Patent Publication Number: US-2011071585-A1

Title: Intravascular implantable device having superior anchoring arrangement

Description:
RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 11/999,519 filed Dec. 4, 2007, which claims the benefit of U.S. Provisional Application No. 60/868,434 filed Dec. 4, 2006, and claims the benefit of U.S. Provisional Application No. 60/868,437, filed Dec. 4, 2006, and U.S. Provisional Application No. 61/005,354, filed Dec. 3, 2007, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to surgical devices and methods for retaining medical devices within the body, and more specifically to a method and system for anchoring an intravascular implantable device within a vessel that is located superior to the heart. 
     BACKGROUND OF THE INVENTION 
     Implantable medical devices such as pacemakers, defibrillators, and implantable cardioverter defibrillators (“ICDs”) have been successfully implanted in patients for years for treatment of heart rhythm conditions. Pacemakers are implanted to detect periods of bradycardia and deliver low energy electrical stimuli to increase the heart rate. ICDs are implanted in patients to cardiovert or defibrillate the heart by delivering high energy electrical stimuli to slow or reset the heart rate in the event a ventricular tachycardia (VT) or ventricular fibrillation (VF) is detected. Another type of implantable device detects an atrial fibrillation (AF) episode and delivers electrical stimuli to the atria to restore electrical coordination between the upper and lower chambers of the heart. Still another type of implantable device stores and delivers drug ad/or gene therapies to treat a variety of conditions, including cardiac arrhythmias. The current generation for all of these implantable devices are typically can-shaped devices implanted under the skin that deliver therapy via leads that are implanted in the heart via the patient&#39;s vascular system. 
     Next generation implantable medical devices may take the form of elongated intravascular devices that are implanted within the patient&#39;s vascular system, instead of under the skin. Examples of these intravascular implantable devices are described, for example, in U.S. Pat. No. 7,082,336, U.S. Published Patent Application Nos. 2005/0043765A1, 2005/0208471A1 and 2006/0217779A1. These devices contain electric circuitry and/or electronic components that are hermetically sealed to prevent damage to the electronic components and the release of contaminants into the bloodstream. Due to the length of these implantable devices, which in some cases can be approximately 10-60 cm in length, the devices generally are designed to be flexible enough to move through the vasculature while being sufficiently rigid to protect the internal components. 
     The issue of how to secure such an implantable device in the vasculature is one of the challenges for this next generation of intravascular implantable devices. In addition to the mechanical and operational considerations related to an anchoring system, there are physical and biological implications for the patient, as well as considerations for how an anchoring system may affect the manner in which the implantable device delivers therapy. 
     As described in some of the embodiments shown in U.S. Pat. No. 7,082,336 and U.S. Published Patent Application No. 2004/0249431, the anchoring system was arranged proximate the middle of the intravascular implantable device so as to be positioned in the vena cava within the thorax. This arrangement anchored the intravascular implantable device near the middle of the patient&#39;s torso at a location generally corresponding to the diaphragm. In some embodiments, the anchoring system was integrated with the body of the intravascular implantable device. In other embodiments, the anchoring system was a separate device, such as a stent, that was used to pin the body of the intravascular implantable device in position between the stent and the vessel wall. In still other embodiments, a lead extending from a distal end of the body of the intravascular device would also be anchored in the vasculature, such as in a subclavian vein. An alternative integrated anchoring system for an intravascular implantable device is described in some of the embodiments shown in U.S. Published Patent Application No. 2005/0208471A1. This alternative integrated anchoring system utilized a radially expandable member positioned proximate the middle of the body of the device to secure the device. In some embodiments, the radially expandable member centered the device within the diameter of the vessel. In other embodiments, two or more radially expandable members were used to secure the middle of the body of the device within a vessel. 
     The approaches of securing an intravascular implantable device within the thorax by an anchoring system proximate the middle of the body of the device and positioned in the vena cava generally corresponding to the diaphragm of the patient were intended to create a secure and balanced anchoring of the device within the largest diameter vessel in the body. These approaches sought to reduce issues of thrombosis and potential dislodgement of the anchoring system due to impact or movement of the patient. 
     While intravascular implantable devices represent a significant improvement over conventional implantable devices that are implanted subcutaneously, there are opportunities to improve and refine the designs for such intravascular devices. Accordingly, it would be desirable to provide for an improved design of an anchoring arrangement for an intravascular implantable device. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to methods and systems for anchoring an intravascular implantable device within a vessel that is located superior to the heart, i.e. above the heart in a direction toward the head of a patient. In one embodiment, the present invention utilizes only a single anchoring arrangement positioned proximate a distal portion of the intravascular implantable device. In another embodiment, the present invention utilizes an anchoring arrangement that interacts with a distal portion of the intravascular implantable device that is generally smaller in cross-sectional area than a cross-sectional area of the body portion of the device. In a further embodiment, the present invention utilizes an anchoring arrangement that interacts with a distal portion of the intravascular device that is generally separable from the body portion of the device and contains no internal spaces for active components of the device. 
