Patent Publication Number: US-2004054391-A1

Title: Cardiac stimulation apparatus

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates to a cardiac simulation apparatus.  
       BACKGROUND ART  
       [0002] There are occasions where it is necessary to apply electrical stimulation to the hearts of cardiac patients. Typically, electrical stimulation is applied using cardiac stimulation leads. Some cardiac stimulation leads are employed to apply electrical stimulation to the heart of a cardiac patient after surgical procedures to correct arrhythmic beating of the heart The electrical stimulation may be applied to the atrium, to the ventricle, or sequentially to the atrium and the ventricle of the heart. Other electrical stimulation leads are used to apply electrical stimulation to the heart for the purpose of defibrillation.  
       [0003] Such leads employ an electrode or an electrode assembly at thee distal end thereof through which electrical stimulation is applied. The electrode or electrode assembly is adapted to be positioned in electrical contact with the heart wall and retained in such position by a traumatic technique, such as by suturing a portion of the lead to the heart wall or threading a portion of the lead into the heart wall. Such techniques for retaining the electrode or electrode assembly in electrical contact with the heart wall can cause damage to the heart wall, not only during the attachment phase but possibly also during the subsequent detachment phase as the lead is withdrawn from the body of the patient by a pulling process.  
       [0004] It is against this background, and the difficulties associated therewith, that the present invention has been developed.  
       DISCLOSURE OF THE INVENTION  
       [0005] According to one aspect of the present invention there is provided a cardiac stimulation apparatus comprising an electrode for electrical contact with heart or other tissue and means for adhesively attaching the electrode in position in relation to the heart or other tissue.  
       [0006] In this way there is no trauma to the heart or other tissue caused by the attachment process.  
       [0007] In one arrangement, the electrode may be attached directly by virtue of An adhesive substance on the electrode.  
       [0008] In another arrangement, the electrode may be attached indirectly by virtue of an adhesive substance on a support for the electrode.  
       [0009] The electrode may be a single electrode or it may be one of several electrodes in an electrode assembly.  
       [0010] Electrical stimulation may be delivered to the electrode by way of an electroconductive path from a source of electrical stimulation, in which case the stimulation apparatus may comprise a lead with the electrode provided at a distal end thereof and a proximal end thereof adapted to be connected to the source of electrical stimulation.  
       [0011] In another arrangement, electrical stimulation may be delivered to the electrode without the need for a lead to extend through the body of a patient undergoing cardiac stimulation to a source of electrical stimulation external to the body of the patient.  
       [0012] According to another aspect of the invention there is provided an cardiac stimulation lead comprising an electrode support at one end of the lead, first and second electrodes mounted in spaced relation on the electrode support, and a third electrode mounted on the electrode support in spac d relation to said first and second electrod s, said first and second electrodes being dimensioned for cardiac pacing and the third electrode having a larger electrical contact area than the first and second electrodes for cardiac defibrillation, and means for providing an electroconductive path between each electrode and the other end of the lead for electrical connection to a source of electrical stimulation.  
       [0013] Preferably, the third electrode has a large surface area and extends for at least a substantial part around the first and second electrodes.  
       [0014] The stimulation lead may be provided with a further electrode a larger electrical contact area than the first and second electrodes so that bipolar cardiac defibrillation can be performed.  
       [0015] Preferably, the electrode support comprises a wafer.  
       [0016] Preferably, the wafer is adapted to be placed against part of the heart or other tissue requiring stimulation with the necessary electrode or electrodes in electrical contact therewith.  
       [0017] For the purpose of maintaining the electrodes in electrical contact with the heart or other tissue, the wafer may be provided with an adhesive substance to bond it to the heart or other tissue.  
       [0018] Preferably, the wafer is laterally flexible for the purpose of conforming to the profile of that part of the heart or other tissue against which it is placed. For preference, the wafer has a dished configuration.  
       [0019] The stimulating electrode is intended to be temporarily placed in the body of a patient and is therefore preferably removable. A convenient way to remove the stimulating electrode is to simply pull it out of the body of the patient. To allow for removal in this manner, the wafer is preferably collapsible by virtue of its flexible nature to follow the course of the lead as it is drawn from the body of the patient.  
       [0020] On the other hand, the lead or at least part thereof may be constructed of biocompatible bio absorbable material, thereby eliminating the need to remove the lead from the body of the patient.  
       [0021] Preferably, the wafer is at one end of a flexible sheath which houses the electroconductive paths extending between the electrodes and the other end of the lead.  
       [0022] Preferably, the sheath is formed by twisting a ribbon of flexible material about the electroconductive paths.  
       [0023] Preferably, the electroconductive paths are established on the ribbon in electrically insulated relationship before twisting of the ribbon about its length.  
       [0024] The ribbon is preferably formed of the same material as the wafer and is integral herewith.  
       [0025] Preferably, connector means are provided at said other end of the stimulation lead for connection to the source of electrical stimulation, the electroconductive paths each being connected to a respective one of the connection means.  
