Abstract:
A pacing lead for implantation in the pericardial space includes an elongated lead body, a compression fixation element, and at least one electrode on either the lead body or the fixation element. The fixation element defines a resilient structure, and is positioned and dimensioned so that when the lead is disposed in the pericardial space, the resilient fixation element is compressed between the parietal and visceral pericardium, thereby biasing the electrode against the myocardium and providing positional stabilization to the lead. Further positional stability may be provided mechanically with structures enabling the application of adhesive or with fixation screw or tine elements.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/825,139, entitled PACING LEAD AND METHOD FOR PACING IN THE PARICARDIAL SPACE, filed Sep. 10, 2006, and hereby fully incorporated herein by reference. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to pacing leads. More particularly, the present invention relates to pacing leads for implantation between the visceral and parietal pericardium of the heart. 
       BACKGROUND OF THE INVENTION 
       [0003]    As depicted in  FIGS. 1 and 2 , the human heart  30  is contained in the mediastinum  32  within a conical sac of serous membrane called the pericardium  34 . There are generally two layers to pericardium  34 ; the fibrous pericardium  35  and the serous pericardium  36 . The fibrous pericardium  35  is a superficial layer comprising dense connective tissue and it encloses serous pericardium  36 . The serous pericardium  36  itself has two layers. The layer adjacent the fibrous pericardium is the parietal layer  37  and the layer next to the heart is the visceral layer  38 , also known as the epicardium. Between the parietal  37  and visceral  38  layers exists a small cavity known as the pericardial space  39 . This pericardial space may be void or partially filled with a lubricious fluid  39   a.    
         [0004]    Pacing of the heart is usually achieved by pacing leads introduced transvenously. In some cases, however, the chamber of the heart or a specific location on the chamber of the heart is not accessible using a transvenous approach and must be placed surgically. 
         [0005]    Leads placed on the surface of the heart, such as in contact with the visceral pericardium, require a method of fixation to keep them in place. In the prior art, pacing the epicardium is usually accomplished via a screw in lead placed surgically. 
         [0006]    To pace the epicardium, a pacing lead is positioned with one or more electrodes in contact with the visceral pericardium. For effective pacing, electrodes on the pacing lead must be in constant electrical conductive contact with the surface of the visceral pericardium. Conductivity is most preferably sufficient so as to enable a pacing voltage of 3 volts or less, although for various reasons, prior art leads often develop much higher pacing thresholds. 
         [0007]    To accomplish constant contact, different pacing lead configurations have been previously used to assist in the placement and retention of the pacing lead in the desired position. These prior leads, however, all have certain drawbacks making them not entirely satisfactory. For example they require placement through the parietal pericardium either surgically or percutaneously. They are usually screwed into place and frequently develop high thresholds. Other leads have been developed which employ a helical structure oriented along the longitudinal axis of the lead. The helical structure exerts a lateral biasing force against the walls of the space to assist in fixation of the lead. These prior helical leads, however, are sometimes difficult to stabilize and may be prone to “overturn” or rotate about the longitudinal axis of the lead when in place, thereby interrupting electrical contact of the electrodes. 
         [0008]    The present inventor has recognized that prior art leads and fixation methods that do not employ screws or suture are not entirely suitable for placement in the pericardial space through the pericardium (surgical or percutaneously). Further, the present inventor recognizes that prior art leads, fixation and stabilization methods are not entirely suitable for leads introduced into the pericardial space through the venous system. Hence, there is still a need for a lead and passive fixation method assuring stable pacing from the epicardial surface whether introduced transvenously through the coronary venous microcirculation or through the wall of a chamber of the heart or through the fibrous pericardium. Because the general problems discussed above have not been addressed by conventional pacing leads, there is a current need for pacing leads addressing the problems and deficiencies inherent with the prior designs. 
       SUMMARY OF THE INVENTION 
       [0009]    The pacing lead of the various embodiments of the present invention substantially addresses the aforementioned problems of conventional designs by providing lead shapes, methods of fixation, and methods of pacing lead deployment that assure that the electrodes of the lead are firmly in electrical conductive contact with the epicardial surface and the lead is positionally stable. The lead of the present invention may thereby enable relatively low pacing voltages, generally 3 volts or less. In an embodiment, the improved stability and pacing is accomplished when a resilient fixation structure in the form of a helix, loop, or other resilient structure is compressed between the parietal and visceral pericardium when disposed in the pericardial space. The biasing force exerted by compression of the helical fixation element biases electrodes on the lead body against the visceral pericardium thereby improving electrical conductivity between the myocardium and the electrodes, and providing a degree of positional stability. Positional stability of the lead may be further enhanced in some embodiments with bio-compatible adhesive introduced at desired locations to adhere the lead body to surrounding tissues. 
         [0010]    In an embodiment, the lead has a proximal portion and a distal portion comprising a resilient fixation element extending from the proximal portion. The proximal portion includes a pair of electrodes. The compression fixation element may be preformed in a helix or other shape enabling resiliency. The height or width dimension of the fixation element is predetermined so as to be larger than space between the visceral and parietal pericardium. When the lead is advanced into the pericardial space, the fixation element is compressed by the walls of the heart defining the pericardial space, specifically the visceral pericardium and the myocardium. The electrodes of the pacing portion, which may be disposed proximate the fixation element, are biased against the myocardium by the resilience of the fixation element. Electrical conductivity between the electrodes and the myocardium is thereby improved, along with lead stability and pacing and sensing thresholds. 
