Abstract:
Apparatus and surgical methods establish temporary suction attachment to a target site on the surface of a bodily organ for enhancing accurate placement of a surgical instrument maintained in alignment with the suction attachment. A suction port on the distal end of a supporting cannula provides suction attachment to facilitate accurate positioning of a needle for injection penetration of tissue at the target site of for anchoring a cardiac electrode on the moving surface of a beating heart. Force applied via the suction attachment to the surface of the heart selectively distorts the surface of the myocardium for angularly orienting and accurately positioning a surgical instrument or cardiac electrode thereon.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of pending application Ser. No. 10/140,309, entitled “Methods And Apparatus For Endoscopic Cardiac Surgery”, filed on May 6, 2002 by A. Chin. et al, which is a continuation-in-part of pending application Ser. No. 09/635,721, entitled “Apparatus for Endoscopic Access”, filed on Aug. 9, 2000 by A. Chin, which claims the benefit of the filing of provisional application Nos. 60/150,737, on Aug. 25, 1999, and 60/148,130 on Aug. 10, 1999, each of which applications is incorporated herein in its entirety by this reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to endoscopic cardiovascular surgical procedures and instruments, and more particularly to apparatus including a vacuum-assisted cannula and surgical instruments operable therewith, and to surgical procedures utilizing such apparatus.  
         BACKGROUND OF THE INVENTION  
         [0003]    The injection of undifferentiated satellite cells or myocytes or stem cells into the myocardium of a beating heart in the endoscopic procedure of cellular cardiomyoplasty must be performed carefully to avoid complications. A specialized instrument, as described in the aforecited applications, is advanced through an operating channel of an endoscopic cannula to deliver cells in controlled manner into a beating heart. If a needle is used to inject the cells, sufficient control must be provided to ensure that the needle does not puncture a coronary vein or artery and cause hemorrhage within the pericardial space, with subsequent cardiac tamponade. Movement of the beating heart further complicates needle placement because of erratic movement of the coronary vessels as needle insertion is attempted. Similarly, placement of other elements such as epicardial pacing or defibrillation leads into the myocardium of a beating heart must be carefully placed to avoid puncture of a coronary vein or artery with concomitant complications.  
         SUMMARY OF THE INVENTION  
         [0004]    In accordance with the illustrated embodiments of the present invention, a substantially rigid cannula includes separate elongated lumens extending between distal and proximal ends of the cannula to provide an instrument channel and one or more separate vacuum channels that terminate in a suction port located adjacent the distal end of the cannula. The instrument channel is sized to accommodate various surgical instruments including a hollow needle for penetrating the myocardium to deliver the cells. The needle is configured for shallow penetration to avoid puncturing into a chamber of the heart with associated complications. In an alternative embodiment, an instrument channel carried by a ‘needle’ is sized to accommodate epicardial pacing or defibrillating leads. Additionally, the cannula with separate lumens or channels therethrough may be incorporated with or disposed within an instrument channel of an endoscopic cannula that houses an endoscope aligned with a distal transparent tip. This assemblage of surgical instruments may be conveniently positioned through tissue disposed between a subxiphoid incision and a surgical site on the epicardium of a beating heart, or positioned through tissue disposed between a thoracotomy incision and a surgical site on the epicardium of a beating heart. In some cases, a laterally expandable sheath may be employed to form a working cavity in tissue to facilitate the placement of the vacuum port and associated instrument channel at the surgical site on the epicardium, as described in the aforecited related applications. In another embodiment of the present invention, a guide tube carries a suction tube slidably therein and supports a lead-placing channel thereon which includes rotatable or slidable half sections that house a cardiac pacing or defibrillating lead. The lead-placing channel can be configured to enclose a cardiac lead and to release the lead along a longitudinal slot therein that results from reconfiguring the channel after placement of a distal end of the cardiac lead into the myocardium. The suction tube terminates as its distal end in a suction pod that can provide temporary suction attachment of the assembly at a selected surgical location on the myocardium of a beating heart while a cardiac lead is manipulated within the placement channel to anchor the distal end of the cardiac lead to the myocardium. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a side view of a vacuum-assisted insertion cannula in accordance with one embodiment of the present invention;  
