Patent Description:
Malignant tachyarrhythmia, for example, ventricular fibrillation (VF), is an uncoordinated contraction of the cardiac muscle of the ventricles in the heart, and is the most commonly identified arrhythmia in cardiac arrest patients. If this arrhythmia continues for more than a few seconds, it may result in cardiogenic shock and cessation of effective blood circulation. As a consequence, sudden cardiac death (SCD) may result in a matter of minutes.

In patients with a high risk of VF, the use of implantable systems, such as an implantable cardioverter defibrillator (ICD) system has been shown to be beneficial at preventing SCD. Implantable systems, such as pacemakers with or without cardioversion or defibrillation capabilities, may also treat other cardiac dysfunction, such as bradycardia and heart failure. Such implantable systems may include electrical devices configured to deliver therapy via electrodes. Therapy may include shocks and/or anti-tachycardia pacing (ATP). The implantable systems may also be configured to deliver cardiac pacing to, for example, treat bradyarrhythmia or for cardiac resynchronization therapy (CRT).

The implantable system may include one or more implantable medical leads. A distal portion of an implantable medical lead may include one or more electrodes, and may be positioned at a target location within the patient for delivery of electrical therapy and/or electrical sensing via the electrodes. A proximal end of the lead may be coupled to the implantable system. The implantable system may also include one or more housing electrodes, which are sometimes referred to as can electrodes, for delivery of therapy and/or sensing.

Owing to the inherent surgical risks in attaching and replacing implantable medical leads directly within or on the heart, subcutaneous implantable systems have been devised, in which the implantable system and leads are located subcutaneously outside of the thorax. It has also been proposed that the distal portion of a lead of an implantable system may be implanted within the thorax, but not in contact with the heart, e.g., substernally. Additionally, it has been proposed to implant the distal portion of a lead of an implantable system within an extracardiac vessel that is within the thorax, such as the internal thoracic vein (ITV), the intercostal veins, the superior epigastric vein, or the azygos, hemiazygos, and accessory hemiazygos veins.

Implantable medical leads are also used to deliver therapies to tissues other than the heart. Implantable medical leads may be used to position one or more electrodes within or near target nerves, muscles, or organs to deliver electrical stimulation to such tissues. As examples, implantable medical leads may be positioned in the epidural space to deliver spinal cord stimulation, or proximate to other nerves, such as pelvic nerves or renal nerves, to deliver neurostimulation to the nerves. <CIT> relates generally to cardiac leads carrying electrodes for electrically stimulating body tissue and/or for sensing the electrical activity of such tissue.

Relative to electrodes on or within the heart, delivery of pacing pulses using electrodes of extravascular leads may require higher energy levels to capture the heart. Furthermore, conventional pace electrodes placed extravascularly may direct a significant portion of the electrical field produced by a pacing pulse away from the heart. The electrical field directed away from the heart may stimulate extracardiac tissue, such as the phrenic nerve, nerve endings in the intercostal regions, or other sensory or motor nerves. These issues may similarly occur when electrodes are implanted within extracardiac vessels within the thorax, such as the ITV, the intercostal veins, the superior epigastric vein, or the azygos, hemiazygos, and accessory hemiazygos veins, or when electrodes are implanted in other extracardiac locations.

The invention provides an implantable medical lead according to claim <NUM> and a method of manufacturing of said implantable medical lead, according to claim <NUM>. For better understanding of the invention, the present disclosure further describes implantable medical leads and implantable systems, such as ICD systems, utilizing the leads. More particularly, this disclosure describes implantable medical leads that include a shield configured to impede the electric field from a pacing pulse, e.g., block or reduce the electric field, in a direction from the pace electrode, away from the heart, e.g., an anterior direction. In this manner, the shield may reduce the likelihood that pacing pulses delivered via the pace electrode stimulate extracardiac tissue, such as sensory or motor nerves, which may reduce pain or other sensations associated with capture of such tissue. Furthermore, the shield may direct the electrical field toward the heart, allowing lower energy level pacing pulses to capture the heart than may be required without the shield. Lower energy pacing pulses may also reduce the likelihood that pacing pulses delivered via the pace electrode stimulate extracardiac tissue, and may result is less consumption of the power source of the ICD and, consequently, longer service life for the ICD.

Although described herein primarily in the context of ICD systems, various aspects of the techniques of this disclosure may be applied to implantable systems other than ICD systems, including, but not limited to, bradycardia or CRT pacemaker systems. Accordingly, implantable medical leads having one or more shields may be used in contexts other than that of ICD systems, both cardiac and non-cardiac. As one example, implantable medical leads that have a shield over a portion of a surface of an electrode may be used with an extracardiac pacemaker system without defibrillation capabilities. As another example, implantable medical leads that have a shield over a portion of a surface of an electrode may impede an electrical field resulting from delivery of neurostimulation from the electrode in a direction away from a target nerve. In this manner, the shield may direct the neurostimulation to intended tissue, and reduce the likelihood that the neurostimulation stimulates unintended tissues.

In one example, an implantable medical lead comprises a first defibrillation electrode and a second defibrillation electrode, the first and second defibrillation electrodes configured to deliver anti tachyarrhythmia shocks, and a pace electrode disposed between the first defibrillation electrode and the second defibrillation electrode, the pace electrode configured to deliver a pacing pulse that generates an electric field proximate to the pace electrode. The implantable medical lead further comprises a shield disposed between the first defibrillation electrode and the second defibrillation electrode, over a portion of an outer surface of the pace electrode, and extending laterally away from the pace electrode, wherein the shield is configured to impede the electric field in a direction from the pace electrode away from a heart.

In another example, an implantable cardioverter-defibrillator (ICD) system comprises the implantable medical lead as described above and an ICD configured to deliver the pacing pulse via the pace electrode.

In another example, a method of implanting an implantable medical lead, which does not form part of the invention, as described above comprises advancing the implantable medical lead to a location within the patient, and rotationally orienting the distal portion of implantable medical lead such that the shield is positioned opposite a heart relative to the pace electrode.

In another example, a method of manufacturing an implantable medical lead as described above comprises attaching the shield to the surface of the pace electrode, and subsequently assembling the shield and the pace electrode on the implantable medical lead.

This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the systems, devices, and methods described in detail within the accompanying drawings and description below. Further details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the statements provided below.

As used herein, relational terms, such as "first" and "second," "over" and "under," "front" and "rear," and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements.

