GB2182566A - Defibrillator electrode - Google Patents

Abstract

A patch type defibrillator electrode for direct contact with the heart has a thin, flat, flexible generally circular mesh or foil conductive member 20 with a pattern of slits for enabling continuous contact with the three dimensional, time-varying heart surface topography. The slit pattern includes two pairs of non-intersecting semicircular slits oriented along mutually perpendicular axes, and interior portions of the conductive member are flexibly movable in a direction normal to the plane member and are flexibly tiltable about the axes to provide the conforming contact. The slits may also be radial slits which do not meet at the center so the leaves of conductive members are independently mobile with respect to every other leaf. A Dacron (R.T.M.) envelope 70, 72 having a thrombus formation inhibiting agent surrounds the conductive member including the peripheral edges to reduce the risk of tissue burning from current supplied to the center of the conductive member by an electrode lead 16. <IMAGE>

Description

SPECIFICATION Defibrillator electrode The present invention relates to electrodes implantable in living beings and, more particularly, to improved flexible defibrillator electrodes for attaching directly to the surface of the heart muscle, or over pericardial tissue.

Description ofthepriorart: It is well known that cardiac arrhythmias such as atrial fibrillation ("A.F.") and ventricularfibrillation ("V.F.") can be overcome by electrical energy applied across the myocardium. In situations where A.F. and V.F. does occur, defibrillation is accomplished by external paddles placed on the chest or, during surgery, internal paddles may be placed directly onto the heart, usually across the ventricles. These procedures have become fairly common and have proven to be quite effective.

More recently, implantable defibrillators have been suggested for automatic sensing and control of cardiac arrhythmias. Such defibrillators require electrodes which may be in contact with the heart surface or are intravascular catheters or are a combination of these.

Defibrillatorelectrodes have so far been of two types, namely endocardial types with large surface areas usually in the form of rings and located in the Superiorvena Cava ("SVC"), and patch-type electrodes to be placed on the external wall ofthe heart. The endocardial electrodes are implanted through a vein in the same manneras pacemakerelectrodes and are positioned in the SVC area.

The patch-type electrodes known to the art have been variedtypes, usually rectangular in shapewith suturesusedforfixingtothe heart. In general,the prior art patch-type electrodes have been relatively stiff devices which have difficulty in maintaining conforming contact with the heart which presents a three dimensional, time-varying surface topography. One patch-type prior art electrode is made from a titanium mesh but is nonetheless relatively inflexible. Most common implant techniques require thoracicsurgerytoexposetheepicardium on which the electrodes are sutured. The implant methods are awkward and difficult and thus it is very important to have an electrode that maintains conforming contact with the heart surface to preclude corrective surgery.

Summary of the invention In accordance with the invention as embodied and broadly described herein, the apparatus for use as an electrode adapted for implantation in a patient comprises a tissue-contacting member including a sheet of electrically conductive, flexible material having a generallyunflexed planar shape, and a plurality of elongated slits arranged in a pattern in the sheet. A part of at least one interior portion of the sheet defined bythe pattern is flexibly movable in a direction perpendiculartotheplaneofthesheetpastsheet portions separated from the first portion by the pattern of slits enable contacting thetissue member to conform to tissue having a three dimensional, time-varying surfacetopgraphy.

Preferably, the one interior portion defined bythe slit pattern also is flexibly tiltable about at least one axis lying in the plane ofthe sheet.

It is also preferred that the pattern of slits includes a first pair of complementary slits extending generally in a first sheet direction. A part of the sheet portion central to the pair of slits is flexibly movable past first sheet portions separated from the central sheet portion bythefirst pairofslits, in a direction normal to said sheet proximal and distal surfaces.

ltisfurtherpreferredthattheshapeofeachslitof the first pair and second pair of slits is semicircular, and the shape of the central sheet portion is circular.