         [0006]    [0006]FIG. 2 is a side view of an endoscopic cannula for use with the insertion cannula of FIG. 1;  
         [0007]    [0007]FIG. 3 is a partial side view of the assembled cannulas of FIGS. 1 and 2 in a surgical procedure;  
         [0008]    [0008]FIG. 4 a  is a partial side view of a split needle according to one embodiment of the present invention;  
         [0009]    [0009]FIG. 4 b  is a partial side view of a needle with short bevel sharpened tip according to an embodiment of the present invention;  
         [0010]    [0010]FIG. 5 is a perspective view of another embodiment of an insertion cannula in accordance with the present invention;  
         [0011]    [0011]FIGS. 6 a  and  6   b  comprise a flow chart illustrating a surgical procedure in accordance with the present invention;  
         [0012]    [0012]FIG. 7 is a plan view of an epicardial lead with screw-in distal tip and attached proximal connector;  
         [0013]    [0013]FIG. 8 is a partial plan view of a needle in one configuration incorporating an open instrument channel for placement of an epicardial lead;  
         [0014]    [0014]FIG. 9 is a partial plan view of the needle of FIG. 8 in a complementary configuration incorporating a closed instrument channel;  
         [0015]    [0015]FIG. 10 is a plan view of a cannula with attached instrument channel;  
         [0016]    [0016]FIG. 11 is a plan view of a releasable guide for a cardiac lead according to another embodiment of the present invention;  
         [0017]    [0017]FIG. 12 is a partial plan view of the distal end of the releasable guide in the embodiment of FIG. 11;  
         [0018]    [0018]FIG. 13 is a partial plan view of the proximal end of the releasable guide in the embodiment of FIG. 11;  
         [0019]    [0019]FIG. 14 is a top view of the distal end of the releasable guide in the embodiment of FIG. 11;  
         [0020]    [0020]FIG. 15 is a perspective view of the distal end of the releasable guide according to the embodiment illustrated in FIG. 11;  
         [0021]    [0021]FIG. 16 is a partial plan view of a releasable guide in accordance with the embodiment illustrated in FIG. 11;  
         [0022]    [0022]FIG. 17 is a partial plan view of the releasable guide of FIG. 11 assembled with an endoscopic instrument;  
         [0023]    [0023]FIG. 18 is a sectional view of the releasable guide of FIG. 16;  
         [0024]    [0024]FIG. 19 is a partial plan view of one embodiment of the proximal end of the guide channel of the releasable guide of FIG. 16;  
         [0025]    [0025]FIG. 20 is an end view of the proximal end of the guide channel of FIG. 16; and  
         [0026]    [0026]FIGS. 21 a  and  21   b  comprise a flow chart illustrating a surgical procedure for implanting a cardiac lead in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    Referring now to FIG. 1, there is shown one embodiment of a suction assisted insertion cannula  10  according to the present invention including a closed channel  9  and a superior channel  11  attached to the closed channel. The closed channel  9  includes a suitable hose connection  13  and a three-way vacuum control valve  15  including an irrigation port  16  at the proximal end, and a suction pod  17  positioned on the distal end. The suction pod  17  includes a porous distal face or suction ports  19  that serves as a vacuum port which can be positioned against the epicardium to facilitate temporary fixation thereto as a result of the reduced air pressure of vacuum supplied to the suction pod  17 . The distal end of the superior instrument channel  11  that is attached to the closed channel  9  may thus be held in accurate fixation in alignment with a selected surgical site on the epicardium relative to the suction fixation location of the suction pod  17  on the epicardium. A rounded smooth surface of suction pod  17  may be used to apply gentle pressure on the epicardium to stop bleeding at small puncture sites, or to allow injected cells to be absorbed without exiting back out of the injection.  
         [0028]    The superior channel  11  is sized to accommodate slidable movement therein of a hollow needle  21  that may exhibit lateral flexibility over its length from the needle hub  23  at the proximal end to the sharpened distal end  25 . When used to inject cells, the needle  21  may be about 22-25 gauge in diameter and includes an internal bore of sufficient size to facilitate injection of cells without incurring cell damage, or lysis. When used to place pacing or defibrillating leads, the needle  21  may be about 2-2.5 mm in diameter with an internal bore of sufficient size to accommodate a lead of diameter up to approximately 2 mm in diameter.  
