Single-chamber leadless intra-cardiac medical device with dual-chamber functionality and shaped stabilization intra-cardiac extension

A leadless intra-cardiac medical device (LIMD) configured to be implanted entirely within a heart of a patient includes a housing configured to be securely attached to an interior wall portion of a chamber of the heart, and a stabilizing intra-cardiac (IC) device extension connected to the housing. The stabilizing IC device extension may include a stabilizer arm, and/or an appendage arm, or an elongated body or a loop member configured to be passively secured within the heart.

FIELD OF THE INVENTION

Embodiments of the present invention generally relate to implantable medical devices, and more particularly to leadless intra-cardiac medical devices that afford dual chamber functionality from a position within a single chamber of the heart. As used herein, the term “leadless” generally refers to an absence of electrically-conductive leads that traverse vessels or other anatomy outside of the intra-cardiac space, while “intra-cardiac” means generally, entirely within the heart and associated vessels, such as the SVC, IVC, CS, pulmonary arteries and the like.

BACKGROUND OF THE INVENTION

Current implantable medical devices (IMD) for cardiac applications, such as pacemakers, include a “housing” or “can” and one or more electrically-conductive leads that connect to the can through an electro-mechanical connection. The can is implanted outside of the heart, in the pectoral region of a patient and contains electronics (e.g., a power source, microprocessor, capacitors, etc.) that provide pacemaker functionality. The leads traverse blood vessels between the can and heart chambers in order to position one or more electrodes carried by the leads within the heart, thereby allowing the device electronics to electrically excite or pace cardiac tissue and measure or sense myocardial electrical activity.

To sense atrial cardiac signals and to provide right atrial chamber stimulation therapy, the can is coupled to an implantable right atrial lead including at least one atrial tip electrode that typically is implanted in the patient's right atrial appendage. The right atrial lead may also include an atrial ring electrode to allow bipolar stimulation or sensing in combination with the atrial tip electrode.

Before implantation of the can into a subcutaneous pocket of the patient, however, an external pacing and measuring device known as a pacing system analyzer (PSA) is used to ensure adequate lead placement, maintain basic cardiac functions, and evaluate pacing parameters for an initial programming of the IMD. In other words, a PSA is a system analyzer that is used to test an implantable device, such as an implantable pacemaker.

To sense the left atrial and left ventricular cardiac signals and to provide left-chamber stimulation therapy, the can is coupled to the “coronary sinus” lead designed for placement in the “coronary sinus region” via the coronary sinus ostium in order to place a distal electrode adjacent to the left ventricle and additional electrode(s) adjacent to the left atrium. As used herein, the phrase “coronary sinus region” refers to the venous vasculature of the left ventricle, including any portion of the coronary sinus, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.

Accordingly, the coronary sinus lead is designed to: receive atrial and/or ventricular cardiac signals; deliver left ventricular pacing therapy using at least one left ventricular tip electrode for unipolar configurations or in combination with left ventricular ring electrode for bipolar configurations; deliver left atrial pacing therapy using at least one left atrial ring electrode as well as shocking therapy using at least one left atrial coil electrode.

To sense right atrial and right ventricular cardiac signals and to provide right-chamber stimulation therapy, the can is coupled to an implantable right ventricular lead including a right ventricular (RV) tip electrode, a right ventricular ring electrode, a right ventricular coil electrode, a superior vena cava (SVC) coil electrode, and so on. Typically, the right ventricular lead is inserted transvenously into the heart so as to place the right ventricular tip electrode in the right ventricular apex such that the RV coil electrode is positioned in the right ventricle and the SVC coil electrode will be positioned in the right atrium and/or superior vena cava. Accordingly, the right ventricular lead is capable of receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle.

Although a portion of the leads, as well as the IMD itself are outside of the patient's heart. Consequently, bacteria and the like may be introduced into the patient's heart through the leads, as well as the IMD, thereby increasing the risk of infection within the heart. Additionally, because the IMD is outside of the heart, the patient may be susceptible to Twiddler's syndrome, which is a condition caused by the shape and weight of the IMD itself. Twiddler's syndrome is typically characterized by a subconscious, inadvertent, or deliberate rotation of the IMD within the subcutaneous pocket formed in the patient. In one example, a lead may retract and begin to wrap around the IMD. Also, one of the leads may dislodge from the endocardium and cause the IMD to malfunction. Further, in another typical symptom of Twiddler's syndrome, the IMD may stimulate the diaphragm, vagus, or phrenic nerve, pectoral muscles, or brachial plexus. Overall, Twiddler's syndrome may result in sudden cardiac arrest due to conduction disturbances related to the IMD.

In addition to the foregoing complications, leads may experience certain further complications, such as incidences of venous stenosis or thrombosis, device-related endocarditis, lead perforation of the tricuspid valve and concomitant tricuspid stenosis; and lacerations of the right atrium, superior vena cava, and innominate vein or pulmonary embolization of electrode fragments during lead extraction.

To combat the foregoing limitations and complications, small sized devices configured for intra-cardiac implant have been proposed. These devices, termed leadless pacemakers (LLPM) are typically characterized by the following features: they are devoid of leads that pass out of the heart to another component, such as a pacemaker outside of the heart; they include electrodes that are affixed directly to the “can” of the device; the entire device is attached to the heart; and the device is capable of pacing and sensing in the chamber of the heart where it is implanted.

LLPM devices that have been proposed thus far offer limited functional capability. These LLPM devices are able to sense in one chamber and deliver pacing pulses in that same chamber, and thus offer single chamber functionality. For example, an LLPM device that is located in the right atrium would be limited to offering AAI mode functionality. An AAI mode LLPM can only sense in the right atrium, pace in the right atrium and inhibit pacing function when an intrinsic event is detected in the right atrium within a preset time limit. Similarly, an LLPM device that is located in the right ventricle would be limited to offering VVI mode functionality. A VVI mode LLPM can only sense in the right ventricle, pace in the right ventricle and inhibit pacing function when an intrinsic event is detected in the right ventricle within a preset time limit. To gain widespread acceptance by clinicians, it would be highly desired for LLPM devices to have dual chamber pacing/sensing capability (DDD mode) along with other features, such as rate adaptive pacing.

It has been proposed to implant sets of multiple LLPM devices within a single patient, such as one or more LLPM devices located in the right atrium and one or more LLPM devices located in the right ventricle. The atrial LLPM devices and the ventricular LLPM devices wirelessly communicate with one another to convey pacing and sensing information there between to coordinate pacing and sensing operations between the various LLPM devices.

However, these sets of multiple LLPM devices experience various limitations. For example, each of the LLPM devices must expend significant power to maintain the wireless communications links. The wireless communications links should be maintained continuously in order to constantly convey pacing and sensing information between, for example, atrial LLPM device(s) and ventricular LLPM device(s). This pacing and sensing information is necessary to maintain continuous synchronous operation, which in turn draws a large amount of battery power.

Further, it is difficult to maintain a reliable wireless communications link between LLPM devices. The LLPM devices utilize low power transceivers that are located in a constantly changing environment within the associated heart chamber. The transmission characteristics of the environment surrounding the LLPM device change due in part to the continuous cyclical motion of the heart and change in blood volume. Hence, the potential exists that the communications link is broken or intermittent.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a leadless intra-cardiac medical device (LIMD) is provided with dual chamber functionality, without leads, despite the fact that the entire device is located in one chamber. In one embodiment, the LIMD stimulates and senses the right atrium (RA) and right ventricle (RV) chambers, even though it is entirely located in the RA. The electrodes enable delivering stimulus and sensing in different chambers of the heart and thus provide physiological synchronization of myocardial contraction in multiple chambers.

In another embodiment, an LIMD is provided that may be located in the RV, deliver stimulus and sense either the RA or the left ventricle (LV). Alternatively, the LIMD may be located in the RA and configured to electrically stimulate the RV and LV. This last LLPM configuration or placement may be done in a manner such that Hisian or para-Hisian pacing is achieved.

In accordance with an embodiment, a leadless intra-cardiac medical device (LIMD) is provided, comprised of a housing configured to be implanted entirely within a single local chamber of the heart, the local chamber having local wall tissue that constitutes part of a conduction network of the local chamber. A base is provided on the housing, the base configured to be secured to a septum that separates the local chamber from an adjacent chamber, the adjacent chamber having distal wall tissue, with respect to the local chamber that constitutes part of a conduction network of the adjacent chamber. A first electrode is provided at a first position on the base such that, when the device is implanted in the local chamber, the first electrode engages wall tissue at a local activation site within the conduction network of the local chamber. A second electrode is provided at a second position on the base and extending outward such that, when the device is implanted in the local chamber, the second electrode engages wall tissue at a distal activation site within the conduction network of the adjacent chamber. A controller is provided within the housing to cause stimulus pulses to be delivered, in a synchronous manner, through the first and second electrodes to the local and distal activation sites, respectively, such that stimulus pulses delivered at the distal activation site are timed to cause contraction of the adjacent chamber in a predetermined relation to contraction of the local chamber. Optionally, the controller is configured to control delivery of the stimulus pulses from the first and second electrodes in accordance with a DDD pacing mode or a DDDR pacing mode.

The septum may represent a portion of the tricuspid annulus. The base of the housing is configured to engage an activation site on the tricuspid annulus. The second electrode delivers stimulus pulses to the tricuspid annulus to initiate activation in a right ventricle. The controller may be configured to control delivery, from the first and second electrodes, of the stimulus pulses to a right atrium and a right ventricle, while the LIMD is entirely located in one of the right atrium and right ventricle.

The distal wall tissue constitutes wall tissue of at least one of a left atrium, a right ventricle, and a left ventricle. The distal wall tissue is physiologically responsive to distal activation events originating in the at least one of left atrium, right ventricle, and left ventricle.

In accordance with an embodiment, the housing may also include an extension arm having the first electrode located on a distal end thereof. The extension arm may be configured to extend into and engage the local wall tissue in an appendage area of the local chamber. Optionally, the housing may also include an extension arm and a stabilization arm joined to a top end of the housing. The extension arm may have the first electrode located on a distal end thereof to extend into and engage the local wall tissue in an appendage area of the local chamber. The stabilization arm may have a distal end that extends to and engages an opposed stabilization area of the local chamber. The stabilization arm may have a distal end that extends to and engages a superior vena cava of the heart. The extension arm and a stabilization arm may be pivotally joined to a hinge assembly located at a top end of the housing. The extension arm and a stabilization arm may be securely joined to a top end of the housing. The extension arm and stabilization arm may be biased to flare outward away from one another when in a deployed position such that distal ends of the stabilization and extension arms engage the local chamber in opposed areas remote from the base of the housing.

Certain embodiments provide a leadless intra-cardiac medical device configured to be implanted entirely within a heart of a patient. The device may include a housing and a stabilizing intra-cardiac intra-cardiac device extension. The housing is configured to be securely attached to an interior wall portion of a chamber of the heart. The extension is connected to the housing, and is configured to be passively secured within the heart.

The extension may include a loop member. The loop member is configured to be passively secured within one or both of the chamber of the heart or a superior vena cava of the heart. The loop member may include first and second loops connected to one another. Each of the first and second loops may have a perimeter that flares in a lateral direction with respect to a longitudinal axis of the loop body. The loop member may include a perimeter shaped as a disc, oval, circle, tube, rectangle, or triangle.

The loop member may include a plurality of interconnected loops. Each of the plurality of interconnected loops may be commonly aligned and oriented with respect to one another. The plurality of interconnected loops may include a first loop and a second loop. The first loop may be oriented orthogonal to the second loop.

A first of the plurality of interconnected loops may be aligned in a first orientation and a second of the plurality of interconnected loops may be aligned in a second orientation. The first orientation differs from the second orientation so that the first and second of the plurality of interconnected loops are oriented out of plane with one another.

The device may also include at least one electrode secured to the loop member. The electrode is configured to contact tissue within the heart, and provide one or both of sensing or stimulus.

The device may also include at least one radio marker secured to the loop member. The radio marker is configured to allow the LIMD system to be tracked within patient anatomy.

The device may also include an anchoring member extending from a distal end. The anchoring member is configured to securely anchor the housing to tissue within the heart. The anchoring member may include a securing helix. The securing helix may serve as an electrode.