The pattern also includes a second pairofcom plementaryslits extending generally in a second sheet direction. The structural, unit comprised ofthe first pair of slits, the included central sheet portion, and the first separated sheet portion is positioned between the second pair of slits, and a part ofthe structural unit is flexibly movable in the normal direction past a second sheet portion separated from the unit bythesecond pairofslits.

It is still further preferred that the apparatus include a continuously porous non-conductive layer covering the proximal and distal sheet surfaces and enveloping the peripheral edges of the sheet, to re ducethe riskoftissueburning,andthattheporous layer contains a biologically active agent to combat thrombusformation.

Brief description ofthe drawings Figure 7 is a perspective schematic view of an electrode made in accordance with the present invention and contacting a tissue body; Figure 2 is a perspective view of the electrode shown in Figure 1 with a cover member folded back to show internal details; Figure 3A is a top view of the sheet conductor el ement of the electrode shown in Figure 1 ; Figure 3B is a side view of the sheet conductor element shown in Figure 3A viewed in the direction AA, in an unflexed state.

Figure 4 is a side view of the sheet conductor el ementshown in Figure 3Aviewed in the direction AA, with flexible translation of parts thereof shown in dotted lines; Figure 5 is a side-view of the sheet conductor element shown in Figure 3Aviewed in the direction BB, with flexible tilting of a part thereof depicted with dotted lines; Figure 6 is a side view of the sheet conductor el ementshown in Figure3Aviewed in a directionAA, with flexible tilting of another part thereof depicted with dotted lines; Figure 7shows further details of parts of the electrode shown in Figure 1.

Figure 8 isthetop of a flexible sheet conductor el ement in the shape of a four leaf clover; Figure 9 is the top view of a flexible sheet conductor element in the shape of a spiral; Figure 10 is the top view of a flexible sheet conduc tor element with a multitude of radial slits; Figure 11 is the top view of a flexible sheetconduc torelementwhich is similartothat in Figure 3A but has the inner lip missing; Figure 12 is a perspectiveviewofa spotwelded connection between a connector pin and flexible sheet conductor elements of the type shown in Fig ures8to 11; and Figure 13 is a perspective view of a thin highlyflex- ible patch electrode.

Description of the preferred embodiment Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawing.

An example ofthe preferred embodiment of an electrode made in accordance with the present invention and especially suited for use as a defibrillatorelectrode is shown in Figure 1 and is designated generally by the numeral 10. Electrode 10 has a generally planar member 1 2 for contacting a suitable tissue body such as body 14to be stimulated by an electric current. In the example shown in Figure 1, electric current is supplied to planar member 12 by an electri cal conductor 1 Gfram a source (notshown) which can be, for instance, an extracorporeal power supply.

As is apparent from the preceding discussion, one ofthe preferred applications forthe electrode for direct attachmentto the heart muscle. The heart muscle presents not only a three dimensional sur face topgraphy to be contacted by the electrode, but a time-varying surface shape as a consequence of the pumping action ofthe heart. Thus, it becomes especiallyimportantin such applications to havethe electrode be able to continuously conform to the surface shape without impeding pumping action. The electrode of the present invention has been found to provide such continuously conforming contact by means which will be discussed in greater detail hereinafter.

In accordance with the present invention, the elec trodeadaptedforimplanation in a patient includes a tissue-contacting member formed from a sheet of electrically conductive, flexible material. As embodied herein, and with reference to Figures 2 and 3,tissue contacting member 12 includes a circular sheet element 20 having a distal surface 22 (see Figures 3A and 7) for contacting tissue body 14 and a proximal surface 24. Sheet 20 is preferably formed from a thin, fine woven mesh of a conductive material such as titanium, platinum, MP35N, stainless steel, carbon, or other bio-compatible conductive material. Electrodes according to the present invention and having a tissue contact member as shown in Figure 3 have been fabricated using 0.036 mm 316L stainless steel wire in a 0.075 mm thick mesh having 325 wires/inch.

