change its shape in response to being exposed to a particular change in temperature or to an electric current. As one example, the clamp is made of a memory shape alloy, such as Nitinol, that is adapted: (1) to remain in the shape of a clamp at standard animal body temperatures; and (2) to relax into the form of a flexible wire in response to being cooled to a temperature that is a few degrees below standard animal body temperatures. This may allow a user to remotely release the clamp from the living tissue (e.g., without substantially damaging the living tissue) by simply subjecting the proximal end of the pacing wire to an appropriate change in temperature. The user may then withdraw the distal end of the pacing wire from the individual&#39;s body in the form of a low-profile, flexible wire rather than in the form of a clamp. 
     In a particular embodiment, the pacing wire may include a clamp and an actuator, the actuator being adapted to respond to a change in temperature to bias the clamp towards an open position from a closed position. In another embodiment, the pacing wire may include a physical mechanism (similar to a bike brake cable) that is adapted to allow a user to remotely open and close the clamp from outside a patient&#39;s body while the clamp is attached to tissue inside the patient&#39;s body. 
     To use the pacing wire to pace a user&#39;s heart, a user (typically a cardiac surgeon): (1) passes the Keith needle and the proximal end of the pacing wire through the patient&#39;s chest wall and skin; (2) attaches the clamp to a portion of the patient&#39;s heart; (3) snaps the Keith needle off at a score line on the Keith needle; and (4) connects the proximal end of the pacing wire to a pacemaker. The pacemaker is then used to pace the patient&#39;s heart by sending periodic electrical pulses to the heart through the pacing wire. 
     Once a physician determines that the patient&#39;s heart no longer requires pacing, a user may remove the pacing wire by detaching the clamp from the patient&#39;s heart, and then removing the clamp through the patient&#39;s chest wall. In the case of a pacing wire that has a clamp made from a memory shape alloy, this may be done, for example, by subjecting the proximal end of the pacing wire to a change in temperature (e.g., by submerging the proximal end of the pacing wire in liquid nitrogen). In this example, due to the wire&#39;s thermal conductivity, the clamp&#39;s temperature will soon decrease, which will, in turn, cause the wire forming the clamp to relax from its clamp shape into the shape of a flexible wire. In another example, the change in temperature may be affected by subjecting the pacing wire to a voltage, which may cause the clamp&#39;s temperature to increase, which will in turn, cause the wire forming the clamp to relax from its clamp shape. A user may then remove the wire from the patient&#39;s body through the patient&#39;s chest wall. 
     In other embodiments, the clamp may be made from a superelastic material and the pacing wire may further comprise an actuator in mechanical contact with the clamp. In such embodiments, the actuator may be made of a memory shape alloy adapted to change its shape in response to a change in temperature. In various embodiments, the change in shape may cause the actuator to bias the clamp to an open position, allowing a user to remove the clamp from a piece of tissue to which it was clamped. 
     In the various embodiments in which a more traditional mechanical clamp is used (which is configured to be remotely opened and closed via suitable mechanical or electromechanical means), the operator simply: (1) uses the mechanical or electromechanical control mechanism to release the clamp from the patient&#39;s heart; and (2) withdraws the wire (including the clamp) through the patient&#39;s chest wall. For example, in a particular embodiment in which a bike brake cable is used to remotely control the opening/closing of the clamp, the user may: (1) open the clamp by pushing on the end of the brake cable; and then (2) withdraw the wire and the clamp from the patient&#39;s body through the patient&#39;s chest wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described various embodiments in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  is a schematic diagram of a cardiac pacing wire according to a particular embodiment. 
         FIG. 2  is a top view of a cardiac pacing wire according to another embodiment. 
         FIG. 3  is a schematic diagram of a pacing wire according to a further embodiment. 
         FIG. 4  is a schematic diagram of a pacing wire according to yet another embodiment. 
         FIG. 5  is perspective view of a pacing wire according to a further embodiment. 
         FIG. 6  is a top view of the pacing wire of  FIG. 5  with the pacing wire&#39;s clamp in an open position. 
         FIG. 7  is a top view of the pacing wire of  FIG. 5  with the pacing wire&#39;s clamp in a closed position. 
         FIG. 8  is a side view of the pacing wire of  FIG. 5  with the pacing wire&#39;s clamp in the open position. 
         FIG. 9  is a perspective view of a pacing wire according to yet another embodiment. 
         FIG. 10  is a top view of the pacing wire of  FIG. 9  with a clamp in an open position. 