In an embodiment, the stabilizing intra-cardiac device extension may include a first curved portion with respect to the housing. The first curved portion may be connected to a first linear region that connects to a second curved portion. The first curved portion may be approximately 90 degrees with respect to the housing. The second curved portion may be approximately 180 degrees away from the housing. The second curved portion may connect to a second linear region that connects to a third curved portion. The second curved portion may be configured to be implanted within a right atrial appendage of the heart. An electrode may be located proximate a junction of the second curved portion and the second linear region. The third curved portion may form an extending arc that approximates a 90 degree turn away from the housing that terminates at a tail end.

Certain embodiments provide a method of implanting a leadless intra-cardiac medical device (LIMD) entirely within a heart of a patient. The device includes a housing and a stabilizing intra-cardiac device extension connected to the housing. The method may include navigating the device into the heart with an introducer assembly, the extension held in a collapsed installation shape within the introducer assembly, positioning the introducer assembly so that the housing is proximate an implant site within the heart, securely anchoring the housing to the implant site, separating the introducer assembly and the device, thereby allowing the extension to expand to a deployed implanted shape, and securing the extension within a portion of the heart so that the device is entirely within the heart of the patient.

In accordance with embodiments herein, the stabilizing intra-cardiac device extension comprises an elongated body, and expanding includes permitting the elongated body to expand to a pre-loaded shape in which a first curved segment bends at an angle with respect to a longitudinal axis of the housing, wherein the first curved segment merges into a first linear region that extends laterally from the housing toward a tissue of interest, the elongated body including an electrode provided thereon at a position configured to contact the tissue of interest.

In accordance with optional embodiments herein, the stabilizing intra-cardiac device extension comprises an elongated body, and expanding includes permitting the elongated body to expand to a pre-loaded shape such that a first linear region extends laterally from the housing, along a lateral axis, and merges with a second curved segment, the second curved segment turning at an angle with respect to a longitudinal axis of the housing and a lateral axis of the first linear region.

In accordance with other embodiments herein, the stabilizing intra-cardiac device extension comprises an elongated body, and expanding includes permitting the elongated body to expand to a pre-loaded shape in which first and second linear regions are joined to one another through a curved segment, the method further comprising positioning the first linear region and the curved segment to extend into a right atrial appendage, and positioning the second linear region to extend from the right atrial appendage toward the SVC.

In accordance with embodiments herein, the extension comprises an elongated body that includes first and second curved segments joined to one another by a linear region, at least one of the first and second curved segments including an electrode, the method further comprising positioning the electrode to contact tissue of interest.

In accordance with embodiments herein, the extension comprises an elongated body that is tubular in shape and includes a metal braid, the method further comprising applying at least one of rotational and longitudinal pressure upon the IC device extension, the braid resisting rotational torque and longitudinal compression to facilitate delivery of rotational forces and longitudinal pressure to the housing of the device.

Optionally, the method may comprise guiding the extension to engage a first region of the heart, the first region representing at least one of a superior vena cava, an inferior vena cava, a coronary sinus, and a pulmonary artery. Optionally, the extension may include a stabilizer end-segment that is pre-formed to bend at an angle and fit against an interior of at least one of a superior vena cava, an inferior vena cava, a coronary sinus, and a pulmonary artery.

In accordance with embodiments herein, the method may comprising configuring a controller of the device to control delivery of stimulus pulses from first and second electrodes in accordance with a DDD pacing mode to a right atrium and right ventricle, while the device is entirely located in one of the right atrium and right ventricle.

DETAILED DESCRIPTION

Dual-chamber permanent pacemakers (PPM), operating in the DDD or DDDR mode, are indicated for patients with complete atrioventricular (AV) block, sick sinus syndrome, and paroxysmal AV block. The use of DDD or DDDR mode PPMs in patients with a high degree of AV block is shown to improve subjective metrics of patient life and increase peak velocity and cardiac output, compared to VVIR PPMs. Additionally, another study demonstrates reduced incidence of atrial fibrillation (AF) and increased patient longevity in patients with sick sinus syndrome after the time of DDDR PPM implant. These significant benefits, accrued to the three previously-described subgroups of implant patients, provide a strong impetus for using DDDR PPMs in those recipients.

The benefits of conventional DDD or DDDR PPMs are counterbalanced by the increased risk of complications with the additional lead necessary for these PPMs (compared to single-chamber devices). A preferred solution to this dilemma as offered by embodiments herein eliminate the need to use leads by providing an LIMD with DDDR mode functionality. As a result, patients suffering from various degrees of AV block or sick sinus syndrome may receive dual-chamber pacing therapy without an increased risk of complications (such as lead-associated infections caused by biofilm formation14or explant-related difficulties). In particular, decreased incidence of device-related infections may be achieved by a DDDR mode-capable LIMD as a result of the device body's small surface area (compared to conventional PPMs and leads), which presents a reduced substrate for bacterial or fungal adhesion.

Myocardial contraction results from a change in voltage across the cell membrane (depolarization), which leads to an action potential. Although contraction may happen spontaneously, it is normally in response to an electrical impulse. In normal physiologic behavior, this impulse starts in the sino-atrial (SA) node where a collection of cells are located at the junction of the right atrium and superior vena cava. These specialized cells depolarize spontaneously, and cause a wave of contraction to follow a conduction network along the tissue wall of the atria. Following atrium contraction, the impulse is delayed at the atrio-ventricular (AV) node, located in the septum wall of the right atrium. From here HIS-Purkinje fibers allow rapid conduction of the electrical impulse to propagate along the conduction network formed by the right and left branches in the RV and LV tissue walls, causing almost simultaneous depolarization of both ventricles, approximately 0.2 seconds after the initial impulse has arisen in the sino-atrial node. Depolarization of the myocardial cell membrane causes a large increase in the concentration of calcium within the cell, which in turn causes contraction by a temporary binding between two proteins, actin and myosin. The cardiac action potential is much longer than that of skeletal muscle, and during this time the myocardial cell is unresponsive to further excitation. Hence, in a general sense, the tissue walls of each chamber constitute part of a conduction network of the corresponding chamber.

FIG. 1provides a sectional view of a patient's heart33and shows a leadless intra-cardiac medical device300. The leadless implantable medical device300has been placed through the superior vena cava28into the right atrium30of the heart33.FIG. 1also shows the inferior vena cava35, the left atrium36, the right ventricle37, the left ventricle40, the atrial septum41that divides the two atria30,36, the ventricular vestibule VV, the right atrial appendage (RAA), and the tricuspid valve42between the right atrium30and right ventricle37. The reader will appreciate that the view ofFIG. 1is simplified and somewhat schematic, but that neverthelessFIG. 1and the other views included herein will suffice to illustrate adequately the placement and operation of embodiments of the present invention. The term “septum” shall be used throughout to generally refer to any portion of the heart separating two chambers (e.g. RA to LA, RV to LV). The leadless implantable medical device (LIMD)300is formed in accordance with an embodiment. The LIMD300may represent a pacemaker that functions in a DDD mode or a DDDR-mode, a cardiac resynchronization device, a cardioverter, a defibrillator and the like. When in DDD or DDDR-mode, the LIMD300may sense in two chambers, pace in two chambers and inhibit pacing in either chamber based on intrinsic events sensed in that chamber or in the other chamber. The LIMD300comprises a housing configured to be implanted entirely within a single local chamber of the heart. For example, the LIMD300may be implanted entirely and solely within the right atrium or entirely and solely within the right ventricle. Optionally, the LIMD300may be implanted entirely and solely within the left atrium or left ventricle through more invasive implant methods.

For convenience, hereafter the chamber in which the LIMD300is implanted shall be referred to as the “local” chamber. The local chamber includes a local chamber wall that is physiologically response to local activation events originating in the local chamber. The local chamber is at least partially surrounded by local wall tissue that forms or constitutes at least part of a conduction network for the associated chamber. For example, during normal operation, the wall tissue of the right atrium contracts in response to an intrinsic local activation event that originates at the sinoatrial (SA) node and in response to conduction that propagates along the atrial wall tissue. For example, tissue of the right atrium chamber wall in a healthy heart follows a conduction pattern, through depolarization, that originates at the SA node and moves downward about the right atrium until reaching the atria ventricular (AV) node. The conduction pattern moves along the chamber wall as the right atrium wall contracts.

The term “adjacent” chamber shall refer to any chamber separated from the local chamber by tissue (e.g., the RV, LV and LA are adjacent chambers to the RA; the RA and LV are adjacent chambers to the LA; the RA and RV are adjacent to one another; the RV and LV are adjacent to one another, and the LV and LA are adjacent to one another).

The local chamber (e.g., the right atrium) has various tissue of interest, such as a septum, that separate the local chamber from the adjacent chambers (e.g., right ventricle, left atrium, left ventricle). In certain portions or segments of the septum, segments of the septum, behave in physiologically different manners. For example, in certain segments of the septum for the right atrium, even during normal healthy operation, the septum wall tissue does not propagate the conduction in the same manner or pattern as in a majority of the wall tissue of the right atrium wall. For example, septum wall tissue in the right atrium, referred to as the ventricular vestibule tissue, does not behave physiologically in the same manner as the non-septum atrial wall tissue. Instead, the right ventricular vestibule tissue is physiologically coupled to the wall tissue in the right ventricle and in accordance therewith exhibits a conduction pattern that follows the conduction pattern of the right ventricular wall tissue. The right ventricular vestibule tissue is one example of a septum segment that partially separates a local chamber (e.g., the right atrium) from an adjacent chamber (e.g., right ventricle), yet is physiologically coupled to conduction in the adjacent chamber (e.g., right ventricle).

In the example ofFIG. 1, the LIMD300is implanted in an area near different regions of tissue that follow the conductive pattern of different chambers of the heart. Optionally, the LIMD300may be implanted such that at least one electrode on the base of the LIMD300engages tissue that is part of the conductive network of the one chamber, while at least one other electrode projects from the base into tissue that is part of the conductive network of another chamber. For example, when the LIMD300may be implanted within or near the triangle of Koch in an area adjacent the ventricular vestibule. The conductive network of the tissue in the ventricular vestibule follows the conductive pattern of the right ventricle. Therefore, the LIMD300may be implanted near the edge of the triangle of Koch such that one or more proximal electrodes, extending from the LIMD300, are electrically coupled to the conductive network of the right atrium, while one or more other distal electrodes, extend diagonally to become electrically coupled to the conductive network of the right ventricle (e.g., the ventricular vestibule). Optionally, the LIMD300may be positioned with the base located against the RA wall above the mitral valve, but with a distal electrode that projects into the septum to ventricular tissue of the right or left ventricle.

FIGS. 3A and 3Billustrate the LIMD300in more detail.FIG. 3Aillustrates a side perspective view of the LIMD300ofFIG. 1oriented with the base304facing upward to illustrate electrodes310-312in more detail.FIG. 3Billustrates a bottom plan view of the LIMD300. The LIMD300comprises a housing302having a proximal base304, a distal top end306, and an intermediate shell308extending between the proximal base304and the distal top end306. The shell308is elongated and tubular in shape and extends along a longitudinal axis309.

The base304includes one or more electrodes310-312securely affixed thereto and projected outward. For example, the outer electrodes310,311may be formed as large semi-circular spikes or large gauge wires that wrap only partially about the inner electrode312. The electrodes310,311may be located on opposite sides of, and wound in a common direction with, the inner electrode312. The first or outer electrodes310,311are provided directly on the housing302of the LIMD300at a first position, namely at or proximate a periphery of the base304of the housing. The outer electrodes310,311are positioned near the periphery of the base304such that, when the LIMD300is implanted in the local chamber (e.g., right atrium), the outer electrodes310,311engage the local chamber wall tissue at tissue of interest for a local activation site that is near the surface of the wall tissue, and that is within the conduction network of the local chamber. The outer electrodes310,311are physically separated or bifurcated from one another and have separate distal outer tips315,316. The outer electrodes310,311are electrically joined to one another (i.e., common), but are electrically separated from the inner electrode312.