These electrodes have been successfully implanted in dogs. However, a mesh fabricated from platinumi 10% iridium is specifically contemplated forfuture human and animal implants, or any other material which is conductive and biocompatible could be used. Conductive foil also can be usedforsheetel ement 20. The mesh or foi I is welded along all cut edges, such as peripheral edge 26, to remove sharp points. This welding operation is especially important if a mesh material is used. Other methods to remove sharp joints such as laser cutting, spark erosion etc. could also be used. In the undeformed or unflexed state, sheet element 20 is generally planar, as is shown in Figures 3 amd 4.

Further in accordance with the present invention, the electrically conductive flexible sheet includes a plurality of elongated slits arranged in a pattern. Importantly, a part of an interior portion of the sheet defined by the pattern is flexibly movable in a direction perpendicularto the plane of the sheet. Movement ofthe interior portion part past the sheet portion separated by the pattern of slits enables the con tacting memberto conform to the three dimensional tissue surface and accommodatetime-varying surface changes.

As embodied herein, and with reference to Figures 3 and 4, a slit pattern designated generally bythe numeral 30 isformed in sheet 20 such as bystamping, cutting, etc. Pattern 30 includes an inner pair of complementary semicircular slits 32,34 extending generally in the direction designated by axis 36 lying in the plane of sheet 20. Complementary slits 32,34 define and partially enclose a circular, central sheet portion 38 to which conductor 16 is attached in a mannerthatwill be explained in more detail subsequently.Slits 32,34 are non-intersecting and, as are- sult, central sheet portion 38 is connected by a pair of opposed web portions 42, 44to annular sheet por- tion 40 which is separated from central sheet portion 38 by slits 32,34. Slits 32,34thereby enable a substantial part of central sheet portion 38 to move in the direction normal to sheet surfaces 22, 24 (into and out ofthe paper in Figure 3A) and past the adjacent parts ofannularsheet portion 40. Of course, the parts of central sheet portion 38 immediately adjacent web portions 42,44 are constrained by the respective web portions to move together with the adjacent parts of sheet portion 40.

Preferably, and as embodied herein, slit pattern 30 includes a second pairofcomplementaryslits46,48 of semicircular shape extending in a direction at an angle to the direction of slits 32. 34. With continued reference to Figure 3A, slits 46,48 extend generally in the direction of axis 50 which is perpendicularto the direction of axis 36. Slits 46,48 serve to define and partially close the sub-unit (designated by the numeral 52) of sheet 20 that includes annular portion 40, slits 32,34, and central portion 38.Sub-unit 52 is connected to peripheral sheet portion 54 by a pair of op posing web portions 56,58. By virtue of the flexibility of sheet 20 and the arrangement of the slits46,48, a major portion of sub-unit 52 can flexibly move in the normal direction past adjacent parts of peripheral sheet portion 54, in response to the changing shape ofthe contacted tissue, in a mannersimilartothe previously described movement of central portion 38 past annular portion 40.

Importantly, and as best seen in Figure 4, the combination of slit pairs 32,34 and 46,48 enables the interior of sheet 20 to flexibly deform to accommodate changes in the curvature of tissue body 14. The mode offlexing deformation ofthe interior portion of sheet 20 is not unlike that found in Japanese lantern type hanging ornaments. In Figure 4, the deformed stage shown in dotted lines is exaggerated for clarity, with prime numerals designating the deformed or "flexed " respective parts of sheet 20.

It is also preferred that the width of each of the web portions 42,44 and 56,58 be made as small as possible consistent with the need to maintain structural integrity during flexing and to have sufficient con ductor volume to distribute current without creating a tissue burning condition. For relativelythin webbed portions, the respective interconnected sections of sheet 20 can twist or "tilt" to a limited extent with respectto one another about an axis drawn through the respective pairs of webs. This flexible tilting relative movement increased the ability of sheet 20 to conform to a three dimensional shape, especially a time-varying three dimensional shape, such as the surface ofthe beating heart.