Referring now to the drawings in which like reference designators refer to like elements, there is shown in <FIG> conceptual diagrams illustrating various views of an example extracardiovascular implantable cardioverter-defibrillator (ICD) system <NUM>. ICD system <NUM> includes an ICD <NUM> connected to an implantable medical lead <NUM>. <FIG> is a front view of a patient implanted with extracardiovascular ICD system <NUM>. <FIG> is a side view of the patient implanted with extracardiovascular ICD system <NUM>. <FIG> is a transverse view of the patient implanted with extracardiovascular ICD system <NUM>.

ICD <NUM> may include a housing that forms a hermetic seal that protects components of the ICD <NUM>. The housing of ICD <NUM> may be formed of a conductive material, such as titanium or titanium alloy, which may function as a housing electrode (sometimes referred to as a can electrode). In some embodiments, ICD <NUM> may be formed to have or may include a plurality of electrodes on the housing. ICD <NUM> may also include a connector assembly (also referred to as a connector block or header) that includes electrical feedthroughs through which electrical connections are made between conductors of lead <NUM> and electronic components included within the housing of ICD <NUM>. As will be described in further detail herein, the housing may house one or more processors, memories, transmitters, receivers, sensors, sensing circuitry, therapy circuitry, power sources and other appropriate components. The housing is configured to be implanted in a patient, such patient <NUM>.

ICD <NUM> is implanted extra-thoracically on the left side of the patient, e.g., under the skin and outside the ribcage (subcutaneously or submuscularly). ICD <NUM> may, in some instances, be implanted between the left posterior axillary line and the left anterior axillary line of the patient. ICD <NUM> may, however, be implanted at other extra-thoracic locations on the patient as described later.

Lead <NUM> may include an elongated lead body <NUM> having a distal portion <NUM> sized to be implanted in an extracardiovascular location proximate the heart, e.g., intra-thoracically, as illustrated in <FIG>, or extra-thoracically. For example, lead <NUM> may extend extra-thoracically under the skin and outside the ribcage (e.g., subcutaneously or submuscularly) from ICD <NUM> toward the center of the torso of the patient, for example, toward the xiphoid process <NUM> of the patient. At a position proximate xiphoid process <NUM>, the lead body <NUM> may bend or otherwise turn and extend superiorly. The bend may be pre-formed and/or lead body <NUM> may be flexible to facilitate bending. In the example illustrated in <FIG>, the lead body <NUM> extends superiorly intra-thoracically underneath the sternum, in a direction substantially parallel to the sternum.

In one example, distal portion <NUM> of lead <NUM> may reside in a substernal location such that distal portion <NUM> of lead <NUM> extends superior along the posterior side of the sternum substantially within the anterior mediastinum <NUM>. Anterior mediastinum <NUM> may be viewed as being bounded laterally by pleurae <NUM>, posteriorly by pericardium <NUM>, and anteriorly by the sternum <NUM>. In some instances, the anterior wall of anterior mediastinum <NUM> may also be formed by the transversus thoracis and one or more costal cartilages. Anterior mediastinum <NUM> includes a quantity of loose connective tissue (such as areolar tissue), adipose tissue, some lymph vessels, lymph glands, substernal musculature (e.g., transverse thoracic muscle), the thymus gland, branches of the internal thoracic artery, and the ITV.

In another example, lead body <NUM> may extend superiorly extra-thoracically (instead of intra-thoracically), e.g., either subcutaneously or submuscularly above the ribcage/sternum. Lead <NUM> may be implanted at other locations, such as over the sternum, offset to the right of the sternum, angled lateral from the proximal or distal end of the sternum, or the like. In other examples, lead <NUM> may be implanted within an extracardiac vessel within the thorax, such as the ITV, the intercostal veins, the superior epigastric vein, or the azygos, hemiazygos, and accessory hemiazygos veins. In some examples, distal portion <NUM> of lead <NUM> may be oriented differently than is illustrated in <FIG>, such as orthogonal or otherwise transverse to sternum <NUM> and/or inferior to heart <NUM>. In such examples, distal portion <NUM> of lead <NUM> may be at least partially within anterior mediastinum <NUM>.

Lead body <NUM> may have a generally tubular or cylindrical shape and may define a diameter of approximately <NUM>-<NUM> French (Fr). However, lead bodies of less than <NUM> Fr and more than <NUM> Fr may also be utilized. In another configuration, lead body <NUM> may have a flat, ribbon, or paddle shape with solid, woven filament, or metal mesh structure, along at least a portion of the length of the lead body <NUM>. In such an example, the width across lead body <NUM> may be between <NUM>-<NUM>. Other lead body designs may be used without departing from the scope of this application.

Lead body <NUM> may be formed from a non-conductive material, including silicone, polyurethane, fluoropolymers, mixtures thereof, and other appropriate materials, and shaped to form one or more lumens (not shown), however, the techniques are not limited to such constructions. Distal portion <NUM> may be fabricated to be biased in a desired configuration, or alternatively, may be manipulated by the user into the desired configuration. For example, the distal portion <NUM> may be composed of a malleable material such that the user can manipulate the distal portion into a desired configuration where it remains until manipulated to a different configuration.

Lead body <NUM> may include a proximal end <NUM> and a distal portion <NUM> which include electrodes configured to deliver electrical energy to the heart or sense electrical signals of the heart. Distal portion <NUM> may be anchored to a desired position within the patient, for example, substernally or subcutaneously by, for example, suturing distal portion <NUM> to the patient's musculature, tissue, or bone at the xiphoid process entry site. In some examples, distal portion <NUM> may be anchored to the patient or through the use of rigid tines, prongs, barbs, clips, screws, and/or other projecting elements or flanges, disks, pliant tines, flaps, porous structures such as a mesh-like elements and metallic or non-metallic scaffolds that facilitate tissue growth for engagement, bio-adhesive surfaces, and/or any other non-piercing elements.

Lead body <NUM> may define a substantially linear portion <NUM> (<FIG>) as it curves or bends near the xiphoid process <NUM> and extends superiorly. As shown in <FIG>, at least a part of distal portion <NUM> may define an undulating configuration distal to the substantially linear portion <NUM>. In particular, distal portion <NUM> may define an undulating pattern, e.g., zigzag, meandering, sinusoidal, serpentine, or other pattern, as it extends toward the distal end of lead <NUM>. In other configurations, lead body <NUM> may not have a substantially linear portion <NUM> as it extends superiorly, but instead the undulating configuration may begin immediately after the bend.

Distal portion <NUM> includes one or more defibrillation electrodes configured to deliver an anti-tachyarrhythmia, e.g., cardioversion/defibrillation, shock to heart <NUM> of patient <NUM>. In some examples, distal portion <NUM> includes a plurality of defibrillation electrodes spaced a distance apart from each other along the length of distal portion <NUM>. In the example illustrated by <FIG>, distal portion <NUM> includes two defibrillation electrodes 28a and 28b (collectively, "defibrillation electrodes <NUM>").