         [0029]    Due to the relatively large diameter of the needle for epicardial lead placement (approximately 2-2.5 mm in diameter), a solid obturator  20  may optionally be used with the slotted needle  21 , as illustrated in FIG. 4 a , for insertion into the myocardium. The obturator  20  closes off the distal end of the needle, to prevent the needle from coring out a section of the myocardium during needle insertion, with associated excessive bleeding. The obturator  20  may be removed from the needle  21  after needle insertion and the epicardial lead advanced into the myocardium. The epicardial lead, as illustrated in FIG. 7, is flexible and may be positioned within its own split sheath or tube for easier insertion through the slotted needle.  
         [0030]    After the lead is implanted in the heart by the procedure described above, the proximal end is disposed out through the small initial incision in the patient. The proximal end may then be tunneled subcutaneously from the initial incision to an incision in the patient&#39;s upper chest where a pacemaker or defibrillator will be located. A small, elongated clamp is passed through the subcutaneous tunnel to grasp the proximal end of the epicardial lead to facilitate pulling the lead through the tunnel for placement and attachment to the pacemaker or defibrillator.  
         [0031]    Both the superior channel  11  and the needle  21  may be longitudinally slotted for placing an epicardial lead that may incorporate a large diameter connector, as illustrated in FIG. 7. A split sheath can be used around the lead to facilitate advancement and rotation of the lead via the slotted needle. After anchoring such lead in the myocardium, for example by screwing in the distal tip, the slotted needle  21  is rotated to align its slot with the slot in the superior channel  11 , thus allowing the lead to be released from the cannula.  
         [0032]    The structure according to this embodiment of the invention, as illustrated in FIG. 1, is disposed to slide within the instrument channel in an endoscopic cannula  27 , as shown in FIG. 2. This cannula includes an endoscope  29  therein that extends from a tapered transparent tip  31  attached to the distal end, to a viewing port  33  at the proximal end that can be adapted to accommodate a video camera. In this configuration, the structure as illustrated in FIG. 1 may be positioned within the instrument channel in the cannula  27  of FIG. 2 to position the suction pod  17  and sharpened needle tip  25  in alignment with a surgical target on the heart, as illustrated in FIG. 3. The suction pod  17  is temporarily affixed to the epicardium in response to suction applied to the porous face  19  of the suction pod  17  under control of a suction valve  15 , and the sharpened tip  25  of the needle  21  may then be advanced to penetrate into the myocardium at an accurately-positioned surgical site, all within the visual field of the endoscope  29  through the transparent tip  31 . Following injection, the needle is withdrawn and the suction pod  17  may be rotated or otherwise manipulated to position a surface thereof on the injection site with gentle pressure to allow time for the injected cells to be absorbed and to control any bleeding occurring out of the injection site.  
         [0033]    As illustrated in FIGS. 2 and 3, the various channels in the endoscopic cannula  27  and the insertion cannula  10  have specific orientations with respect to each other in order to provide stabilization of the epicardial surface and allow visual control of the injection process. In the endoscopic cannula  27 , the instrument channel is positioned below the endoscopic channel and this allows the cannula  27  and the transparent tapered tip  31  on the endoscope  29  to retract the pericardium away from the epicardial surface of the heart at the operative site. This creates a space  95  for contacting the heart below the pericardium, as illustrated in FIG. 3. As the cell insertion cannula  9  is advanced forward out of the instrument channel of the endoscopic cannula  27 , the suction pod  17  is visualized through the endoscope  29  and transparent tip  31 , as the suction pod  17  is placed on the epicardial surface of the heart. At a selected site on the heart, for example, at the site of an old myocardial infarct, the suction is activated to attach the pod  17  to the heart. The configuration of the instrument channel of the cell insertion cannula  10  on top of the suction channel  9  allows the needle  21  to be visible as soon as it exits from the instrument channel, and remain visible within the visual field of the endoscope along the entire path of travel of the needle  21  from the insertion cannula  10  to its insertion into the myocardium. Continuous visualization of the needle  21  in this manner helps to prevent inadvertent puncture of a coronary vessel.  
