AN ELECTRODE HEAD FIXATION ARRANGEMENT

Abstract: A fixation arrangement on the outer surface (12) of an electrode head (20), which is mounted at a distal end of a pacing lead, said arrangement including an attachment mechanism comprising at least one tine (22). Each tine is connected to the electrode head by a tine base portion (24) including heat responsive positioning means (28) allowing the position of the tine in relation to the electrode head (20) to be adjusted by a temperature change in the heat responsive positioning means.

Description: AN ELECTRODE HEAD FIXATION ARRANGEMENT Technical Field of the Invention The present invention relates to a fixation arrangement on the outer surface of an electrode head mounted at a distal end of a pacing lead. Description of Prior Art A pacing lead may be a multipolar (or unipolar or bipolar) electrode lead used for providing intracardial stimulation of heart tissue, and/or for sensing heart signals, by means of a pulse generator or some other type of heart stimulation apparatus. The pacing lead carries the stimulus from the pulse generator to the cardiac tissue, or relays intrinsic cardiac signals back to a sense amplifier of such pulse generator. The fixation arrangement on the outer surface of the electrode head normally includes an attachment mechanism comprising one or more tines (and/or fins) adapted to lodge in the trabeculae lining the inner wall of the heart without actually penetrating the cardiac wall. A fined electrode head (i.e. an electrode head provided with tines) is useful for providing reliable anchoring of the electrode head and its lead in the trabeculae (trab- ecular network) inside the heart. The barb- or fluke-like tines become entangled in the trabecular network thereby securing the electrode head position. However, although tines are very effective in securing anchoring of the electrode head, implantation and repositioning procedures may be facilitated if the tines are foldable and extendable as for instance disclosed in US Patent 4,957,118. This document illustrates a mechanical way of extend and fold the tines by means of a threaded stylet. Objects of the Invention A primary object of the present invention is to provide an alternative, improved electrode head fixation arrangement comprising one or more foldable and extendable tines. Another object of the invention is to provide tine controllability by electric means. Summary of the Invention According to the invention the above-mentioned objects are achieved with an electrode head fixation arrangement as defined in the preamble of claim 1, and having the features of the characterising clause of claim 1. In the dependent claims 2-9 there are stated additional features developing the invention further, and being characteristic of various preferred embodiments thereof. The core of the invention is that each tine is connected to the electrode head by a tine base portion which includes heat responsive positioning means allowing the position of the tine to be adjusted i relation to the electrode head by a temperature change brought about in the heat responsive positioning means. Since the inventive features renders possible to change the directionality of the indi- vidual tine protruding from the outer surface of the electrode head it will now be possible to eliminate interference problems which may otherwise - as a result of the configuration of the tines - be encountered during implantation (or repositioning) of the pacing lead and its electrode head. Interference problems with the trabeculae may also be avoided or at least reduced thanks to the controllability of the "movable tines". When the electrode head is provided with a number of tines circumferentially spaced apart about the electrode head the tine base portions may constitute integrated parts of the exterior of the electrode head. However, said base portions may instead be integrated parts of a separate tines-carrying means (e.g. in the form of a ring) attached to the exterior of the electrode head. Furthermore, the tines may have their base portions positioned in the same annular region on the electrode head surface. However, it would also be possible to use a tines assembly wherein some of the tines have their base portions positioned in a first annular region, and the re- maining tines have their base portions placed in a different, second annular region which is axially spaced from said first annular region. Preferably, in a preferred embodiment the positioning means in each tine base portion comprises an adjustable hinge element including a sequence of co-operating bending actuators connected in series. Each such bending actuator may with advantage be a so-called polyimide micro-joint. In the hinge element the sequence of bending actuators is adapted to make possible an adjustable relative angular movement (remote-controlled adjustable bending angle) between a first rigid hinge element part, which is connected to the electrode head, and a second rigid hinge ele- ment part, which is anchored to the respective tine in the area of the base portion thereof. Some basic designs/structures of and operation principles for polyimide micro-joint actuators have been described in various scientific papers and discussed during in- ternational workshops. As an example of such a scientific paper reference is herewith made to a paper ("Three dimensional silicon triple-hot-wire anemometer based on polyimide joints") by Th. Ebefors, E. Kalvesten and G. Stemme, presented at IEEE Int. Workshop on Micro Electro Mechanical System (MEMS'98), Heidelberg, Germany, January 25-29, 1998. In order to provide a suitable tined electrode head, each tine base portion thereof may be positioned at a forward end of a matching elongated recess in the outer surface of the electrode head. This recess is shaped to extend axially along the electrode head and is so dimensioned that it will accommodate (within a cylindrical outer contour of the electrode head) the tine when same has been folded down to an axial position adjacent to and along the head. To facilitate a required adjustment of the position of a tine it is appropriate to use means adapted to make possible a controlled heating of the polyimide