Defibrillation electrodes <NUM> may be disposed around or within the lead body <NUM> of the distal portion <NUM>, or alternatively, may be embedded within the wall of the lead body <NUM>. In one configuration, defibrillation electrodes <NUM> may be coil electrodes formed by a conductor. The conductor may be formed of one or more conductive polymers, ceramics, metal-polymer composites, semiconductors, metals or metal alloys, including but not limited to, one of a combination of the platinum, tantalum, titanium, niobium, zirconium, ruthenium, indium, gold, palladium, iron, zinc, silver, nickel, aluminum, molybdenum, stainless steel, MP35N, carbon, copper, polyaniline, polypyrrole and other polymers. In another configuration, each of defibrillation electrodes <NUM> may be a flat ribbon electrode, a paddle electrode, a braided or woven electrode, a mesh electrode, a directional electrode, a patch electrode or another type of electrode configured to deliver a cardioversion/defibrillation shock to heart <NUM> of patient <NUM>.

In one configuration, defibrillation electrodes <NUM> are spaced approximately <NUM>-<NUM>, and in some instances between <NUM>-<NUM> apart from each other. In another configuration, defibrillation electrodes <NUM> are spaced approximately <NUM>-<NUM> apart from each other. In a further configuration, defibrillation electrodes <NUM> are spaced approximately <NUM>-<NUM> apart from each other.

In the configuration shown in <FIG>, defibrillation electrodes <NUM> span a substantial part of distal portion <NUM>. Each of defibrillation electrodes <NUM> may be between approximately <NUM>-<NUM> in length, between approximately <NUM>-<NUM> in length, or between approximately <NUM>-<NUM> in length. However, lengths of greater than <NUM> and less than <NUM> may be utilized in accordance with the techniques of this disclosure. A total length of defibrillation electrode on distal portion <NUM>, e.g., length of the two defibrillation electrodes <NUM> combined, may vary depending on a number of variables. In one example, the total length may be between approximately <NUM>-<NUM>. However, the defibrillation electrodes <NUM> may have a total length less than <NUM> and greater than <NUM> in other embodiments. In some instances, defibrillation electrodes <NUM> may be approximately the same length or, alternatively, different lengths.

Defibrillation electrodes <NUM> may be electrically connected to one or more conductors, which may be disposed in the body wall of lead body <NUM> or in one or more insulated lumens (not shown) defined by lead body <NUM>. In an example configuration, each of defibrillation electrodes <NUM> is connected to a common conductor such that a voltage may be applied simultaneously to all defibrillation electrodes <NUM> to deliver an anti-tachyarrhythmia shock to heart <NUM>. In other configurations, defibrillation electrodes <NUM> may be attached to separate conductors such that each defibrillation electrode <NUM> may apply a voltage independent of the other defibrillation electrodes <NUM>. In this case, ICD <NUM> or lead <NUM> may include one or more switches or other mechanisms to electrically connect the defibrillation electrodes together to function as a common polarity electrode such that a voltage may be applied simultaneously to all defibrillation electrodes <NUM> in addition to being able to independently apply a voltage.

Distal portion <NUM> may also include one or more pacing and/or sensing electrodes configured to deliver pacing pulses to heart <NUM> and/or sense electrical activity of heart <NUM>. Such electrodes may be referred to as pacing electrodes, sensing electrodes, or pace/sense electrodes. In the example illustrated by <FIG>, distal portion <NUM> includes two pace/sense electrodes 32a and 32b (collectively, "pace/sense electrodes <NUM>").

In the illustrated example, pace/sense electrode 32b is positioned between defibrillation electrodes <NUM>, e.g., within a gap between the defibrillation electrodes, and pace/sense electrode 32a is positioned more proximal along distal portion <NUM> than proximal defibrillation electrode 28a. In some examples, more than one electrode <NUM> may exist within the gap between defibrillation electrodes <NUM>. In some examples, an electrode <NUM> is additionally or alternatively located distal of the distalmost defibrillation electrode 28b.

In one example, the distance between the closest defibrillation electrode <NUM> and electrodes <NUM> is greater than or equal to approximately <NUM> and less than or equal to approximately <NUM>. In another example, electrodes <NUM> may be spaced apart from the closest one of defibrillation electrodes <NUM> by greater than or equal to <NUM> and less than or equal to <NUM>. In a further example, electrodes <NUM> may be spaced apart from the closest one of defibrillation electrodes <NUM> by greater than or equal to <NUM> and less than or equal to <NUM>.

Electrodes <NUM> may be configured to deliver low-voltage electrical pulses to the heart or may sense a cardiac electrical activity, e.g., depolarization and repolarization of the heart. As such, electrodes <NUM> may be referred to herein as pace/sense electrodes <NUM>. In one configuration, electrodes <NUM> are ring electrodes. However, in other configurations electrodes <NUM> may be any of a number of different types of electrodes, including ring electrodes, short coil electrodes, paddle electrodes, hemispherical electrodes, or directional electrodes. Each of electrodes <NUM> may be the same or different types of electrodes as others of electrodes <NUM>. Electrodes <NUM> may be electrically isolated from an adjacent defibrillation electrode <NUM> by including an electrically insulating layer of material between electrodes <NUM> and adjacent defibrillation electrodes <NUM>. Each electrode <NUM> may have its own separate conductor such that a voltage may be applied to or sensed via each electrode independently from another electrode <NUM>.

Electrodes <NUM> are referred to as defibrillation electrodes, and electrodes <NUM> are referred to as pace/sense electrodes, because they may have different physical structures enabling different functionality. Defibrillation electrodes <NUM> may be larger, e.g., have greater surface area, than pace/sense electrodes <NUM> and, consequently, may be configured to deliver anti-tachyarrhythmia shocks that have relatively higher voltages than pacing pulses. The relatively smaller size of pace/sense electrodes <NUM> may provide advantages over defibrillation electrodes for delivering pacing pulses and sensing intrinsic cardiac activity, e.g., lower pacing capture thresholds and/or better sensed signal quality. Nevertheless, a defibrillation electrode <NUM> may be used to deliver pacing pulses and/or sense electrical activity of the heart, such as in combination with a pace/sense electrode <NUM>.

In the configuration shown in <FIG>, each electrode <NUM> is substantially aligned along a major longitudinal axis ("x"). In one example, the major longitudinal axis is defined by a portion of elongate body <NUM>, e.g., substantially linear portion <NUM>. In another example, the major longitudinal axis is defined relative to the body of the patient, e.g., along the anterior median line (or midsternal line), one of the sternal lines (or lateral sternal lines), left parasternal line, or other line.