         [0034]    The configuration of the suction pod  17  and the needle  21  on the insertion cannula  10  also facilitates delivery of substances or devices in an orientation perpendicular to the epicardial surface. For placement of pacing or defibrillation leads, it is particularly desirable to have the leads enter the myocardium in an orientation that is generally perpendicular to the epicardial surface for secure anchoring in the myocardium. Generally, the insertion cannula  10  is advanced through the endoscopic cannula  27  and approaches the epicardial surface of the heart at a tangential angle. Accordingly, the insertion cannula  10  is configured to facilitate deforming the epicardial surface in order to achieve perpendicular entry of the needle  21  into the myocardium, as illustrated in FIG. 3. The suction pod  17  of the insertion cannula  10  temporarily attaches to the epicardial surface upon application of vacuum under control of the valve  15 . Downward pressure can be exerted on the epicardial surface via the substantially rigid insertion cannula  10 . The pliable myocardium thus deforms to create a surface ledge  100  distal to the suction pod  17  oriented perpendicular to the axis of the superior instrument channel  11  of the insertion cannula  10 , as illustrated in FIG. 3. As the needle  21  is advanced, it enters the myocardium generally perpendicularly to the epicardial surface as thus deformed for desirable lead placement or cell injection.  
         [0035]    Referring now to FIGS. 3 and 4 b , it should be noted that the insertion cannula  10  is sized to fit in slidable orientation within the working channel of about 5-7 mm diameter in the endoscopic cannula  27 . The outer dimensions of the suction pod  17  are less than 5-7 mm diameter and is configured on the distal end of the closed channel  9  not to obstruct the forward movement of the needle  21  past the closed, back surface  19  of the suction pod  17 .  
         [0036]    As illustrated in FIG. 4 b , the sharpened distal end  25  of the needle  21  includes a relatively short, sharpened bevel of length approximately 2-3 times the diameter of the needle. The short bevel length of the needle assures that cells are injected within the myocardium, and that part of the needle bevel does not extend into a heart chamber, with resultant intracardiac cell delivery. A visual and tactile marker  30  of extended diameter may be incorporated into the distal portion of the needle  21 . As the needle is advanced into the myocardium, the marker  30  of enlarged diameter offers increased resistance to tissue insertion. The marker  30  is positioned just proximal to the bevel of the needle and extends proximally a distance of approximately 5-7 mm.  
         [0037]    A needle stop may also be built into the proximal end of the needle  21 . Such a stop may simply be the hub  23  of the needle, and the needle  21  may be sufficiently limited in length that only a specific length of needle, for example 1 cm, may extend out of the instrument channel of the cell insertion cannula  10  when the needle hub  23  abuts against the proximal face of the instrument channel  11 . However, the distal visual and tactile marker  30  provides generally more precise guide to depth of needle penetration under conditions of different angles of possible needle insertion with respect to the epicardial surface. With an extremely shallow angle of entry, a needle of short length may not enter the heart at all. In use, the transparent tip  31  and the suction pod  17  of the assembled cell injection device may be manipulated to reshape a localized portion of the epicardial surface of the heart to allow perpendicular entry of the needle into the myocardium, as illustrated in FIG. 3. With the suction pod  17  activated, gentle manipulation of the insertion cannula allows adjustment of the needle entry angle while maintaining temporary vacuum-assisted attachment to the epicardial surface, as shown in FIG. 3.  
         [0038]    The insertion device may also inject substances other than cells. Angiogenic agents such as vascular endothelial growth factor (VEGF) may be injected into myocardial scar tissue in an attempt to stimulate neovascularization, or growth of new blood vessels into the area. Insertion of the needle itself into myocardial tissue may be therapeutic as a form of transmyocardial revascularization (TMR). It is believed that needle insertion injury may stimulate angiogenesis, or growth of new vessels into a devascularized portion of the heart. The cell insertion cannula thus promotes accurate placement of a needle  21  into myocardium under continuous visualization. When combined with the endoscopic cannula, the needle placement may be accomplished through a small, 2 cm subxiphoid skin incision.  
