Abstract:
The disclosure describes apparatuses and methods for the luminal delivery of therapeutic devices. The apparatus includes a decoupling assembly comprising a retention element, a energy-responsive element and a thermally sensitive element. The application of heat to the thermally sensitive element alters its configuration such that it no longer maintains the retention element in engagement with the therapeutic device, releasing the therapeutic device.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the intraluminal delivery of therapeutic devices which includes deploying the devices from delivery vehicles by remote activation of a detachment system closely proximal to the therapeutic device. The disclosure describes apparatuses and methods for accurately and rapidly delivering a therapeutic device at a desired location by applying heat to a thermally-responsive element, resulting in the disengagement of a retention element with the therapeutic device. 
     BACKGROUND OF THE INVENTION 
     The use of catheters to insert and position therapeutic devices in the body has become a widely-used form of treatment for various conditions. Such devices are particularly useful in treating areas where traditional procedures are difficult such as in narrow cranial blood vessels. For example, vaso-occlusive devices such as embolic coils or wires are inserted at sites of aneurysm to occlude blood flow. The decreased blood flow reduces the pressure on the aneurysm and reduces the risk of a ruptured aneurysm. The coil also promotes thrombus formation. Embolic coils and wires can assume different shapes to better occlude a blood vessel. The coils can be coated with various materials to improve thrombogenicity. U.S. Pat. No. 6,723,108 describes some of the characteristics of different shapes of embolic coils. This patent and all other patents and patent application publications identified herein are hereby incorporated herein by reference. 
     Typically, procedures using a catheter involve inserting the distal end of the catheter into the vasculature of a patient and guiding it to a predetermined delivery site. A vascular occlusion device, such as an embolic coil, is attached to the end of a structure capable of manipulating the therapeutic device. This structure may, for example, be used to push the coil through the catheter and out of its distal end into the delivery site. The coil is then released from the pusher. The small size of some blood vessels requires that mechanism that releases the coil from the pusher be simple and not require complicated equipment. In addition, the release mechanism must accurately and rapidly place the therapeutic device at the determined site. Problems that have been associated with the release of the coil include the force of the coil exiting the delivery catheter causing the coil to overshoot the desired site or dislodge previously deployed coils. 
     In response to the above mentioned concerns, numerous devices and release mechanisms have been developed in an attempt to provide a delivery system which provides a rapid release or detachment mechanism to release the device at the correct location. One such device is disclosed in Geremia et al. U.S. Pat. No. 5,108,407, which shows a fiber optic cable including a connector device mounted to the end to the optic fiber. An embolic coil is attached to the connector device by a heat releasable adhesive. Laser light is transmitted through the fiber optic cable to increase the temperature of the connector device, which melts the adhesive and releases the embolic coil. One drawback to using this type of system is the potential risk of melted adhesives contaminating the blood stream. 
     Yet another embolic coil positioning and delivery system is described in Saadat et al. U.S. Pat. No. 5,989,242, which discloses a catheter having a shape memory alloy connector attached to the distal end of the catheter. The connector includes a socket having a pair of spaced-apart fingers which are responsive to a change in temperature. The fingers are bent towards each other and hold a ball which is connected to an end of an embolic coil. The connector absorbs laser light transmitted through an optical cable and transforms the light into heat energy. The heat energy raises the temperature of the connector and opens the fingers, thereby releasing the embolic coil. This type of ball and socket connection is rigid and causes the catheter to be stiff, making it difficult to guide the catheter through the vasculature of the body. 
     U.S. Patent application publication 2005/0113864 A1 by Gandhi et al describes an apparatus for the release and deployment of a therapeutic device where the therapeutic device is secured to the distal end of a pusher by a collar. When heated, the collar alters its configuration and releases the therapeutic device into the vasculature. The collar can be formed from shape memory metals or from thermoplastic polymers. In another embodiment found in the same disclosure, the therapeutic device is secured to the pusher by a connector fiber that can be broken by heating, releasing the therapeutic device. The connector fiber can be formed from a thermoplastic material or a biodegradable material that degrades or decomposes with heating. One difficulty associated with these arrangements is that the material forming the collar or fibre may fragment or dissolve when heated, releasing materials into the bloodstream. The Gandhi et al disclosure addresses this by performing the heating step completely within a catheter such that the pusher and therapeutic device become disengaged within the catheter. This approach is problematic because it may reduce the ability of the pusher to manipulate the therapeutic device to precisely the correct location in the vasculature. 