In one configuration, the midpoint of each electrode 32a and 32b is along the major longitudinal axis "x," such that each electrode 32a and 32b is at least disposed at substantially the same horizontal position when the distal portion is implanted within the patient. In some examples, the longitudinal axis "x" may correspond to a caudal-cranial axis of the patient and a horizontal axis orthogonal to the longitudinal axis "x" may correspond to a medial-lateral axis of the patient. In other configurations, the electrodes <NUM> may be disposed at any longitudinal or horizontal position along the distal portion <NUM> disposed between, proximal to, or distal to the defibrillation electrodes <NUM>. In the example illustrated in <FIG>, electrodes <NUM> are disposed along the undulating configuration of distal portion <NUM> at locations that will be closer to heart <NUM> of patient <NUM> than defibrillation electrodes <NUM> (e.g., at a peak of the undulating configuration that is toward the left side of the sternum). As illustrated in <FIG>, for example, electrodes <NUM> are substantially aligned with one another along the left sternal line. In the example illustrated in <FIG>, defibrillation electrodes <NUM> are disposed along peaks of the undulating configuration that extend toward a right side of the sternum away from the heart. This configuration places pace/sense electrodes <NUM> at locations closer to the heart than electrodes <NUM>, to facilitate cardiac pacing and sensing at relatively lower amplitudes.

In some examples, pace/sense electrodes <NUM> and the defibrillation electrodes <NUM> may be disposed in a common plane when distal portion <NUM> is implanted extracardiovasculalry. In other configurations, the undulating configuration may not be substantially disposed in a common plane. For example, distal portion <NUM> may define a concavity or a curvature.

Proximal end <NUM> of lead body <NUM> may include one or more connectors <NUM> to electrically couple lead <NUM> to ICD <NUM>. ICD <NUM> may also include a connector assembly that includes electrical feedthroughs through which electrical connections are made between the one or more connectors <NUM> of lead <NUM> and the electronic components included within the housing. The housing of ICD <NUM> may house one or more processors, memories, transmitters, receivers, sensors, sensing circuitry, therapy circuitry, power sources (capacitors and batteries), and/or other components. The components of ICD <NUM> may generate and deliver electrical therapy such as anti-tachycardia pacing, cardioversion or defibrillation shocks, post-shock pacing, and/or bradycardia pacing.

The undulating configuration of distal portion <NUM> and the inclusion of electrodes <NUM> between defibrillation electrodes <NUM> provides a number of therapy vectors for the delivery of electrical therapy to the heart. For example, at least a portion of defibrillation electrodes <NUM> and one of electrodes <NUM> may be disposed over the right ventricle, or any chamber of the heart, such that pacing pulses and anti-tachyarrhythmia shocks may be delivered to the heart. The housing of ICD <NUM> may be charged with or function as a polarity different than the polarity of the one or more defibrillation electrodes <NUM> and/or electrodes <NUM> such that electrical energy may be delivered between the housing and the defibrillation electrode <NUM> and/or electrode <NUM> to the heart.

Each defibrillation electrode <NUM> may have the same polarity as every other defibrillation electrode <NUM> when a voltage is applied to it such that a shock may be delivered from all defibrillation electrodes together. In examples in which defibrillation electrodes <NUM> are electrically connected to a common conductor within lead body <NUM>, this is the only configuration of defibrillation electrodes <NUM>. However, in other examples, defibrillation electrodes <NUM> may be coupled to separate conductors within lead body <NUM> and may therefore each have different polarities such that electrical energy may flow between defibrillation electrodes <NUM>, or between one of defibrillation electrodes <NUM> and one of pace/sense electrodes <NUM> or the housing electrode, to provide anti-tachyarrhythmia shock, pacing therapy, and/or to sense cardiac depolarizations. In this case, defibrillation electrodes <NUM> may still be electrically coupled together, e.g., via one or more switches within ICD <NUM>, to have the same polarity.

In some examples, distal portion <NUM> of lead <NUM> may include one or more shields. The shield or shields may be configured to impede an electric field from delivery of an electrical therapy via an electrode, e.g., from a pacing pulse, in a direction from the electrode away from the heart, e.g., in an anterior direction. In this manner, the shield may reduce the likelihood that the electrical field will stimulate extracardiac tissue, such as sensory or motor nerves. Furthermore, the shield may direct the electrical field toward the heart, allowing lower energy level pacing pulses to capture the heart than may be required without the shield. Lower energy pacing pulses may also reduce the likelihood that pacing pulses delivered via the pace electrode stimulate extracardiac tissue, and may result in less consumption of the power source of ICD <NUM> and, consequently, longer service life for the ICD. It should be understood that various aspects of the techniques of this disclosure may be applied to implantable systems other than ICD <NUM>, including, but not limited to, bradycardia pacemaker systems. For example, a lead that does not include defibrillation electrodes may include one or more shields and may be used with a pacemaker system without defibrillation capabilities.

<FIG> is a conceptual diagram illustrating an example configuration of distal portion <NUM> of implantable medical lead <NUM>. As illustrated in <FIG>, the undulating configuration of distal portion <NUM> may include a plurality of peaks along the length of the distal portion. In the example illustrated by <FIG>, distal portion includes three peaks 24a, 24b, and 24c (collectively, "peaks <NUM>"). Other configurations, however, may include any number of peaks <NUM>.

The undulating configuration may define a peak-to-peak distance <NUM>, which may be variable or constant along the length of distal portion <NUM>. In the configuration illustrated in <FIG>, the undulating configuration defines a substantially sinusoidal configuration, with a constant peak-to-peak distance <NUM> of approximately <NUM>-<NUM>. The undulating configuration may also define a peak-to-peak width <NUM>, which may also be variable or constant along the length of the undulating configuration. In the configuration illustrated in <FIG>, the undulating configuration defines a substantially sinusoidal shape, with a constant peak-to-peak width <NUM> of approximately <NUM>-<NUM>. However, in other instances, the undulating configuration may define other shapes and/or patterns, e.g., S-shapes, wave shapes, or the like.

Defibrillation electrodes <NUM> may extend along, e.g., be disposed on or cover, a substantial part of the undulating configuration of distal portion <NUM>, e.g., along at least <NUM>% of the undulating portion. Defibrillation electrodes <NUM> may extend along more or less than <NUM>% of the undulating configuration. As another example, defibrillation electrodes <NUM> may extend along at least <NUM>% of the undulating configuration.