     Unlike the previous approaches to anchoring intravascular implantable devices near the middle of the patient&#39;s torso, embodiments of the present invention anchor the body portion of the intravascular implantable device in a vein that is located superior to the heart and still generally within the torso, such as the right or left cephalic veins, the right or left innominate (brachiocephalic) veins or the right or left subclavian veins. In conducting investigations with the previous approach of anchoring in the middle of the device in the thorax, the inventors of the present invention discovered that the previous anchoring arrangement generally moved in synchrony with respiration, rubbing the anchor and the intravascular implantable device against the vascular walls of the inferior vena cava and thereby causing unwanted irritation, thrombosis and/or fibrosis. Anchoring in the middle of the device also tended to constrain the movement of the device within the inferior vena cava and created more locations along the vessel for unwanted irritation, thrombosis and/or fibrosis. 
     In accordance with the present invention, the intravascular implantable device is anchored superior to the heart, and in one embodiment is anchored in veins that are superior to the superior vena cava and still within the torso of the body, such as the cephalic vein, the innominate vein and the subclavian vein. The intravascular implantable device may be any one or a combination of defibrillator, cardioverter, pacemaker, monitor or drug/gene therapy delivery device and may be either a temporary or permanent device. 
     In one embodiment, the tether portion of the implantable device extends across the sub-clavicle crush zone and the anchor is located peripheral of the sub-clavicle crush zone. The distal portion of the body of the device is proximate, but generally does not extend into, the subclavian crush zone. In this way, the anchor is located superior to the heart and in a manner so as to minimize interference with the patient&#39;s muscular-skeletal anatomy. 
     In one embodiment, the present invention solves the problems of previously utilized anchor locations by providing a tether portion at a distal portion of the body of the implantable device. In one embodiment, the tether portion is anchored into the vasculature superior to the heart with a conventional stent. In one embodiment, the vascular anchor is preferably separate from the implantable device and captures a tether portion that extends from the implantable device between the anchor and the vasculature. Alternatively, the anchor may be incorporated as part of the implantable device. In one embodiment, the vascular anchor and/or the tether portion of the implantable device include mechanisms to optimize interference between the anchor and the tether portion in a manner that does not induce a rupture of the vessel while providing for adequate clinical attachment of the implantable device within the patient. 
     In one embodiment, the anchoring of the present invention at the distal portion of the body of the intravascular implantable device permits the main body portion and proximal body portions of the device to more effectively float in the bloodstream, thereby reducing the risk of thrombosis for those portions, as well as reducing the risk of impact or trauma on the vessel walls. It is theorized that the reduction in the risk of thrombosis may be at least partly due to the more intermittent and random nature of the interaction of these portions of the body of the device with the vessel walls which reduces the indwelling time required for effective fibrosis of the device against the vessel wall, and also tends to reduce the size of any thrombosis formed on the device. With respect to thrombosis and fibrosis at the distal portion of the device, the present invention takes advantage of the fact that stenosis of the cephalic vein, the innominate vein or the subclavian vein is less critical than stenosis of many other veins and that closure or loss of those veins is not life threatening. 
     In another embodiment, the anchoring of the intravascular implantable device superior to the heart in accordance with the present invention, such as in the pectoral region, for example, provides for easier bailout in the event of a problem with the device requiring explantation or in the event that the device is to be removed and replaced with, for example, a conventional can-based device. 
     The above summary of the various embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. This summary represents a simplified overview of certain aspects of the invention to facilitate a basic understanding of the invention and is not intended to identify key or critical elements of the invention or delineate the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective illustration depicting human cardiac anatomy. 
         FIG. 2  is a cross-sectional plan view of an implantable intravascular pacing device according to one embodiment of the present invention. 
         FIG. 2A  is a schematic representation of  FIG. 2 . 
         FIG. 3  is a cross-sectional plan view of an implantable intravascular pacing device according to another embodiment of the present invention. 
         FIG. 3A  is a schematic representation of  FIG. 3 . 
         FIG. 4  is a cross-sectional plan view of an implantable intravascular pacing device according to another embodiment of the present invention. 
         FIG. 5  is a cross-sectional plan view of an implantable intravascular pacing device according to another embodiment of the present invention. 
         FIG. 5A  is a schematic representation of  FIG. 5 . 
         FIG. 6  is a cross-sectional plan view of an implantable intravascular defibrillation device according to one embodiment of the present invention. 
         FIG. 6A  is a schematic representation of  FIG. 6 . 
         FIG. 7  is a perspective view an implantable intravascular defibrillation device according to one embodiment of the present invention. 
         FIG. 8  is a perspective view of an anchoring arrangement according to a further embodiment of the present invention. 
         FIG. 9  is an exploded view of the anchoring arrangement of  FIG. 8 . 
         FIG. 10  is a perspective view of an anchor and cleat according to one embodiment of the present invention. 
         FIG. 10A  is a closeup detail view of  FIG. 10 , depicting the connection between the cleat and the anchor. 
         FIG. 10B  is a side plan view of  FIG. 10 . 
         FIG. 10C  is a top plan view of  FIG. 10 . 
         FIG. 11  is a cutaway view of one embodiment of an anchor arrangement implanted within a vessel. 
         FIG. 12  is a cutaway view of a further embodiment of an anchor arrangement implanted within a vessel. 
         FIG. 13  is a perspective view depicting an anchor arrangement according to the present invention. 
         FIG. 14  is a close-up perspective view of  FIG. 13 . 
         FIG. 15  is a perspective view of one embodiment of the present invention. 