       [0026] According to another aspect of the invention there is provided an epicardial simulation lead comprising an elongated sheath, an electrode support at one end of the sheath and an electrode mounted on the electrode support, an electroconductive path passing through the sheath between the electrode and the other end of the sheath, characterised in that the sheath comprises a ribbon of flexible material twisted about its length.  
       [0027] Preferably, the electroconductive path is provided on the ribbon.  
       [0028] Preferably, the electrode support is integral with the ribbon.  
       [0029] According to still another aspect of the inv ntion there is provided a method of making a stimulation lead comprising the steps of providing a ribbon of flexible material and an electrode support at on end of the ribbon, providing an electrode on the electrode support, forming an electroconductive path along the ribbon from the electrode to the other end of the ribbon, and twisting the ribbon about its length to create a sheath for housing the electroconductive path.  
       [0030] The electroconductive path may be of any suitable material such as a wire bonded onto the ribbon or a track of electroconductive material sprayed, printed or otherwise deposited on the ribbon.  
       [0031] There may be a plurality of electrodes supported on the electrode support and a plurality of electroconductive paths extending along the sheath. With such an arrangement, the electroconductive pates are electrically insulated from each other.  
       [0032] According to a still, further aspect of the invention there is provided an epicardial stimulation electrode comprising an electrode support, an electrode on the electrode support, and an adhesive substance associated with the electrode for bonding the electrode to the heart or other tissue to maintain the electrode in electrical contact therewith.  
       [0033] According to a still further aspect of the invention there is provided a cardiac stimulation apparatus comprising ah electrode and an electrical current generation means associated with the electrode for delivering an electrical current to the electrode when subjected to an external influence such as an energy wave.  
       [0034] The apparatus may further comprise an adhesive means for bonding the apparatus to head or other tissue with the electrode in electrical contact thereof. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0035] The invention will be better understood by reference to the following description of several specific embodiments thereof as shown in the accompanying drawings in which:  
     [0036]FIG. 1 is a plan view of an epicardial stimulation lead according to a first embodiment, shown in a condition prior to installation in the body of a cardiac patient;  
     [0037]FIG. 2 is a view of the stimulation lead according to the first embodiment, with the lead in a collapsed condition following withdrawn from the patients body;  
     [0038]FIG. 3 is a view similar to FIG. 2 with the exception that the lead is now shown fitted with a threading needle used to facilitate threading of the lead through pat of the body of the patient;  
     [0039]FIG. 4 is a plan view of the lead prior to twisting part of it to create a sheath;  
     [0040]FIG. 5 is a plan view of the lead according to a second embodiment prior to installation and showing a threading needle in position;  
     [0041]FIG. 6 is a collapsed view of an epicardial stimulation lead according to the second embodiment in a condition following withdrawn from a patient&#39;s body;  
     [0042]FIG. 7 is a plan view of the lead of the second embodiment prior to twisting to form a sheath;  
     [0043]FIG. 8 is a schematic view of a heart to which two stimulating electrodes according to the second embodiment have been attached;  
     [0044]FIG. 9 is a schematic plan view of a stimulation apparatus according to a third embodiment;  
     [0045]FIG. 10 is a cross-section along the line  10 - 10  of FIG. 9;  
     [0046]FIG. 11 is a schematic view of a heart to which two electrodes according to the third embodiment have been applied, one in association with the atrium and the other in association with the ventricle; and  
     [0047]FIG. 12 is a schematic view Illustrating a procedure for applying electrical stimulation utilising the two electrodes illustrating position in FIG. 11. 
    
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION  
     [0048] The embodiment shown in FIGS.  1  to  4  of the drawings is directed to an epicardial stimulation electrode which can be employed for either bipolar pacing or monopolar defibrillation of a heart.  
     [0049] The epicardial stimulating lead  10  comprises a length of polyethylene or other suitable material sheeting  11  of thickness up to approximately  30  microns which has been shaped to define a ribbon  13  and a wafer  15  of generally circular form at one end of the ribbon. The wafer  15  provides an electrode support on one face of which three electrodes are mounted, being first and second electrodes  17  and  19 , and a third electrode  21 , each spaced from the other. The first and second electrode  17  and  19  operate as a pair and are much smaller in terms of their electrically contact area than the third electrode  21 , as can be seen from the drawings. Indeed, the electrical contact area of the third electrode far exceeds that of the first and second electrodes and it occupies a major part of the surface area of the side of the wafer  15  on which the electrodes are mounted.  
     [0050] The other end of the ribbon  13  branches into three sections  23  each of which supports an electrical terminal  25 . Each electrical terminal  26  is connected to one of the electrodes by way of an electroconductive path  27 .  
     [0051] The electroconductive paths  27  are provided on the ribbon and are electrically insulated from each other.  
     [0052] While the electrodes  17 ,  19  and  21 , the terminals  25  and the electroconductive paths  27  may be of any suitable form, in this embodiment they have been deposited onto the sheet material by any suitable means such as printing or spraying.  
     [0053] The ribbon  13  is twisted along its length so as to create a sheath  29  which houses the electroconductive paths. The sheath  29  is laterally flexible by virtue of the flexible nature of the polyethylene.  