Defibrillation electrode 28a extends along a substantial portion of the undulating configuration of distal portion <NUM> from the proximal end to peak 24b, e.g., along a substantial portion of the first "wave" associated with peak 24a, and the defibrillation electrode segment 28b extends along a substantial portion of the undulating configuration from peak 24b to the distal end of the undulating configuration, e.g., along a substantial portion of the second "wave" associated with peak 24c). In the example illustrated in <FIG>, a part of the undulating configuration on which defibrillation electrodes <NUM> are not disposed is a gap between defibrillation electrodes 28a and 28b, on peak 24b, where electrode 32b is disposed.

As illustrated by <FIG>, distal portion <NUM> of lead <NUM> may comprise a shield <NUM>. In the illustrated example, shield <NUM>, like pace/sense electrode 32b, is positioned between defibrillation electrodes 28a and 28b, e.g., on peak 24b of the undulating configuration of distal portion <NUM>. Shield <NUM> covers or is otherwise disposed over a portion of an outer surface of pace/sense electrode 32b. Shield <NUM> does not cover an entirety of the outer surface of pace/sense electrode 32b.

Pacing pulses delivered by ICD <NUM> via pace/sense electrode 32b result in an electrical field proximate the electrode, that "spreads" from the electrode surface toward one or more other electrodes used to deliver the pacing pulse. Shield <NUM> impedes the electrical field in directions from the electrode toward the shield, and allows the spread in directions from the electrode away from the shield. In this manner, shield <NUM> is configured to make pace/sense electrode 32b directional.

As illustrated in <FIG>, shield <NUM> may extend laterally away from pace/sense electrode 32b, e.g., in a substantially planar manner, such that the dimensions of shield <NUM> in a plane are greater than those of pace/sense electrode 32b in the plane. In this manner, shield <NUM> may further (or more effectively) limit the directions, e.g., radial angles, of the spread of the electrical field generated by the pacing pulse from pace/sense electrode 32b. The plane in which shield <NUM> extends laterally from pace/sense electrode 32b may be the same plane in which peaks <NUM> of the undulating configuration extend, or a substantially parallel plane. In some examples, such as that illustrated by <FIG>, shield <NUM> extends symmetrically from pace/sense electrode 32b, e.g., is symmetrical about a longitudinal axis and/or a transverse axis of pace/sense electrode 32b, such that pace/sense electrode 32b is substantially centered within the outer profile of shield <NUM> in the plane.

The portion of the outer surface of pace/sense electrode 32b over which shield <NUM> is positioned may be referred to as an "anterior portion" of the outer surface of pace/sense electrode 32b, since that portion of pace/sense electrode 32b may be more anteriorly positioned within the patient when distal portion <NUM> of lead <NUM> is implanted within patient. With shield <NUM> positioned over an anterior portion of the outer surface of pace/sense electrode 32b, shield <NUM> may be positioned anteriorly relative to the central longitudinal axis of pace/sense electrode 32b. With shield <NUM> positioned over an anterior portion of the outer surface of pace/sense electrode 32b, and distal portion <NUM> implanted within the patient as illustrated in <FIG>, shield <NUM> may impede the electrical field in directions away from heart <NUM>, referred to as anterior directions.

Shield <NUM> may be electrically insulative. In some examples, shield <NUM> comprises a polymer, such as polyurethane. In some examples, shield <NUM> is configured to be folded or wrapped around pace/sense electrode 32b for delivery via a lumen of an implant tool, and configured to elastically unfold or unwrap to a relaxed condition, e.g., such as the condition shown in <FIG>, when released from the lumen. In some examples, shield <NUM> comprises elastic or super-elastic polymer or metallic structures, e.g., Nitinol structures, to encourage the deployment of shield <NUM>, support articulation of shield <NUM>, and/or support shield <NUM> in the deployed, relaxed configuration. The deployed and/or articulated configuration may be substantially planar, as illustrated in <FIG>, or may be non-planar. For example, portions of shield <NUM> spaced further away laterally from pace/sense electrode 32b may be situated more posteriorly than portions closer to the electrode, e.g., in the shape of a cup or bowl.

Such support structures may be partially or fully embedded within a primary material of shield <NUM>, or attached to one or more outer surfaces of shield <NUM>. In some examples, a support structure is located circumferentially around a perimeter of shield <NUM>, e.g., spaced a greatest distance laterally from the shield. However, other support structure locations are possible. For example, one or more support structures may extend in radial or lateral direction from the electrode, e.g., from near electrode to near a periphery of the shield.

<FIG> are conceptual diagrams illustrating views of shield <NUM> of implantable medical lead <NUM>. In particular, <FIG> illustrates a "top" view in the anterior direction, <FIG> illustrates a side view, and <FIG> a cross-sectional view taken at line A-A in <FIG>.

As illustrated in <FIG> and <FIG>, shield <NUM> may extend from a distal end 41a of proximal defibrillation electrode 28a to a proximal end 41b of distal defibrillation electrode 28b in the direction of longitudinal axis "x" of distal portion <NUM>. In some examples, shield <NUM> may extend over a portion or entirety of one or both of defibrillation electrodes <NUM>. In some examples, shield <NUM> may not extend to one or both of defibrillation electrodes <NUM>, leaving a gap between the shield and defibrillation electrode.

<FIG> and <FIG> illustrate shield <NUM> extending laterally away from pace/sense electrode 32b. As shown in <FIG>, shield <NUM> may be substantially circular in the plane in which the shield extends. In other examples, shield <NUM> may have other shapes, such as ovoid or rectangular.

A length <NUM> of shield <NUM> is greater than a length <NUM> of pace/sense electrode 32b, such as at least twice the length of pace/sense electrode 32b. A width <NUM> of shield <NUM> is greater than a width <NUM> of pace/sense electrode 32b, such as at least twice width <NUM> of the pace electrode. In some examples, shield <NUM> extends a distance <NUM> beyond pace/sense electrode 32b in the direction of its width, e.g., in a direction orthogonal to its longitudinal axis. In some examples, distance <NUM> is at least <NUM>, at least <NUM>, or at least <NUM>. One or both of length <NUM> and width <NUM> of shield <NUM> may be at least <NUM>, such as approximately <NUM>. In examples in which shield <NUM> is circular a dimeter of shield <NUM> may be at least <NUM>, such as approximately <NUM>.