The second or inner electrode312is also provided directly on the housing302of the LIMD300at a second position, namely at or proximate to a central portion of the base304of the housing. The inner electrode312is positioned near the center of the base304and is elongated such that, when the LIMD300is implanted in the local chamber, the inner electrode312extends a majority of the way through the wall tissue (e.g. septum) until reaching tissue of interest near the adjacent chamber wall. The inner electrode312is inserted to a depth such that a distal tip thereof is located at tissue of interest for an activation site that is physiologically coupled to wall tissue of the adjacent chamber (e.g. right ventricle). For example, the inner electrode312may extend until the distal tip extends at least partially through a septum to a position proximate to a distal wall tissue within the conduction network of the adjacent chamber. Optionally, the inner electrode312may be inserted at a desired angle until the distal end enters the ventricular vestibule. By located the distal tip of the inner electrode312at an adjacent chamber activation site, the inner electrode312initiates contraction at a distal activation site within the conduction network of the adjacent chamber without physically locating the LIMD300in the adjacent chamber. The inner and outer electrodes310-312may be formed as multiple cathode electrodes that are actively fixated to the myocardium. The outer cathode electrodes310,311may be configured as screws with a large pitch (e.g. length between adjacent turns), large diameter and may have a length that is relatively short, while the inner electrode312is configured as a screw with a common or smaller pitch, small diameter and longer length. The screw shape of the outer electrodes310,311is used to firmly adhere them to the cardiac tissue. The outer electrodes310,311may have very little or no insulation material thereon to facilitate a good electrical connection to local wall tissue along the majority or the entire length of the outer electrodes310,311for delivering stimulus pulses and sensing electrical activity in the local chamber where the LIMD300is located.

The inner electrode312is shaped in a helix or screw and is longer (e.g., extends a greater distance from the base) than the outer electrodes310,311. The inner electrode312is fashioned to an appropriate length that permits it to drill a predetermined distance into, or entirely through, the septum at the desired location. For example, the inner electrode312may be provided with a desired length sufficient to extend through, or to a desired distance into, a septum region separating two chambers of the heart. For example, the outer electrodes310,311may contact atrial wall tissue within the triangle of Koch, while the inner electrode312extends diagonally along the septum into the ventricular vestibule.

The inner electrode312may be formed as a single conductive wire or a bundle of conductive wires, where a proximal portion of the wire is covered with insulation, while the distal tip314is covered with insulation and is exposed. By covering the proximal portion of the electrode312with insulation, this limits electrical conduction of the conductive wire to tissue surrounding the distal tip314. When implanted, the distal tip314of the electrode is located far below the surface tissue of the chamber wall in which the LIMD300is located. As a consequence, the distal tip314of the inner electrode312directly engages or is located proximate to the surface tissue of an adjacent chamber wall. Hence, the distal tip will314senses electrical activity from the conductive network of the adjacent chamber that is representative of physiologic behavior (e.g., conduction pattern) of the adjacent chamber. Also, when delivering stimulus pulses, the distal tip314will deliver the pulses into the conductive network of the adjacent chamber wall.

The combination of the inner and outer screw type electrodes310-312also imparts extra mechanical stability to the LIMD300, preventing unwanted torque and shear effects as the heart wall moves during contraction. Otherwise, such effects would otherwise predispose the LIMD300to dislodgement. Extraction could simply entail a combination of unscrewing of the two cathodes in conjunction with a slight tugging force directed away from the myocardial wall.

Optionally, a single anode electrode or multiple anode electrodes318may be provided. The anode electrode(s)318may be located along one or more sides of the shell308, and/or on the top end306of the LIMD300.

The LIMD300includes a charge storage unit324and sensing circuit322within the housing302. The sensing circuit322senses intrinsic activity, while the change storage unit324stores high or low energy amounts to be delivered in one or more stimulus pulses. The electrodes310-312may be used to deliver lower energy or high energy stimulus, such as pacing pulses, cardioverter pulse trains, defibrillation shocks and the like. The electrodes310-312may also be used to sense electrical activity, such as physiologic and pathologic behavior and events and provide sensed signals to the sensing circuit322. The electrodes310-312are configured to be joined to an energy source, such as a charge storage unit324. The electrodes310-312receive stimulus pulse(s) from the charge storage unit324. The electrodes310-312may be the same or different size. The electrodes310-312are configured to deliver high or low energy stimulus pulses to the myocardium.

The LIMD300includes a controller320, within the housing302to cause the charge storage unit324to deliver activation pulses through each of the electrodes310-312in a synchronous manner, based on information from the sensing circuit322, such that activation pulses delivered from the inner electrode312are timed to initiate activation in the adjacent chamber. The stimulus pulses are delivered synchronously to local and distal activation sites in the local and distal conduction networks such that stimulus pulses delivered at the distal activation site are timed to cause contraction of the adjacent chamber in a predetermined relation to contraction of the local chamber. The inner and outer electrodes310-312are spaced radially and longitudinally apart from one another such that the local activation site (e.g., right atrium) and the distal activation side in the adjacent chamber (e.g., right ventricle) are sufficiently remote from one another within the heart's conductive network to initiate activation in different branches of the hearts conductive network in a time relation that corresponds to the normal hemodynamic timers (e.g. AV delay).

FIG. 2illustrates a right anterior oblique view representing the interior surface of the right atrium wall. As shown inFIG. 2, the right atrium wall includes the superior vena cava (SVC) inlet202, the fosa ovalis204, coronary sinus206, IVC208, tricuspid valve210and tricuspid annulus212that surrounds the tricuspid valve210. The LIMD300may be implanted in various locations within the RA. For example, the LIMD300may be implanted in region214which is located immediately adjacent the coronary sinus206. Region214may be contained within the Triangle of Koch. For example, the LIMD300may be implanted in region216which may represent the ventricular vestibule in an area located adjacent the tricuspid valve210along a segment of the tricuspid annulus212. Region214represents a local activation site in the local chamber wall at which contractions may be initiated when stimulus pulses are delivered to the surface tissue in the region214. Region216constitutes a distal activation site at which contractions may be initiated in the right ventricle when stimulus pulses are delivered in the region216.

The controller320may operate the LIMD300in various modes, such as in select pacemaker modes, select cardiac resynchronization therapy modes, a cardioversion mode, a defibrillation mode and the like. For example, a typical pacing mode may include DDIR, R, DDOR and the like, where the first letter indicates the chamber(s) paced (e.g., A: Atrial pacing; V: Ventricular pacing; and D: Dual-chamber (atrial and ventricular) pacing). The second letter indicates the chamber in which electrical activity is sensed (e.g., A, V, or D). The code O is used when pacemaker discharge is not dependent on sensing electrical activity. The third letter refers to the response to a sensed electric signal (e.g., T: Triggering of pacing function; I: Inhibition of pacing function; D: Dual response (i.e., any spontaneous atrial and ventricular activity will inhibit atrial and ventricular pacing and lone atrial activity will trigger a paced ventricular response) and O: No response to an underlying electric signal (usually related to the absence of associated sensing function)). The fourth letter indicates rate responsive if R is present.

As one example, the controller320may be configured with DDI, DDO, DDD or DDDR mode-capable and the LIMD300would be placed in the RA. The screw type electrodes310,311are used to secure it in conductive branch region214(FIG. 2). Conductive branch region214is contained within the Triangle of Koch and is characterized by more ready activation of RA tissue compared to conductive branch region216. When the LIMD300is secured in conductive branch region216, it is possible to achieve Hisian/para-Hisian pacing from the RA and perform biventricular stimulation that is more consistent with normal physiology. It may be possible to also perform AV pacing from conductive branch region216.

As one example, the conductive branch region216represents the adjacent chamber activation site within the ventricular vestibule. The inner electrode312delivers stimulus pulses to the ventricular vestibule to initiate activation in the right ventricle37of the heart. When the LIMD300is secured in the conductive branch region septum216, the inner electrode312is located in a minor tissue portion that is non-responsive to the local events and local conduction occurring in the right atrium. The distal end314of the inner electrode312electrically engages the minor tissue portion that is responsive to non-local events and non-local conduction originating in another chamber.

The sensing circuit322receives sensed signals from one or more of the electrodes310-312. The sensing circuit322discriminates between sensed signals that originate in the near field and in the far field. For example, the electrodes310-311sense electrical potential across small areas and thereby allow the sensing circuit322to discriminate between different sources of electrical signals. In one embodiment, the electrode spacing between electrodes310,311is limited or minimized in order to achieve a select type of sensing such as bipolar sensing which limits or minimizes sensing of far field signals. For example, the electrode310may operate as an anode electrode and the electrode311may operate as a cathode electrode with a small separation there between such that when far field signals (e.g., signals from the right ventricle) reach the first and second electrodes these far field signals are sensed as a common mode signal with no or a very small potential difference between the electrodes.

In another example, an electrode312may be provided with a pair of electrically separate sensing regions thereon. The sensing regions may operate as an anode and as a cathode electrode with a small separation there between such that when far field signals (e.g., signals from the right atrium) reach the first and second sensing regions these far field signals are sensed as a common mode signal with no or a very small potential difference between the sensing regions.

The housing302also include a battery326that supplies power to the electronics and energy to the change storage unit324.

FIG. 3Cillustrates some of these possible configurations, namely at350-356. The previous examples involve an LIMD implanted in the RA and capable of pacing the RV. Optionally, the LIMD may also be located in other locations. At350, the LIMD is capable of HISian or para-HISian pacing to produce excitation of the RV and LV. When the LIMD is implanted at352, the LIMD is able to provide RA/RV sensing and pacing from the RA. When the LIMD is implanted at354, the LIMD is able to provide RA/RV sensing and pacing from the RV. When the LIMD is implanted at356, the LIMD is able to provide RV/LV sensing and pacing from the RV. The LIMDs357,358,359afford LA/RA pacing and sensing, LV/RA pacing and sensing, and LV/RV pacing and sensing, respectively. These implementations produce excitation of the RV and LV in a manner more consistent with normal physiological function.

FIGS. 4A-4Gillustrate various embodiments of fixation mechanisms that may be used with an LIMD400.FIG. 4Aillustrates a LIMD400that has a base404with spikes410,411as cathode electrodes extending there from. The spikes410,411are used to fixate the LIMD400, as well as to deliver stimulus pulses and sense in the local chamber416(e.g. atrium). The LIMD400also includes an elongated cathode electrode412that is used for delivering stimulus pulses and for sensing electrical activity in the conduction network of the adjacent chamber414(e.g., the ventricle). The electrode412extends entirely through the chamber wall into the adjacent chamber414. Optionally, the electrode412may extend near or up to, but not penetrate the wall tissue into the adjacent chamber414.

FIG. 4Billustrates an LIMD400that has a base404with an electrode formed as serrated edges420that project outward from the base404. The serrated edges420form a skirt encircling the base404. The serrated edges420are electrically active and can be used for delivering stimulus pulses and for sensing conductive activity in the local chamber416as well as fixation. The LIMD400also includes an elongated cathode electrode412that is used for delivering stimulus pulses and for sensing conductive activity in the adjacent chamber414(e.g., the ventricle).

FIG. 4Cillustrates an LIMD400that has a base404with electrodes formed as a fixation mechanisms430,431similar to a pair of large diameter double-helix, but with a positive deflection432near the base404. The purpose of this shape is to ease in the LIMD400during implant, but rendering unscrewing of the LIMD400very difficult due to its firm adhering to the wall. There may also be a single helix that varies in diameter or pitch from the proximal end to the distal end, which ensures ease of insertion at implant but causes detachment to be more difficult as tissue conforms to the helix's shape. The fixation mechanism430enclosed in insulation except for a proximal region433that is exposed and is electrically active in a proximal region near the base404in order to deliver stimulus pulses and to sense conductive activity in the local chamber416. The fixation mechanism431is covered in insulation except for a distal region435that is exposed and is electrically active near the distal end remote from the base404in order to deliver stimulus pulses and to sense conductive activity in the adjacent chamber414(e.g., the ventricle).