         FIG. 11  is a top view of the pacing wire of  FIG. 9  with the clamp in a closed position. 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     Various embodiments now will be described more fully hereinafter with reference to the accompanying drawings. It should be understood that the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     Various pacing wires described herein provide improvements over prior art pacing wires. Although, in various examples within this patent application, we refer to the heart as the primary organ being paced, it should be understood that the pacing wires described herein may be used to pace human or animal tissue other than the heart. For example, various embodiments may be used to pace a patient&#39;s central or peripheral nerves and/or the patient&#39;s brain. It should be understood that the clamp-shaped distal electrode (as described subsequently) can be configured to any other suitable shape to accommodate various surface areas of different organs. 
     A pacing wire  10  according to a particular embodiment is shown schematically in  FIG. 1 . In this embodiment, the pacing wire  10  includes an elongated flexible conductor  300  that may comprise, for example, a single filament conductor (or, alternatively, a multi-filament conductor) that is insulated except for its proximal end  200  and distal end  400  (which serve as electrodes). The pacing wire  10  further comprises a Keith needle  100  that is attached to the flexible conductor&#39;s proximal electrode  200  and that is scored for easy removal. 
     The flexible conductor&#39;s non-insulated distal end  400  comprises a wire (or other structure) that has been engineered and manufactured to assume a certain shape of a clamp as shown, for example, in  FIG. 2 . It should be understood that the flexible conductor&#39;s non-insulated distal end may be a continuous portion of the flexible conductor  300  or it may be separate wire (or other structure) that is suitably attached to the flexible conductor  300 . 
     In the embodiment shown in  FIG. 2 , the clamp  400 A (which may, for example, consist essentially of one or more shape metal alloys) is a single wire that is shaped to form two, substantially parallel, substantially planar, substantially triangular, clamp portions (e.g., first clamp portion A-B-C  420 A and second clamp portion A 1 -B 1 -C 1    430 A) that are positioned adjacent a grip  410 A that includes wire portions G and H. 
     In  FIG. 2 , the first clamp portion A-B-C  420 A is in contact with the second clamp portion A 1 -B 1 -C 1    430 A and both of these wire loops are in an XY plane. Wire portions G and H are in a plane ZY that is substantially perpendicular to the XY plane. As a result, a user may selectively separate the clamp portion&#39;s respective distal edges (B-C and B 1 -C 1 ) from each other by compressing wire portions G and H together (e.g., using a suitable clamp or a thumb and index finger). 
     Various portions of a pacing wire  10 E according to an alternative embodiment are shown in  FIG. 5 . In this embodiment, the clamp  400 E (which may, for example, consist of or consist essentially of one or more shape metal alloys) includes: (1) a substantially planar (e.g., planer), substantially tear-shaped (e.g., tear-shaped) first clamp portion  420 E; (2) a substantially planar (e.g., planar), substantially tear-shaped (e.g., tear shaped) second clamp portion  430 E that is substantially parallel (e.g., parallel) to the first clamp portion; and (3) a grip  410 E that is substantially in the form of an oval.  FIG. 7  shows the pacing wire  10 E from  FIG. 5  in a closed position, in which the first clamp portion  420 E is in contact with the second clamp portion  430 E and both clamp portions are in an XY plane. However, the grip  410 E is in the XZ plane, which is substantially perpendicular to the XY plane. As a result, a user may selectively separate the clamp portion&#39;s respective distal edges from each other by compressing the grip  410 E together (e.g., using a suitable mechanical device or a thumb and index finger). 
     In the embodiments shown in  FIGS. 2 ,  5 , and  6 , a user may attach the pacing wire&#39;s clamp  400  to a portion of a patient&#39;s heart by squeezing the clamp&#39;s grip  410  which causes the clamp&#39;s opposing clamp portions  420 ,  430  (the clamp&#39;s “jaws”) to open. The user then positions the clamp  400  so that a small piece of heart tissue is positioned between the clamp&#39;s opposing clamp portions  420 ,  430 . The user then slowly releases the clamp  400  (which is mechanically biased to urge the opposing clamp portions  420 ,  430  towards each other), until the clamp  400  firmly grasps a small amount of the heart&#39;s tissue. In various embodiments, no holes are created in the heart which may minimize or entirely eliminate any bleeding associated with attaching the clamp  400  to the heart. In particular embodiments, the jaws of the clamp  400  are engineered to apply enough pressure to hold the tissue non-ischemically, yet firmly enough to prevent slippage. 
     By virtue of its design and material composition, in various embodiments, the clamp  400  can be applied and removed multiple times during an operation without injuring the heart or losing the clamp&#39;s grasping power. In particular embodiments, the proximal end of the pacing wire  10  sits outside the chest and allows a user to pace the heart if and when rhythm disturbances occur. 