As illustrated in <FIG>, shield <NUM> includes a plurality of radiopaque markers, including radiopaque marker 42a and radiopaque marker 42b (collectively, "radiopaque markers <NUM>"). Shield <NUM> may include any number of radiopaque markers or no radiopaque markers. Radiopaque markers <NUM> may be distributed symmetrically on shield <NUM>, e.g., relative to pace/sense electrode 32b. Radiopaque markers <NUM> may be positioned on shield <NUM> to allow a user to visualize at least one of a position or an orientation of the shield within the patient by identification of the radiopaque markers in a fluoroscopic or other image. Radiopaque markers <NUM> may be different from each other in one or more ways, e.g., size, shape, or orientation, to allow, for example, a physician to differentiate between radiopaque markers <NUM>, in this way facilitating visualization of the orientation of shield <NUM>. For example, one of radiopaque markers <NUM> positioned on shield <NUM> may be larger than the rest such that the physician may determine, based on the position of the larger radiopaque marker (e.g., relative to the rest of radiopaque markers <NUM>), the orientation of shield <NUM>.

As illustrated in <FIG> and <FIG>, distal portion <NUM> of lead <NUM> may include lead body portion 40a and lead body portion 40b (collectively, "lead body portions <NUM>"). Lead body portions <NUM> extend between pace/sense electrode 32b and a respective one of defibrillation electrodes <NUM>. Lead body portions <NUM> may provide a relatively even or smooth surface transition between the outer profile of pace/sense electrode 32b and the outer profiles of defibrillation electrodes <NUM>. Conductors coupled to electrodes 32b and 28b may extend through lead body portion 40a, and a conductor coupled to electrode 28b may extend through lead body portion 40b. Lead body portions 40a and 40b may formed of one or more polymers, which may be the same as or different from shield <NUM> and/or other portions of lead body <NUM>.

As illustrated in <FIG>, pace/sense electrode 32b may define a lumen <NUM>, e.g., may be in the form of a ring, and a conductor coupled to electrode 28b may extend through lumen <NUM>. Although illustrated in <FIG> as a ring, pace/sense electrodes <NUM> may have other shapes, including partial or segmented ring shapes or arc shapes, in which one or more electrodes or electrode segments extend less than <NUM>-degrees around a circumference of the lead.

Since shield <NUM> only covers an anterior portion of outer surface <NUM> of pace/sense electrode 32b, a depth <NUM> of shield <NUM> may be less than a depth <NUM> of pace/sense electrode 32b, such as less than one half of the depth of the electrode. Although illustrated as substantially constant, depth <NUM> of shield <NUM> may vary. For example, depth <NUM> may increase toward pace/sense electrode 32b and/or decrease toward an edge of the shield, e.g., to provide a smooth or otherwise desired transition between shield <NUM> and pace/sense electrode 32b and/or between shield <NUM> and tissue of the patient. Additionally, although defibrillation electrodes <NUM>, pace/sense electrode 32b, and lead body portions 40a and 40b are shown in <FIG> as having substantially equal depths (e.g., circumferences) that are greater than depth <NUM> of shield <NUM>, in other examples depth <NUM> of shield <NUM> may be similar to that of lead body portions 40a and 40b and pace/sense electrode 32b may extend outward from lead body portions 40a and 40b and shield <NUM>, e.g., due to having a greater depth or being offset from a longitudinal axis defined by lead body portions 40a and 40b.

As illustrated in <FIG>, pacing pulses delivered by ICD <NUM> via pace/sense electrode 32b result in an electrical field <NUM> proximate the electrode, that "spreads" from electrode outer surface <NUM>. Shield <NUM> may reduce and/or impede the electrical field in directions from the electrode toward the shield, and allows the spread in directions from the electrode away from the shield. In this manner, shield <NUM> is configured to make pace/sense electrode 32b directional.

<FIG> is a flow diagram illustrating an example technique for implanting an implantable medical lead comprising a shield. <FIG> is described with respect to implantable medical lead <NUM> and shield <NUM>. However, the example technique of <FIG> may be used to implant other leads including one or more shields.

A medical practitioner may implant distal portion <NUM> of implantable medical lead <NUM> into a substernal or other extravascular location using an implant tool. In some examples, as illustrated by <FIG>, a medical practitioner or assistant may fold or wrap shield <NUM> around pace/sense electrode 32b, so that it may fit within a lumen (or a channel)of an implant tool, and introduce distal portion <NUM> of lead <NUM> into the lumen (<NUM>). In some examples, distal portion <NUM> may be loaded into the lumen and packaged in a sterile package prior to the implantation procedure, e.g., by a manufacturer of lead <NUM> and/or the implant tool. The lumen of the implant tool may be cylindrical, or may otherwise have a profile that matches the outer profile of distal portion <NUM>. The undulating configuration of distal portion <NUM> may be straightened when within the lumen. In one example, the lumen may comprise a sheath. Configurations other than those including a lumen of an implant tool for releasing shield <NUM> are contemplated by this disclosure.

In some examples, the medical practitioner may introduce the implant tool into the patient via a subxiphoid incision, and advance the implant tool to the extravascular location. Advancement of the tool to the extravascular location may occur before or after lead <NUM> is loaded into the tool. In either case, distal portion <NUM> of lead <NUM> is positioned at the extravascular location using the implant tool, e.g., by advancement through the lumen or advancement of the tool while in the lumen (<NUM>). In one embodiment, the implant tool may include a tunneling tool having a rod or other tunneling member and a sheath configured to be placed on the rod.

According to the example of <FIG>, the medical practitioner removes distal portion <NUM> of lead <NUM> from the implant tool to release the shield (<NUM>). In the case of an implant tool that includes a sheath with a lumen, the medical practitioner may release the shield by withdrawing the sheath proximally from the patient and/or splitting the sheath. In other embodiments, the implant tool or the sheath of the implant tool may be formed to have a channel or other recessed portion accessible via a longitudinal opening to receive distal portion <NUM> of lead <NUM> including shield <NUM> and the medical practitioner may release the shield by laterally separating distal portion <NUM> of lead <NUM> from the channel or other recessed portion of the sheath or implant tool. When shield <NUM> is free from the lumen, shield <NUM> may transition from the folded or wrapped configuration to a deployed configuration, e.g., may be elastically deformed to the folded or wrapped configuration and release to the deployed configuration, which may be a relaxed configuration. In some examples, lead <NUM> may include a fluid, balloon, spring or other actuatable mechanism to transition shield <NUM> to the deployed configuration.

The medical practitioner may visualize shield <NUM> within patient, e.g., using fluoroscopy or other medical imaging to identify radiopaque markers (<NUM>). The medical practitioner may, if necessary, rotationally orient distal portion <NUM> of lead <NUM> so that shield <NUM> is positioned anteriorly relative to pace/sense electrode 32b (<NUM>).