     In keeping with the invention, therefore, a need remains for a therapeutic device delivery apparatus which uses material that changes to effect therapeutic device release while remaining totally encapsulated, which has a reliable operating principle and is simple to use but still provides excellent control over the therapeutic device during the process of inserting and releasing it in the vasculature. 
     SUMMARY OF THE INVENTION 
     The invention concerns systems and methods for accurate and rapid delivery of a therapeutic device to a desired location in a body of a patient. A decoupling assembly is attached to the distal end of a pusher assembly. The decoupling assembly comprises a retention element and a thermally-responsive element. The thermally-responsive element maintains the retention element in a position where the retention element engages the therapeutic device. When energy is applied to an energy-responsive element, heat is transmitted to the thermally-responsive element and the thermally-responsive element changes its configuration such that the retention element is no longer engaged with the therapeutic device. Consequently, the therapeutic device is released at the desired site; 
     The energy-responsive element, which can take the form of a so-called heating element, may be heated using a variety of energy sources such as electrical energy, laser light, a radiofrequency source, or ultrasonic energy. The energy from these sources is transmitted to the energy-responsive element through conductors located in, at, or near the pusher element. In an alternative embodiment, energy to heat the energy-responsive element is provided without the use of conductors in, at or near the pusher. Energy from a radiofrequency source is one such energy source that can be transmitted through the body and direct its energy to the delivery device. 
     A general aspect of the present invention is to provide an apparatus for releasing a therapeutic device into the vasculature and methods for using same. 
     Another aspect of the invention is to provide devices capable of releasing embolic coils into the vasculature and methods for using such devices. 
     Other aspects, objects and advantages of the present invention will be understood from the following description according to the preferred embodiments of the present invention, specifically including stated and unstated combinations of the various features which are described herein, relevant information concerning which is shown in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In describing the preferred embodiments of the present invention, reference will be made to the accompanying drawings, wherein: 
         FIG. 1  is a sectional view of a therapeutic device delivery apparatus in accordance with a preferred embodiment of the present invention at which the retention element is engaged with an embolic coil; 
         FIG. 2  is a sectional view of the apparatus in  FIG. 1  showing the thermally-responsive member in an altered configuration at which the retention element is no longer engaged with the therapeutic device, resulting in release of the therapeutic device into the vasculature; 
         FIG. 3  is a sectional view of another embodiment, the delivery device being shown engaged with a therapeutic device; 
         FIG. 4  is a sectional view of a further embodiment, the delivery device also being shown engaged with a therapeutic device and includes an electrical conductor that transmits energy to the energy-responsive element and the body of the patient acts as a ground; 
         FIG. 5  is a sectional view of an alternative embodiment of the apparatus with the delivery device also being shown engaged with a therapeutic device and where a fiber optic cable located in the lumen of the pusher transmits laser light to the energy-responsive element; and 
         FIG. 6  is a sectional view of an alternative embodiment of the apparatus where an energy source transmits energy to the energy-responsive element in a “wireless” fashion without requiring the transmittal of energy through elements such as conductors associated in the delivery device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriate manner. 
     As shown in  FIGS. 1-6 , the present disclosure provides for systems to deliver a therapeutic device and methods for use such systems. In general, the invention includes a pusher element that has a decoupling assembly located at its distal end. The decoupling assembly includes a retention element that engages the therapeutic device when the device is being guided through the vasculature, typically within a guiding catheter (not shown). A thermally-responsive element maintains the engagement of the retention element with the therapeutic device. When the thermally-responsive element is heated, it assumes an altered configuration such that the retention element is no longer maintained in an engaged position at which it is secured to the therapeutic device. Consequently, the therapeutic device is released at the desired location in the vasculature. 
       FIGS. 1 and 2  show one embodiment of the invention. In this and the other embodiments disclosed here, the therapeutic device  11  is shown as an embolic coil. A decoupling assembly  12  is attached to the distal end of a pusher element  13  by any suitable approach, such as medical grade adhesive, mechanical attachment such as crimping or embedding or shrink wrapping or tubing, for example. The decoupling assembly comprises a retention element  15 , an energy-responsive element  17  and a thermally-responsive element  18 . 