     When it is time to remove the temporary pacing wire  10 , the pacing wire&#39;s proximal electrode  200  can then be used to make the distal electrode  400  of the pacing wire, which is shaped as a clamp, change shape and configuration and become a loose, unshaped (e.g., substantially straight) wire. This releases the heart tissue from the clamp&#39;s grasp and preferably allows for an atraumatic disengagement of the clamp  400  and removal of the pacing wire  10  from the patient&#39;s chest. 
     As noted above, a user may selectively change the shape of the clamp  10  from a clamp configuration to a loose wire configuration by applying an energy source to the proximal end electrode  200  of the pacing wire  10 , which sits outside the patient&#39;s chest. The energy source may for example, cause a change of the wire temperature of only a few degrees above or below what can be considered normal body temperature range. In particular embodiments, the temperature range (which may be any suitable temperature range) that makes the clamp-shaped wire assume a more natural straight wire configuration is determined, for example, by the composition of elements that constitute the SMA wire. 
     One suitable energy source would be one that causes a drop in temperature of the wire by a few degrees below normal body temperature. This can be achieved by safely immersing the proximal electrode of the wire in a cold material, such as liquid nitrogen, for few seconds causing transmittal of the cold from one end of the pacing wire (which is outside the patient&#39;s chest) to the other end of the wire, which is positioned within the patient&#39;s chest. After a predetermined contact time with the energy source (e.g., 10-20 seconds) cooling of the distal end  400  by a few degrees is achieved and the distal end wire  400  will denature, lose its grip on the heart, and become flexible enough to be removed at least substantially atraumatically from the patient&#39;s body. 
     Another example of a suitable energy source would be one that would heat the wire to a temperature that would be sufficient to cause the wire to change configuration. For example, bringing a heating filament into contact with the pacing wire&#39;s proximal electrode  200  for a short period time (e.g., 10-20 seconds) may cause sufficient heat to be transmitted to the clamp  400  to cause clamp  400  to denature, lose its grip on the heart, and become flexible enough to be removed at least substantially atraumatically from the patient&#39;s body. Yet another example of a suitable energy source that may heat the wire to a temperature sufficient to change its configuration may be introducing a voltage across the pacing wire. 
     As noted above, in further embodiments, other mechanical arrangements may be used to selectively disengage more traditional clamps that may, for example, not be made of materials that change form in response to changes in temperature. Two such embodiments are shown in  FIGS. 8 and 9 . 
     Combination Medical Pacing Wire Clamp 
     In various embodiments, it may desired for the pacing wire&#39;s clamp  400  to have two-way motion. In such embodiments, the clamp  400  may have two stable positions. In a first stable position, the clamp  400  may provide a substantially firm and safe connection to a tissue (e.g., a heart tissue). In a second stable position, the clamp  400  may be released from the tissue before a user removes the clamp  400  from a tissue and eventually from a patient&#39;s body with which the tissue is associated. This configuration involving at least two stable positions and two-way motion may be achieved by combining two shape memory alloy elements, two superelastic alloy elements, a mix of at least one superelastic alloy element and one shape memory alloy element, or any other suitable combination of materials. Each of the two elements may provide motion towards either an open or a closed position and may make the clamp  400  stable in one of the two stable positions. In particular embodiments, the superelastic element may provide a firm grabbing of the tissue. In various embodiments, the clamp may include a shape memory element that, when heated (for example through joule heating), may cause the superelastic element to disengage from the tissue. When heating is stopped, the clamp may resume its gripped configuration. In particular embodiments, the clamp  400  may be adapted to repeat the process of opening and closing the clamp  400  without substantially affecting the ability of the clamp  400  to grab and release tissue. 
     For cardiac pacing, a surgeon may put the pacing wire&#39;s clamp  400  on the tissue (e.g., the heart tissue). In various embodiments, the clamp may be removed and put back without any change in temperature. In particular embodiments, the superelasticity of the clamp  400  may make repeated deformations possible. At the time of removal of the pacing wire, a small current may be passed to the shape memory element of the clamp  400 , which may cause slight heating, which in turn may release the clamp  400 , leaving the lead wire free to be easily and safely removed from the patient&#39;s body. 