material in the bending actuators included in the hinge element of the tine. Preferably, this means is an integrated electric heater means. In the sequence of co-operating bending actuators included in the hinge element, each bending actuator preferably comprises two or more silicon plate sections interconnected by at least one polyimide filled V-groove joint. In a useful embodiment each bending actuator comprises at least three silicon plate sections interconnected by two polyimide filled V-groove joints. Preferably, the integrated electric heater means comprises a resistor in each V- groove. Suitably, layers of electrically conductive material, e.g. aluminium, consti- tute each such resistor. These electrically conductive material layers are then preferably linings on the V-groove surfaces of each V-groove joint. Preferably, each tine has a non-adjusted initial position wherein the elongated tine body protruding from the tine base portion makes an acute angle, e.g. 45°, with the longitudinal axis of the electrode head. Description of the drawings The invention will now be further elucidated with reference to a preferred embodi- ment of an electrode head fixation arrangement schematically depicted on the accompanying drawings and described below. On the drawings: Fig. 1 shows, in a longitudinal section, the forward portion of an electrode head including an attachment mechanism comprising non-adjustable tines; Fig. 2 shows schematically and in a side view an electrode head having on its outer surface a fixation arrangement according to the invention; Fig. 3 shows a cross section (at line X-X in Fig. 2) of one of the tines on the elec- trode head in Fig. 2; Fig. 4 shows (on a larger scale) schematically and in a longitudinal section the micro-joint hinge element indicated (by broken line) in the base portion of one of the tines on the electrode head in Fig. 2; and Fig. 5 shows (on a still larger scale) in a longitudinal section, very schematically and on a distorted scale, the basic construction of the micro-joint hinge element in Fig. 4. Description of a preferred embodiment Fig.1 shows the forward portion of an electrode head 2 mounted at a distal end of a bipolar pacing lead of which only the outer coil conductor 4 is visible. The conductor 4 is connected to the tip electrode 6 via connecting means 8,10. The electrode head 2 is provided with a fixation arrangement on its outer surface 12. In this case the fixation arrangement comprises at least two, but preferably four or six, tines 14A, 14B etc. These tines, which are formed as protruding integrated parts of the wall 16 of the electrode head 2, constitute non-adjustable tines extending (in their free unloaded state) in a backward direction and making a fixed, non-adjustable angle with the outer surface 12. In contrast to the electrode head 2 in Fig. 1, the electrode head 20 shown in Fig. 2 is provided on its outer surface with a fixation arrangement including an attachment mechanism comprising four adjustable tines 22A, 22B, 22C and 22D (not visible) being spaced apart about the circumference of the electrode head 20. The adjustability of the tines implies that the angular position of each tine in relation to the electrode head 20 can be controlled and adjusted at the will of an operator who is performing an implantation or repositioning (in a human heart) of a pacing lead at the distal end of which the electrode head 20 is mounted. Each tine 22A, 22B, etc. is connected to the electrode head by a transition portion constituting an integrated tine base portion 24A, 24B, etc. including heat responsive positioning means allowing the tine position to be adjusted by bringing about a temperature change in said heat responsive positioning means. In an alternative embodiment the base portions 24 A- D constitute integral parts of a ring-shaped tines carrying means 25 attached to the exterior of the electrode head 20. In the tine configuration shown in Fig. 2 all the tines have their respective base por- tions 24A, 24B, etc. positioned within one and the same annular region on the outer surface of the electrode head 20. Furthermore, all the tines have elongated tine bodies 26A, 26B, etc. protruding from their respective base portions 24A, 24B, etc. with the same angle of inclination to the longitudinal axis of the electrode head 20. The adjustability of each tine is provided by the respective heat responsive positioning means thereof forming an integral part of the tine and being at least essentially included in the transitional base portion of the tine. This heat responsive positioning means comprises an angularly adjustable hinge element 28 including a plurality of co-operating bending actuators 36 connected in series. Each bending ac- tuator is a so-called polyimide micro-joint, which will be further elucidated below with reference to Figs. 4 and 5. As shown in Fig. 2, for the sake of simplicity only in connection with the tine 22C, the tine base portion 24C is positioned at a forward end of an elongated recess 32 in the outer surface of the electrode head 20. This recess extends axially along the electrode head and is so dimensioned that it will accommodate (within a cylindrical envelope of the head) the tine body 26C when same has been angularly retracted (i.e. folded down) to a faired deactivated "parking position" adjacent to the bottom surface of the recess 32. In Fig. 3 there is shown a suitable cross section of the tine body 26C, at line X-X in Fig. 2. Although not shown in Fig. 2, the other three tines 22A, 22B and 22D would in practice also have their own recesses corresponding to recess 32. A suitable type and structure of the adjustable (bendable) hinge element 28 included in the base portion of each tine will now be described more in detail, with reference to Figs. 4 and 5. The adjustable hinge element 28 comprises a bendable insulating casing 34 made of a suitable polymer. In the casing 34 there are included a sequence of co-operating bending actuators 36 connected in series to be able to provide, together, a reversible, total 180° adjusting (bending) angle to make possible to turn the tine from a fully retracted backward position (in recess 32) to a fully forward position, which