         FIG. 16  is a perspective view depicting a further anchor arrangement according to the present invention. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, one skilled in the art will recognize that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as to not unnecessarily obscure aspects of the present invention. 
     Referring now to  FIG. 1 , the general cardiac anatomy of a human is depicted, including the heart and major vessels. The following anatomic locations are shown and identified by the listed reference numerals: Right Subclavian  102   a,  Left Subclavian  102   b,  Superior Vena Cava (SVC)  103   a,  Inferior Vena Cava (IVC)  103   b,  Right Atrium (RA)  104   a,  Left Atrium (LA)  104   b,  Right Innominate/Brachiocephalic Vein  105   a,  Left Innominate/Brachiocephalic Vein  105   b,  Right Internal Jugular Vein  106   a,  Left Internal Jugular Vein  106   b,  Right Ventricle (RV)  107   a,  Left Ventricle (LV)  107   b,  Aortic Arch  108 , Descending Aorta  109 , Right Cephalic Vein  109   a  (not shown in  FIG. 1 ), Left Cephalic Vein  109   b,  Right Axillary Vein  110   a  (not shown in  FIG. 1 ) and Left Axillary Vein  110   b.    
     One embodiment of the present invention describes intravascular electrophysiological systems that may be used for a variety of functions to treat cardiac arrhythmias with electrical stimulation. These functions include defibrillation, pacing, and/or cardioversion. In general, the elements of an intravascular implantable device for electrophysiological therapy include at least one device body and typically, but optionally, at least one lead coupled to the body. While the present invention is directed to anchoring and retention of the device body of an intravascular implantable device, it will be understood that, in some embodiments, the one or more leads may also be anchored or retained in the vasculature or within the heart. Alternatively, the intravascular implantable device may have no leads, such as for an embodiment of an intravascular implantable drug/gene therapy device, or the one or more leads may not be anchored or retained in the vasculature or within the heart. 
     Various examples of intravascular implantable electrophysiology devices, such as intravascular defibrillation and/or pacing devices  20  and leads  28  will be given in this description. In those examples, reference numerals such as  20   a,    20   b,    20   c,  etc., will be used to describe certain embodiments of the intravascular device  20 , whereas elsewhere reference numeral  20  may be used to more generally refer to intravascular devices of the type that may be used with the present invention for providing therapy other than, or in addition to, cardiac electrophysiology. Likewise, reference number  28  may be used generally to refer to leads of a type that may be used with the system. Reference number  100  refers generally to vessels and/or vessel walls within the human body. 
     In one embodiment, device  20  includes components, known in the art to be necessary to carry out the system functions of an implantable electrophysiology device. For example, device  20  may include one or more pulse generators, including associated batteries, capacitors, microprocessors, communication circuitry and circuitry for generating electrophysiological pulses for defibrillation, cardioversion and/or pacing. Device  20  may also include detection circuitry for detecting arrhythmias or other abnormal activity of the heart. The specific components to be provided in device  20  will depend upon the application for the device, and specifically whether device  20  is intended to perform defibrillation, cardioversion, and/or pacing along with sensing functions. 
     Device  20  can be proportioned to be passed into the vasculature and to be anchored within the vasculature of the patient with minimal obstruction to blood flow. Suitable sites for introduction of device  20  into the body can include, but are not limited to, the venous system using access through the right or left femoral vein or the right or left subclavian vein. For purposes of describing the present invention, the various portions of the device  20  will be referenced to the location of those portions, the proximal portion  22 , the distal portion  24  and the middle portion  26  relative to the introduction site in the femoral vein. Device  20  generally includes a proximal end and a distal end. It will be understood, however, that if an alternate access site were used to introduce the device  20 , such as the subclavian veins, the various portions  22 ,  24  and  26  of the device  20  would be referenced relative to the inferior/superior location of the device  20  within the vascular system in the torso of a patient. In one embodiment, distal portion  24  may be defined as being part of the device body, encompassing up to the distal-most third of the body of device  20 . In another embodiment, distal portion  24  may be defined as encompassing part of the body of device  20  and part of tether portion  52 . In a further embodiment, distal portion  24  is defined as not encompassing the device body at all, rather it encompasses tether portion  52 . 
     In one embodiment, the device  20  can have a streamlined maximum cross sectional diameter which can be in the range of 3-15 mm or less, with a maximum cross-sectional diameter of 3-8 mm or less in one embodiment. The cross-sectional area of device  20  in the transverse direction (i.e. transecting the longitudinal axis) can preferably be as small as possible while still accommodating the required components. This area can be in the range of approximately 79 mm2 or less, in the range of approximately 40 mm2 or less, or between 12.5-40 mm2, depending upon the embodiment and/or application. 
     In one embodiment, the cross-section of device  20  (i.e., transecting the longitudinal axis) may have a circular cross-section, although other cross-sections including crescent, flattened, or elliptical cross-sections may also be used. It can be highly desirable to provide the device with a smooth continuous contour so as to avoid voids or recesses that could encourage thrombus formation on the device. It can also be desirable to provide for a circular cross-section to aid in removal or explantation of the device that more easily permits the device to be torqued or rotated during the removal or explantation to break free of any thrombosis or clotting that may have occurred. In one embodiment, the cross-section of device  20  is generally isodiametric along the entirety of its longitudinal length other than for tapered portions at the proximal and distal ends of the device  20 . In one embodiment, the aspect ratio of the cross-section of the device  20  to a longitudinal length of the body portion of the device  20  is less than 1:10 (e.g., 10 mm diameter to 10 cm length) and in another embodiment is less than 1:50. 