         [0011]    According to an embodiment, a pacing lead for implantation in the pericardial space typically includes a fixation element extending from the pacing portion and defining a generally helical shaped fixation structure extending generally perpendicular to the pacing portion. The helical structure presents a predetermined vertical dimension greater than the dimension of the space between the visceral and parietal pericardium. When the helical structure is advanced into the pericardial space, the helical structure is laterally compressed by the parietal pericardium and at least one electrode is biased against the myocardium 
         [0012]    According to an embodiment of a method according to the invention, a pacing lead is provided having a lead body with a resilient fixation element extending therefrom. The resilient fixation element is preformed in a helical or loop configuration or other configuration as required to provide positional stability and electrode contact within the pericardial space. 
         [0013]    According to the method, the expanded form of the fixation element is deployed by removing a guide wire or stylet slidably disposed in a lumen defined centrally or asymmetrically in the lead. The fixation element, being compressed by the visceral and parietal pericardium, biases electrodes on the lead body or fixation element against the myocardium 
         [0014]    A feature and advantage of an embodiment of the invention is that any chamber of the heart can be paced by positioning the electrodes on the epicardial surface. 
         [0015]    A feature and advantage of an embodiment of the invention is that assuring constant contact between the lead electrodes and myocardium via compression fixation can increase the stability of the fixation and pacing. 
         [0016]    A feature and advantage of an embodiment of the invention is that the design of the pacing lead enables use on various sized leads without sacrificing stability or pacing/sensing thresholds 
         [0017]    A feature and advantage of an embodiment of the invention is a method of pacing lead deployment assuring constant contact between the lead electrodes and the myocardium. 
         [0018]    A feature and advantage of an embodiment of the invention is that the heart can be paced by biasing one or more lead electrode against the myocardium using the resilient fixation element of the lead. 
         [0019]    A feature and advantage of an embodiment of the invention is that positional stability of the electrodes may be enhanced by the application of adhesive in desired locations to adhere the lead to surrounding tissues. 
         [0020]    A feature and advantage of embodiment of the invention is that a lead may be introduced transvenously into the heart and from there into the pericardial space through the coronary venous structure or directly though the wall of one of the chambers such as the right atrial appendage or right atrium. By using the coronary venous microcirculation as a means to access the pericardial space, the final position of the lead and the site where the lead exits the vein into the pericardial space can be kept in close proximity. By comparison, standard leads that stay within the vein can only be placed where there are veins large enough to accommodate the body of the lead. With a lead according to the invention, small veins may be used to position the guide wire where the lead is to be positioned, and the lead may then be advanced along the wire to the desired site by dilating the small veins to the point of rupture at which point the tip of the lead is not within the vein and the tip may be stabilized to ensure electrode contact. 
         [0021]    A feature and advantage of an embodiment of the invention is that when advanced into the pericardial space though the venous microcirculation, the proximal portion of the lead will be stabilized and supported within the venous system. 
         [0022]    A feature and advantage of an embodiment of the invention is that the pacing lead may be introduced transvenously into the heart and from there into the pericardial space through a coronary venous structure or directly through the wall of one of the chambers such as the right atrial appendage or right atrium. 
         [0023]    A feature and advantage of an embodiment of the invention is that the resilient fixation element of the lead may or may not contain electrodes for sensing and pacing the myocardium via the pericardial space. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a view of the mediastinum opened so as to expose the lungs, pleural space, and the heart enclosed in the pericardial sac; 
           [0025]      FIG. 2  is a fragmentary cross-sectional view of the heart and pericardium; 
           [0026]      FIG. 3  is a perspective view depicting an embodiment of the pacing lead for the pericardial space according to the present invention; 
           [0027]      FIG. 3.1  is a perspective view of an alternative embodiment of the lead depicted in  FIG. 3 ; 
           [0028]      FIG. 4  is a side view of the pacing lead depicted in  FIG. 3  deployed in the pericardial space, 
           [0029]      FIG. 4.1  is a side view of the pacing lead depicted in  FIG. 3.1  deployed in the pericardial space; 
           [0030]      FIG. 5  is a top view of the pacing lead depicted in  FIG. 3 ; 
           [0031]      FIG. 5.1  is a top view of an alternative embodiment of the lead depicted in  FIG. 3 ; 
           [0032]      FIG. 5.2  is a top view of another alternative embodiment of the lead depicted in  FIG. 3 ; 
           [0033]      FIG. 5.3  is a top view of another alternative embodiment of a pacing lead according to the present invention; 
           [0034]      FIG. 5.4  is a side view of the lead depicted in  FIG. 5.3 ; 
           [0035]      FIG. 5.5  is a fragmentary side elevation of an adhesive port of a lead according to an embodiment of the present invention; 
           [0036]      FIG. 5.6  is a side view of the pacing lead depicted in  FIG. 5.3  deployed upright in the pericardial space; 
           [0037]      FIG. 5.7  is a side view of the pacing lead depicted in  FIG. 5.3  deployed inverted in the pericardial space; 