     In various embodiments of a medical pacing wire  10 F, such as the embodiment shown in  FIGS. 9-11 , the pacing wire&#39;s clamp  400 F may comprise two or more distinct pieces of material. In particular embodiments, a first piece may have a shape memory state that biases the clamp  400 F toward a closed position as shown in  FIG. 11 . In various embodiments, a second piece may have a shape memory state that biases the clamp  400 F toward an open position as shown in  FIG. 10 . In various embodiments, the pacing wire  10 F may be adapted to produce conditions to place the first piece in its shape memory state and take the second piece out of its shape memory state in order to close the clamp  400 F. 
     The pacing wire  10 F may be further adapted to produce conditions to place the second piece in its shape memory state and take the first piece out of its shape memory state in order to open the clamp  400 F. In various embodiments, these conditions may include, for example a change in temperature. In particular embodiments, the change in temperature may be a change from the typical temperature of an animal (e.g., a human) to a temperature above the typical temperature of an animal (e.g., a human). In various embodiments, the change in temperature may be a change to a temperature above about 37 degrees Celsius (e.g., the typical temperature of a human). In a particular embodiment, the temperature change may be a change to a temperature of between about 40 degrees Celsius and about 55 degrees Celsius. 
     In particular embodiments, the first piece may comprise a superelastic alloy that biases the clamp  400 F toward the closed position. The second piece, which may be attached (e.g., to) the first piece may comprise a memory shape alloy that biases the clamp  400 F toward the open position in response to being subjected to a change in temperature. An example of such an embodiment is described below. 
     Embodiments Including a Superelastic Piece that Biases the Clamp Towards the Closed Position 
     In a particular embodiment of a medical pacing wire clamp  400 , the first piece, which comprises (e.g., comprises, consists of, or consists essentially of) a superelastic alloy, may be in the shape of a clamp as shown in  FIG. 5  or  9 . As shown in  FIG. 5 , the clamp&#39;s distal end may include a scissored crossover  440 E. Alternatively, as shown in  FIG. 9 , the clamp  400 F may have a substantially U-shaped (e.g., U-shaped) distal end. In other embodiments, the clamp&#39;s distal end may be in any other suitable shape. In various embodiments, as shown in  FIGS. 5 and 9 , the clamp  400 E,  400 F may further comprise: (1) a substantially planar (e.g., planer), substantially tear-shaped (e.g., tear-shaped) first clamp portion  420 E,  420 F; and (2) a substantially planar (e.g., planar), substantially tear-shaped (e.g., tear shaped) second clamp portion  430 E,  430 F that is at least substantially parallel (e.g., parallel) to the first clamp portion. In other embodiments, the clamp  400  may include any other suitable clamp portions. 
     In the open position shown in  FIG. 10 , the first and second clamp portions  420 F,  430 F may be spaced apart a distance of between about 0.5 mm and about 3 mm. In a particular embodiment, when in the open position, the first and second clamp portions  420 F,  430 F may be spaced apart a distance of about 1 mm. In various embodiments, the distance between the clamp&#39;s distal end  410 F and the first and second clamp portions&#39; proximal ends may be between about 6 mm and about 17 mm. In a particular embodiment, the distance between the clamp&#39;s distal end  410 F and the first and second clamp portions&#39; proximal ends may be about 11 mm. In various embodiments, the clamp&#39;s distal end  410 F may have a diameter that corresponds to the diameter of a circle whose diameter is between about 1.5 mm and about 5 mm. 
     As shown in  FIGS. 9-11 , the second piece  450 F, which may, in various embodiments, comprise a memory shape alloy, is substantially helical (e.g., helical) and is disposed about a curved portion of the clamp&#39;s distal end  410 F. In particular embodiments, the metal shape alloy (and any other metal shaped alloy described herein) may be a Nickel/Titanium alloy, a Copper/Zinc/Aluminum Alloy, a Copper/Aluminum/Nickel Alloy, or any other suitable memory shape alloy. In various embodiments, the inner radius of the substantially helical second piece  450 F substantially corresponds to (e.g., corresponds to) the radius of the clamp&#39;s distal end  410 F. As may be understood from  FIG. 9 , the clamp&#39;s distal end  400 F extends through the second piece&#39;s substantially helical (e.g., helical) structure and the second piece  450 F is wrapped a plurality of times around the clamp&#39;s distal end  410 F. In the embodiment shown in this figure, the second piece  450 F wraps around substantially all (e.g., all) of the clamp&#39;s substantially U-shaped distal end  410 F. In other embodiments, the second piece  450 F may wrap around any other suitable portion of the clamp&#39;s substantially U-shaped distal end  410 F. In the embodiment shown in  FIG. 9 , the substantially helical second piece is substantially U-shaped (e.g., U-shaped) when in its memory state and when the clamp  400 F is in the open position. 