     [0054] The terminal end of the lead is adapted to receive a detachable needle  31  to facilitate threading of the lead through part of the body of a patient.  
     [0055] The wafer  15  is of dished configuration so that it conforms somewhat to a curved surface of the heart but is also sufficiently flexible to accommodate any variations which may be required to the preformed curvature. An adhesive substance (not shown) is applied to the wafer to facilitate bonding of the wafer to the heart with the electrodes in an electrical contact with the heart. The adhesive is biocompatible and electroconductive which ensures stale electroconductive contact between the electrodes and the heart.  
     [0056] The epicardial simulation lead is intended to be temporarily implanted into the body of a cardiac patient before the pericardium and chest are closed. The wafer is placed in the required position against the heart according to the stimulation requirements and is maintained in such position by the adhesive bond. The sheath  29  is then fed through the pericardium and the thorax of the patient with the aid of the needle  31 . Following penetration of the chest wall of the patient, the needle is detached from the sheath  29  so as to expose the terminals  25 . The surgical procedure on the patient can then be completed as normal.  
     [0057] Should the heart of the patient require electrical stimulation in the post-operative period, it is merely necessary to connect a source of electrical stimulation to the appropriate terminals  26 . If, for example, the patient requires arterial or ventrical pacing, an appropriate source of electrical stimulation is connected to the two terminals  25  which are coupled to the first and second electrodes  17  and  19 . If, on the otherhand, defibrillation is required, an appropriat source of electrical stimulation is conn cted to the terminal  25  which is linked to the third electrode  21  these differing terminals being colour-coded. A return path for the electrical stimulation may be provided by either one of the electrodes  17  or  19 , or a supplementary electrode attached to another part of the body of the patient.  
     [0058] As there is only one electrode sufficiently large enough for use in defibrillation procedures, the epicardial stimulating lead according to the first embodiment can only be employed for monopolar defibrillation.  
     [0059] The epicardial stimulation lead according to the second embodiment, which is shown in FIGS. 5, 6 and  7  is similar to the first embodiment with the exception that there are four electrodes, being a pair of small electrodes  17  and  19  for use in cardiac pacing and a pair of large electrodes  21  for use in bipolar defibrillation.  
     [0060] When the epicardial stimulation lead according to either the first or second embodiment is no longer required in the body of the patient, it is simply pulled out through the chest wall. As the lead is pulled from the patient, the adhesive bond between the wafer and the heart separates and the wafer collapses upon itself as it follows the course of the lead outwardly through the body of the patient  15 . The particular benefit of this arrangement is that there is little likelihood of damage to heart tissue as the wafer separates from the heart owing to the fact that it was only affixed to the heart by virtue of the mild adhesive bond.  
     [0061] The collapsed condition of the water is illustrated in FIGS. 2 and 6.  
     [0062] In the previous embodiments, the stimulation apparatus according to the invention is in the form of a lead, with an electrode or electrode assembly provided at a distal end thereof and the proximal end thereof being adapted to be connected to a source of electrical stimulation. Other arrangements are, of course, possible. One such prior arrangement is illustrated in FIGS.  9  to  12  of the accompanying drawings.  
     [0063] Referring now to FIGS.  9  to  12 , there is shown a stimulation apparatus  50  comprising an electrode  61  and a means  583  for generating an electrical current for the electrode  51 . In this embodiment, the current generation means  53  comprises an electroconductive coil  55  disposed about the electrode  51 . The electrode  51  projects from the coil  55  (as shown in FIG. 10) to facilitate contact with the heart  60  or other tissue to which the apparatus  50  is applied.  
     [0064] The current generation means  53  is provided with adhesive means  57  by way of which the apparatus  50  can be adhesively bonded to the heart  60  or other tissue, with the electrode  61  in contact with the heart  60  or other tissue. In this embodiment, the adhesive means  57  is in the form of a biocompatible absorbable adhesive gel pad  59  positioned about the coil  55 , with the electrode  51  extending beyond the gel pad  59 .  
     [0065] The apparatus  50  is energised to generate an electrical current in the current generation means  53 . In this embodiment, the apparatus  50  is energised by subjecting the coil  55  to an energy wave such as a magnetic wave or radio-frequency wave, with interaction between the coil  55  and energy wave being adapted to generate an electrical current which passes to the electrode  51 .  
     [0066] In this embodiment, the coil  55  is energised by an energy wave (depicted by lines  63 ) generated by a source  57  located exteriorly of the body  61  of the patient, as illustrated in FIG. 12 of the drawings.  
     [0067] The current path through the body  61  of the patient from the electrode  51  may be completed in any suitable fashion such as by provision of a further electrode, such as a skin electrode, positioned on an external portion of the body  61  of the patient.  
     [0068] A particular advantage of the apparatus according to this embodiment is that there is no lead which is passed through the body of the patient and which needs to be subsequently removed.  
     [0069] it should be appreciated that the scope of the invention is not limited to the scope of the embodiments described.  
     [0070] Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will b understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.