<FIG> is a flow diagram illustrating an example technique for manufacturing an implantable medical lead comprising a shield. <FIG> is described with respect to implantable medical lead <NUM> and shield <NUM>. However, the example technique of <FIG> may be used to implant other leads including one or more shields.

According to the example technique of <FIG>, shield <NUM> is attached to an anterior portion of surface <NUM> of pace/sense electrode 32b (<NUM>). In some examples, shield <NUM> is a separately molded element that is attached to pace/sense electrode 32b using an adhesive. In other examples, shield <NUM> is molded onto pace/sense electrode 32b. In some examples, the molding of shield <NUM> onto pace/sense electrode 32b further includes molding lead body portion 40a to a proximal end of pace/sense electrode 32b and lead body portion 40b to a distal end of pace/sense electrode 32b, e.g., shield <NUM> and lead body portions <NUM> may be molded as a single piece of a common material. Pace/sense electrode 32b and shield <NUM> (and in some cases lead body portions <NUM>) may then be assembled onto lead <NUM> as a unit (<NUM>). Lead <NUM> may then optionally be overmolded (<NUM>).

<FIG> is a conceptual diagram illustrating a distal portion <NUM> of an example implantable medical lead comprising a plurality of shields. Distal portion <NUM> is similar to distal portion <NUM> of lead <NUM>, and like numbered elements of distal portion <NUM> are similar to those of distal portion <NUM>. For example, distal portion <NUM> includes defibrillation electrodes 128a and 128b and pace/sense electrodes 132a and 132b, and defines an undulating configuration similar to distal portion <NUM>.

As illustrated in <FIG>, distal portion <NUM> includes a first shield 130a over an anterior portion of a surface of pace/sense electrode 132a and a second shield 130b over an anterior portion of a surface of pace/sense electrode 132b. Shield 130a and shield 130b may be the same as or different than each other. In some examples, each of shields 130a and 130b may be the same as or substantially similar to shield <NUM> described herein with respect to <FIG>, e.g., may include any combination of one or more of the features described above with respect to shield <NUM>.

<FIG> is a conceptual diagram illustrating a distal portion <NUM> of another example implantable medical lead comprising a plurality of shields. Distal portion <NUM> is similar to distal portion <NUM> of lead <NUM>, and like numbered elements of distal portion <NUM> are similar to those of distal portion <NUM>. For example, distal portion <NUM> includes defibrillation electrodes 228a and 228b and pace/sense electrodes 232a and 232b, and defines an undulating configuration similar to distal portion <NUM>.

As illustrated in <FIG>, distal portion <NUM> includes a plurality of shields including labeled shields 230a and 230b (collectively, "shields <NUM>"). Shields <NUM> may be the same as or different than each other. In some examples, each of shields <NUM> may be the same as or substantially similar to shield <NUM> described herein with respect to <FIG>, e.g., may include any combination of one or more of the features described above with respect to shield <NUM>.

As illustrated in <FIG> shields <NUM> may collectively cover an anterior portion of an outer surface for each of electrodes <NUM> and <NUM>. In some examples, defibrillation electrodes <NUM> may be used to deliver pacing pulses, and shields <NUM> may provide the same directionality of electrical fields proximate defibrillation electrodes <NUM> as described with respect to pace sense electrodes <NUM>. Use of a plurality of shields <NUM> arranged as illustrated in <FIG> may provide directionality of electrical fields, while allowing distal portion <NUM> to be straightened for implantation and then assume the illustrated undulating configuration when implanted.

<FIG> is a conceptual diagram illustrating a distal portion <NUM> of another example implantable medical lead comprising a shield. Like numbered elements of distal portion <NUM> are similar to those of distal portion <NUM>. For example, distal portion <NUM> includes defibrillation electrodes 328a and 328b, pace/sense electrodes 332a and 332b. Unlike distal portion <NUM>, however, distal portion <NUM> defines a straight or substantially straight configuration, rather than an undulating configuration. As illustrated in <FIG>, distal portion <NUM> includes a single shield <NUM> that covers an anterior portion of an outer surface for each of electrodes <NUM> and <NUM>. Shield <NUM> may be the same as or substantially similar to shield <NUM> described herein with respect to <FIG>, e.g., may include any combination of one or more of the features described above with respect to shield <NUM>.

Although the example implantable medical lead distal portions illustrated herein have generally included two defibrillation electrodes and two pace/sense electrodes, with one of the pace/sense electrodes between the defibrillation electrodes and the other of the pace/sense electrodes proximal of the defibrillation electrodes, any the shields described herein may be included as part of differently configured implantable medical leads. For example, some implantable medical leads may include a single defibrillation electrode and one or more pace/sense electrodes located distal and/or proximal of the defibrillation electrode. In other examples, an implantable medical lead that includes one or more stimulation electrodes, not necessarily for cardiac pacing, does not include a defibrillation electrode. In any such examples, one or more shields configured as described herein may be located over a portion of a surface of one or more electrodes.

<FIG> is a conceptual diagram illustrating part of a distal portion <NUM> of another implantable medical lead comprising a shield. Distal portion <NUM> may be similar to distal portion <NUM> of lead <NUM>, and like numbered elements of distal portion <NUM> may be similar to those of distal portion <NUM>. For example, distal portion <NUM> includes defibrillation electrodes 528a and 528b (collectively, "defibrillation electrodes <NUM>") and pace/sense electrode <NUM>.

Distal portion <NUM> also includes a lead body portion <NUM> extending from defibrillation electrode 528a to defibrillation electrode 528b. Lead body portion <NUM> may provide a relatively even or smooth surface transition between the outer profiles of defibrillation electrodes <NUM>. Lead body portion <NUM> may be formed of an insulative material and conductors coupled to electrodes <NUM> and 528b may extend through lead body portion <NUM>.

In the example illustrated by <FIG>, pace/sense electrode <NUM> is located within a recessed portion <NUM> of lead body portion <NUM>. Lead body portion <NUM> having recessed portion <NUM> may cover an anterior portion of a surface of pace/sense electrode <NUM> and impede an electrical field in at least an anterior direction. Although not illustrated in <FIG>, distal portion <NUM> may further include a shield <NUM> or any other shield as described herein over the anterior portion of the surface of pace/sense electrode <NUM> to impede the electrical field in the anterior direction.

