Multipolar medical electrical lead

[0001] The present invention is directed to implantable medical devices and more particularly to medical electrical leads including a plurality of electrodes.

[0002] Implantable medical electrical stimulation and/or sensing leads are well known in the field of cardiac stimulation and monitoring, for example cardiac pacing and/or cardioversion/defibrillation, and in other fields of electrical stimulation or monitoring, for example of the central nervous system. In the field of cardiac stimulation and monitoring, lead electrodes are positioned at an endocardial or epicardial site and an implantable pulse generator (IPG), pacemaker or cardioverter/defibrillator, or a monitor is coupled to the heart through one or more of such endocardial or epicardial leads. Means for implanting such cardiac leads are known to those skilled in the art of pacing and defibrillation therapy.

[0003] More recently, medical electrical leads have been constructed to include a plurality of pacing and/or sensing electrodes from which one or more of the electrodes may be selected in order to optimize electrical stimulation therapy and/or monitoring. Additionally leads adapted for deep brain stimulation, and other leads adapted to stimulate other muscles of the body may include a plurality of electrodes from which one or more electrodes may be selected to optimize therapy.

[0009] The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides a practical illustration for implementing exemplary embodiments of the invention.

[0010] FIG. 1 is a plan view of a medical electrical lead 100 according to one embodiment of the present invention. FIG. 1 illustrates lead 100 including a elongate body 16 carrying a first elongate conductor 101, a second elongate conductor 102 and a third elongate conductor 105, each illustrated schematically with dashed lines; according to one embodiment, lead body 16 is formed of a multilumen insulative sheath, either silicone or polyurethane, and conductors 101, 102, 105 from cabled bundles of MP35N wires. FIG. 1 further illustrates lead body 16 terminated at a proximal end by a connector 17, which includes electrical contacts 120, 110 and 150 coupled to conductors 102, 101 and 105, respectively; lead 100 further includes electrodes 12, 10 and 15 formed about a distal portion of lead body 16, proximal to a distal end 13 of lead 100, and coupled to contacts 120, 110 and 150, respectively, via conductors 102, 101 and 105. Connector 17, an in-line lead connector, is just one embodiment of many connector types that may be incorporated; the scope of the present invention includes any type of lead connector known to those skilled in the art for coupling a pulse generator device, such as a pacemaker, to a medical electrical lead.

[0011] According to some embodiments of the present invention the distal portion of lead body 16 is sized to fit within a coronary vein in order to pace and sense from an epicardial surface of a heart; thus an outer diameter of electrodes 10, 12 and 15 is less than approximately 2 mm and according to a particular embodiment a diameter of flexible electrode 15 is approximately 1.3 mm. Furthermore, although not shown in FIG. 1, the distal portion of lead body 16 may include one or more preformed bends to urge electrodes 10 and 12 into contact with the epicardial surface; an example of such a lead distal portion is described by Sommer et al. in U.S. Pat. No. 5,999,858, which is incorporated by reference herein in its entirety.

[0012] An implanted position of lead electrodes is often constrained by coronary vasculature anatomy, thus embodiments of the present invention provide at least two options for a pacing electrode position. FIG. 2 is a schematic showing the lead 100 implanted within a coronary vasculature. FIG. 2 illustrates electrodes 10, 12 and 15 positioned in a great cardiac vein 28 wherein either a pair formed by electrode 10 and electrode 15, electrode 10 as cathode and electrode 15 as anode, or a pair formed by electrode 12 and electrode 15, electrode 12 as cathode and electrode 15 as anode, may be selected for stimulation/pacing of a left ventricle 20. According to some embodiments of the present invention, the selection is based either upon a pacing/stimulation threshold, lower being more desirable, or upon an absence of phrenic nerve stimulation resulting from the pacing from the pair, or upon hemodynamic response of the heart, for example as observed via echocardiography, or upon a combination of any of these factors; selection at time of implant would be determined by delivering test pulses to each of the pairs and observing the results. According to another aspect of the present invention, one of electrodes 10 and 12, which is not selected, may be used to sense an evoked response to pacing/stimulation delivered by the pair including the selected one of electrodes 10 and 12; the sensing may be bipolar, for example the unselected electrode in conjunction with electrode 15 or another electrode included on another implanted lead, or unipolar.