         [0039]    The illustrated embodiment of the insertion cannula includes a substantially rigid cannula containing a closed channel  9  ending in a distal suction pod  17 , and a superior instrument channel  11  ending immediately proximal to the suction pod  17  on the closed channel  9 . In operation, a long needle is advanced through the instrument channel  11 . The needle  21  contains a marker  30  immediately proximal to its beveled tip  25  that serves as a visual or other sensory indicator of the depth of needle insertion. The marker  30  may be a segment of expanded diameter to provide tactile feedback upon insertion into myocardial tissue. For example, a gold-colored metallic sleeve  30  may be welded or soldered onto the needle  21  to provide both visual and tactile feedback of the depth of penetration of the needle tip into the myocardium. The marker may alternatively include a series of rings etched in the needle or a band etched or sandblasted in the same area. A three-way valve  15  on the cannula  9  allows suction in the pod  17  to be turned on or off, and allows irrigation fluid such as saline to be injected through the suction pod  17  while suction is turned off.  
         [0040]    Referring now to FIG. 5, there is shown a perspective view of another embodiment of an insertion cannula  35  similar to insertion cannula  10  described above, including an elongated body  36  having a central bore  37  there through to serve as an instrument channel, and including one or more eccentric channels  39  that serve as suction conduits. The central bore may be sized to slidably support surgical instruments  41  therein such as tissue cutters anddissectors, electrocoagulators, injection needles, and the like. For example, surgical instrument  41  may be an energy-supplying ablation probe for epicardial ablation of myocardial tissue in the treatment of cardiac arrhythmia such as atrial flutter or atrial fibrillation. The ablation probe  41  may use radio frequency, microwave energy, optical laser energy, ultrasonic energy, or the like, to ablate myocardial tissue for arrhythmia correction. The suction pod  17  attaches to the epicardial surface while suction is turned on at valve  15  to facilitate advancing the ablation probe  41  through the cannula  35  into contact with the heart at the desired site under direct endoscopic visualization for precise myocardial ablation.  
         [0041]    The left atrial appendage is frequently the site or source of thromboemboli (blood clots) that break away from the interior of the left atrial appendage and cause a stroke or other impairment of a patient. An ablation probe  41  can be used in the cannula  35  to shrink and close off the appendage to prevent thromboemboli from escaping.  
         [0042]    In a similar procedure, a suture loop or clip can be placed through the cannula  35  and applied tightly around the atrial appendage to choke off the appendage.  
         [0043]    The suction channels  39  in the cannula  35  of FIG. 5 may form a suction attachment surface at the distal end of the cannula  35 , or may be disposed in fluid communication with a suitable suction pod with a porous distal face and with a central opening in alignment with the central bore  37 . The suction-ataching distal face provides an opposite reaction force against a tool that exerts a pushing force such as a needle, screw-in lead tip, or other device deployed through the central bore  37  of the cannula  35 . The proximal ends of the eccentric channels  39  are connected via a manifold or fluid-coupling collar  43  to a vacuum line  45 . Alternatively, a single channel  39  may communicate with an annular recess or groove disposed concentrically about the central bore  37  within the distal end to serve as a suction-assisted attachment surface.  
         [0044]    In this configuration, an injection needle  21  slidably disposed within the central bore  37  may be extended beyond the distal end of the cannula  35 , within the visual field of an endoscope, in order to orient the needle in alignment with a surgical target site on the pericardium prior to positioning the distal end of the cannula on the pericardium and supplying suction thereto to temporarily affix the cannula  35  in such position. A cannula  35  formed of transparent bioinert material such as polycarbonate polymer facilitates visual alignment of the cannula  35  and the central bore  37  thereof with a surgical site, without requiring initial extension of a surgical instrument, such as a cell-injection needle, forward of the distal end within the visual field of an endoscope. In an alternative embodiment, the central lumen or bore  37  may serve as a suction lumen with multiple injection needles disposed in the outer lumens  39 .  
         [0045]    Referring now to the flow chart of FIGS. 6 a ,  6   b , the surgical procedure for treating the beating heart of a patient in accordance with one embodiment of the present invention proceeds from forming  51  an initial incision at a subxiphoid location on the patient. The incision is extended  52  through the midline fibrous layer (linea alba). The tissue disposed between the location of subxiphoid incision and the heart is bluntly dissected  53 , for example, using a blunt-tip dissector disposed within a split-sheath cannula of the type described in the aforecited patent application. The channel thus formed in dissected tissue may optionally be expanded  55  by dilating tissue surrounding the channel, for example, using a balloon dilator or the split-sheath cannula referenced above, in order to form a working cavity through the dissected and dilated tissue, although this may be unnecessary.  