will to a great extent facilitate a pacing lead explanation. The hinge element 28 may com- prise a first inflexible or non-bending part 27 connected to the electrode head 20, and a second non-bending part 29 anchored to the tine base portion 24 or the tine body 26. Each bending actuator 36 comprises two silicon plate sections or beam sections 38 interconnected by an intermediate polyimide filled V-groove joint 40. The poly- imide filling in each joint 40 is constituted by a cured polyimide body 42 positioned in a support channel (defining the V-groove) consisting of a bottom portion 44 and a pair of opposite flanks 46A and 46B being integral parts of a cross corrugated metal foil strip 48. The V-groove angle between the flanks 46 A, 46B constitute a dynamic and reversible "bending angle" or "adjusting angle". The magnitude of this bending/adjusting angle can be changed by electrically controlling the thermal expansion of the cured polyimide body 42. In this case the metal foil strip 48 is used as a resistive heater producing local heat dissipation (temperature increase) in the polyimide body of the joint 40. A temperature increase in the polyimide body 42 results in an expansion of the polyimide, thereby providing a dynamic change of the bending angle. A large total bending angle, e.g. 180°, can be obtained by connecting in series a plurality of V-groove joints 40. Each actuator 36 (V-groove micro-joint 40) will be able to provide say 4° maximum adjustability, so that a series of about 45-50 cooperating actuators (micro-joints) will be required for obtaining a total bending an- gle of l80°. Instead of using a metal foil strip 48 as a heating means for controlling the expansion of the heat responsive polyimide bodies 42, it is also possible to use some other type of heating means, e.g. an electric heating means fully integrated (embedded or contained) in the polyimide bodies 42. Irrespective of the type of heating means used for controlling the bending angles of the V-groove micro-joints 40 it is only required to have such heating means connected to a pair of electric wires (pole means) for supplying the electric current necessary to provide the required local heat dissipation in the joints. When the pacing lead (being provided with the electrode head 20 at its distal end) is a bipolar electrode lead it would be suitable to use the two (coil) conductors thereof as the pole means for supplying the current needed for the heating of the heat responsive positioning means in the hinge element 28.

Claims: Claims 1. A fixation arrangement on the outer surface (12) of an electrode head (2;20) which is mounted at a distal end of a pacing lead, said arrangement including an at- tachment mechanism comprising at least one tine (14;22), characterized in that each tine (22) is connected to the electrode head (20) by a tine base portion (24) including electrically controlled heat responsive positioning means (28) allowing the angular position of the tine (22) in relation to the electrode head to be selectively adjusted by a temperature change in said heat responsive positioning means. 2. An arrangement according to claim 1, wherein the attachment mechanism comprises two or more tines (22A,22B;22C) spaced apart about the circumference of the electrode head, characterized in that the tine base portions (24A,24B,24C) constitute integrated parts of the exterior of the electrode head (20). 3. An arrangement according to claim 1, wherein the attachment mechanism comprises two or more tines (22A,22B,22C) spaced apart about the circumference of the electrode head, characterized in that the tine base portions (24A,24B,24C) constitute integrated parts of a separate tines carrying means (25) being attached to the exterior of the electrode head (20). 4. An arrangement according to claim 2 or 3, characterized in that all the tines (22) have their tine base portions (24) positioned within the same annular region on the surface of the electrode head (20). 5. An arrangement according to claim 2 or 3, characterized in that some of the tines have their base portions positioned in a first annular region, and the remaining tines have their base portions placed in a second annular region being axially spaced from said first annular region. 6. An arrangement according to any of claims 1-5, characterized in that the positioning means in each tine base portion comprises an adjustable hinge element (28) including a sequence of co-operating bending actuators (36) connected in series, each bending actuator being a polyimide micro-joint (40), and that the se- quence of bending actuators in the hinge element is adapted to make possible an adjustable relative angular movement (bending angle) between a first rigid hinge element part (27) connected to the electrode head (20) and a second rigid hinge element part (29) anchored to the tine in the area of the base portion (24) thereof. 7. An arrangement according to any preceding claim, characterized in that each tine base portion (24) is positioned at a forward end of an elongated recess (32) in the outer surface of the electrode head (20), the recess extending axially along the electrode head and being dimensioned to accommodate, within a cylindrical outer contour of the head, the tine when same has been retracted (folded down) to an axial position adjacent to the head. 8. An arrangement according to claim 6 or 7, characterized in that the hinge element (38) in each tine (22) comprises an integrated heater means (48), preferably an electric heater means, for providing a controlled heating of the polyimide material (42) in the bending actuators (36) included in the hinge element. 9. An arrangement according to any preceding claim, characterized in that each tine (22) has a non-adjusted initial position wherein the elongated tine body (26) protruding from the tine base portion (24) makes an acute angle, e.g. an angle in the interval 30°- 60°, with the longitudinal axis of the electrode head (20).

Inventors: DAHLBERG KENNETH, HILL ROLF, DAHLBERG, KENNETH, HILL, ROLF
Applicants: DAHLBERG KENNETH, HILL ROLF, ST JUDE MEDICAL, DAHLBERG, KENNETH, HILL, ROLF, ST. JUDE MEDICAL AB
Application year: 2001
Main classification: A61N1
IPC codes: A61N1