[0013] According to common knowledge of those skilled in the art, a bipolar pacing pair including an anode having a greater geometric surface area than that of the cathode results in lower pacing thresholds. According to embodiments of the present inventions a ratio of a surface area of electrode 15 to a surface area of either electrode 10 or electrode 12 is greater than approximately 3:1 or greater than or equal to approximately 6:1. In order to accommodate an enlarged surface area for electrode 15, embodiments of the present invention include anode electrode 15 having a flexibility to navigate within the coronary vasculature; electrode 15 may be formed by a coiled conductive wire, as illustrated, or by a layer of a conductive polymer. Examples of suitable wire materials include, but are not limited to, platinum and tantalum, and examples of conductive polymers include, but are not limited to metallic or carbon filled silicone, polyacetylene, polypyrrole and polyanaline. Embodiments of the present invention may further include those wherein electrode 15 includes a coating to reduce post-pace polarization; examples of such coatings include, but are not limited to, titanium nitride, platinum black and iridium oxide.

[0014] Returning now to FIG. 1, a distance D1 between electrode 10 and flexible electrode 15 is approximately equal to a distance D2 between electrode 12 and flexible electrode 15 according to embodiments of the present invention; distances D1 and D2 may be between approximately 5 mm and approximately 15 mm or between approximately 9 mm and approximately 15 mm. Furthermore, according to embodiments of the invention, a length L of electrode 15 is less than approximately 10 mm, preferably between approximately 3 mm and approximately 10 mm. According to an exemplary embodiment, electrode 15 has a length L of approximately 8 mm and a diameter of approximately 1.3 mm while electrodes 10 and 12 each have a length of approximately 1 mm and a diameter of approximately 1.6 mm.

[0015] FIG. 3 is a plan view of a lead connector 47 according to another embodiment of the present invention. FIG. 3 illustrates bifurcated lead connector 47 terminating a proximal end of lead body 16 and including a first leg 471 and a second leg 472; according to one embodiment of the present invention first leg 471 and second leg 472 each conform to the IS-1 industry standard. FIG. 3 further illustrates conductor 101 and a branch 105a of conductor 105 extending into first leg 471 to couple with contact 110 and a contact 150a, respectively, and conductor 102 and a branch 105b of conductor 105 extending into second leg 472 to couple with contact 120 and a contact 150b, respectively. According to the illustrated embodiment, once lead 100 is implanted and one of electrodes 10 and 12 (FIGS. 1 and 2) has been selected as the cathode to function in conjunction with anode electrode 15, the connector leg corresponding with the selected cathode, for example leg 471 for cathode 10 or leg 472 for cathode 12, is connected to a pulse generator device. The non-selected leg may be capped according to means known to those skilled in the art.

[0016] FIG. 4 is a plan view of a distal portion of a medical electrical lead 300 according to another embodiment of the present invention. FIG. 4 illustrates a lead body 316 in the form of an elongate insulative sheath carrying a multi-filar coiled conductor 313 shown by dashed lines; coiled conductor 313 includes three sets of filar pairs 301, 302 and 305 electrically isolated from one another. According to the illustrated embodiment first filar pair 301 is coupled to tip electrode 310 at a junction 31, second filar pair 302 is coupled to a proximal electrode 312 at a junction 32, and third filar pair 305 is coupled to a flexible anode electrode 315 at junction 35. Junctions 31, 32 and 35 may be formed according to methods known to those skilled in the art, for example by crimps, stakes or welds. According to an exemplary embodiment of the present invention, filar pairs 301, 302 and 305 are isolated from one another by means of a hydrolytically stable polyimide coating formed about each filar of two or all of the pairs; a similar multi-filar conductor construction is described in co-pending patent application U.S. 2003/0216800, which is incorporated by reference in its entirety herein. According to yet another embodiment each conductor may be formed as an independent coil according to a coaxial construction well known to those skilled in the art. Although not shown, tip electrode 310 may include a longitudinally extending lumen, in communication with a lumen of coiled conductor 313, for passage of guidewire therethrough, and a tip seal; such a configuration is described by Sommer and Hine in U.S. Pat. No. 6,192,280 which is incorporated by reference herein in its entirety.

[0017] In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.