     In one embodiment, the housing of device  20  may be covered by an electrically insulative layer or coating such as ePTFE. It may be desirable to provide a coating that is anti-thrombogenic (e.g., perfluorocarbon coatings applied using supercritical carbon dioxide) so as to prevent thrombus formation on device  20 . It may also be beneficial that the coating have anti-proliferative properties so as to minimize endothelialization or cellular in growth, since minimizing growth into or onto device  20  will help minimize vascular trauma when the device is explanted. The coating may thus also be one which elutes anti-thrombogenic compositions (e.g., heparin sulfate) and/or compositions that inhibit cellular in growth and/or immunosuppressive agents. If the housing of device  20  is conductive, this layer or coating may be selectively applied or removed to leave an exposed electrode region on the surface of the housing where necessary, such as depicted in  FIGS. 2-6A . 
     In some embodiments one or more leads  28  may extend from device  20  proximate any of the various portions  22 ,  24  and  26  of the device  20 . In the embodiment shown in  FIGS. 2 ,  3 , and  6 , for example, a single lead  28  is shown, extending from the proximal end  22  of device  20 . A lead  28  includes one or more electrodes, such as tip electrodes, ring electrodes, or defibrillation electrodes. In embodiments having a tether portion  52 , a lead  28  may be included within tether portion  52 . If two leads  28  are used, they may extend from opposite ends of device  20 , or they may extend from the same end of the device  20 , such as depicted in  FIGS. 4-5 . Either or both of the leads may be equipped to sense electrical activity of the heart. Monitoring of the heart&#39;s electrical activity is needed to detect the onset of an arrhythmia. Activity sensed by the sensing electrode(s) is used by device  20  electronics to trigger delivery of a defibrillation shock that in one embodiment may be delivered via lead  28  having a defibrillation electrode or delivery of a pacing impulse that in one embodiment may be delivered via lead  28  via a pacing electrode. 
     The lead  28  may be a conventional defibrillation/pacing lead, although alternative lead configurations may be desirable if warranted by the desired placement of the device  20  and lead within the body. An optimal lead will preferably give the physician implanting the device flexibility to position the device at an appropriate location in the chosen vessel without concern that the leads extending from the device will not reach their intended location. Thus, for some patients it may be necessary to use a lead that is slightly longer than conventional leads, or the lead may include a coiled section that is similar to the configuration of a coiled telephone cord. A coiled section can allow elongation of the effective length of the lead when tension is applied to the coil. The coiled section or any alternate type of yieldable lead section may be a plastically deformable metal or polymer that will retain its extended configuration after it has been stretched to that configuration. Other configurations that will allow additional lead length to pull out from the device if needed may also be used. 
     For leads  28  that are to be positioned within a chamber of the heart such as in  FIG. 11 , the lead may include a helical screw-in tip or be of the tined variety for fixation to the cardiac tissue. A detachable screw-in lead tip may be provided, which allows the lead tip to be left within the chamber of the heart when lead  28  is extracted. 
     Lead  28  may have a steroid-eluding tip to facilitate tissue in-growth for fixation purposes, or may include non-thrombogenic and/or non-proliferative surfaces or coatings similar to those as may be applied to device  20 . For example, lead  28  may include a coating that is anti-thrombogenic (e.g. perfluorocarbon coatings applied using supercritical carbon dioxide) so as to prevent thrombus formation on the lead. It is also beneficial for the coating to have anti-proliferative properties so as to minimize endothelialization or cellular ingrowth, since minimizing growth into or onto the lead will help minimize vascular trauma when the device is explanted. The coating may thus also be one which elutes anti-thrombogenic compositions (e.g. heparin sulfate) and/or compositions that inhibit cellular in-growth and/or immunosuppressive agents. 
     It should be appreciated that in this disclosure the term “lead” is used to mean an element that includes conductors and electrodes in an elongated, sealed and insulated protective configuration that is adapted to withstand chronic implantation and is generally floppy in flexibility to permit the electrodes to be positioned somewhat remotely from the circuitry that energizes the electrodes via the conductors. The lead  28  may be integrated with the device body, or attachable to the device body in situ or prior to implantation, or the lead  28  may be integral with the device body as an extension of the device itself. Thus, leads may include elements that are simply extensions or tapers of the device  12   a  itself (such as the portion of the device  12   a  at which electrodes  22   a  are located) as well as more conventional leads. More than one lead  28  may be provided, and leads may be included on the proximal/inferior end of the device body, on the distal/superior portion of the device body, generally on the device body, and/or any combination thereof. In one embodiment, an end of the device body may be modified to include a stepped portion proximate the lead connection, such as on the proximal end of the device. The stepped portion allows a smooth transition between the exterior surface of the lead and the device body. 