           [0038]      FIG. 6  is a longitudinal cross-sectional view of the pacing lead depicted in  FIG. 3 , straightened with a stylet disposed in a lumen of the lead; 
           [0039]      FIG. 6.1  is a longitudinal cross-sectional view of an alternative embodiment of the pacing lead depicted in  FIG. 3 , straightened with a stylet disposed in a lumen of the lead; 
           [0040]      FIG. 6.2  is a longitudinal cross-sectional view of another alternative embodiment of the pacing lead depicted in  FIG. 3 , straightened with a guidewire disposed in a lumen of the lead; 
           [0041]      FIG. 6.3  is a fragmentary longitudinal cross-sectional view of an adhesive port in a lead according to an embodiment of the invention; 
           [0042]      FIG. 6.4  is a transverse cross-sectional view of the lead of  FIG. 6.3  taken at section  6 . 4 - 6 . 4 ; 
           [0043]      FIG. 6.5  is a cross-sectional view of the lead of  FIG. 5.5  taken at section  6 . 5 - 6 . 5 ; 
           [0044]      FIG. 6.6  is a top view of another alternative embodiment of a pacing lead according to the present invention; 
           [0045]      FIG. 6.7  is a longitudinal cross-section of the lead depicted in  FIG. 6.6 ; 
           [0046]      FIG. 6.8  is a side elevation view of the lead depicted in  FIG. 6.6 ; 
           [0047]      FIG. 6.9  is a transverse cross-sectional view of the lead of  FIG. 6.8  taken at section  6 . 9 - 6 . 9 ; 
           [0048]      FIG. 7  is a perspective view depicting an alternative embodiment of the pacing lead for the pericardial space according to the present invention; 
           [0049]      FIG. 8  is a side view of the pacing lead depicted in  FIG. 7  deployed in the pericardial space, 
           [0050]      FIG. 9  is an end view of the pacing lead depicted in  FIG. 7 ; 
           [0051]      FIG. 10  is a perspective view depicting another alternative embodiment of the pacing lead for the pericardial space according to the present invention; 
           [0052]      FIG. 11  is a side view of the pacing lead depicted in  FIG. 10  deployed in the pericardial space, 
           [0053]      FIG. 12  is an end view of the pacing lead depicted in  FIG. 10 ; 
           [0054]      FIG. 13  is a simplified diagrammatic, partially cut-away side view of a human heart depicting the vascular system of the heart; 
           [0055]      FIG. 14  is a simplified diagram of the venous vascular mesh on the epicardial surface; 
           [0056]      FIG. 15  is a simplified diagrammatic side cross section view of an enlarged scale of the region in circular dotted outline in  FIG. 14  depicting dilation of the microvasculature with a balloon prior to insertion of a pacing lead; 
           [0057]      FIG. 16  is a simplified diagrammatic side cross section view of the region of  FIG. 15  depicting the disposition of a catheter into the microvasculature or pericardial space; 
           [0058]      FIG. 17  is a simplified diagrammatic side cross section view of the region of  FIG. 15  depicting the disposition of a guidewire and introducer into the microvasculature or pericardial space; 
           [0059]      FIG. 18  is a simplified diagrammatic side cross section view of the region of  FIG. 15  depicting the disposition of a pacemaker lead into the microvasculature or pericardial space; 
           [0060]      FIG. 19  is a simplified diagrammatic side cross section view of the region of  FIG. 15  depicting the pacemaker lead in the microvasculature or pericardial space having assumed a preformed shape after a stiffening stylet or wire has been withdrawn; 
           [0061]      FIG. 19.1  is a simplified diagrammatic view of an enlarged scale of a venous vascular region proximate the epicardial space depicting the disposition of a guidewire therein; 
           [0062]      FIG. 19.2  is a simplified diagrammatic view of the venous vascular region depicted in  FIG. 19.1 , depicting a pacing lead being advanced into position over the guidewire, thereby dilating small venous structures; 
           [0063]      FIG. 19.3  is a simplified diagrammatic view of the venous vascular region depicted in  FIG. 19.1 , depicting the pacing lead in position after withdrawal of the guidewire, with the body of lead stabilized in the venous circulation; and 
           [0064]      FIG. 20  is a simplified diagrammatic side view of the disposition of an elongate instrument from a first venous bed through the venous vascular mesh and implantation in a second venous drainage area to enable emplacement of a pacing lead. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0065]    Referring to  FIGS. 3-6 , a pacing lead  40  according to the various embodiments of the present invention generally includes a lead body  41  with a proximal lead portion  42  having a pair of electrodes  44 ,  46 , and presenting a longitudinal lead axis  47 , and a resilient fixation portion  48 . Resilient fixation portion  48  is preformed in a helical configuration, with the helix being generally symmetrical about a fixation portion axis  50 . Fixation portion axis  50  may be generally normal to longitudinal lead axis  47  so that resilient fixation portion  48  extends laterally relative to proximal lead portion  42 . Pacing leads are generally known in the art and are disclosed in U.S. Pat. No. 6,321,123 to Morris et al. and U.S. Pat. No. 5,683,445 to Swoyer, both of which are incorporated herein by reference in their entirety. 
         [0066]    In the embodiment depicted in  FIG. 6 , lead body  41  generally includes inner body  52  with defining central lumen  54 , inner conductor  56  which is electrically coupled with distal electrode  44 , inner insulative sheath  58 , outer conductor  60  which is electrically coupled with proximal electrode  46 , and outer insulative sheath  62 . Electrodes  44 ,  46 , may be structured as rings  64  encircling lead  40 , or may be any other structure such as dorsal protuberances  90  (not depicted) enabling electrical coupling with the epicardial wall. Conductors  56 ,  60 , may be coiled wire as commonly used in the art, or may be any other suitable generally flexible conductive structure. Inner body  52  and insulative sheathes  58 ,  62 , may be formed from silicone, polyurethane, or other resilient biocompatible material. 