FIG. 4Dillustrates an LIMD400that has a base404with a fixation mechanism440that has a screw non-circular shape with different cross-sectional thicknesses at the proximal and distal ends441,442. By varying the cross sectional thickness at different locations along the fixation mechanism440, this will afford better fixation of the LIMD400. The cross-section may gradually increase or step-wise increase along the length of the mechanism440with greater distance from the base404. For example, the fixation mechanism440may exhibit progressively widening cross-section toward the distal end442to afford better fixation.

FIG. 4Eillustrates an LIMD400that has a base404with a fixation mechanism450that has a screw wire shape with different circular diameter at the proximal and distal ends451,452. By varying the wire diameter at different locations along the fixation mechanism450, this will afford better fixation of the LIMD400. The diameter of the wire may gradually increase or step-wise increase along the length of the mechanism450with greater distance from the base404. The fixation mechanism450is formed with two isodiametric sections at the proximal and distal ends451,452which are used to secure the LIMD400. For example, the proximal end451may be thinner in diameter, while the distal end452is thicker in diameter.

FIG. 4Fillustrates an LIMD400with a variation in the fixation mechanism430,431shown inFIG. 4C. InFIG. 4F, the LIMD400includes fixation mechanisms460,461with the distal ends463of the large double-helices having serrated edges462that prevent the LIMD400from unscrewing out of the heart chamber wall.

FIG. 4Gillustrates an LIMD400with a helical cathode electrode470that surrounds a long spike electrode471. Once implanted, the spike electrode471deploys a small mesh472similar in shape to an umbrella. The mesh472helps secure the LIMD400on both ends of the chamber wall.

Optionally, the LIMD400may have a single helical active-fixation mechanism that contains one or more passive electrodes on the LIMD400body that remain in the heart chamber where the LIMD400is implanted. The electrode could be brought into contact with the myocardium when the fixation is engaged. The electrodes shown inFIGS. 4A-4Gmay be cathodes, anodes or one of each. Optionally, an anode or cathode may be provided on the housing of the LIMD400.

Next alternative embodiments are described in connection withFIGS. 5A to 7BandFIGS. 9A to 14, in which the LIMD includes an intra-cardiac (IC) device extension. In the embodiments ofFIGS. 5A to 7B, the IC device extension includes one or both of at least two portions, namely a stabilization arm and an appendage arm. In the embodiments ofFIGS. 9A to 14, the IC device extension is formed as a single elongated body that includes multiple linear regions and curved segments. The elongated body of the IC device extension may have various cross-sectional shapes, such as disc-shaped, oval, circular, tubular, rectangular, square, polygonal, triangular, and the like. Optionally, the IC device extension may have a cross-sectional shape that is paddle shaped or flat, semi-circular, donut shaped and the like. The IC device extensions in the embodiments described herein may be formed from silicon alone, or in combination with one or more other materials.

By way of example, the IC device extension may be formed by curing the silicon such as to a desired crosslink structure to hold a predetermined shape in which the IC device extension is positioned during curing. Once the IC device extension is cured to the desired cross link structure, the IC device extension is retains the predetermined “preload” shape.

FIG. 5Aillustrates an LIMD500formed in accordance with an alternative embodiment. The LIMD500includes a body or housing502having a shell508that hermetically encloses the electronics, controller, battery, charge storage unit, and all other electrical components of the LIMD500. The housing502has a proximal base504and a distal top end506, with the intermediate shell508extending there between. The shell508is elongated and may be tubular in shape to extend along a longitudinal axis509. The base504includes at least one electrode512. The electrode512may be a helical shaped screw to actively secure the base504at a desired site within a selected local chamber of the heart. The electrode512includes a conductor that is surrounded by insulation along the majority of the length thereof, but exposes the distal tip514of the conductor, such that the electrode512only delivers stimulus pulses and senses electrical activity in the region denoted at515which corresponds to an distal activation site proximate an adjacent chamber wall (and distal from the local chamber in which the LIMD500is implanted).

The LIMD500further includes an appendage arm520pivotally connected to and extending outward from the top end506. The appendage arm520includes a distal end522upon which an electrode524is located. The electrode524may be a passive electrode that is configured to simply rest against a select activation site. Alternatively, the electrode524may be an active fixation electrode that is configured to be secured to the tissue at the activation site (e.g. through a helix, spike, serrated edge, barb, and the like).

The appendage arm520includes a proximal end526that is rotatably coupled through a hinge assembly542to the top end506of the housing502. The appendage arm520extends along an appendage axis528and rotates along the appendage rotation arc544between limits. The hinge assembly542is configured to permit the appendage arm520to rotate from a collapsed installation position to a deployed implanted position. When in the collapsed position, the appendage arm520is rotated in the direction of arrow543until the appendage axis528forms a very small acute angle, or is oriented substantially parallel to, a longitudinal axis509of the shell508of the LIMD500. When in the deployed position, the appendage arm520rotates in the direction of arrow545until reaching a fully deployed outer limit of the arc of rotation as defined by the hinge assembly542. When fully deployed, the appendage axis528projects outward at a larger acute angle (e.g. 10-150°) from the longitudinal axis509of the shell508. The outer limit of the deployed position for the appendage arm520is controlled by the rotation range permitted at the hinge assembly542and may have spring tension tensioning it with respect to the stabilizer arm or the housing502.

The LIMD500also includes a stabilizer arm530having a distal end532and a proximal end536. The distal end532is formed integral with a pusher cup534that includes some type of pusher reception feature, such as a pusher receptacle540. The pusher cup534and receptacle540are configured to receive an external pusher tool that is used by the physician when implanting the LIMD500(as explained below in more detail). As one example, the pusher receptacle540may include a threaded recess541that is configured to threadably and securely receive a tip of the pusher tool to ensure a secure attachment to the pusher tool during installation. Once the LIMD500is fully implanted, the tip of the pusher tool is unscrewed from the threaded receptacle541. An expandable collet may be used, instead of a screw to attach the pusher tool to the stabilizer arm530.

The stabilizer arm530is rotatably secured, at its proximal end536, to the hinge assembly542to permit the stabilizer arm530to rotate along arc546. The stabilizer arm530may be rotated between a collapsed installation position at which the stabilizer axis538is arranged at a very small acute angle or substantially parallel to the longitudinal axis509. Once implanted, the stabilizer arm530is then permitted to rotate outward along arc546to a deployed position such that the stabilizer axis538forms a larger acute angle (e.g. 10-150°) with respect to the longitudinal axis509. The hinge assembly542controls the range of rotation afforded to the stabilizer arm530and may have spring tension tensioning it with respect to the appendage arm520or the housing502. At least one of the stabilizer arm530and appendage arm520may be constructed to have a core structure that is torque and compression resistant such that when the pusher tool is rotated or moved longitudinally, the stabilizer arm530and/or appendage arm520conveys rotational and longitudinal force from the pusher tool to the housing of the LIMD500. For example, the core structure may include a metal (e.g. aluminum or stainless steel) braid encased in a biocompatible material, such as PTFE, ETFE or silicon rubber. The braid may have a hollow core in which insulated conductors run between electrodes and the LIMD500.

Optionally, the stabilizer arm530may be fixedly secured to the distal end506of the LIMD500, such that the stabilizer arm530does not rotate relative to the longitudinal axis509. Instead, in this alternative embodiment, the stabilizer arm530is rigidly secured to the distal end506and may be oriented such that the stabilizer axis530extends directly parallel or at an angle to the longitudinal axis509at all times, during installation and after deployment. Again, the stabilizer arm530and the appendage arm520collectively form an IC device extension.

As a further option, a pusher cup or multiple pusher cups550may be provided about the exterior surface of the shell508or on the distal top end506. The pusher cup550includes a pusher receptacle552configured to receive the tip of a pusher tool that is used during implantation. The pusher cup550may be provided in place of, or in addition to, the pusher cup534. For example, the stabilizer arm530may be entirely removed, in which case the pusher cup550may be provided on the side or top end506of the housing502. Alternatively, when the stabilizer arm530is included, but is too flexible to convey rotational and/or longitudinal force onto the housing502, then the pusher cup550may be included. As a further option, pusher cups534,550may both be included such as when it is desirable to maintain secure connections to the housing502and the appendage arm520and stabilizer arm530while manipulated and navigated to respective implanted positions. For example, once the LIMD500is secured to the chamber wall, the introducer may be partially removed, yet one pusher tool or stylet may remain secured to the pusher cup550to maintain the LIMD500in a desired position and orientation while a second tool manipulates the appendage arm520and stabilizer arm530to implant positions. In this manner, the tool or stylet in pusher cup550prevents excess forces from being applied to the electrode512while the arms520,530are navigated to installed positions. Further, the tool or stylet may remain in pusher cup550until a separate tool is disconnected from pusher cup534.

Optionally, a third pusher cup could be located on the distal end of the appendage arm520to afford direct control over positioning of the electrode524.

FIG. 5Billustrates the LIMD500ofFIG. 5Aduring installation, while located within an introducer560. The introducer has a distal end562that is open to permit the LIMD500to be implanted and deployed there through. The introducer560includes a proximal end564along which a pusher or other form of tool (e.g. a stylet) is used guide the LIMD500into position. As shown inFIG. 5B, the stabilizer arm530and appendage arm520are contracted in their collapsed position to define an outer envelope substantially no greater than the outer envelope of the body508of the LIMD500. The pusher device562may engage one or both of the pusher receptacle540in the pusher cup534and/or the pusher receptacle552and the pusher cup550. During implantation, the pusher or stylet562is securely attached at the receptacle cup534to guide the LIMD500to its activation site. Once the electrode512is located against the desired tissue at the activation site, the pusher or stylet562may then be rotated to similarly cause the LIMD500and electrode512to rotate until securely affixed within the select tissue. As one example, the receptacle540and/or receptacle552may have a noncircular cross section as viewed from the top down (e.g. a rectangular triangle, hexagon, or other polygon shape) such that when the pusher or stylet562is rotated, it remains securely fixed within the receptacle540to induce rotation at the electrode512.

FIG. 6Aillustrates an LIMD600that resembles the LIMD500, except that the appendage arm620and stabilizer arm630are configured in a manner different than those ofFIG. 5A. In the embodiment ofFIG. 6A, the stabilizer arm630and appendage arm620are integrally joined with one another in a base area621, but are formed of a flexible material that has a desired preformed resting shape, corresponding to the deployed configuration illustrated inFIG. 6A. When in the deployed position, the stabilizer arms628,630are flared outward away from one another by an angle denoted at644.

The appendage arm620and stabilizer arm630have a common proximal end636that is secured to the top end606of the body602. The appendage arm620has a distal end622with an electrode624thereon as configured to passively or actively engage tissue at a desired activation site. The stabilizer arm630has a distal end632at which a pusher cup634is formed integral therewith. The pusher cup634includes a pusher receptacle640that is configured to receive a pusher tool during installation. During installation, the appendage arm620and stabilizer arm630are flexed inward to collapse against one another such that the angle644is very small or approximately zero in order that the appendage axis628and stabilizer axis638extend substantially parallel to the longitudinal axis609of the LIMD600. When the appendage and stabilizer arms620,630are collapsed against one another, the outer envelope thereof is no greater than the outer envelope of the shell608to provide a form factor small enough to be received within an introducer for installation in a desired chamber of the heart.

The LIMD600includes a body or housing602having a shell608that hermetically encloses the electronics, controller, battery, charge storage unit, and all other electrical components of the LIMD600. The housing602has a proximal base604and a distal top end606, with the intermediate shell608extending there between. The shell608is elongated and may be tubular in shape to extend along a longitudinal axis609. The base604includes at least one electrode612. The electrode612may be a helical shaped screw to actively secure the base604at a desired site within a selected local chamber of the heart. The electrode612includes a conductor that is surrounded by insulation along the majority of the length thereof, but exposes the distal tip614of the conductor, such that the electrode612only delivers stimulus pulses and senses electrical activity in the region denoted at615which corresponds to an distal activation site proximate to an adjacent chamber wall (and distal from the local chamber in which the LIMD600is implanted).

The LIMD600further includes an appendage arm620pivotally connected to and extending outward from the top end606. The appendage arm620includes a distal end622upon which an electrode624is located. The electrode624may be a passive electrode that is configured to simply rest against a select activation site. Alternatively, the electrode624may be an active fixation electrode that is configured to be secured to the tissue at the activation site (e.g. through a helix, spike, serrated edge, barb and the like).