     The retention element  15  is formed from a material that is resilient; that is, the element will move from one configuration to another when permitted and is not susceptible to fracture when stressed or deformed. While shape memory materials such as Nitinol are suitable, it is not necessary that the material have shape memory properties. The retention element may, for example, be manufactured from spring steel or other resilient metals or polymers. As shown in  FIG. 1 , the retention element  15  may assume an expanded or offset configuration such that its external surface  16  pushes with sufficient force against the inner surface  19  of a therapeutic device  11 . This is illustrated in  FIG. 1  by the engagement of a turn  22  on an embolic coil by the retention element  15 . The engagement of the retention element  15  with the therapeutic device  11  allows the pusher  13  to be used to manipulate the position of the therapeutic device  11 . As shown in  FIG. 2 , the retention element  15 , assumes a generally collapsed and somewhat more straight line orientation when not engaging the embolic coil, when compared with the extended or bulbous shape of  FIG. 1 . The shape illustrated in  FIG. 1  is that of a substantially spherical retention element. 
     The thermally-responsive element  18  is manufactured from a material that is thermally sensitive; that is, it assumes a different configuration when sufficient heat is applied. In its unheated configuration shown in  FIG. 1 , the thermally-responsive element  18  contacts the retention element  15  and maintains the retention element  15  in its expanded or offset position such that the retention element  15  engages the therapeutic device  11 . As a consequence, the desired position of the therapeutic device  11  within the vasculature can be achieved by manipulating the pusher  13 . 
     The thermally-responsive element  18  can be made from a material that deforms, contracts or otherwise alters its configuration when heated. For example, the thermally-responsive element  18  may be formed from a material that changes from a solid to a flowable form, such as a liquid, when heat energy is applied above a selected temperature and a exceeding a selected time period. Suitable materials for the thermally-responsive element include low temperature solder, hot melt adhesives, waxes and low melting point metals. When the thermally-responsive element  18  assumes a liquid form, it is no longer able to maintain the retention element  15  in its expanded configuration and the retention element  15  assumes its collapsed configuration and disengages from the therapeutic device. 
     The change in form of the thermally-responsive element  18  should not occur spontaneously at body temperature and ideally should only occur when the thermally-responsive element  18  is exposed to heat produced by the energy-responsive element  17 . In addition, the amount of heat and the length of exposure to heat produced by the energy-responsive element  17  should not exceed an acceptable level in a surgical context. For example, the heat produced should not cause unwanted adverse reactions in the patient, such as coagulation or denaturing of the blood or undesirable alterations in other tissues. 
     To ensure the thermally-responsive element  18  remains in its unaltered configuration before heating by the energy-responsive element  17 , the thermally-responsive element should change from a solid to a flowable form above a temperature of at least about 40° C. and preferably from at least about 43° C. To reduce the risk of damage to the tissues of a patient, the thermally-responsive element should change its form at a temperature that does not exceed about 50° C. and preferably should not exceed about 47° C. That is, a preferred range for the change of form of the thermally-responsive element is from about 40° C. to 50° C. and a particularly preferred range is 43° C. to 47° C. However, a particular procedure may require different conditions. In such cases, temperatures greater than 50° C. may be acceptable when applied for a shorter time such that there is no significant alteration in tissues of the patient. 
     It may be necessary to include a membrane or the like to encapsulate a thermally-responsive element when it transforms to a flowable form, depending for example upon the encapsulating capabilities, if any, of the rest of the decoupling assembly. The encapsulating material serves a barrier function. Encapsulation prevents release of the material forming the thermally sensitive material when it is heated. In a preferred embodiment, the thermally-responsive element is encapsulated in a flexible membrane  23 . The membrane should be flexible enough to accommodate the collapse of the retention element  15  when the thermally-responsive membrane  23  is heated. The integrity of the membrane  23  should not be compromised at the conditions used to heat the thermally-responsive element  18  to alter its configuration. For example, the membrane  23  should not undergo a phase transition from solid to liquid at the conditions used to heat the thermally-responsive element. A preferred material for the membrane is a silicone. 
     In the embodiment shown in  FIGS. 1 and 2 , electrical wires  20 ,  21  connect with the energy-responsive element which may be considered a heating element. The wires complete a circuit between an electrical energy source (not shown) and the energy-responsive or heating element. The pusher  13  can have a lumen  14  through which wires  20 ,  21  extend between the electrical energy source and the energy-responsive element  17 . 
     The energy-responsive element  17  and the thermally-responsive element  18  are designed, sized and positioned such that the energy-responsive element  17  helps to transform energy applied to it into heat energy which then is transmitted to the thermally-responsive element  18 . As shown in  FIG. 2 , heat transmitted from the energy-responsive element  17  alters the configuration of the thermally-responsive member  18  such that it no longer maintains the retention element  15  in an expanded, offset position. The retention element moves from an expanded, offset position to a generally collapsed or somewhat straight-line position and disengages from the therapeutic device  11 . Consequently, as show in  FIG. 2 , the therapeutic device  11  is released from the pusher  13  and placed in the vasculature at the desired location. 