For example, and as best seen in Figures 3A and 5, central portion 38 can tilt relative to both intermediate annular portion 40 and peripheral sheet portion 54, about axis 36 drawn through web portions 42,44 (tilt orientation represented by 38'). In a similar fashion, and with respect to Figures 3A and 6, intermediate annular sheet portion 40 and included central portion 38 can tilt relative to peripheral sheet portion 54, about axis 50 which is perpendicular to axis 36 and runs through web portions 56,58. Although not shown in Figure 6, central portion 38 could simultaneously tilt with respect to annular portion 40.

Also not shown, the angular directions of tilt can be reversed and the flexing movement in the normal direction can be superimposed onthetilting movement.

The several degrees of freedom resulting from the construction according to the present invention was found to provide a remarkable degree of conformity between sheet 20 and a beating heart muscle. The test sample included a sheet 20 manufactured from 0.036 mm wire woven into a 0.075 mm thick 325/inch mesh. Sheet 20 had a circularshape as depicted in Figure 3Awith an outside diameter of 38 mm, and having innersemicircularslits 32, 34on a 20 mm diameter and outersemicircularslits46,48 on a 30 mm diameter. The slits were each about 2 mm wide, and all webb portions were about 2.5 mm in width.

Further details of the present preferred embodiment of an electrode made in accordance with the present invention will now be described with referenceto Figures 1,2 and 7. Specifically, conductor 16 which should be formed from a low resistance material (e.g. platinum, platinum/iridium, DBS,tungsten etc.) and in a fatigue resistant form such as a multifilar helix or ribbon, is connected to tab portion 60 formed in sheet 20, by a titanium connector pin 62.

Tab portion 60 is located in the central sheet portion 38 and, because of the concentric arrangement ofthe remainder of sheet 20, a more even distribution of any mechanical stress imparted to sheet 20 can be achieved compared to an attached location for instance on peripheral portion 54. The shape of sheet 20 need not be circular but can be elliptical or even rectangular with well-rounded corners. Pin 62 is swaged to conductor 16 at pin end 62a and is riveted to tab portion 60 at pin end 62b. Silicone insulative sheath 64 (Figures 1 and 2) is disposed around conductor 16.

As embodied herein and with reference now to Figures 1 and 2, electrode 10 includes porous dacron layer 70 covering distal surface 22 and enveloping edge 26 of sheet 20. Layer 70 helps prevent severe tissue burning atthe peripheral edge, which hasthe highest electrical field intensity. Porous layer70 also provides for tissue ingrowth, helping to secure electrode 10 to tissue, particularly when non-woven foil material is used for sheet 20. It is also preferred that proximal surface be enclosed bya porous layer 72 to provide a complete envelope for electrode 10. As embodied herein, and as best seen in Figures 1 and 2, Dacron (R.T.M.) layer72 covers proximal surface 24 and is attached to the porous layer 70 by bead 76 of silicone glue.Layer 72 can be less porousthan layer 70 because firm tissue attachment to proximal sur face 24 is not critical. Bead 78 of silicon glue orsimilar material is used to attach insulated sheath 64 to Dacron layer 72.

The maintheme behind this invention isthe idea of a flexible electrode patch. Although a specific electrode design has been mentioned, the spirit of this invention is such that the flexibility of the electrode is of main concern ratherthanthe actual shape. The patch 20 described thus far in this invention is only one of many other shapes which could be used to achieve the desired effect. Some of the other shapes are shown in Figures 8to 11. The flexibiiityofthe patch can be increased with thinner wire in the construction of the mesh, and for best flexibility, a conductive cloth should be used. The cloth could be made from a conductive, biocompatible material such as platinum, platinum/iridium, carbon, etc.

Such a patch is depicted in Figure 13. The conductor 16 is attached to the flexible patch 20 (shown dashed) by a method described later. This connection is protected byasilicone rubber(orsimilar) moulding 88.