     Given the minimal space allowed for components, it is desirable to arrange the components within device  20  so as to make efficient use of the available space. Examples of devices having space efficient arrangements of their contents are shown in  FIGS. 2-6A . One example is identified by reference numeral  20   a  in  FIG. 2 . One embodiment of device  20   a  includes one or more elongate housings or enclosures  32  depicted in cross-section in  FIG. 2A  to allow the components housed within it to be seen. In one embodiment, enclosure  32  is a rigid or semi-rigid housing preferably formed of a material that is conductive, biocompatible, capable of sterilization and capable of hermetically sealing the components contained within the enclosure  32 . One example of such a material is titanium, although other materials may also be used. 
     Within enclosure  32  are the electronic components  34  that govern operation of the device  20   a.  For example, components  34   a  are associated with delivery of a defibrillation pulse via a lead  28  ( FIG. 6 ), whereas components  34   b  are associated with the sensing function performed using sensing electrodes on the defibrillation lead, on a separate lead  28  (e.g.,  FIGS. 4 and 5 ), or on the device body itself Isolating components  34   a  from components  34   b  may be desirable if noise generated by the high voltage defibrillation circuitry  34   a  during charging might interfere with performance of the sensing circuitry  34   b,  or if practical limitations exist with respect to circuit interconnects  42 . 
     Device  20   a  further includes one or more batteries  36  for supplying power to the device, and in some embodiments, and/or one or more exposed body electrodes  40  on an exterior surface of enclosure  32 . One or more circuit interconnects  42  can provide the electrical coupling between the electronic components  34 , one or more leads  28 , electrode(s)  40 , and batteries  36 . Additional circuitry may be provided to facilitate recharging batteries  36 . 
     A second example of an arrangement of components for the intravascular implantable pacing device is identified by reference numeral  20   b  and shown in  FIGS. 3-3A . As depicted in 
       FIGS. 3-3A , the components of device  20   b  may be arranged in series with one another to give device  20   b  a streamlined profile. Because device  20   b  is intended for implantation within the patient&#39;s vasculature, some flexibility is desired so as to allow the elongate device to be easily passed through the vasculature. Flexibility may be added by segmenting device  20   b,  such as by forming one or more breaks in the enclosure, and by forming one or more hinge zones or bellows at each break which form dynamic flexible zones that can bend relative to the longitudinal axis of the device  20   b  in response to passage and/or positioning of device  20   b  through curved regions of the vasculature. 
     In device  20   b,  each segment may be separately enclosed by its own titanium (or similar) enclosure in the form of containers or compartments  32 . The components within the containers  32  may be electrically connected by flexible circuit connects  42 , for example. In one embodiment, the containers  32  are connected using a flexible material such as silicone rubber filler to form hinge zones. In another embodiment, flexible device  20  includes one or more rigid enclosures or containers  32  used to contain electronic components  34  to be implanted inside the vasculature of a patient and having the hinge zones formed of a bellows arrangement  48 . 
     Containers  32  can be of any appropriate shape, cross-section, and length, but in this example are shown to have a cylindrical shape with a diameter of approximately 3-15 mm and a length of approximately 20 mm to 75 mm. Containers  32  can be used to house electromechanical parts or assemblies to form sophisticated implantable devices such as defibrillators, pacemakers, and drug delivery systems. Any appropriate number of these containers  32  can be combined using interconnecting bellows  48 . Interconnecting mechanical bellows  48  can be used, to connect a number of rigid containers  32  in order to form a flexible device  20 . For many devices, this will include a string of at least three containers  32 . In one embodiment, the aspect ratio of the cross-sectional diameter to the longitudinal length of each container is less than at least 1.5:2 (e.g., 15 mm diameter to 20 mm length) and in another embodiment the aspect ratio is at least 1:4. 
     In one embodiment, the bellows  48  can be of any appropriate shape, but can preferably have a shape similar in cross-section to the cross-section of the container, in order to prevent the occurrence of edges or ridges that can give rise to problems such as the formation of blood clots in the vasculature. The bellows can be made of a biocompatible material similar to the containers. Any coatings used for electrically insulating the containers and/or making the containers more hemo-dynamically compatible also can be used with the bellows. In addition to the ability of the bellows  48  to bend away from the central or long axis of device  20 , the bellows  48  also allow for flexibility along the central axis of the device. The ability to flex along the central axis provides shock absorption in the long axis as well as 3-dimensional flexing. Shock absorption can help to protect device  20  and internal components during the implant process by minimizing the motion of the implanted device. Further, shock absorption can provide a 1:1 torque ratio for steering during the implant process. The shock absorption also can help during the life of device  20 , as the natural movement of the body of a patient can induce some stress on the device  20 . 
     For a more detailed explanation of the various embodiments of the bellows arrangements  48 , reference is made to U.S. Published Patent Application Nos. 2006/0217779, filed Mar. 24, 2005, and 2007/0265673, filed Apr. 3, 2007, the disclosures of each of which are hereby incorporated by reference herein. 
     Referring now to  FIGS. 4-5A , another embodiment of the device, identified by reference numeral  20   c,  is depicted. Device  20   c  is similar to the embodiment depicted in  FIGS. 3-3A , however device  20   c  includes multiple leads  28  on the proximal portion  22  of device  20   c.    
     Referring now to  FIGS. 6-6A , another embodiment of the device identified by reference numeral  20   d  is depicted. Device  20   d  is an intravascular implantable defibrillation device, having a lead  28  adapted to inserted into the right ventricle of a patient. Device  20   d  further includes one or more sensing electrodes, which may be located on the exterior of enclosure  32 , similar to body electrodes  40 . Device  20   d  also includes one or more defibrillation electrodes on the exterior of enclosure  32 . 