         [0067]    Stylet  66  or a guidewire (not depicted) may be selectively, slidably disposed in central lumen  54  to initially straighten the preformed shape and which then may be withdrawn to enable the preformed shape to develop. Stylet  66  or guidewire (not depicted) enables pacing lead  40  to be selectively maintained in a relatively stiff condition as lead  40  is advanced into and positioned within the venous system and pericardial space. It will be appreciated that in other embodiments of the invention, a guidewire may be employed to initially straighten the lead. In such embodiments, the lead will typically have an end or sidewall aperture proximate the distal end of the lead to enable the lead to be advanced over the guidewire. 
         [0068]    As depicted in  FIGS. 3-6 , resilient fixation portion  48  may be integral with inner body  52  of lead body  41 . As previously described, resilient fixation portion  48  may be preformed so as to define a resilient helical structure  68  forming a helical spring extending laterally relative to longitudinal lead axis  47 . Helical structure  68  presents a width dimension, annotated “W” in the figures, an uncompressed height dimension annotated “H 1 ” in the figures, and a compressed height dimension annotated “H 2 ” in the figures when disposed in the pericardial space. 
         [0069]    In alternative embodiments such as depicted in  FIGS. 5.1  and  5 . 2  a lateral s-curve  69  may be provided for additional stability against overturning of fixation portion  48  when implanted within the pericardial space. Moreover, as depicted in  FIGS. 3.1 ,  4 . 1 , and  6 . 1  a fixation screw element  69 . 1  or tines  69 . 2 , with or without barbs  69 . 3  may be employed at the end  69 . 4  or base  69 . 5  of fixation portion  48  to provide additional stability. 
         [0070]    The biasing force exerted by the resilience of fixation portion  48  is a function of the material properties, the cross-sectional dimension of fixation portion  48 , and the amount of lateral deflection, that is, the difference between H 1  and H 2  of fixation portion  48 . The amount of lateral deflection (H 1 −H 2 ) of fixation portion  48  will vary depending on the relative resilience of the epicardium and the parietal pericardium, and will generally be between about 0.1 centimeters and 10 centimeters, most typically from about 0.3 centimeters to about 1 centimeter. It will be appreciated that the magnitude of biasing force may be predetermined by adjusting the material properties and dimensions of fixation portion  48  using known principles of engineering. Generally, it is desirable if the compression fixation portion  48  provides between about 1 gram to about 30 grams of biasing force and more desirably between about 3 grams to about 10 grams when emplaced in the pericardial space. 
         [0071]    It will be readily appreciated that, in addition to the embodiment discussed above, a pacing lead according to the invention may take a variety of alternative forms, each including a resilient fixation element for biasing one or more electrodes on the lead against the myocardium when the lead is disposed in the pericardial space. For example, in an alternative embodiment depicted in  FIGS. 7-9 , pacing lead  70  generally includes lead body  72  with proximal lead portion  74  and distal lead portion  76 . Proximal lead portion  74  presents longitudinal lead axis  78 . Distal lead portion  76  is preformed in a helical configuration, with the helix  80  being generally symmetrical about a fixation portion axis  82  that is generally parallel with longitudinal lead axis  78 . Distal lead portion  76  generally includes a first proximal helix  82  a second distal helix  84  and a connecting stabilizing portion  86 , which may be formed as an s-shaped curve as depicted, or in any other shape enabling lateral stability against overturning within the pericardial space so as to ensure constant electrical contact for electrodes  90 ,  92 . 
         [0072]    Again, lead body  72  defines central lumen  88  for receiving a stylet (not depicted) or guidewire (not depicted) for selectively straightening the lead during implantation. Electrodes  90 ,  92 , may be provided on straight portion  86  or on proximal lead portion  74  (not depicted). 
         [0073]    Helix  80  presents a length dimension, annotated “L” in the figures, an uncompressed width dimension annotated “W 1 ” in the figures, and a compressed width dimension annotated “W 2 ” in the figures when disposed in the pericardial space. The biasing force exerted by the helix  80  is a function of the material properties, the cross-sectional dimension of lead body  72 , and the amount of deflection, that is, the difference between W 1  and W 2  of helix  80 . The magnitude of biasing force may be predetermined by adjusting the material properties and dimensions of helix  80  using known principles of engineering. Generally, it is desirable if helix  80  provides between about 1 gram to about 30 grams of biasing force and more desirably between about 3 grams to about 10 grams when emplaced in the pericardial space. 
         [0074]    In another embodiment depicted in  FIGS. 10-12 , pacing lead  94  generally includes lead body  96  with proximal lead portion  98  and distal lead portion  100 . Proximal lead portion  98  presents longitudinal lead axis  102 . Lead body  96  defines central lumen  104  for receiving a stylet (not depicted) for selectively straightening the lead during implantation. Distal lead portion  100  comprises a fixation element  106  having a first portion  108  and a second portion  110 , which together define a loop structure  112  laterally adjacent lead portion  98 . Including stabilizing extension  113 , loop structure  112  presents a width dimension, annotated “W 3 ” in the figures, an uncompressed height dimension annotated “H 3 ” in the figures, and a compressed height dimension annotated “H 4 ” in the figures when disposed in the pericardial space. Either or both of first portion  108  and second portion  110  may be generally arcuate in shape or may be generally straight. In embodiments of the invention, a straight portion  114  may be interposed between first portion  108  and second portion  110 . First portion  108  preferably forms an angle γ with longitudinal lead axis  102  of less than 90 degrees. Second portion  110  preferably forms an angle δ with respect to first portion  108  of between about 90 and about 150 degrees. Width dimension W 3  is preferably a distance sufficient to inhibit overturning of the lead  94  when emplaced in the pericardial space. 