The LIMD600also includes a stabilizer arm630having a distal end632and a proximal end636. The distal end632is formed integral with a pusher cup634that includes some type of pusher reception feature, such as a pusher receptacle640. The pusher cup634and receptacle640are configured to receive an external pusher tool that is used by the physician when implanting the LIMD600(as explained below in more detail). As one example, the pusher receptacle640may include a threaded recess641that is configured to threadably and securely receive a tip of the pusher tool to ensure a secure attachment to the pusher tool during installation. Once the LIMD600is fully implanted, the tip of the pusher tool is unscrewed from the threaded receptacle641.

The stabilizer arm630may be flexed between a collapsed installation position at which the stabilizer axis638is arranged at a very small acute angle or substantially parallel to the longitudinal axis609. Once implanted, the stabilizer arm630is then permitted to return to its flared state to a deployed position such that the stabilizer axis638forms a larger acute angle (e.g. 10-60°) with respect to the longitudinal axis609.

Optionally, the stabilizer arm630may be fixedly secured to the distal end606of the LIMD600, such that the stabilizer arm630does not rotate relative to the longitudinal axis609. Instead, in this alternative embodiment, the stabilizer arm630is rigidly secured to the distal end606and may be oriented such that the stabilizer axis630extends directly parallel to the longitudinal axis609at all times, during installation and after deployment. Again, the stabilizer arm630and the appendage arm620collectively form an IC device extension.

As a further option, a pusher cup or multiple pusher cups650may be provided about the exterior surface of the shell608. The pusher cup650includes a pusher receptacle652configured to receive the tip of a pusher tool that is used during implantation. As explained above in connection withFIG. 5A, one or more pusher cups may be provided in various locations.

FIG. 6Billustrates the LIMD600ofFIG. 6Aduring installation, while located within an introducer660. The introducer has a distal end662that is open to permit the LIMD600to be implanted and deployed there through. The introducer660includes a proximal end664along which a pusher or other form of tool (e.g. a stylet) is used guide the LIMD600into position. As shown inFIG. 6B, the stabilizer arm630and appendage arm620are contracted in their collapsed position to define an outer envelope substantially no greater than the outer envelope of the body608of the LIMD600. The pusher device662may engage one or both of the pusher receptacle640in the pusher cup634and/or the pusher receptacle652and the pusher cup650. During implantation, the pusher or stylet662is securely attached at the receptacle cup634to guide the LIMD600to its activation site. Once the electrode612is located against the desired tissue at the activation site, the pusher or stylet662may then be rotated to similarly cause the LIMD600and electrode612to rotate until securely affixed within the select tissue. As one example, the receptacle640and/or receptacle652may have a noncircular cross section as viewed from the top down (e.g. a rectangular triangle, hexagon, or other polygon shape) such that when the pusher or stylet662is rotated, it remains securely fixed within the receptacle640to induce rotation at the electrode612.

FIGS. 7A and 7Billustrate an alternative embodiment for an LIMD700when in the collapsed installation configuration (FIG. 7A) and in the deployed flared position (FIG. 7B). The LIMD700includes a stabilizer arm730having a distal and proximal end732,736. An appendage arm720is integrally formed, with and extends outward at an intermediate position from, the stabilizer arm730. The appendage arm720includes a proximal end726that is joined to the stabilizer arm730at an intermediate position away from the body702of the LIMD700. The appendage arm720includes an electrode724on the distal end thereof. As shown inFIG. 7A, before deployment and while in the collapsed position, the appendage arm720does still slightly project outward beyond the outer envelope of the body702, but the stabilizer arm730extends along the direction substantially parallel to the longitudinal axis of the body702. In the example ofFIG. 7A, the pusher cup750is located at the distal top end of the body702. The stabilizer arm730has a hollow passage there through that receives a tool762that pushes the LIMD700to a desired deployed position. For example, the passage through the stabilizer arm730aligns with the pusher cup750in the distal top end such that the tool762is inserted into the passage until securely engaging the pusher cup750. When in the passage, the tool762maintains the stabilizer arm730in a straight, elongated shape extending along the longitudinal axis of the tool762.

Turning toFIG. 7B, once the LIMD700is implanted and the introducer and tool762removed, the stabilizer arm730and appendage arm720are permitted to flare outward to form a Y-shaped configuration. It should be recognized that the shape formed by the stabilizer arm730and appendage arm720after deployment may be modified and controlled during construction to achieve a desired final configuration when implanted. By removing the tool762, the stabilizer arm730is permitted to return to its natural pre-formed shape.

FIG. 5Cillustrates the LIMD500in an exemplary deployed position. When deployed as illustrated inFIG. 5C, the LIMD500may be located directly against the ventricular vestibule. The electrode512is secured to the ventricular vestibule and/or extended to a point such that the distal end of the electrode512projects into or is located directly against the surface tissue of the right ventricle. The appendage arm520is flared to its deployed position to locate the electrode524against atrial tissue in the atrial appendage area. In the example ofFIGS. 5A-5C, the electrode524is configured to simply be pressed against the tissue at the atrial appendage. Optionally, spikes or a serrated edge or other fixation means may be added to the electrode at524to further facilitate engagement to the tissue in the atrial appendage.

When deployed and in the flared position, the stabilizer arm530extends into the SVC and rests against the side of the SVC to provide stabilization for the overall positioning of the LIMD500. It should be recognized, that throughout operation, as the right atrium moves during contraction, the stabilizer arm530and appendage arm520constantly pivot, rotate and/or flex to avoid interference with the normal mechanical movement of the right atrium.

FIG. 6Cillustrates an exemplary deployment of the LIMD600when located in the right atrium. The electrode612is securely affixed through the ventricular vestibule and/or locate the distal end thereof within or immediately adjacent the surface of the right ventricular wall. The appendage arm620is flared to a deployed position to locate the electrode624in the atrial appendage. The stabilizer arm630is also flared in the opposite direction to its deployed position such that the distal end632extends into and engages tissue within the SVC. As explained above, the appendage arm620and stabilizer arm630are flexible and will constantly move in connection with the mechanical contraction of the right atrium to avoid interference with the normal mechanical movement of the heart.

As shown inFIGS. 5A-5C,6A-6C, and7A-7B, the LIMD may be provided with two or more fixation mechanisms at the top end of the device body. One fixation mechanism, which is not electrically active, acts as to stabilize and passively-fixate the LIMD300in the superior vena cava (SVC). The other fixation mechanism is shorter but has an electrode at its tip and has the dual role of passive fixation to the RA appendage and pacing and sensing the RA. Additionally, the LIMD300has two or more possible configurations for attachment to the implant (and possibly explant) tool at either the end of the SVC stabilization fixation mechanism or at the side of the LIMD body. When the LIMD is affixed to the desired target site and the introducer (which protects blood vessels and myocardium from being damaged by the helical cathode) is removed, the passive fixation mechanisms swivel away from the longitudinal axis of the LIMD and contact their respective sites. The degree by which these fixation mechanisms swivel away from each other may be pre-determined or controlled by a ratcheting mechanism via the implant tool. Alternatively, the LIMD may use a stylet after affixation to the target site, which transmutes the morphology of the fixation mechanisms from a “J-shape” to a “U-shape,” as shown inFIG. 7B.

InFIGS. 5C and 6C, the LLPM is affixed to the target site on the atrioventricular wall and is deployed in the RA. Here, it can be seen that there are three points of contact between the LIMD and myocardium, significantly reducing the possibility of dislodgement. In addition, dual chamber (e.g. DDD or DDDR mode) functionality is achieved via the RA appendage fixation mechanism (which paces and senses the RA) and the helical cathode electrode (which paces and senses the RV).

If dual-chamber pacing and sensing is achieved with a long helical fixation electrode covered proximally with insulation, it may be desirable to know when the helix has extended through the myocardium to the adjacent chamber. This may be determined using real-time impedance measurement between the helical tip electrode and another electrode. When the helical electrode is in pooled blood of any heart chamber, characteristic low impedance will be between it and any other electrode in the blood. As the helical electrode is screwed into the myocardium, impedance will rise. When the helix has been affixed sufficiently to break through the wall to the other chamber, impedance will drop. The changes in impedance may be used to know how far to screw in the helix, which portions of walls delineating heart chambers are an appropriate thickness for the helix, and whether any other spacer is needed to prevent the device from torqueing with the heart's mechanical motion.

Before disconnecting from the insertion tool, a pacing test provides an indication of the chamber paced and capture threshold. If the test shows that pacing is not occurring in the desired chamber or that thresholds are inappropriate, the tool may be used to remove the fixation and attempt to attach at another location.

For each attempt, the distance traversed by the lead's AV helix through the wall between the RA and RV between each turn of the screw may be closely controlled. Atrial and ventricular capture thresholds may be recorded with a pacing system analyzer (PSA) between each turn or at set degrees of rotation. The PSA may use the electrodes on the LIMD or may use electrodes on the exterior or outer end of the introducer to test for capture thresholds prior to affixing the LIMD in place. The distance between each turn may be generally between 0.5 to 2.0 mm. For example, all lead helical electrodes may be coated with an insulating material such as Parylene®-coated except for the most distal portion of the pitch of the screws (thus ensuring that only tissue near the tip is stimulated). For example, the helical electrode may be advanced in small increments, and after each increment, the PSA may then test for a capture. An interactive process may be repeated whereby the electrode is advanced and then the PSA determines if a capture threshold has been satisfied. This process is repeated until impulses from the distal electrode capture the ventricular tissue. Similarly, a capture test may be performed for the atrial electrode. The atrial electrode is adjusted until the PSA confirms atrial capture. In accordance with the foregoing, it is possible for an AV helical electrode on a lead to burrow from the RA and excite ventricular tissue. This allows a dual chamber mode-capable LIMD to have its main body located in the one chamber and pace and sense another chamber.

The term “distal” as used to describe wall tissue and activation sites, is used with respect to the local chamber.

FIG. 8shows an exemplary LIMD800configured for dual-chamber functionality from a primary location within a single chamber of the heart. For example, the LIMD800may be implemented as a pacemaker, equipped with both atrial and ventricular sensing and pacing circuitry. Alternatively, the LIMD800may be implemented with a reduced set of functions and components. For instance, the LIMD800may be implemented without ventricular sensing and pacing. The LIMD800may also be implemented with an increased set of functions. For example, if the LIMD800includes a coil type electrode, the LIMD may be configured to include cardioversion and/or shocking therapy capability.

The LIMD800has a housing801to hold the electronic/computing components. The housing801(which is often referred to as the “can”, “case”, “encasing”, or “case electrode”) may be programmably selected to act as the return electrode for certain stimulus modes. Housing801further includes a plurality of terminals802,804,806,808,810that interface with electrodes of the LIMD. For example, the terminals may include: a terminal802that connects with a first electrode associated with the housing (e.g. electrode410) and located in a first chamber; a terminal804that connects with a second electrode associated with the housing (e.g., electrode411) and also located in the first chamber; a terminal806that connects with a third electrode associated with the housing (e.g. electrode412) and located in the first chamber and possibly partially extending into tissue associated with a second chamber; and two additional terminals808,810that connect with one or more additional electrodes (e.g., electrode524), if available. The type and location of each electrode may vary. For example, the electrodes may include various combinations of ring, tip, coil and shocking electrodes and the like.

The LIMD800includes a programmable microcontroller820that controls various operations of the LIMD800, including cardiac monitoring and stimulation therapy. Microcontroller820includes a microprocessor (or equivalent control circuitry), RAM and/or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry.

LIMD800further includes a first chamber pulse generator822that generates stimulation pulses for delivery by one or more electrodes coupled thereto. The pulse generator822is controlled by the microcontroller820via control signal824. The pulse generator822is coupled to the select electrode(s) via an electrode configuration switch826, which includes multiple switches for connecting the desired electrodes to the appropriate I/O circuits, thereby facilitating electrode programmability. The switch826is controlled by a control signal828from the microcontroller820.

In the example ofFIG. 8, a single pulse generator822is illustrated. Optionally, the LIMD800may include multiple pulse generators, similar to pulse generator822, where each pulse generator is coupled to one or more electrodes and controlled by the microcontroller820to deliver select stimulus pulse(s) to the corresponding one or more electrodes.