     Referring again generally to device  20 , the device is preferably able to communicate via wireless telemetry to an instrument outside of the patient&#39;s body. This is commonly referred to as device interrogation and/or programming and allows the physician to monitor the state and performance of the device. It also allows the physician to reconfigure the device in the case of programmable settings. The circuitry used for device interrogation and/or programming can be included in all of device  20  embodiments, with the device telemetry antenna either encapsulated within the device enclosure or as part of the tether potion  52  discussed in more detail below. The circuitry may include a circuit that will respond in the presence of a magnetic field, electric field, a near-field or a far-field, all which are features also known in the implantable device industry. 
     These communication techniques, either alone or in various combinations, are intended to allow device  20  to communicate the device&#39;s status to the physician. For example, the status information may include the state of the battery system, and whether or not a therapeutic energy delivery had occurred or not. The communication might also identify the parameters device  20  used, including stored electrograms, to allow reconstruction of the delivery episode by the instrument. The telemetry feature may also be used to program certain features governing function of device  20 , such as the threshold heart rate in beats per minute which, when detected by the device, will cause the device to provide appropriate energy therapy. 
     Referring now to  FIGS. 7-16 , in one embodiment distal portion  24  of device  20  includes a tether portion  52 . During implantation according to one embodiment, device  20  is routed through the inferior vena cava  103   b,  through superior vena cava  103   a,  and then on to one of a number of locations superior to the superior vena cava  103   a  as will be described. Device  20  is then anchored within the vasculature using an anchor  50 . 
     Anchor  50  is configured to retain device  20  within a patient&#39;s vasculature, and in one embodiment anchor  50  comprises a conventional intravascular stent. In one embodiment, the anchor  50  may include features that give some structural stability to cause the anchor to radially support device  20  against a vessel wall  100 . For example, a mesh or other framework formed of shape memory (e.g., nickel titanium alloy, nitinol or shape memory polymer) elements or stainless steel wires may be used to form anchor  50 . In another embodiment, the anchor  50  is provided with a smooth polymeric barrier that is both anti-proliferative and anti-thrombogenic and that thereby prevents endothelial growth and thrombus formation on the anchor. Examples of materials for the polymeric barrier include, but are not limited to ePTFE, or other fluoropolymers, silicone, non-woven nylon, or biomimetic materials. The polymeric barrier is preferably formed by layers of barrier material on the interior and exterior surfaces of the framework, although it will be appreciated that the framework and barrier may be combined in a variety of ways to prevent thrombus formation and endothelialization on the anchor walls. As one alternative (or in addition to the polymeric barrier), the anchor material could include surfaces for eluting non-coagulative, anti-platelet (e.g. IIBIIIA glycoprotein receptor blockers), anti-proliferative, and/or anti-inflammatory substances. Additional information pertaining to the construction, materials and operation of anchors suitable for use with the present invention are described in U.S. Pat. No. 7,082,336 and U.S. Published Patent Application No. 2004/0249431, the disclosures of each of which are hereby incorporated by reference herein. 
     In one anchoring embodiment, the anchor relies solely on a non-biological fixation to secure the anchor within the vessel, such as mechanical fixation by the radial expansion force of an anchor  50  or hooking, latching, catching or cleating the anchor  50  with respect to the vessel. In another embodiment, the mechanical fixation may be augmented with by a glue or other non-biological adhesive interfaced between the anchor and the vessel which for purposes of the present invention would be considered part of a non-biological, as opposed to biological, fixation of the anchor. In still another embodiment, the fixation of the anchor may be accomplished solely by a glue or other non-biological adhesive interfaced between the anchor and vessel. In another embodiment, the anchor may eventually rely on biological fixation such as from endothelialization or thrombus formation to assist in retaining the anchor within the vessel in addition to the initial non-biological fixation at the time of implantation. 
     Referring now to mechanical fixation anchoring embodiments, device  20  may generally be anchored by active or passive means. In one passive anchoring embodiment, tether portion  52  may be secured by being “sandwiched” between a vessel wall  100  and anchor  50 , as depicted in  FIG. 11 . In one active anchoring embodiment, tether portion  52  may be secured by a mechanical coupling with anchor  50 , such as depicted in  FIGS. 8 and 12 . 
     Anchor  50  may be separate from tether portion  52 , although in one embodiment anchor  50  may also be integrated with tether portion  52 . In an alternate embodiment, anchor  50 , either integrated or separable, may be used to secure the body of the device  20  at the distal portion  24 , where the body does not include a unique tether portion  52 . In one embodiment, the tether portion  52  is selectively detachable from the body of the device  20  to facilitate extraction and/or explantation of the device  20 . Device  20  is preferably able to communicate via wireless telemetry to an instrument outside of the patient&#39;s body and in one embodiment, tether portion  52  may include an internal antenna to facilitate device interrogation and/or programming. In another embodiment, the internal antenna is not within detachable portion  52 . For more details of the various embodiments of the tether portion  52 , reference is made to Provisional Application No. 60/868,434, filed Dec. 4, 2006, the disclosure of which has been incorporated by reference herein. 