     The retention element can be provided in any number of shapes with the only requirement being that it is capable of engaging the therapeutic device in at least one configuration and disengaging the therapeutic device in another configuration. For example, in the embodiment shown in  FIG. 3 , decoupling assembly  32  has a retention element  34  shaped such that a portion  35  of the retention element intercalates between the turns  22  of the embolic coil therapeutic device  11 . A thermally responsive element  37  is provided in this embodiment. It can be encapsulated within a membrane  31 . 
     In another embodiment, shown in  FIG. 4 , decoupling assembly  42  includes a thermally-responsive element  46 . This is shown with an encapsulating membrane  41 . The thermally-responsive element is positioned generally within retention element  44  which has one or more protrusions  45  that intercalate with the turns  22  of the embolic coil therapeutic device  11 . 
       FIGS. 1 and 2  present one embodiment that can be used to deliver electrical energy to the energy-responsive element. In an alternative embodiment shown in  FIG. 3 , electrical wires  38 ,  39  are positioned externally on the surface of the pusher  33  and connect the energy source (not shown) and the energy-responsive element or heating  36  to form a circuit. The pusher  33  can be solid. After the application of energy to the energy-responsive or heating element  36 , heat is generated and/or transmitted to the thermally-responsive member  37 . Heating alters the configuration of the thermally-responsive member  37  and the retention element  34  moves from an expanded, offset position to a generally collapsed position (not shown) in the matter of that shown in  FIG. 2  and the retention element disengages from the therapeutic device  11 . 
     In alternative embodiments, energy is provided to the energy-responsive or heating element through different means and using different types of energy sources. For example, as shown in  FIG. 4 , the pusher  47  is formed, at least in part, from a material that conducts electricity. In this embodiment, the pusher  47  is in communication with the energy-responsive or heating element  49 . A support sheath  43  is shown surrounding all but the distal end portion of the pusher  47  and the energy-responsive or heating element  49 . An electrical circuit develops with the body performing the function of an electrical ground. In a preferred embodiment, the pusher  47  and energy-responsive or heating element  45  are formed from the same piece of material. Alternatively, the element  45  is manufactured from a separate piece of material and attached to the distal end of the pusher  47  by means known in the art. The embodiment that employs a unitary construction for the pusher is preferred for its simplicity and reduced chance of failure due to improper attachment of the pusher  47  and energy-responsive or heating element  49 . 
     In another embodiment, the energy-responsive or heating element is heated by light energy, preferably laser light. As shown in  FIG. 5 , pusher  53  includes a fibre optic cable  57  in a lumen thereof for transmitting light from a laser light source (not shown) to the energy-responsive or heating element  55  found in the decoupling assembly  52 . The element  55  receives the light energy, transforms same into heat energy which is then transmitted to the thermally-responsive element  56 , shown encapsulated in a membrane  51 . As a consequence of transmittal of heat, the thermally-responsive element  56  assumes its altered configuration. As a result, the retention element  54  moves from an expanded, offset position to a generally collapsed or somewhat more straight-line position similar to that of  FIG. 2  so the retention element  54  disengages from the therapeutic device  11 . 
     Alternatively, the pusher may contain materials that conduct ultrasonic energy from an ultrasonic energy source (not shown). The ultrasonic energy conductor may be placed in the lumen of the pusher. In this approach, the energy responsive element  55  transforms the ultrasonic energy to thermal energy to collapse the thermally-responsive element  56 . 
     In the embodiment shown in  FIG. 6 , an external energy source  67  heats the energy-responsive element  65  without the use of energy-conducting elements in the pusher  63  or decoupling assembly  62 . In this embodiment, energy is directly transmitted to the  65  from the external energy source  67  through the body of the patient, including through the vasculature  68 . 
     Typically, energy source  67  is a radiofrequency (RF) source of the type generally known in the art. As in previous embodiments, heat alters the configuration of the thermally-responsive element  66  (shown encapsulated in membrane  61 ) such that it no longer maintains the retention element  64  in an expanded, offset position. The retention element  64  moves from an expanded, offset position to a generally collapsed or somewhat more straight-line position along the lines of  FIG. 2  and disengages from the therapeutic device  11 . 
     It will be understood that the embodiments of the present invention which have been described are illustrative of some of the applications of the principles of the present invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention. Various features which are described herein can be used in any combination and are not limited to procure combinations that are specifically outlined herein.