Microcontroller820is illustrated as including timing control circuitry832to control the timing of the stimulation pulses (e.g., pacing rate, atrio-ventricular (AV) delay etc.). The timing control circuitry832may also be used for the timing of refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, and so on. Microcontroller820also has an arrhythmia detector834for detecting arrhythmia conditions. Although not shown, the microcontroller820may further include other dedicated circuitry and/or firmware/software components that assist in monitoring various conditions of the patient's heart and managing pacing therapies.

The LIMD800includes sensing circuitry844selectively coupled to one or more electrodes through the switch826. The sensing circuitry detects the presence of cardiac activity in the right chambers of the heart. The sensing circuitry844may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. It may further employ one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and threshold detection circuit to selectively sense the cardiac signal of interest. The automatic gain control enables the unit802to sense low amplitude signal characteristics of atrial fibrillation. Switch826determines the sensing polarity of the cardiac signal by selectively closing the appropriate switches. In this way, the clinician may program the sensing polarity independent of the stimulation polarity.

The output of the sensing circuitry844is connected to the microcontroller820which, in turn, triggers or inhibits the pulse generator822in response to the absence or presence of cardiac activity. The sensing circuitry844receives a control signal846from the microcontroller820for purposes of controlling the gain, threshold, polarization charge removal circuitry (not shown), and the timing of any blocking circuitry (not shown) coupled to the inputs of the sensing circuitry.

In the example ofFIG. 8, a single sensing circuit844is illustrated. Optionally, the LIMD800may include multiple sensing circuit, similar to sensing circuit844, where each sensing circuit is coupled to one or more electrodes and controlled by the microcontroller820to sense electrical activity detected at the corresponding one or more electrodes. The sensing circuit844may operate in a unipolar sensing configuration or in a bipolar sensing configuration.

The LIMD800further includes an analog-to-digital (ND) data acquisition system (DAS)850coupled to one or more electrodes via the switch826to sample cardiac signals across any pair of desired electrodes. The data acquisition system850is configured to acquire intracardiac electrogram signals, convert the raw analog data into digital data, and store the digital data for later processing and/or telemetric transmission to an external device854(e.g., a programmer, local transceiver, or a diagnostic system analyzer). The data acquisition system850is controlled by a control signal856from the microcontroller820.

The microcontroller820is coupled to a memory860by a suitable data/address bus862. The programmable operating parameters used by the microcontroller820are stored in memory860and used to customize the operation of the LIMD800to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveshape and vector of each shocking pulse to be delivered to the patient's heart808within each respective tier of therapy.

The operating parameters of the LIMD800may be non-invasively programmed into the memory860through a telemetry circuit864in telemetric communication via communication link866with the external device854. The telemetry circuit864allows intracardiac electrograms and status information relating to the operation of the LIMD800(as contained in the microcontroller820or memory860) to be sent to the external device854through the established communication link866.

The IMD802can further include magnet detection circuitry (not shown), coupled to the microcontroller820, to detect when a magnet is placed over the unit. A magnet may be used by a clinician to perform various test functions of the unit802and/or to signal the microcontroller820that the external programmer854is in place to receive or transmit data to the microcontroller820through the telemetry circuits864.

The LIMD800may be equipped with a communication modem (modulator/demodulator)840to enable wireless communication with a remote device, such as a second implanted LIMD in a master/slave arrangement, such as described in U.S. Pat. No. 7,630,767. In one implementation, the communication modem840uses high frequency modulation. As one example, the modem840transmits signals between a pair of LIMD electrodes, such as between the can800and anyone of the electrodes connected to terminals802-810. The signals are transmitted in a high frequency range of approximately 20-80 kHz, as such signals travel through the body tissue in fluids without stimulating the heart or being felt by the patient. The communication modem840may be implemented in hardware as part of the microcontroller820, or as software/firmware instructions programmed into and executed by the microcontroller820. Alternatively, the modem840may reside separately from the microcontroller as a standalone component.

The LIMD800can further include one or more physiologic sensors870. Such sensors are commonly referred to as “rate-responsive” sensors because they are typically used to adjust pacing stimulation rates according to the exercise state of the patient. However, the physiological sensor870may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states). Signals generated by the physiological sensors870are passed to the microcontroller820for analysis. The microcontroller820responds by adjusting the various pacing parameters (such as rate, AV Delay, V-V Delay, etc.) at which the atrial and ventricular pacing pulses are administered. While shown as being included within the unit802, the physiologic sensor(s)870may be external to the unit802, yet still be implanted within or carried by the patient. Examples of physiologic sensors might include sensors that, for example, sense respiration rate, pH of blood, ventricular gradient, activity, position/posture, temperature, minute ventilation (MV), and so forth.

A battery872provides operating power to all of the components in the LIMD800. The battery872is capable of operating at low current drains for long periods of time, and is capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse (e.g., in excess of 2 A, at voltages above 2 V, for periods of 10 seconds or more). The battery872also desirably has a predictable discharge characteristic so that elective replacement time can be detected. As one example, the unit802employs lithium/silver vanadium oxide batteries.

The LIMD800further includes an impedance measuring circuit874, which can be used for many things, including: impedance surveillance during the acute and chronic phases for proper LIMD positioning or dislodgement; detecting operable electrodes and automatically switching to an operable pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance; detecting when the device has been implanted; measuring stroke volume; and detecting the opening of heart valves; and so forth. The impedance measuring circuit874is coupled to the switch826so that any desired electrode may be used.

The microcontroller820further controls a shocking circuit880by way of a control signal882. The shocking circuit880generates shocking pulses of low (e.g., up to 0.5 joules), moderate (e.g., 0.5-10 joules), or high energy (e.g.,811to 40 joules), as controlled by the microcontroller820. Such shocking pulses are applied to the patient's heart808through shocking electrodes, if available on the LIMD. It is noted that the shock therapy circuitry is optional and may not be implemented in the LIMD, as the various LIMDs described above and further below will typically not be configured to deliver high voltage shock pulses. On the other hand, it should be recognized that an LIMD may be used within a system that includes backup shock capabilities, and hence such shock therapy circuitry may be included in the LIMD.

FIG. 9Aprovides a sectional view of a patient's heart33and shows an LIMD900. The LIMD900may have been placed through the superior vena cava28into the right atrium30of the heart33. The LIMD900comprises a housing902configured to be implanted entirely within a single local chamber of the heart. The housing902includes a proximal base end904and a distal top end906. The proximal base end904includes an active fixation member, such as a helix, that is illustrated to be implanted in the ventricular vestibule (VV). A shaped intra-cardiac (IC) device extension903extends from the distal top end906of the housing902. The IC device extension903comprises an elongated body that may be tubular in shape and may include a metal braid provided along at least a portion of the length therein (as explained herein in more detail). The extension body including a transition sub-segment, an active interim-segment and a stabilizer end-segment, all of which are illustrated in a deployed configuration and some of which are preloaded against anatomical portions of tissue of interest. For example, the active interim-segment (e.g., second curved segment911, and all or portions of the first and second linear regions909and913) and the stabilizer end-segment (e.g., third curved segment915and all or portions of the second linear region913) are shown preloaded against anatomical tissue of interest. The braid resists torque compression but permits lateral flex. One or more electrodes905are carried by the IC device extension903and are electrically connected to electronics within the housing902through conductors extending through the body of the IC device extension.

The IC device extension903is formed with shape memory characteristics that allow the IC device extension903to transform between a collapsed state, in which the IC device extension assumes a substantially linear shape, and an expanded state, in which the IC device extension assumes a multiple curved shape, such as shown inFIGS. 9A-9D. In one embodiment, the curved configuration of the IC device extension903comprises multiple sharply curved segments, obtusely curved segments, generally linear regions and the like. The number, length, and order of the segments and regions, as well as the degree to which individual segments or regions are curved or linear may vary depending upon the anatomical contour to be followed.

The IC device extension includes a short stem930that extends a short distance from the distal top end906of the housing902. The stem930merges into a first curved segment907that turns at a sharp angle with respect to a longitudinal axis of the housing902. Optionally, the first curved segment907may form an acute angle, 90 degree angle, or obtuse angle approximately with respect to a longitudinal axis of the housing902. The first curved segment907merges into and is followed by a first generally linear region909that extends laterally from the housing902, along a lateral axis, until merging with a second curved segment911. The second curved segment911turns at a sharp angle with respect to the longitudinal axis of the housing902and the lateral axis of the first linear region909. Optionally, the second curved segment911may form an acute angle, 90 degree angle, or obtuse angle approximately with respect to the lateral axis of the first linear region909. As one example, the second curved segment911may approximate a 180 degree sharp or “hairpin” curve away from the lateral axis of the first linear region909and away from the longitudinal axis of the housing902. The second curved segment911merges into and is followed by a second generally linear region913that extends along a second lateral direction.

One or more electrodes905are located along the second curved segment911. Optionally, the electrode(s) may be provided in the region proximate to the junction of the second curved segment911and the second linear region913. Optionally, one or more electrodes905may be provided along the second linear region913.

The second linear region913merges with and extends to a third curved segment915. The third curved segment915follows an extending “slow” arc and then terminates at a tail end917of the IC device extension903. The third curved segment915follows a slow arc with respect to the longitudinal axis of the housing902and the lateral axis of the first linear region909. As one example, the third curved segment915may approximate a 90 degree turn away from the longitudinal axis of the housing902until terminating at the tail end917of the IC device extension902.

The shaped IC device extension903is formed into a pre-loaded shape in which the first, second and third curved segments907,911and915extend along desired arcuate paths and project from longitudinal/lateral axes at desired pitch, roll and yaw angles, where the pitch, roll and yaw angles are measured from reference angular positions. To avoid overly complicatingFIG. 9A, examples of longitudinal/lateral axis, arcuate paths, pitch, roll and yaw angles are shown in the embodiment ofFIG. 9E, but are equally applicable to any other embodiments described herein.

With continued reference toFIG. 9A, the LIMD900is configured to place the housing902in the lower region of the right atrium between the OS and IVC with a distal helix electrode, on the housing902, in the ventricular vestibule to provide ventricular pacing and sensing. The IC device extension903extends upward in the right atrium toward and into the SVC. The IC device extension903is configured (length wise and shape wise) such that the second curved segment911may be implanted within the right atrial IC device extension (RAA), along with those portions of the first and second linear regions909,913near the second curved segment911. The configuration inFIG. 9Aplaces the electrode905in the RAA to allow for right atrial pacing and sensing. The configuration inFIG. 9Aalso places the proximal portion of the third curved segment915against a wall of the SVC to provide overall stability to the LIMD900.

FIG. 9Billustrates a model of an interior of a canine heart and shows a leadless implantable medical device having a shaped IC device extension similar to that describe with reference toFIG. 9A. The embodiments ofFIGS. 9A and 9Bmay have IC device extensions that traverse a two-dimensional space, i.e., lie substantially flat in a plane, while extending in x and y directions along its length, or a three-dimensional space, i.e., extending in x, y and z directions along its length.

FIGS. 9C and 9Dfurther illustrate a model of an interior of a human heart and shows an example of the LIMD900having the shaped IC device extension903described with reference toFIG. 9A.FIG. 9Cgenerally illustrates an exemplary right lateral view of a heart, whileFIG. 9Dgenerally illustrates an exemplary anterior-posterior (AP) view. As points of reference, the RV vestibule920, atrial IC device extension924, and RV outflow track922are illustrated in one or both ofFIGS. 9C and 9D. The AP view ofFIG. 9Dis oriented relative to the right lateral view ofFIG. 9D, such that the viewer's line of sight (inFIG. 9D) is directed into the atrial IC device extension924along arrow926inFIG. 9C, whereas the viewer's line of sight inFIG. 9Cis directed in the direction of arrow928inFIG. 9D.