     In one embodiment, tether portion  52  is preferably of a smaller diameter than device  20 . Minimizing the diameter of tether portion  52  is desirable so as to reduce bulging and/or irritation of the vessel  100 . In one embodiment, tether portion  52  is sufficiently flexible to allow bending during implantation, yet is more rigid than the floppy flexibility of leads  28 . In one embodiment, tether portion  52  includes a retention tip  60 , which is configured to prevent tether portion  52  from being pulled out from anchor  50 . Tip  60  functions as a stop, interfering with the distal end of anchor  50  and preventing tether  52  from being pulled out from between anchor  50  and vessel wall  100 . 
     In another embodiment, tether portion  52  may include an electrode for defibrillation, pacing, or sensing of cardiac electrical activity. The use of an electrode positioned in tether portion  52  may be especially useful for defibrillation to generate a shock vector across the heart. 
     Referring now to  FIGS. 8-10C  and  12 , one embodiment of a tether portion  52  is depicted. Tether  52  is coupleable to a device  20 , and may include a passage suitable for insertion of a guidewire to assist in implantation. As with other embodiment, tether  52  may also include an antenna for communication purposes. Referring to  FIG. 9 , a cleat  90  is depicted, being configured to couple to tether  52  and an anchor  50 . Cleat  90  includes one or more features for coupling to anchor  50 , such as clips  92  which are configured to interact with the mesh features of anchor  50 . One or more fins  93  are disposed on the cleat body. A platform area  94  may be provided on cleat  90 , the platform providing a suitable surface for deploying a self-expanding anchor therefrom during implantation. Cleat  96  also may include a connection point for coupling to tether  52 , and includes one or more attachment features  96 . Cleat  90  may be configured to be removably coupled to tether  52 , or integrated therewith, or may be molded to tether  52 , or other connection arrangements as will be appreciated by one skilled in the art. 
     The design of cleat  90  is configured to correctly orient the cleat during implantation such that engagement of anchor  50  is easy to achieve. The placement of clips  92  and fins  93  act together, such that when cleat  90  is in a target vessel, any rotational orientation of the cleat will result in one of clips  92  being able to be engaged with anchor  50 . In an embodiment wherein anchor  50  comprises a stent, cleat  90  may be adapted to couple to a strut  51  of stent  50 . 
     Referring now to the implantation of device  20 , specific details of various implantation embodiments are discussed in U.S. Provisional Application titled “Implantation Methods, Systems and Tools for Intravascular Implantable Devices”, filed Dec. 3, 2007, the disclosure of which has been incorporated by reference herein. In one general embodiment, device  20  is implanted by making an incision in the patient&#39;s femoral vein, and inserting an introducer sheath through the incision into the vein. The introducer sheath keeps the incision open during the procedure, and includes a seal adapted to prevent blood from exiting the body while allowing the insertion of various tools and devices into the body. Device  20  may be introduced in a number of ways. In one embodiment, the device  20  may be introduced by an over-the-wire technique. The distal end or distal portion of device  20  is provided with a passageway configured to receive a guidewire, and the device is slid onto the guide wire, then the distal end of device  20  is introduced through the seal. Device  20  is guided through the vasculature of the patient, into the inferior vena cava, then the superior vena cava, and into the subclavian vein or other vessel superior to the heart. A device delivery catheter may be used to facilitate introducing the device. 
     Next, the anchor  50  is introduced. Anchor  50  may be inserted through the seal in the femoral incision used to implant device  20 . In another embodiment, anchor  50  is inserted from another incision such as through an incision closer to the location of tether portion  52 . In one embodiment, anchor  50  may be introduced after device  20  has been positioned at the desired location within the vessel. In another embodiment, anchor  50  may be introduced prior to device  20  being introduced. 
     Referring to an embodiment wherein anchor  50  is introduced via the femoral incision, the anchor may be delivered over the guide wire, such as with an anchor delivery catheter. Anchor  50 , compressed to a streamlined position, is passed through the vasculature and approaches the distal portion of the device where the anchor will interfere with where the wire enters the tip of the device. The guide wire must be removed from the device and guided around the tip of the device to provide a path for the anchor. The anchor is then guided around the device and past the distal-most portion of the device tip. Anchor  50  may be self-expanding and/or it may be expanded using an inflation tool such as a balloon passed into the anchor&#39;s central lumen and subsequently inflated. When anchor  50  is expanded, its radial forces engage tether portion  52  and secure tether portion  52  against vessel wall  100 , as depicted in  FIG. 11 . Depending on the characteristics of anchor  50 , the expansion force of the anchor against tether portion  52  may cause the vessel wall  100  to bulge outwardly. Alternatively, the anchor  50  may deform around the shape of tether portion  52 , leaving vessel  100  at its normal shape. In another embodiment, both anchor  50  and vessel  100  deform to accommodate tether portion  52 . It is desirable to minimize the diameter of tether portion  52 , to minimize deformation of anchor  50  and/or vessel  100 . 