         [0046]    An endoscopic cannula, for example, as illustrated in FIG. 2 including an endoscope and a lumen for receiving surgical instruments therein is inserted  57  into the working cavity through the subxiphoid incision toward the heart to provide a field of vision around a target site on the heart, and to provide convenient access via the lumen for surgical instruments of types associated with surgical procedures on the heart. The first such instrument is the pericardial entry instrument, as described in the aforementioned provisional applications, which generally grasp the pericardium in a side-bite manner to form an elevated ridge of tissue through which a hole can be safely formed without contacting the epicardial surface. Once the pericardium is penetrated  58 , other instruments can be inserted through the hole and into the working space  58 . One such instrument is an insertion cannula, for example, as illustrated in FIG. 1, that includes a suction channel and an instrument channel and is slidably supported  59  within the instrument lumen of the endoscopic cannula. The suction channel of such instrument extends through the length thereof from a proximal end to a suction pod at the distal end that can be extended into contact  61  with the beating heart of the patient at a selected target site. The suction pod can be carefully positioned on the epicardium under visualization through the endoscope, and the suction can be applied to establish temporary attachment of the injection cannula to the epicardium. A needle or other surgical instrument such as surgical scissors or an electrocauterizer, or the like, is then moved into contact  63  with the epicardium to perform a surgical procedure at or near the target site. One surgical procedure includes penetrating the epicardium and myocardial tissue with the needle, typically in a region of a previous infarct, to stimulate transmyocardial revascularization or to inject undifferentiated satellite cells to promote regrowth of scarred myocardial tissue. During such surgical procedure, it is important to limit the depth of penetration of the needle in order to assure injection penetration only into the myocardium, and to avoid puncture into a heart chamber. A penetration indicator  30  may be disposed about the needle near the distal end thereof to provide visual and/or tactile feedback as mechanisms for limiting  65  the depth of needle penetration, as illustrated in FIG. 4 b . Specifically, visualization of the penetration indicator via the endoscope facilitates control of manual extension of the needle into the myocardium. Additionally, an indicator of increased diameter disposed about the needle at an appropriate position proximal the distal end serves as a penetration indicator by providing increased tactile feedback of limiter by increasing the resistance to insertion of the needle into the myocardium. After needle penetration and cell injection, the suction pod  17  may be manipulated to apply gentle pressure  66  at a surface thereof to the injection site to allow cell absorption and to tamponade any bleeding from the injection site.  
         [0047]    After one or more injections of the myocardium, positioned and performed as described above, the injection cannula and the needle supported therein are removed  67  through the instrument lumen of the endoscopic cannula which is then also retrieved  69  from the working cavity, and the initial subxiphoid entry incision is then sutured closed  71  to conclude the surgical procedure.  
         [0048]    The endoscopic cannula and pericardial entry instrument may also be applied from a thoracotomy incision to gain access to the heart. A 2 cm incision is performed in an intercostal space in either the left or the right chest. Ideally, the incision is made between the midclavicular line and the anterior to mid axillary line. The incision is extended through the intercostal muscles and the pleura, until the pleural cavity is entered. The endoscopic cannula is then inserted into the pleural cavity and advanced to the desired area of entry on the contour of the heart, visualized within the pleural cavity. The pericardial entry instrument and procedure as described in the aforementioned applications are used to grasp the pleura, and a concentric tubular blade cuts a hole in the pleura, exposing the pericardium underneath. The pericardium is then grasped by the pericardial entry instrument, and the tubular blade is used to cut a hole in the pericardium, allowing access to the heart. The transparent tapered tip  31  of the endoscopic cannula  29  aids in pleural and pericardial entry by retracting lung and pleural tissue that may impede visualization of the pericardial entry site. Once the pericardium is entered, the endoscopic cannula  29  may be moved around to visualize anterior and posterior epicardial surfaces.  