The LIMD900is shown to be actively affixed near the RV vestibule920. The views illustrated inFIGS. 9C and 9Dare merely exemplary models of a potential three dimensional shape of the IC device extension903. To further illustrate the 3D geometry of the IC device extension903, planes932-934are shown in dashed line. The plane932generally follows X and Y axes that are defined with respect to the orientation of the housing902. For example, the Y axis may correspond to the longitudinal axis of the housing902. The plane933generally follows X and Z axes, wherein the X axis is oriented laterally with respect to the longitudinal axis of the housing902(e.g., from left to right across the drawing sheet). The Z axis is oriented transversely with respect to the longitudinal axis of the housing902and the lateral X axis (e.g., in and out of the drawing sheet).

The plane932(also referred to as the LIMD plane) is generally defined by the longitudinal axis of the housing902, and a lateral axis along which the first linear region909extends. The plane933(also referred to as the RAA plane) is generally defined by the lateral axis along which the first linear region909extends and the transverse axis along which the second linear region913extends. The plane934(also referred to as the stabilization or SVC plane) is generally defined by the transverse axis along which the second linear region913extends and a stabilization path along which the third curved region915extends.

FIG. 9Eprovides an enlarged view of a portion of a shaped IC device extension953, while in the right atrial IC device extension974, accordance with an alternative embodiment. The shaped IC device extension953includes a short stem980that extends a short distance from the distal top end906of the housing952of an LIMD. The stem980merges into a first curved segment957that turns at a sharp angle with respect to a longitudinal axis942of the housing902. Optionally, the first curved segment957may form an acute angle, a 90 degree angle, or an obtuse angle approximately with respect to the longitudinal axis942of the housing952. The first curved segment957merges into and is followed by a first generally linear region959that extends laterally from the housing902, along a lateral axis943, until merging with a second curved segment961. The second curved segment961turns at a compound sharp angle with respect to the longitudinal axis942of the housing952and the lateral axis943of the first linear region959. Optionally, the second curved segment961may form an acute angle, a 90 degree angle, or an obtuse angle approximately with respect to the lateral axis943of the first linear region959. As one example, the second curved segment961may approximate a 180 degree sharp or “hairpin” curve away from the lateral axis943of the first linear region959and away from the longitudinal axis942of the housing952. The second curved segment961merges into, and is followed by, a second generally linear region963that extends along a second lateral direction944.

One or more electrodes955are located along the second curved segment961. Optionally, the electrode(s)955may be provided in the region proximate to the junction951of the second curved segment961and the second linear region963. Optionally, one or more electrodes955may be provided along the second linear region963. The electrode955includes a bracket ring956that at least partially surrounds the perimeter of the body of the shaped IC device extension903. The bracket ring956is formed with a spring arm957that includes an outer bend958that terminates at a distal tip959.

The second curved segment961follows an arcuate path947, while the spring arm957extends outward from the arcuate path947in a tangential direction946to form an acute angle with the second lateral axis944. The distal tip959may be directed inward toward the second linear region963such as to avoid damaging wall tissue. The spring arm957pivots, relative to the second curved segment961and relative to the second linear segment963, inward and outward along arrow948and949. The spring arm957is biased outward in the direction of arrow949to a normal resting position. When implanted, the tissue wall places a load against, and slightly deflects, the spring arm957inward along arrow948, thereby affording constant and steady contact between the electrode955and the tissue wall in the right atrial IC device extension974.

The second linear region963merges with and extends to a third curved segment965. The third curved segment965follows an extending “slow” arc and then terminates at a tail end of the IC device extension953. The third curved segment965follows a slow arc, along an arcuate path945, with respect to the longitudinal axis942of the housing952and the first and second lateral axes943and944of the first and second linear regions959and963.

The lateral axis943of the first linear region959projects from the longitudinal axis942at a yaw angle975, where the yaw angle975is measured from a zero reference yaw angle about the longitudinal axis942. The second curved segment974bends in a direction that projects from, or about, the lateral axis943, at a roll angle976, where the roll angle976is measured from a zero reference roll angle about the lateral axis943. The second linear region963extends along the second lateral axis944at a complex angle with respect to the lateral axis943. The third curved segment965projects from the second lateral axis944, at a pitch angle977from a zero reference pitch angle about the second lateral axis944.

It should be understood that the axes, directions, curves, and linear paths followed by the regions and segments of the shaped IC device extension903ofFIG. 9Amay resemble or differ from the axes, directions, curves, and linear pathes followed by the regions and segments of the shaped IC device extension953ofFIG. 9E.

FIG. 9Fillustrates a longitudinal axial view of an introducer assembly280, formed according to an embodiment with the LIMD900including the IC device extension903ofFIG. 9Ainserted therein. The IC device extension903includes an extension body having a proximal end353. The introducer assembly280includes a flexible, longitudinal, cylindrical open-ended sheath282defining a central internal passage284. The sheath282may be a flexible tube formed of rubber, for example, that is configured to be maneuvered through patient anatomy, such as veins and the heart. In this respect, the sheath282may be similar to that of a cardiac catheter.

A physician or surgeon operates user controls on the introducer assembly280at a proximal end (not shown). The proximal end may include user controls that allow the sheath282to be bent, curved, canted, rotated, twisted, or the like, so as to be navigated through a patient's vasculature. For example, a distal end288of the sheath282may be bent, curved, canted, rotated, twisted, articulated, or the like through operation by the physician or surgeon manipulating the user controls at the proximal end of the assembly280.

The LIMD900is held in the distal end288of the sheath282. As shown, the housing902of the LIMD900slides along inner walls292of the sheath282. The LIMD900is configured to be pushed out of, or ejected from, the sheath282in the direction of arrow A. The top end906of the LIMD900connects to the IC device extension903. The proximal end353of the IC device extension903is coupled to the housing902of the LIMD900. The extension body extends between the proximal end353and a distal end355. The extension body including a transition sub-segment357, an active interim-segment360and a stabilizer end-segment362, all of which are “stretched out” or elongated to extend generally along the length of the internal passage284of the sheath282.

With cross-reference toFIGS. 9A-9E, the transition sub-segment357generally includes the stem930, first curved segment907and at least a portion of the first linear region909. The active interim-segment360includes the second curved segment911, and may include portions of the first and second linear regions909and913. The stabilizer end-segment362includes the third curved segment915and may include a portion of the second linear region913. It should be recognized that the correlation between the segments and regions ofFIGS. 9A-9Eand the transition sub-segment357, active interim-segment360and stabilizer end-segment362, are exemplary implementations. Similarly, the transition sub-segment357, active interim-segment360and stabilizer end-segment362may be correlated to the stabilization arms and appendage arms described in connection with the embodiments ofFIGS. 5-7.

The extension body is formed of materials that are flexible, yet offer good shape memory such that the extension body may be stretched out while within the sheath282and, when removed from the sheath282, then return to its original (normal, resting) shape as shown inFIG. 1A. For example, the extension body may be formed of silicon that is cured to desired crosslink structure that holds (or is biased to return to) a pre-loaded shape (e.g., through a thermal set process).

In the example shown inFIG. 9F, the active interim-segment360(e.g., corresponding to second curved segment911) is straightened to remove the curved shape only while in the sheath282. Similarly, the stabilizer end-segment362(e.g., corresponding to the third curved segment915) is straightened. While the example ofFIG. 9Fillustrates a slight wave or curve that remains in the extension body, optionally, the extension body may be constrained to be much straighter or permitted to remain even more curved or bent. The amount to which the active interim-segment360and stabilizer end-segment362are straightened or curved may vary depending upon the outer dimensions of the extension body and the inner dimensions of the sheath282.

A pusher rod296is provided to be slidably inserted into the sheath282in order to manipulate the IC device extension903and LIMD900. For example, the pusher rod296may linearly translate the IC device extension903and LIMD900along the longitudinal axis283and rotate the IC device extension903and LIMD900about the rotational axis285. The pusher rod296includes a pusher tip connector298that is configured to securely engage the distal end355of the extension body. The distal tip355includes a connection member394that is configured to securely mate with the pusher tip connector298(e.g., through a threaded connection, an interference fit, or the like). The pusher rod296may extend into and retract from the sheath282under a physician's control. The pusher rod296and LIMD900are located at opposite ends of the extension body. However, rotational force applied by the pusher rod296on the distal end355of the extension body is substantially all transferred to the LIMD900. This rotational force may be used to actively secure the LIMD900to the wall tissue through the active fixation member, such as a helical anchor, a coil, a helical wire having a sharp point, a hook, a barb, or the like.

FIG. 9Falso illustrates the general internal components of the LIMD900. The housing902include a charge storage unit324and a battery326that supplies power to the electronics and energy to the charge storage unit324. The housing302also includes a sensing circuit322and a controller320.

The sensing circuit322senses intrinsic activity, while the change storage unit324stores high or low energy amounts to be delivered in one or more stimulus pulses. Electrodes311,905may be used to deliver lower energy or high energy stimulus pulses, such as pacing pulses, cardioverter pulse trains, defibrillation shocks and the like. The electrodes311,905may also be used to sense electrical activity, such as physiologic and pathologic behavior and events and provide sensed signals to the sensing circuit322. The electrodes311,905are configured to be joined to an energy source, such as the charge storage unit324. The electrodes311,905receive stimulus pulse(s) from the charge storage unit324. The electrodes311,905may be the same or different size.

The controller320, within the housing302, controls the overall functionality of the LIMD900including causing the charge storage unit324to deliver activation pulses through each of the electrodes311,905in a synchronous manner, based on information from the sensing circuit322, such that activation pulses delivered from the electrode311are timed to initiate activation in the adjacent chamber, while activation pulses delivered from the electrodes905are timed to initiate activation in the local chamber. The stimulus pulses are delivered synchronously to local and distal activation sites in the local and distal conduction networks such that stimulus pulses delivered at the distal activation site are timed to cause contraction of the adjacent chamber in a predetermined relation to contraction of the local chamber. The electrodes311,905are spaced radially and longitudinally apart from one another such that the local activation site (e.g., right atrium) and the distal activation side in the adjacent chamber (e.g., right ventricle) are sufficiently distant from one another within the heart's conductive network to initiate activation in different branches of the hearts conductive network in a time relation that corresponds to the normal hemodynamic timers (e.g. AV delay).

The controller320may operate the LIMD900in various modes as discussed herein. The sensing circuit322receives sensed signals from one or more of the electrodes311,905. When pairs of electrodes are provided in the location of electrode311or in the location of electrode905, the sensing circuit322discriminates between sensed signals from respective pairs of electrodes that originate in the near field and in the far field. For example, a pair of electrodes905may sense electrical potential across small areas and thereby allow the sensing circuit322to discriminate between different sources of electrical signals. In one embodiment, the inter-electrode gap370between electrodes905is limited or minimized in order to achieve a select type of sensing such as bipolar sensing which limits or minimizes sensing of far field signals. With a small inter-electrode gap or separation370, when far field signals (e.g., signals from the right ventricle, left atrium or left ventricle) reach the electrodes905these far field signals are sensed as a common mode signal with no or a very small potential difference between the electrodes. Similarly, if a pair of electrodes311are provided on the active fixation member310, the electrodes311may be separated by a small inter-electrode gap such that, when far field signals (e.g., signals from the right atrium or left ventricle) reach the electrodes311these far field signals are sensed as a common mode signal with no or a very small potential difference between the electrodes.

Optionally, an electrode312may be provided on the housing302and operate as an anode electrode, while the electrode311and/or electrodes905may operate as cathode electrodes. When an anode electrode312is provided on the housing302, the controller320may be configured to cause stimulus pulses to be delivered between the anode electrode312and the first electrode311to stimulate the local chamber. When an anode electrode312is provided on the housing302, the sensing circuit312may be configured to sense between the anode312and the second electrode905or311.

FIG. 9Gillustrates a cross section of a portion of the IC device extension ofFIGS. 9A-9E. Optionally,FIG. 9Gmay also represent the cross section of the appendage arm ofFIGS. 5A to 7Bor the stabilization arm ofFIGS. 5A to 7Bbut with the electrodes and insulated conductors removed. The IC device extension360includes one or more insulated conductors376that are connected to corresponding electrodes368. The conductors376are connected through a switch to electronics within the LIMD900to perform sensing and/or deliver stimulus pulses. The conductors376may be wound about one another in a helical manner. The conductors376extend along a core378and the conductors376are radially surrounded by an elongated braid380. The braid380may be made of steel or wire mesh, or have a honeycomb pattern that resists compression or IC device extension along the length of the IC device extension body (as denoted by longitudinal direction386). The braid380is flexible in a lateral direction388in order to be bent side to side during implant and following implant. The mesh or honeycomb configuration of the braid380affords strong resistance to torque about the length of the IC device extension body when turned in the rotational direction390about the longitudinal direction386. It is desirable to be resistant to torque in order that, during implant, when a rotational force is applied to one end of the IC device extension body, substantially all of such rotational force is conveyed along the length of the IC device extension body to the opposite end. As explained hereafter, the braid380facilitates delivery of rotational forces and longitudinal pressure to the LIMD900and the active fixation member during implant.

Optionally, the IC device extension body may further includes an insulation material382provided around the conductors376and around the braid380. An insulated, flexible, biocompatible shell384is formed over the braid380. The electrodes368are connected to separate corresponding conductors376at contacts392. The electrodes368may be formed as ring electrodes, coil electrodes, pin or bump electrodes and the like. While two electrodes368are illustrated it is understood that only one or more than two electrodes368may be provided on the IC device extension body. The electrodes368may be provided at various points about the perimeter of the IC device extension body and at multiple points along the length of the IC device extension body.

The electrodes368are separated from the braid380by insulation (e.g. part of the shell384). The electrodes368, braid380and conductors376may be arranged concentrically with one another in a coaxially configuration.

FIG. 10illustrates a LIMD1000, according to an embodiment. The LIMD includes a housing1002having a heart-wall securing base1004and a top or proximal end1006. An anchoring member, such as a securing helix1008, which may be formed of a conductive material, such as metal, extends from the base1004of the housing1002and is configured to securely anchor the housing1002, and therefore the LIMD1000, to tissue within a chamber of a heart. The securing helix1008may also serve as an electrode. Instead of the securing helix1008, a barb, hook, or the like may extend from the housing1002. Additionally, the anchoring member may be any of the securing configurations shown inFIGS. 4A-G.

The proximal end1006of the housing1002connects to a stabilizing IC device extension1010having a stabilizing loop member. The stabilizing loop member of the stabilizing IC device extension1010may include a linear beam1012that connects to a first or inner loop1014that, in turn, connects to a second or outer loop1016. The outer loop1016is distally located from the housing1002. Alternatively, the IC device extension1010may not include the linear beam1012, but instead may include just the loops1014and1016that join directly to the housing1002. Additionally, more or fewer loops than shown may be used. For example, the LIMD1000may include only one loop, or the LIMD1000may include three or more loops.

The inner and outer loops1014and1016each have a perimeter that may be flared (for example, diverges and then re-merges) in a direction generally toward and away from the lateral axis X which extends in a lateral direction with respect to the longitudinal axis Y of the loops1014and1016and housing1002. The inner and outer loops1014and106may have different contoured shapes, as shown inFIG. 10. By way of example, the loops1014and1016may have a perimeter, when viewed from the top down, that is disc-shaped, oval, circular, tubular, rectangular, triangular, and the like.

The loops1014and1016have opposed top and bottom sides that are aligned generally in parallel planes that extend in a generally common direction as the longitudinal axis Y. The loops1014and1016are aligned along a common path. Alternatively, the loops1014and1016may be oriented in a different manner with respect to one another. For example, the loops1014and1016may be oriented orthogonal to one another, such that the loop1014is oriented in a plane defined by the X and Y axes, while the loop1016is oriented in a plane defined by the Y and Z axes, or vice versa. Moreover, it is recognized that, whileFIG. 10illustrates the loops1014and1016aligned in a straight manner, this is for illustration purposes. When implanted, the loops1014and1016will curve and wrap to follow the contour of an interior of the heart in a manner determined by the implanting physician. The loops1014and1016are shown inFIG. 10in a deployed implanted shape, but are flexible and are compressed into a collapsed installation shape while being installed.

Electrodes1018are secured to the inner loop1014on either side and are configured to contact interior wall portions of the superior vena cava of the heart. A radio marker1020may be secured next to an electrode1018. Although the electrodes1018are shown on the inner loop1014, the electrodes1018may be positioned on the outer loop1016. Alternatively, each loop1014and1016may have one or more electrodes.

The electrodes1018are spaced apart from one another by an inter-electrode spacing (for example, the diameter of the loop segment1014). The electrodes1018may be wrapped around, or otherwise secured to, a peripheral portion of the inner loop1014. As shown inFIG. 10, two electrodes1018are secured around circumferential portions of the inner loop1018at diametrically opposite sides1022and1024.

The inner and outer loops1014and1016are joined to one another at connection links or joints. As shown, the electrodes1018are distally located from one another on the inner loop1014and may be positioned generally at a radial angle θ that is 90° from the connection link or joint with outer loop1016, for example. The opposed electrodes1018are configured to contact tissue portions within a heart. The number of electrodes1018may vary depending on a particular application. For example, additional electrodes may be secured to the inner and/or outer loops1014and1016. Additionally, while the electrodes1018are shown at opposite sides1022and1024of the inner loop1014, the electrodes1018may be positioned at various other locations on the inner loop1014, and even at different locations from the connection joint. Also, more or less electrodes1018than those shown on the inner loop1014may be used. For example, the inner loop1014may include only one electrode1018.

The electrodes1018may be used to deliver low energy or high energy stimulus, such as pacing pulses, cardioverter pulse trains, defibrillation shocks and the like. The electrodes1018may also be used to sense electrical activity, such as physiologic and pathologic behavior and events.

The dual-loop IC device extension1010includes shape memory characteristics that allow the inner and outer loops1014and1016to transform between collapsed states, in which the loops1014and1016assume a substantially flat or compressed shape, and an expanded deployed state, in which the loops1014and1016assume a more rounded loop shape. In an alternate configuration one or both of the loops may have an open configuration provided by a break in loop continuity along the perimeter of the loop.

The radio marker1020may be used to determine the position of the inner loop1014within patient anatomy. For example, the radio marker1020may be used in conjunction with an electromagnetic surgical navigation system and an imaging device, such as a fluoroscope, to track the position of the LIMD1000within patient anatomy. For example, a fluoroscope may image the patient anatomy. The position of the radio marker1020may then be registered with respect to the fluoroscopic images. Thus, as the LIMD1000moves within the patient anatomy, a display showing the fluoroscopic image(s) and a representation of the LIMD1000may track movement of the LIMD1000through movement of the radio marker1020, which was previously registered with the fluoroscopic image(s).

While one radio marker1020is shown, more radio markers may be used. For example, radio markers may be secured to both loops1014and1016and/or the linear beam1012. Alternatively, the LIMD1000may not include a radio marker.

FIG. 11illustrates an LIMD introducer assembly1100, according to an embodiment. The introducer assembly1100includes a flexible tube, sheath, or the like1102, such as a catheter, having an internal longitudinal passage1104into which the LIMD1000, including the loops1014,1016and the housing1002, are retained. The introducer assembly1100is maneuvered by a physician at a proximal end (not shown) into a heart of a patient such that the housing1002is positioned in a lower region of the right atrium between the OS and IVC. The housing1002is anchored in place through the securing helix1008.

As shown inFIG. 11, the inner and outer loops1014and1016of the LIMD1000are collapsed or compressed within the flexible tube1102into a collapsed installation shape. This arrangement is designed to prevent premature deployment of the LIMD1000and prevent damage to vascular access ways for implantation. A pusher implant tool1106affixes to the proximal end1006of the housing1002and may use hooks or expanding collets to lock into inner loop1014. The introducer assembly1100is designed to be steerable so that the LIMD1000can be finely navigated to the desired implant site.

Once the implantation site in the right atrium is located (via fluoroscopy, echocardiography, or other means), a distal end1108of the introducer assembly1100is positioned at the implantation site and the pusher implant tool1106is pushed in the direction of arrow A to place the securing helix1008adjacent tissue. The pusher implant tool1106is then rotated in the direction of arc B. The rotation translates to the housing1002and in turn to the securing helix1008. The securing helix1008, which as noted above may also serve as an electrode, extends into the myocardium through the right atrium, causing it to drill into ventricular tissue that bounds the right atrium. Then, the fidelity of the implantation process may be verified by ventricular capture and sensing tests.

Next, the introducer assembly1100is retracted enough to allow the inner loop1014to extend out of the sheath in the region of the high right atrium at the SVC/RA junction. The steerable introducer assembly1100is adjusted to have the radio marker1020(shown inFIG. 10) located at the desired location and the inner loop1014in good contact with atrial tissue.

Finally, the introducer assembly1100is further retracted relative to the LIMD1000until the outer loop1016passes out of the tube1102. That is, the introducer assembly1100is pulled back in the direction of arrow A′, leaving the housing1002secured to the heart12within the right atrium. The introducer assembly1100disengages from the LIMD1000as the introducer assembly1100is pulled away in the direction of arrow A′. Accordingly, the outer loop1016expands until it reaches the inner diameter of the SVC. The pusher tool1106is then disengaged from the housing1002and/or the first loop1014.

FIG. 12illustrates the LIMD1000implanted within a heart1200of a patient, according to an embodiment. The LIMD1000is implanted entirely within the heart1200. The LIMD1000is configured to place the housing1002in the lower region of the right atrium1202between the OS and the IVC1204with the securing helix1008in the ventricular vestibule1206to provide ventricular pacing and sensing. The LIMD1000is further configured such that the dual-loop IC device extension1010extends upward in the right atrium1202toward and into the SVC1210. The dual-loop IC device extension1010is configured (length-wise and shape-wise) such that the inner loop1014may be implanted in the upper region of the right atrium1202near the junction of the right atrium1202and the SVC1210. As shown, the electrodes1018are compressed into inner walls of the heart1200proximate the junction of the SVC1210and the right atrium1202. As such, the inner loop1014in the right atrium is configured for right atrial pacing and sensing. When in its expanded state, the inner loop1014has an outer diameter greater than the inner diameter of the SVC1210.

As shown, the outer loop1016is secured within the heart1200such that the majority of the outer loop1016is positioned within the SVC1210to provide passive mechanical stabilization of the LIMD1000. When in its expanded state, the outer diameter of the outer loop1016is greater than the inner diameter of the SVC1210.

FIG. 13illustrates a LIMD1300, according to an embodiment. The LIMD1300is similar to the LIMD1000shown and described with respect toFIG. 10, except that the LIMD1300includes a stabilizing loop member having a single loop1302connected to a housing1304through a linear beam1306. Alternatively, instead of using a linear beam, the single loop1302may connect directly to the housing1304. A securing helix1320extends from a base of the housing1304. Electrodes1310are positioned on outer portions of the loop1302, as discussed above, and a radio marker1312may also be positioned on the loop1302. The single loop1302anchors the LIMD1300within a local chamber of the heart, such as the right atrium.

FIG. 14illustrates the LIMD1300implanted within a heart1400of a patient, according to an embodiment. The housing1304is contained within the right atrium1402. The single loop1302is secured within the SVC1404such that the electrodes1310are compressed into inner walls of the SVC1404. The securing helix1320is anchored into the tissue of the right atrium1402, as discussed above.

As shown inFIGS. 12 and 14, embodiments provide an LIMD that may be contained within the right atrium such that the housing is entirely within the right atrium and the IC device extension is passively secured within the SVC and/or a junction of the SVC and right atrium. Alternatively, the LIMD may be contained within any other local chamber. For example, the housing may be secured within the right ventricle, while the IC device extension is passively secured within the SVC and/or a junction of the SVC and right atrium.

As explained above, embodiments provide a LIMD that is compact and configured to be retained within a chamber of the heart. Embodiments herein utilize an intra-cardiac implantable medical device having securing IC device extension that is pre-formed into planar disc-shaped segments, such as loops. The IC device extension is coupled to a housing of the LIMD. The LIMD is configured to be positioned within a local chamber of the heart, with the IC device extension extending into, and being passively anchored within, the SVC, for example. For example, the housing of the LIMD may be completely contained within the right atrium of the heart.

Optionally, droplets or small amounts of a steroid may be added at select points along the IC device extension and LIMD to promote tissue growth.