The upper insulating sheet72 can be made of Dacron cloth, thin Dacron reinforced silicone, PTFE orsimilar biocompatibleinsulating material. The sheet 70 in contactwiththehearttissuel4ismadefromthin porous Dacron material orsimilar material. Thetwo sheets 70 and 72 are joined together around the edge 90 by an adhesive (such as silicone), welded, sewn or by other means. The patches may also be made from inherently stretchy materials such as conductive polymers, or a specially knitted mesh which allows stretching and springy type of weaving, which allow deformation ofthe patch with the ensuing heart movement.

It is also within the spirit of this invention thatthe connection from the electrode patch to the conductor may va ry. Hence, the connector pin 62 may change in material and shape. One type of pin 80 is shown in Figure 12. In this case, the connector pin 80 is spot welded 84to the patch electrode 82. The connector pin is also swaged or crimped 86 to the conductor 16.

The pin 80 and the patch electrode 82 should be madeofcompatiblematerialsforwelding. Preferably, the two materials should be the same, such as platinum or platinum/iridium alloy. In some instances, the conductor 16 may be welded, soldered or glued with conductive adhesive directly to the electrode patch.

The presence of a patch electrode, as of any other implant material, could lead to formation of a fibrous capsulewhich could thicken dueto excessive mech anical stress. Athick layer of insulating tissue that cannot be stimulated can also result in higherenergy requirements. For these reasons it is importantthat the patch electrode not only have a shape and flex ibilitythat minimize adverse tissue reaction, while allowing for rapid and firm fixation ofthe electrode to the heartwall, but also preferably have meansforinhibiting thrombus formation in the electrode contact area.As embodied herein, and with reference to Figures 1 and 2, thrombus formation is prevented byteh inclusion in porous layers 70,72 of an appropriate biologically active agent such as a collagen formation inhibitorora heart muscle cell growth stimulator, or both, naturally or artificially derived. One skilled in theartwould be ableto choose an appropriate agent once the selection ofthe porous material is made, given the present disclosure.

The above described electrode may be attached to the heartwall or pericardium during surgery using various attachment methods including the use of glue, staples, or suture barbs to actively fix the electrode to the myocardium. However, if during the surgical procedure, the pericardium is sewn back and, considering the flexibility properties of the electrode made in accordance with the present invention, active fixation may not be necessaryto maintain positioning ofthe electrode against the heart surface.

Itwill be apparentto those skilled in the artthat various modifications and variations could be made in the electrodes of the present invention without departing from the scope or spirit ofthe invention.

These modifications and variations are intended to come within the scope ofthe appended claims and their equivalents.

Claims (22)

1. An apparatus for use as an electrode adapted for implantation in a patient comprising: a tissue-contacting member including a sheet of electrically conductive, flexible material having a generally unflexed planar shape, and a plurality of elongated slits arranged in a pattern in said sheet, a part of at least one interior portion of said sheet defined by said pattern being flexibly movable in a direction per pendicularto the plane of said sheet past sheet portions separated from said first portion by said pattern of slits said tissue-contacting member being con formable to tissue having a three dimensional, time- varying surface topography.

2. Apparatus as in claim 1 wherein said one interior portion defined by said slit pattern also isflex- iblytiltableaboutatleastone axis lying in the plane of said sheet.

3. Apparatus as in claim 1 wherein said one interior portion defined by said slit pattern also is flexiblytiltable abouttwo axes lying in the plane of said sheet, said axes being substantially mutually per pendicularto one another.

4. Apparatus as in claim 1 wherein each of said plurality of slits terminates short of the edge of said sheet, said sheet having an unslit peripheral portion.

5. Apparatus for use as an electrode adapted for implantation in a patient for contact with tissue having a timevarying,three dimensional surfacetop- ography, the apparatus comprising: a sheet of electrically conductive flexible material having a distal surface for contacting the tissue and an opposed proximal surface; and a plurality of slits formed in said sheet in a pattern, said plurality of slits including a first pair of complementary slits extending generally in a first sheet direction, a part of the sheet portion central to said pair of slits being flexibly movable past first sheet portions separated from said central sheet portion by said first pair of slits, in a direction normal to said sheet proximal and distal surfaces.