<FIG> is a functional block diagram of an example configuration of electronic components and other components of ICD <NUM>. ICD <NUM> includes a processing circuitry <NUM>, sensing circuitry <NUM>, therapy delivery circuitry <NUM>, sensors <NUM>, communication circuitry <NUM>, and memory <NUM>. In other examples, ICD <NUM> may include more or fewer components. The described circuitry and other components may be implemented together on a common hardware component or separately as discrete but interoperable hardware or software components. Depiction of different features is intended to highlight different functional aspects and does not necessarily imply that such circuitry and other components must be realized by separate hardware or software components. Rather, functionality associated with one or more circuitries and components may be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

Sensing circuitry <NUM> may be electrically coupled to some or all of electrodes <NUM>, which may correspond to any of the defibrillation, pace/sense, and housing electrodes described herein. Sensing circuitry <NUM> is configured to obtain signals sensed via one or more combinations of electrodes <NUM> and process the obtained signals.

The components of sensing circuitry <NUM> may be analog components, digital components or a combination thereof. Sensing circuitry <NUM> may, for example, include one or more sense amplifiers, filters, rectifiers, threshold detectors, analog-to-digital converters (ADCs) or the like. Sensing circuitry <NUM> may convert the sensed signals to digital form and provide the digital signals to processing circuitry <NUM> for processing or analysis. For example, sensing circuitry <NUM> may amplify signals from the sensing electrodes and convert the amplified signals to multi-bit digital signals by an ADC. Sensing circuitry <NUM> may also compare processed signals to a threshold to detect the existence of atrial or ventricular depolarizations (e.g., P- or R waves) and indicate the existence of the atrial depolarization (e.g., P-waves) or ventricular depolarizations (e.g., R-waves) to processing circuitry <NUM>. As shown in <FIG>, ICD <NUM> may additionally include one or more sensors <NUM>, such as one or more accelerometers, which may be configured to provide signals indicative of other parameters of a patient, such as activity or posture, to processing circuitry <NUM>.

Processing circuitry <NUM> may process the signals from sensing circuitry <NUM> to monitor electrical activity of heart <NUM> of patient <NUM>. Processing circuitry <NUM> may store signals obtained by sensing circuitry <NUM> as well as any generated EGM waveforms, marker channel data or other data derived based on the sensed signals in memory <NUM>. Processing circuitry <NUM> may analyze the EGM waveforms and/or marker channel data to detect arrhythmias (e.g., bradycardia or tachycardia). In response to detecting the cardiac event, processing circuitry <NUM> may control therapy delivery circuitry <NUM> to deliver the desired therapy to treat the cardiac event, e.g., defibrillation shock, cardioversion shock, ATP, post shock pacing, or bradycardia pacing.

Therapy delivery circuitry <NUM> is configured to generate and deliver electrical therapy to heart <NUM>. Therapy delivery circuitry <NUM> may include one or more pulse generators, capacitors, and/or other components capable of generating and/or storing energy to deliver as pacing therapy, defibrillation therapy, cardioversion therapy, cardiac resynchronization therapy, other therapy or a combination of therapies. In some instances, therapy delivery circuitry <NUM> may include a first set of components configured to provide pacing therapy and a second set of components configured to provide defibrillation therapy. In other instances, therapy delivery circuitry <NUM> may utilize the same set of components to provide both pacing and defibrillation therapy. In still other instances, therapy delivery circuitry <NUM> may share some of the defibrillation and pacing therapy components while using other components solely for defibrillation or pacing. Processing circuitry <NUM> may control therapy delivery circuitry <NUM> to deliver the generated therapy to heart <NUM> via one or more combinations of electrodes <NUM>. Although not shown in <FIG>, ICD <NUM> may include switching circuitry configurable by processing circuitry <NUM> to control which of electrodes <NUM> is connected to therapy delivery circuitry <NUM> and sensing circuitry <NUM>.

Communication circuitry <NUM> includes any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as a clinician programmer, a patient monitoring device, or the like. For example, communication circuitry <NUM> may include appropriate modulation, demodulation, frequency conversion, filtering, and amplifier components for transmission and reception of data with the aid of an antenna.

The various components of ICD <NUM> may include any one or more processors, controllers, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or equivalent discrete or integrated circuitry, including analog circuitry, digital circuitry, or logic circuitry. Processing circuitry <NUM> may include fixed function circuitry and/or programmable processing circuitry. The functions attributed to processing circuitry <NUM> herein may be embodied as software, firmware, hardware or any combination thereof.

Memory <NUM> may include computer-readable instructions that, when executed by processing circuitry <NUM> or other components of ICD <NUM>, cause one or more components of ICD <NUM> to perform various functions attributed to those components in this disclosure. Memory <NUM> may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random-access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), static non-volatile RAM (SRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other non-transitory computer-readable storage media.

The leads and systems described herein may be used at least partially within the substernal space, e.g., within anterior mediastinum of patient, to provide an extravascular ICD system. An implanter (e.g., physician) may implant the distal portion of the lead intra-thoracically using any of a number of implant tools, e.g., tunneling rod, sheath, or other tool that can traverse the diagrammatic attachments and form a tunnel in the substernal location. For example, the implanter may create an incision near the center of the torso of the patient, e.g., and introduce the implant tool into the substernal location via the incision. The implant tool is advanced from the incision superior along the posterior of the sternum in the substernal location. The distal portion of the lead is introduced into the tunnel via implant tool (e.g., via a sheath). As the distal portion is advanced through the substernal tunnel, the distal portion is relatively straight. The pre-formed or shaped undulating configuration is flexible enough to be straightened out while routing the lead through a sheath or other lumen or channel of the implant tool. Once the distal portion is in place, the implant tool is withdrawn toward the incision and removed from the body of the patient while leaving the lead in place along the substernal path. As the implant tool is withdrawn, the distal end of the lead takes on its pre-formed undulating configuration, and the shield transitions to its deployed configuration.

In some examples, rather than extending in a superior direction along the sternum, the distal portion of the lead may be oriented orthogonal or otherwise transverse to the sternum and/or inferior to the heart. In such examples, the lead may include one or more shields that cover a portion of an outer surface of one or more electrodes, e.g., an anterior and/or inferior portion, according to any of the examples described herein. Such shield(s) may impede an electrical field in a direction away from the heart, which may be an anterior and/or inferior direction.

Claim 1:
An implantable medical lead (<NUM>) comprising:
a first defibrillation electrode (<NUM>) and a second defibrillation electrode (<NUM>), the first and second defibrillation electrodes configured to deliver anti-tachyarrhythmia shocks;
a pace electrode (<NUM>) disposed between the first defibrillation electrode and the second defibrillation electrode, the pace electrode configured to deliver a pacing pulse that generates an electric field proximate to the pace electrode; and
a shield (<NUM>) disposed between the first defibrillation electrode and the second defibrillation electrode, over a portion of an outer surface of the pace electrode, and extending laterally away from the pace electrode, characterized in that the shield is configured to impede the electric field in a direction from the pace electrode away from a heart (<NUM>).