         [0075]    For the purposes of the present invention, the term loop structure includes any lead wherein the lead tip  116 , is doubled back along the lead body and a longitudinal axis extending from the lead tip  116  parallels longitudinal lead axis  102  when the tip axis and longitudinal lead axis  102  are projected onto a common plane parallel to and including longitudinal lead axis  102 . For instance, the fixation element forming a loop structure may include a plurality of more or less straight segments angled with respect to each other, or a plurality of curved segments of various radii, a single segment with a more or less continuous curve, or a plurality of straight and curved segments joined together. The fixation element and lead body may be made with any material having suitable engineering and biocompatibility properties. The lead electrodes may take any suitable form including without limitation, coils or rings, and “buttons” or protuberances, and may be positioned on the lead body or the fixation element or any combination thereof. It may be relatively more desirable, however, to locate the electrodes proximal to any relatively sharp angles or bends in the lead so as to avoid fractures in the conductors leading to the electrodes. 
         [0076]    It will be appreciated that any of the above embodiments may further include such stabilizing and fixation elements as are known in the art such as screw fixation means and tines. The screw fixation means or tines may be located anywhere on the body of the lead or fixation portion as may be desirable so as to promote lead stability when implanted. 
         [0077]    It will be further appreciated that biocompatible adhesive may be used as an additional fixation means to ensure stability of the lead. For example, in the embodiment depicted in  FIG. 6.2 , lead body  41 . 1  generally includes inner body  52 . 1  with defining first lumen  54 . 1 , second lumen  54 . 2 , inner conductor  56 . 1  which is electrically coupled with distal electrode  44 . 1 , inner insulative sheath  58 . 1 , outer conductor  60 . 1  which is electrically coupled with proximal electrode  46 . 1 , and outer insulative sheath  62 . 1 . Again, electrodes  44 . 1 ,  46 . 1 , may be structured as rings  64 . 1  encircling lead  40 . 1 , or may be any other structure such as dorsal protuberances (not depicted) enabling electrical coupling with the epicardial wall. Conductors  56 . 1 ,  60 . 1 , may be coiled wire as commonly used in the art, or may be any other suitable generally flexible conductive structure. Inner body  52 . 1  and insulative sheathes  58 . 1 ,  62 . 1 , may be formed from silicone, polyurethane, or other resilient biocompatible material. 
         [0078]    First lumen  54 . 1  has open end  54 . 3  to enable guidewire  66 . 1  to pass through so that lead  40 . 1  may be advanced into position over guidewire  66 . 1 . Guidewire  66 . 1  may be selectively, slidably disposed in first lumen  54 . 1  to initially straighten the preformed shape and which then may be withdrawn to enable the preformed shape to develop. 
         [0079]    Second lumen  54 . 2  may have end opening  54 . 4  or one or more sidewall openings  54 . 5  or any combination thereof. Openings  54 . 4 ,  54 . 5 , are positioned wherever application of adhesive for fixation of lead  40 . 1  is desired, for example at lead end  54 . 6 , proximate fixation portion base  69 . 5 , or proximate electrodes  44 . 1 ,  46 . 1 . 
         [0080]    When lead  40 . 1  is positioned on the epicardium, adhesive in the form of biocompatible glue such as for example cyanoacrylate (butyl-2-cyanoacrylate monomer), Dermabond (2-octyl cyanoacrylate), Fibrin, or BioGlue (biological bovine serum albumin and glutaraldehyde), may be forced through second lumen  54 . 2 . The glue will exit lumen openings  54 . 4 ,  54 . 5  and be F deposited in the desired location in order to cement lead  40 . 1  in place. 
         [0081]    In addition to embodiments wherein liquid adhesive is applied through openings from a lumen in the lead, it will also be appreciated that in other embodiments, a solid adhesive may be disposed at predetermined locations on the lead. In such embodiments, the solid adhesive is activated by blood or other fluid when the lead is emplaced. 
         [0082]    Moreover, as depicted in  FIGS. 6.3  and  6 . 4 , the efficacy of the adhesive bond may be enhanced with a patch or band of absorbant material  54 . 7  disposed over the lumen openings  54 . 4 ,  54 . 5 . Absorbant material  54 . 7  may be any suitably biocompatible material, such as polytetrafluoroethylene (PTFE) felt, that will “wick” adhesive from lumen openings  54 . 4 ,  54 . 5 . It will be appreciated that the wicking action may be enhanced by selecting an adhesive  54 . 8  having a relatively low viscosity, such as Dermabond. Absorbant material  54 . 7  may be attached to lead  40 . 1  on outer surface  40 . 2  or may be insert molded in lead body  41 . 1  so that outer surface  54 . 81  of absorbent material  54 . 7  is flush with outer surface  40 . 2 . 