         [0049]    Referring now to plan view of FIG. 11, there is shown an assembly of suction tube  81  slidably disposed within a guide tube  83  to which is mounted a lower, slotted segment  85  of a guide channel. An upper, slotted segment  87  of the guide channel is slidably rotatably received within the lower slotted segment  85  and a cardiac pacing or defibrillating lead  89  is housed within the guide channel that is configured in the one orientation of the upper and lower segments as a closed guide channel. Another configuration of the upper and lower segments of the guide channel, as later described herein, forms an open channel or slot, as shown in FIG. 14 later described herein, for convenient release of the cardiac lead  89 .  
         [0050]    The suction tube includes a suction pod  91  at the distal end thereof and a suction-line connection fitting  93  at the proximal end for convenient hose or tubing attachment to a source of vacuum. Optionally, the connection fitting  93  may include a suction control valve  95  for adjusting the suction attachments of the suction pod to the epicardium of a patient&#39;s heart.  
         [0051]    The cardiac pacing or defibrillating lead  89  is slidably and rotatably housed within the guide channel  85 ,  87  in the closed configuration, and includes a helical or screw-in electrode  97  attached to the distal end of the cardiac lead  89 , as illustrated in FIG. 12. This greatly facilitates electrically connecting and mechanically anchoring the electrode in the myocardium of a patient&#39;s beating heart by rotating and advancing the proximal end  99  of the cardiac lead  89  within the guide channel  85 ,  87 . For this purpose, the cardiac lead  89  exhibits high torsional and compressional rigidity and high lateral flexibility so that the electrode  97  may be accurately manipulated into screw-like attachment to the myocardium via manual manipulation of the proximal end  99  of the cardiac lead  89 . Such cardiac lead  89  may include braided multiple strands of wire coated with a layer of insulating material such as Teflon, or the like. The accuracy of placement of the screw-in electrode  97  in the myocardium of a patient&#39;s beating heart is significantly enhanced by temporary suction attachment of the suction pod  91  to the pericardium or exposed myocardium. The suction pod  91  includes a suction port  98  that may be disposed in lateral or skewed orientation relative to the elongated axis of the suction tube  81 . This facilitates the temporary suction attachment while the electrode  97  at the distal end of the cardiac lead  89  that is slidably guided within the guide channel  85 ,  87  (which is disposed in substantially fixed axial orientation relative to the suction pod  91  and vacuum tube  81 ) is being anchored into the myocardium.  
         [0052]    After the electrode  97  on the distal end of the cardiac lead  89  is anchored into the myocardium of a patient&#39;s beating heart, the guide channel that houses the cardiac lead  89  may be re-configured into the alternate configuration including a slot along the length of the guide channel, as illustrated in FIG. 14, from which the cardiac lead  89  may be easily extracted or released. This open slot configuration may be achieved by sliding the upper segment  87  proximally along the lower segment  85 , as illustrated in FIG. 13, or by rotating the upper segment  87  within the lower segment  85 , as illustrated in FIG. 15. In this way, a longitudinal slot or groove is opened along the entire length of the guide channel that is wide enough to extract the cardiac lead  89  therethrough. This is particularly important for anchoring a cardiac lead  89  of about 2 mm diameter that includes a proximal connector  99  which is too large to pass through a guide channel  85 ,  87  of reasonable interior dimension.  
         [0053]    As illustrated in the perspective view of FIG. 15,the suction port  98  in suction pod  91  is oriented in skewed, typically perpendicular, orientation relative to the elongated axis of the guide channel that is formed by the upper and lower segments  87 ,  85 . This facilitates establishing temporary vacuum-assisted attachment of the suction pod  91  to the epicardium, or to myocardium exposed via the entry under the pericardium, that can then be depressed or otherwise distorted by manual application of axial or lateral force at the proximal end of the instrument in order to position the electrode  97  at the proper location and angle for anchoring in the myocardium of the patient&#39;s beating heart.  