6. Apparatus as in claim 5 wherein the respective ends of said slits are positioned closely adjacent one another to form opposed first web portions connect- ing said central sheet portion to said first separated sheet portion, and wherein said central sheet portion isflexiblytiltable about an axis passing through said first web portions, relative to said first separated sheet portion.

7. The apparatus as in claim 6wherein eachslitof said first pairofslits has a shape that is substantially the mirror image of the other of said pairtakenabout a line passing through said first web portions.

8. Apparatus as in claim Swhereintheshapeof each of said first pair of slits is semicircular, and the shape of said central sheet portion is circular.

9. Apparatus as in claim Sfurtherincluding a second pair of complementary slits extending generally in a second sheet direction, the structural unit comprised of said first pair of slits, said included central sheet portion and said first separated sheet portion being positioned between said second pair of slits, a part of the structural unitbeingflexiblymov- able in said normal direction past a second sheet portion separated from said unit by said second pair of slits.

10. Apparatus as in claim 9 wherein said second sheet direction is substantially perpendicular to said firstsheetdirection.

11. Apparatus as in claim 9 wherein said central portion is connected to said first separated sheet portion by a pair of opposed first web portions, and said first separated sheet portion is connected to said second separated sheet portions by a pairofop- posed second web portions, and wherein said central sheet portion and said first separated sheet portions are independentlyflexibly tiltable about respective axes passing through said firstand second web portions.

12. Apparatus as in claim 9 wherein said central sheet portion iscircularandsaidfirstandsecond pairs of slits are semicircular, and wherein said second sheet direction is substantially perpendicular to said first sheet direction.

13. Apparatus as in claim Swherein said sheet member is concentrically shaped with respect to said central sheet member, the apparatus further including means connected to said central sheet portion for supplying an electric current to said tissuecontacting member.

14. Apparatus as in claim 5 further including a continuously porous non-conductive layer covering said proximal sheet surface and enveloping the peripheral edges of said sheet, said porous layer being disposed between said sheet and the contacted tissue to reduce the risk oftissue burning.

15. Apparatus as in claim 14further including a second continuously porous layer substantially covering said distal sheet surface, said second porous layer being connected to said first porous layer adjacent said sheet peripheral edges.

16. Apparatus as in claim 1 Swherein said second porous layer is less porous than said first porous layer.

17. Apparatus as in claim 14wherein said porous layer includes a biologically active agentforinhibit- ingthrombusformation, said agent being distributed throughoutthe entire porous layer.

18. Apparatus as in claim 1 Swherein both said porous layer and said second porous layer include a biologicallyactiveagentforinhibitingthrombusformation, said agent being distributed throughout the respective porous layers.

19. Apparatus for use as an electrode adapted for implantation in a patient and intended for contact with a tissue body having a time-varying, three dim ensional surface topography, the apparatus compris- ing: agenerallyplanarelectricallyconductivetissue contacting member, said member having (i) an annular peripheral portion, (ii) an annular intermediate portion position con centric with and spaced from, said peripheral portion, said intermediate portion being connected to said peripheral portion by a pair of opposed outer web portions, and (iii) a central portion positioned concentriowith, and spaced from, said intermediate portion, said central portion being connected to said intermediate portion bya pairofopposed innerweb portions, said peripheral, intermediate, and central portions being flexibly movable with respecttooneanotherinadir- ection normal to the plane of said tissue contacting member.

20. Apparatus as in claim 19 wherein a line drawn through said pairofouterweb portions is substanti- allyangularly displaced from a line drawn through said pair of outer web portions is substantially an gularlydisplacedfrom a line drawn through said pair of inner web portions.

21. Apparatus as in claim 19 wherein said inner and outerweb portion are reduced in width, said intermediate portion being flexibly tiltable about a first axis passing through said outer web portions, and said central portion being flexiblytiltable about a second axis passing through said inner web portions.

22. Apparatusasinclaim 17whereinsaidelectrode is adapted for contact with the heart for use as a defibrillator electrode.