         [0083]    In operation, with lead  40 . 1  positioned as desired in pericardial space  39 , adhesive  54 . 8  is introduced proximate lumen openings  54 . 4 ,  54 . 5 , through second lumen  54 . 2  Adhesive  54 . 8  may be forced directly through the length of second lumen  54 . 2  as depicted in  FIG. 6.3 , or may be introduced only in the vicinity of lumen openings  54 . 4 ,  54 . 5 , using a hollow stylet  66 . 2  as depicted in  FIG. 6.5 . Adhesive  54 . 8  is drawn into and through absorbent material  54 . 7  by capillary action. When adhesive  54 . 8  sets, absorbent material  54 . 7  and lead body  41 . 1  are adhered to the tissue with which they are in contact. 
         [0084]    In an embodiment depicted in FIGS.  5 . 3 - 5 . 7  and  6 . 5 , lead  40 . 11  generally includes lead body  41 . 11  with inner body portion  52 . 11  defining lumen  54 . 11 , which may have either a closed end  54 . 31  or an open end (not depicted) to accommodate a guide wire (not depicted) to enable emplacement of the lead as previously described. A first electrode  44 . 11  is provided on lead body  41 . 11  proximate base  69 . 51  of fixation portion  48 . 11 , while a second electrode  46 . 11  is disposed proximate end  54 . 31 . Fixation portion  48 . 11  may be formed as a generally symmetrical helix with a single rotation. Preferably, fixation portion  48 . 11  may have an uncompressed height H 11  of from about 0.2 cm to about 4 cm. 
         [0085]    The spaced apart disposition of electrodes  44 . 11 ,  46 . 11 , proximate base  69 . 51  and end  54 . 31 , respectively, enables fixation portion  48 . 11  to be positioned in either a first “upright” orientation as depicted in  FIG. 5.6 , wherein electrode  44 . 11  is contacting visceral pericardium  38  while electrode  46 . 11  is contacting parietal pericardium  37 , or in a second “inverted” position as depicted in  FIG. 5.7 , wherein electrode  46 . 11  is contacting visceral pericardium  38  while electrode  44 . 11  is contacting parietal pericardium  37 . As a consequence, even if lead  40 . 11  “flips-over” so as to become inverted within pericardial space  39 , electrodes  44 . 11 ,  46 . 11 , will maintain electrical contact so that pacing is not interrupted. 
         [0086]    As before, lumen  54 . 11  may have one or more adhesive openings  54 . 4 ,  54 . 5 , to enable application of adhesive for fixation of lead  40 . 11 . Openings  54 . 4 ,  54 . 5 , are positioned wherever application of adhesive for fixation of lead  40 . 11  is desired, for example at lead end  54 . 31 , proximate fixation portion base  69 . 51 , or proximate electrodes  44 . 11 ,  46 . 11 . Absorbent material  54 . 7  may be disposed proximate and/or over openings  54 . 4 ,  54 . 5 , to facilitate distribution of adhesive  54 . 8  and to improve the resultant tissue bond. Again, the adhesive  54 . 8  may be forced directly through lumen  54 . 11 , or may be applied only in the vicinity of openings  54 . 4 ,  54 . 5 , though lumen  66 . 3  of hollow stylet  66 . 2 . 
         [0087]    It will be readily appreciated that adhesive fixation means in accord with the present invention may be incorporated as desired to provide stability to any pericardial lead by enabling cementation of the lead at desired locations, especially proximate electrodes. Moreover, with the compression fixation elements of any of leads  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 , the electrodes may be disposed spaced apart so as to engage both the visceral pericardium  38  and parietal pericardium  37  when disposed in pericardial space  39  to alleviate lack of electrical contact due to overturning of the lead. 
         [0088]    For example, referring to FIGS.  6 . 6 - 6 . 9 , a pacing lead  340  generally includes a lead body  341  with a proximal lead portion  342  having a pair of electrodes  344 ,  346 , and presenting a longitudinal lead axis  347 , and a resilient compression fixation portion  348 . Resilient compression fixation portion  348  is preformed in a generally helical configuration having a single coil  349 , with coil  349  being generally symmetrical about a fixation portion axis  350 . Fixation portion axis  350  may be generally normal to longitudinal lead axis  347  so that resilient fixation portion  348  extends laterally relative to proximal lead portion  342 . Coil  349  presents a width dimension, annotated “W 10 ” in the figures, and an uncompressed height dimension annotated “H 11 ” in the figures. 
         [0089]    The biasing force exerted by the resilience of coil  349  is a function of the material properties, the cross-sectional dimension of coil  349 , and the amount of lateral deflection, that is, the difference between H 11  and the compressed height of coil  349  when emplaced in pericardial space  39 . The amount of deflection of coil  349  will vary depending on the relative resilience of the epicardium and the parietal pericardium, and will generally be between about 0.1 centimeters and 10 centimeters, most typically from about 0.3 centimeters to about 1 centimeter. It will be appreciated that the magnitude of biasing force may be predetermined by adjusting the material properties and dimensions of coil  349  using known principles of engineering. Generally, it is desirable if coil  349  provides between about 1 gram to about 30 grams of biasing force and more desirably between about 3 grams to about 10 grams when emplaced in pericardial space  39 . 
         [0090]    Lead body  341  generally includes inner body  352  defining lumen  354 , inner conductor  356  which is electrically coupled with distal electrode  344 , inner insulative sheath  358 , outer conductor  360  which is electrically coupled with proximal electrode  346 , and outer insulative sheath  362 . Stylet  366  or a guidewire (not depicted) may be selectively, slidably disposed in lumen  354  to initially straighten the preformed shape and which then may be withdrawn to enable the preformed shape to develop. As depicted, stylet  366  may be hollow, defining lumen  366 . 1  to enable introduction of adhesive as described further hereinbelow. Although electrodes  344 ,  346 , are both depicted on the same side of coil  349 , it will be appreciated that, in an alternative embodiment, one of electrodes  344 ,  346 , may be disposed on the other side of coil  349  to enable the lead to be oriented in either an upright or inverted position as previously described. 