     In particular embodiments, the second piece  450 F is given a shape memory state of a substantially U-shaped (e.g., U-shaped) helix. In various embodiments, the second piece is adapted to return to its shape memory state position in response to a change in temperature (e.g., a change to a temperature above about 45 degrees Celsius or above about 50 degrees Celsius) or to any other suitable stimulus. Once the second piece  450 F is given its shape memory state, it may be wrapped around the clamp&#39;s distal end  410 F as described above. Once wrapped around the clamp&#39;s distal end  410 F, the second piece  450 F may be selectively used to bias the clamp  400 F toward the open position (e.g., bias the first and second clamp portions  420 F,  430 F away from one another) by selectively increasing the temperature of the second piece  450 F. In response to the change in temperature, the second piece  450 F may bias the clamp  400 F with at least a force sufficient to oppose the first piece&#39;s biasing of the clamp  400 F toward the closed position. 
     In various embodiments, the pacing wire  10 F may include a lead wire that runs along the length of the pacing wire and that is attached adjacent (e.g., to) the second piece  450 F. The lead wire may be a conductive wire and may be adapted to transfer a voltage to the second piece  450 F. This transfer of voltage may be configured to facilitate a change in temperature of the second piece  450 F as described above. In a particular embodiment, a voltage of about 2 volts may be applied to the lead wire to facilitate the change in temperature in the second piece  450 F that is suitable to move the second piece  450 F from a non-memory state position into its memory state position. In other embodiments, other suitable voltages may be applied to facilitate the change in temperature. In particular embodiments, the voltage may be a voltage suitable to change the temperature in the second piece  450 F to a temperature between about 45 degrees Celcius and about 55 degrees Celsius. 
     Embodiments Including a Superelastic Piece that Biases the Clamp Towards the Open Position 
     In alternative embodiments, the first piece (e.g., the clamp  400 F) may bias the clamp  400 F toward the open position rather than the closed position. In such embodiments, the second piece  450 F may selectively bias the clamp  400 F toward the closed position in response to the second piece  450 F being subjected to an appropriate stimulus (e.g., an appropriate change in temperature). A clamp with such components may be structurally similar to (e.g., the same as) the embodiment described above. In this alternative embodiment, the second piece  450 F may respond to a change in temperature by biasing the clamp  400 F toward (e.g., into) the closed position with at least a force sufficient to oppose the first piece&#39;s biasing of the clamp  400 F toward the open position. 
     Alternative Embodiments 
     Combination Medical Pacing Wire with Alternate Materials 
     In particular embodiments, the first piece of the pacing wire&#39;s clamp  400  may comprise a memory shape alloy, and the second piece may comprise a super elastic alloy. In certain embodiments, both pieces may be memory shape alloys. In various embodiments, the first and/or second piece may comprise any material suitable for maintaining a shape memory state. 
     Continuous Combination Medical Pacing Wire Clamp 
     In various embodiments, the clamp may comprise a substantially continuous (e.g., continuous) piece of material that combines at least a superelastic alloy and a memory shape alloy rather than two distinct pieces which separately contain each material. 
     Alternatively Shaped Second Piece 
     In various embodiments, the second piece may have a structure other than a substantially helical structure. In such embodiments, the second piece may comprise, for example, a linear spring, a torsion spring, or any other suitable structure. In particular embodiments, the second piece may be disposed on the clamp in a position other than that shown in  FIGS. 9-11 . In such embodiments, the second piece may be disposed in any suitable position for biasing the clamp in response to a suitable stimulus (e.g., a temperature change). 
     Open Clamp Indicator 
     In various embodiments, the pacing wire&#39;s clamp  400  may include a light that is configured to indicate when the clamp  400  is in the open position (e.g., and therefore safe to remove from a patient). In particular embodiments, the light may be adapted to turn on or off as the clamp is in the open or closed position respectively. In other embodiments, the light may be adapted to change colors in response to the clamp opening or closing. In other embodiments, the clamp may include any suitable indicator other than a light to indicate that the clamp is in the open or closed position. 
     CONCLUSION 
     Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. For example, in various embodiments (including, potentially, certain embodiments described above), the pacing wire&#39;s clamp is made of a metal shape alloy (or other suitable material) that: (1) remains in the form of a clamp when the clamp is at a temperature that is within a temperature range that includes both typical operating-room temperatures and typical animal body temperatures; and (2) that relaxes into the form of a flexible wire in response to being cooled and/or heated outside of this range of temperatures. It should also be understood that the invention may take form in a variety of different mechanical and operational configurations. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for the purposes of limitation.