     Referring now to deployment and/or fixation of the anchor  50 , in an embodiment utilizing cleat  90 , anchor  50  in its compressed state is guided proximate platform  94  of cleat  90 . Using the anchor delivery catheter, a sheath holding the anchor compressed is released, allowing the anchor to radially expand into the vessel. Cleat  90 , coupled to device  20  via tether  52 , is sandwiched between deployed anchor  50  and vessel wall  100 . To secure cleat  90  to anchor  50 , device  20  is manipulated, such as by its proximal end, so that cleat  90  is pulled into anchor  50 . Clip  92  is then secured onto the mesh of anchor  50 , such as depicted in  FIGS. 8 ,  10  and  10 A. Device  20  is then secured in the vasculature. A cutaway view of cleat  90  secured to anchor  50  in a vessel  100  is depicted in  FIG. 12 . 
     The lead is then delivered and implanted according to the desired application of device  20 . Additional details pertaining to the lead can be found in U.S. Provisional Application titled “Implantation Methods, Systems and Tools for Intravascular Implantable Devices”, filed Dec. 3, 2007, the disclosure of which has been incorporated by reference herein. Referring now to the location of device  20  within the vasculature in accordance with the present invention, suitable locations for anchoring device  20  are referred to as superior (i.e., generally above the heart in a direction toward the head) for purposes of describing the various embodiments of the present invention in that these locations are superior of the heart and in some embodiments superior of the superior vena cava  103   a.  Further, a suitable superior anchoring location proximate a distal portion of the device  20  effectively permits the remainder of device  20  to float, rather than lay, within the vasculature. By allowing the middle and proximal portions of device  20  to move relatively freely within the vena cava, for example, blood is able to flow all around the device, and thrombus formation and endothelial growth will be minimized. Therefore, suitable superior locations for anchoring the distal portion of device  20  include the right or left innominate (brachiocephalic) veins  105   a  or  105   b,  the right or left subclavian veins  102   a  or  102   b,  the right or left cephalic veins  109   a  or  109   b.    
     In addition, many of these superior anchoring locations such as the right or left innominate (brachiocephalic) veins  105   a  or  105   b,  the right or left subclavian veins  102   a  or  102   b,  the right or left cephalic veins  109   a  or  109   b,  are veins within the torso where alternative venous drain routes will exist in the event of fibrosis and/or stenosis proximate the anchoring location. Suitable superior anchoring locations further tend to provide for easier bailout in the event of a problem with device  20  requiring explantation by virtue of easier surgical accessibility. Furthermore, all of these locations create an effective anchoring location that is generally oriented transverse to the general direction (in a standing human patient) of gravitational force or drop force on the portion of the device  20  that may reside within the vena cava. The generally transverse orientation to the direction of gravitational or drop force afforded by these locations aids in dissipating these forces without dislodging the anchor  50 . 
     While the distal portion of device  20  potentially could be anchored in the left internal jugular vein  106   b  or the right internal jugular vein  106   a,  these veins are less medically desirable locations because the veins are located generally outside the torso and in the neck and therefore will have more potential complications in the event of fibrosis and/or stenosis proximate the anchoring location. The right internal jugular vein  106   a  is also a less desirable anchoring location due to the challenges associated with drop tests. Similar to the problems associated with anchoring the device lower in the torso, anchoring the present invention in the right internal jugular vein  106   a  may not adequately secure the implantable device during drop tests that simulate the effect of a patient falling or jumping. This may be due in part to the axis of right internal jugular vein  106   a  being closely aligned with the axis of superior vena cava  103   a,  resulting in the anchor and most of the mass of device  20  being vertically aligned, as opposed to providing an anchoring location that is oriented generally transverse to the direction of gravitational or drop force, as previously discussed. 
     A first suitable superior anchor location is proximate the subclavian crush zone  111 , which is defined as the region of the right subclavian vein  102   a  or left subclavian vein  102   b  that can be compressed between a patient&#39;s clavicle and first rib due to upward movement of the patient&#39;s arm. Typically, when a foreign object (such as a device body or lead) is introduced intravascularly and placed within subclavian crush zone  111 , the object can become damaged, potentially leading to failure of the object or damage to the vessel. This problem is compounded if multiple leads or other intravascular devices are located within the crush zone, as there is a tendency for the leads and/or devices to abrade one another, resulting in an increased potential for failures of the leads and/or devices. In this embodiment, device  20  is positioned proximate subclavian crush zone  111 , while tether portion  52  extends across and through the crush zone, and is secured with an anchor  50  located beyond and peripheral of subclavian crush zone  111 , as depicted in  FIGS. 13-15 . 
     A second suitable superior anchor location is within the right  105   a  or left  105   b  cephalic veins, as depicted in  FIG. 16 . Again, device  20  is generally positioned proximate subclavian crush zone  111 , while tether portion  52  extends across and through the crush zone, and into the cephalic vein. Tether portion  52  is secured with an anchor  50  in the cephalic vein. 
     It should be pointed out that many of the device configurations, components, retention devices and methods, implantation methods and other features are equally suitable for use with other forms of intravascular implants. Such implants might include, for example, implantable neurostimulators, artificial pancreas implants, diagnostic implants with sensors that gather data such as properties of the patient&#39;s blood (e.g. blood glucose level) and/or devices that deliver drugs or other therapies into the blood from within a blood vessel. 
     Various embodiments of systems, devices and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the present invention. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, implantation locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the invention. 
     For purposes of interpreting the claims for the present invention, it is expressly intended that the provisions of Section 112, sixth paragraph of 35 U.S.C. are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.