         [0091]    Adhesive openings  368 ,  370 ,  372 ,  374 ,  376 , may be provided, extending from lumen  354  to exterior surface  378  of lead  340  to enable application of adhesive for fixation of lead  340 . Openings  368 ,  370 ,  372 ,  374 ,  376 , are positioned wherever application of adhesive for fixation of lead  340  is desired, for example at lead end  353 , on top surface  380  of coil  349 , or proximate electrodes  344 ,  346 . Again, absorbent or other material  382  exhibiting capillary action may be disposed proximate and/or over the adhesive openings, to facilitate distribution of adhesive and to improve the resultant tissue bond. As depicted in FIGS.  6 . 6 - 6 . 9 , a ring of material  382  is disposed around openings  368 ,  370 , and  372 , while a band of material  382  is disposed around lead  340  covering openings  374 ,  376 . Again, the adhesive may be forced directly through lumen  354 , or may be applied only in the vicinity of openings  368 ,  370 ,  372 ,  374 ,  376 , though lumen  366 . 1  of hollow stylet  366 . 
         [0092]    Leads  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , may be disposed in pericardial space  39  by any suitable method either surgically or percutaneously. In an exemplary embodiment, pacemaker lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , is disposed in pericardial space  39 , on or in the epicardium or in the microvasculature by first disposing an elongate instrument into the venous system of the heart and puncturing the venous system at a predetermined position, disposing the elongate instrument into the pericardial space, epicardium or in the microvasculature at a predetermined location in the pericardial space, epicardium or in the microvasculature; and disposing a pacemaker lead at the predetermined position. It should be clear that lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , can be disposed either into the pericardial space  39  or into the vascular mesh in or on the heart wall surface just adjacent to pericardial space  39 . Other suitable methods for introduction of the lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , of the present invention into the pericardial space or the microcirculation are disclosed in published U.S. patent application Ser. No. 10/497,763, entitled METHOD AND APPARATUS FOR ANCHORING OF PACING LEADS, hereby fully incorporated herein by reference. 
         [0093]    The step of disposing a pacemaker lead at the predetermined position includes disposing the lead in a position on the surface of the left ventricle in a position of optimized pacing efficacy through the venous microvasculature on the ventricular surface or in the pericardial space. In an embodiment the elongate instrument may be disposed into a first venous bed through the vascular mesh and subsequently into a second venous drainage bed for optimal positioning at or near the ventricular surface or adjacent pericardial space. The microvasculature may also be dilated prior to implanting the pacemaker lead in order to allow for access of the guiding instrument or lead. In either case, the biasing force exerted by the resilient fixation element of the pacemaker lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , in combination with friction, and adhesive in some embodiments, is used to fix the lead in place and bias the lead electrodes against the epicardium for good electrical conductivity. Returning to the exemplary embodiment of a method according to an embodiment of the invention, and referring now to  FIGS. 13-20 , a wire, catheter, lead, introducer or other instrument  118  is endovascularly disposed by conventional means into the coronary venous system  120  to a point  122  in the coronary venous system  120  where a puncture of the venous system  120  may take place as depicted in  FIG. 13 . 
         [0094]    At this point  120 , a coronary vein  124  is punctured or otherwise opened to allow the disposition of the wire, catheter, lead, introducer or other instrument  118  to be disposed through the vein  124  and then inserted, steered or disposed in the pericardial space  39  to the desired location on the myocardial surface. 
         [0095]    There are many means whereby the incision or puncture through the wall of vein  124  may be accomplished. A hollow or solid needle  126  as depicted in  FIGS. 14 and 15  can be disposed through a catheter  118  and positioned at the venous site  122  selected. Advancement of the needle  126  beyond the distal tip of the catheter  118  enables the needle to puncture the vein  124  at the desired location  122 . The vein  124  may also be punctured employing cutting or puncturing probes using ohmic heating, laser light, radiofrequency or microwave heating, ultrasonic or other energy sources, a balloon or blunt probe may also be used to open the vein into the pericardial space. 
         [0096]    Once the vein  124  is punctured confirmation must be obtained that entry into the pericardial space  39  is accomplished. This can be practiced by injecting a contrast agent through the puncture site  122  into the pericardial space  39 , obtaining an ultrasound image of the field of operation, or inserting a guidewire or other radio opaque means into the puncture site  122  for fluoroscopic confirmation. 
         [0097]    With confirmation of entry into the pericardial space  39  a guidewire or probe  128  is then advanced into the space  39  through catheter  118 , which may be removed and then followed, if desired, by an introducer or other introducing instrument  130  which is steerable or otherwise navigable to the desired location in the pericardial space  39  adjacent to or proximal to the desired location in the left ventricular wall as shown in  FIG. 17 . 
         [0098]    Finally, a pacing lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , straightened with stylet  66  is then brought or disposed at the desired location using the introducer or other introducing instrument  130  or the pacing lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , itself may be self-guiding as depicted in  FIG. 18 . Once the desired location has been accessed; the stylet  66  is withdrawn from the lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , enabling it to assume its preformed shape, compressed between the parietal paricardium and epicardium as depicted in  FIG. 19 , keeping the electrodes oriented toward the myocardium. In the case of patients who have cardiac bypass surgery, the pericardial space  39  often includes adhesive tissues, which provide a naturally adhesive or embedding tissue field, enhancing frictional engagement of the lead. 