         [0054]    Referring now to the partial plan view of FIG. 16 and the sectional view of FIG. 17, there is shown a non-round guide tube  96  that is attached to the lower segment  85  of the guide channel and that slidably supports therein the suction tube  81  of corresponding non-round cross section. In this way, the guide channel formed by segments  85 ,  87  is retained in substantially parallel axial alignment with the suction tube  81  as the suction pod  91  and the distal end of the guide channel are relatively slidably positioned near and against the epicardium of a patient&#39;s heart. In addition, as illustrated in the partial view of FIG. 18, the assembly of guide tube  96  and suction tube  81  and guide channel  85 ,  87  may all be disposed within an endoscopic cannula  101  having a distal end disposed to facilitate endoscopic viewing of the suction pod  91  and distal end of the guide channel  85 ,  87 . Also, the upper and lower segment  85 ,  87  of the guide channel may include stepped flanges  103 ,  105  at the proximal ends thereof, as illustrated in FIGS. 16, 19 and  20 , to facilitate positive orientation of the upper and lower segments  85 ,  87  in the closed configuration until the upper segment  87  is slid proximally, or slid proximally and rotated, relative to the lower segment  85  in order to re-configure the guide channel in the alternate configuration of an elongated slot along the entire length hereof. As shown in the sectional view of FIG. 17, the upper  87  segment can be rotated in the lower segment  85  from the closed configuration in order to align the respective elongated slots  106 ,  107  sufficiently to release a cardiac lead  89  from within the guide channel.  
         [0055]    In operation, as illustrated in the flow chart of FIGS. 21 a  and  21   b , the initial surgical procedures are similar to the surgical procedures, as previously described with reference to FIGS. 6 a  and  6   b , from the initial entry incision  51  through the penetration and entry through the pericardium  58 . Thereafter, the releasable guide assembly of section tube  81  and guide channel  85 ,  87  is slid through the endoscopic cannula  109  toward the heart. The suction pod  91  is advanced into contact with the myocardium through the penetrated pericardium and suction is established to temporarily anchor  110  the suction pod  91  via the suction port  98  at a desired surgical site. A cardiac lead or wire  89  with a screw-in electrode  97  on the distal end of the cardiac lead is positioned at or near the distal end of the guide channel in the closed configuration as the guide channel is advanced  111  toward the desired surgical site adjacent the temporary anchor site of the suction pod  91  on the myocardium. The proximal end of the cardiac lead  89  may now be manually manipulated to screw in the electrode  97  at the distal end into the myocardium via rotation and urging forward of the cardiac lead  89  to thereby anchor  112  of the cardiac lead  89  in the myocardium.  
         [0056]    The guide channel  85 ,  87  may now be reconfigured  113  to open an elongated slot along the entire length of the guide channel, and this may be accomplished by sliding the upper segment  87  proximally and completely from the lower segment  85  to thereby release  114  the cardiac lead  89  from within the guide channel  85 ,  87 . Alternatively, the upper segment  87  may be rotated within the lower segment  85  to align the elongated axial slots in each segment to thereby open the guide channel for release of the cardiac lead  89  from within the guide channel  85 ,  87 . Thereafter, the assembly of suction tube  81  and guide channel  85 ,  87  may be retracted from the endoscopic cannula, and the endoscopic cannula may be removed  115  from within the working cavity, with the cardiac lead  89  in position therein. A subcutaneous tract is formed from the subxiphoid incision to the location of the pacing or defibrillation generator, usually placed in the patient&#39;s upper chest, and the cardiac lead is then connected to the generator. The subxiphoid (or other) incision is sutured closed  116  to complete the surgical procedure. Of course, the surgical procedures described above including steps  109 - 114  may be performed multiple times in order to anchor multiple cardiac leads in the myocardium prior to removing  115  the endoscopic cannula and suturing  116  the initial incision closed.  
         [0057]    Therefore the surgical apparatus and methods of the present invention provide careful placement of an injection needle or other surgical instrument on the surface of a beating heart by temporarily affixing the distal end of a guiding cannula at a selected position on the heart in response to suction applied to a suction port at the distal end. The guiding cannula can be positioned through a working cavity formed in tissue between the heart and a subxiphoid or other entry incision to minimize trauma and greatly facilitate surgical treatment of a beating heart. Such treatments and procedures may include needle punctures of the myocardium, or injections therein of undifferentiated satellite cells, or other materials, to promote vacularization or tissue reconstruction, for example, at the site of a previous infarct. Such treatments and procedures may also include placing of pacing or defibrillating leads into the myocardium and may further include positioning and manipulating an ablation probe to ablate myocardial tissue for correcting cardiac arrhythmias.