         [0099]    It will be appreciated by those of skill in the art that when lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , is introduced transvenously into the heart and from there into the pericardial space through the coronary venous structure, the proximal portion of lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , will be stabilized and supported within the venous system. Moreover, by using the coronary venous microcirculation as a means to access the pericardial space, the final position of the lead and the site where the lead exits the vein into the pericardial space can be kept in close proximity. By comparison, standard leads that stay within the vein can only be placed where there are veins large enough to accommodate the body of the lead. With a lead and method according to the invention, small veins may be used to position the guide wire where the lead is to be positioned, and the lead may then be advanced along the wire to the desired site by dilating the small veins to the point of rupture at which point the tip of the lead is not within the vein and the tip may be stabilized to ensure electrode contact. 
         [0100]    For example, as depicted in FIGS.  19 . 1 - 19 . 3 , guidewire  200  may be advanced through large  202  and small  204  coronary veins into desired lead implantation region  206  which may be within the pericardial space. Next, lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , is advanced over guidewire  200 , dilating small veins  204  to the point of rupture as depicted in  FIG. 19.2 . Once lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , is properly positioned, guidewire  200  is withdrawn to enable  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , to assume its pre-formed shape as depicted in  FIG. 19.3 . The proximal portion  208  of lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , is stabilized by virtue of close frictional engagement within small veins  204 , while lead tip  210  is stabilized by fixation portion  48 . 
         [0101]    No restrictions or limitations are envisioned as being included which would in any way reduce the scope of the means whereby the wire, catheter, lead or other instrument  118 ,  128 ,  130 , or  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , may be steered, by which the vein  124  is punctured, by which the vein is sealed around the wire, catheter, lead, other instrument,  118 ,  128 ,  130 , or pacing lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , or by which the lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , is secured at the desired location. 
         [0102]    Lead,  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , may also be disposed in the vascular mesh. The ventricular surface of the heart has disposed therein and/or thereon a microvasculature  132  as diagrammatically shown in  FIG. 14  between the arterial system  134  and venous system  120  forming what comprises a vascular mesh. The vascular mesh is comprised of a multiplicity of small vessels radiating from the more distal portions of the coronary venous system. The vascular mesh subdivides into smaller and smaller multi-branched vessels and ultimately communicates to the capillary system in the heart walls. Blood drains from the heart muscle into the vascular mesh and then into the coronary veins. Generally, a flow path can be found through the vascular mesh communicating one vessel of the coronary venous system with another vessel of the coronary venous system. 
         [0103]    The microvasculature  132  may also be opened or dilated with a balloon  136  or blunt instrument that opens the distal microvasculature  132  to allow for a catheter or other instrument  118  to be advanced. The balloon  136  may be withdrawn, or a central channel through a balloon catheter  118  may be used to withdraw needle  126 , so that another catheter, lead or other instrument  118  can be deployed into the microvasculature  132 . 
         [0104]    In one embodiment access to the venous system  120  through the coronary sinus is accomplished using a fine, flexible 0.014 inch guidewire  138 . The guidewire  138  is steered through a selected venous path to the very end of a venous bed  140  shown in,  FIG. 19 . At the end of a venous bed  140 , the vascular system  120 ,  134 , communicates with an adjacent vascular bed through a vascular mesh  132  located on the epicardium  38  and also communicating with one or more other venous beds  142 . Theoretically, a path can be traced through the vascular mesh  132  between any two venous beds  140  and  142  in the entire cardiac vascular system  120 ,  134 . In theory the wire  138  can be advanced through the vascular mesh  132  into an adjacent or another venous bed  140  and ultimately looping back to the coronary sinus. 
         [0105]    In this manner the wire  138  can be then steered from a first venous bed  140  to a selected position in a second venous bed  142 , which position  140  might be accessible or easily accessible through the coronary sinus and the second venous bed  142  accessible as a practical matter only by a path through the coronary sinus, the first venous bed  140 , the vascular mesh  132  and into the second venous bed  142 . Therefore, the ideal or desired position for a pacing lead becomes accessible even if located in the second venous bed  142  through the first venous bed  140 . 
         [0106]    The pacemaker lead  142  is stabilized in its position by virtue of its frictional engagement or intimacy with the terminal end of the first venous bed  140  and with the vascular mesh  132 . If necessary, the end of the first venous bed  140  and the vascular mesh  132  can be opened by positioning an angioplasty balloon  136  on the guidewire  138  at the position of terminal constriction of the first and second venous beds  140 ,  142  and in the vascular mesh  132 . This allows for the easy passage then of a pacemaker lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , through the terminal constriction of the first and second venous beds  140 ,  142 , and the vascular mesh  132 . The lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 , is then secured in position in the second venous bed  142  by virtue of its embedment in the terminal constriction of the first and second venous beds  140 ,  142 , and/or the vascular mesh  132 . 
         [0107]    It is further possible that use of the balloon  136  may be used to intentionally rupture the microvasculature  132  allowing the lead  40 ,  40 . 1 ,  40 . 11 ,  74 ,  94 ,  340 , to then enter the pericardial space  39  and become anchored therein as described above in a manner similar to venous puncture. 
         [0108]    Although the present invention has been described with reference to particular embodiments, one skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and the scope of the invention. Therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive.