Patent Description:
Cardiac therapy can be provided by some implantable medical devices, such as cardiac pacemakers or implantable cardioverter defibrillators, which may deliver therapeutic electrical stimulation to a heart of a patient via electrodes of one or more implantable leads. Therapeutic electrical stimulation may be delivered to the heart in the form of pulses or shocks for pacing, cardioversion, or defibrillation. In some cases, implantable medical devices may sense intrinsic depolarizations, or intrinsic activations, of the heart and control the delivery of therapeutic stimulation to the heart based on the sensed intrinsic activations,.

Cardiac resynchronization therapy (CRT) is one type of therapy that is delivered by some implantable medical devices. CRT may help enhance cardiac output by resynchronizing the electromechanical activity of the ventricles of the heart. Ventricular desynchrony may occur, for example, in patients that suffer from congestive heart failure. CRT may change depending on various parameters, such as the presence of atrial fibrillation (AF). <CIT> relates to a system and method for controlling cardiac pacing mode switching. <CIT> relates to an adaptive cardiac resynchronization therapy. <CIT> relates to a multi-chamber intracardiac pacing system. <CIT> relates to pace mode switching in a ventricular pacemaker.

The present invention provides an implantable medical system according to independent claim <NUM>.

The dependent claims define embodiments and preferred features of the present invention.

The techniques of this disclosure generally relate to cardiac therapy systems and exemplary methods that utilize mode switching to administer different sensing and pacing modes, for example, during CRT based on the presence of AF. In particular, mechanical activity may be used to confirm electrical activity that indicates the presence of AF. In some embodiments, the signal from a motion sensor may be used to confirm whether one or both atria are in AF or whether P-wave detection parameters should be adjusted, such as detection sensitivity parameters or P-wave blanking periods.

In one aspect, the present disclosure provides an implantable medical system including: a first electrode to sense electrical activity of one or both ventricles of a patient's heart or to deliver cardiac therapy to one or both ventricles of the patient's heart; a second electrode to sense electrical activity of one or both atria of the patient's heart; a motion sensor to sense mechanical activity of the patient's heart; and a controller operably coupled to the first electrode, second electrode, and the motion sensor. The controller is configured to: switch between a dual-chamber sensing mode to deliver pacing based on sensing electrical activity of at least one atrium and at least one ventricle of the patient's heart and a single-chamber sensing mode to deliver pacing based on sensing electrical activity of only one or both ventricles of the patient's heart; deliver pacing to at least one of the ventricles of the patient's heart using the first electrode in the dual-chamber sensing mode; determine whether the electrical activity of one or both atria sensed by the second electrode is indicative of atrial fibrillation; in response to determining that the electrical activity of one or both atria is indicative of atrial fibrillation, determine whether mechanical activity of the patient's heart sensed by the motion sensor represents atrial contraction; and in response to determining that the mechanical activity of the patient's heart does not represent the atrial contraction, deliver inhibited pacing using the first electrode in the single-chamber sensing mode.

In another aspect, the present disclosure provides an exemplary method including:
delivering pacing to at least one of the ventricles of a patient's heart in a dual-chamber sensing mode to deliver pacing based on sensing electrical activity of at least one atrium and at least one ventricle of the patient's heart; determining whether electrical activity of one or both atria of the patient's heart is indicative of atrial fibrillation; in response to determining that the electrical activity of one or both atria is indicative of atrial fibrillation, determining whether mechanical activity of the patient's heart represents an atrial contraction; and in response to determining that the mechanical activity of the patient's heart does not represent the atrial contraction, delivering inhibited pacing to at least one of the ventricles of the patient's heart in a single-chamber sensing mode to deliver pacing based on sensing electrical activity of only one or both ventricles of the patient's heart.

In yet another aspect, the present disclosure provides an implantable medical system including: a first medical device having a housing implantable in at least one of the ventricles of a patient's heart. The first medical device includes at least one electrode to sense electrical activity of at least one of the ventricles or to deliver cardiac therapy to at least one of the ventricles of the patient's heart, and at least one motion sensor to sense mechanical activity of the patient's heart. The system further includes a second medical device in operative communication with the first medical device having at least one electrode to sense electrical activity of one or both atria of the patient's heart and a controller. The controller is configured to: switch between a dual-chamber sensing mode to deliver pacing based on sensing electrical activity of at least one atrium and at least one ventricle of the patient's heart and a single-chamber sensing mode to deliver pacing based on sensing electrical activity of only one or both ventricles of the patient's heart; deliver pacing to at least one of the ventricles of the patient's heart in the dual-chamber sensing mode; determine whether the electrical activity of one or both atria sensed by the second medical device is indicative of atrial fibrillation; in response to determining that the electrical activity of one or both atria is indicative of atrial fibrillation, determine whether mechanical activity of the patient's heart sensed by the first medical device represents the atrial contraction; and in response to determining that the mechanical activity of the patient's heart does not represent the atrial contraction, deliver inhibited pacing to at least one of the ventricles of the patient's heart in the single-chamber sensing mode.

The present disclosure relates to cardiac therapy and particularly relates to CRT. Some types of CRT may utilize mode switching, such as switching between different types of sensing and pacing modes, in response to a particular condition of the patient's heart. For example, some cardiac therapy systems may be configured to switch from a VDD/DDD mode to a VVI mode upon detecting AF.

Some cardiac therapy systems are implanted in only some regions, or chambers, of the heart. Such cardiac therapy systems may utilize far-field sensing techniques to detect activity in other regions of the heart. During CRT of a patient's heart, P-waves (which may also be referred to as atrial P-waves) may be sensed by a cardiac therapy system and used to trigger pacing after a predetermined atrioventricular (AV) delay, for example, in VDD/DDD sensing and pacing modes.

Using far-field sensing techniques to accurately sense P-waves may be more challenging than using near-field sensing techniques due to the relatively smaller size, such as magnitude or amplitude, of far-field P-waves compared to near-field P-waves and possible sources of noise. Atrial fibrillation may even further reduce the size of the far-field P-wave, which may compound the challenge of using far-field sensing techniques to detect P-waves.

The present disclosure provides cardiac therapy systems and methods that utilize mode switching to administer different sensing and pacing modes during CRT based on the presence of AF. In particular, mechanical activity may be used to confirm electrical activity that indicates the presence of AF. In some embodiments, the signal from a motion sensor may be used to confirm whether one or both atria are in AF or whether P-wave detection parameters should be adjusted, such as detection sensitivity parameters or P-wave blanking periods.

For example, when far-field P-waves are not detected, mechanical activity may be used to determine whether the patient's heart is in AF based on concomitant measurements. In particular, cardiac therapy systems may measure mechanical activity using a motion sensor to facilitate the determination of whether the patient's heart is in AF. Based on the AF determination, the system may be configured to mode switch or adjust P-wave sensitivity levels to better detect far-field P-waves when the patient's heart is not in AF.

As used herein, the term "or" is generally employed in its inclusive sense, for example, to mean "and/or" unless the context clearly dictates otherwise. The term "and/or" means one or all of the elements or a combination of at least two of the elements.

The drawings of the present disclosure depict one or more aspects described in this disclosure. However, other aspects not depicted in the drawings also fall within the scope of this disclosure. Like numbers may be used in the figures to refer to like components, steps, or other elements. However, the use of a reference character to refer to an element in a given figure is not intended to limit the element in another figure labeled with the same reference character, and vice versa, the use of different reference characters to refer to elements in different figures is not intended to indicate that the differently referenced elements cannot be the same or similar.

<FIG> is one example of a cardiac therapy system <NUM> in use with a patient <NUM>. The systems, devices, and techniques described in this disclosure provide for mode switching that may be robust enough for use with far-field sensing, for example, of atrial activation. In general, the system <NUM> may include one or more implantable medical devices (IMDs) to carry out cardiac therapy with mode-switching capability. Each IMD may be configured to detect electrical activity in one or more chambers of the patient's heart <NUM>. One or more IMDs may be used to detect the ventricular electrical activity, atrial electrical activity, and mechanical activity of one or more chambers. In particular, one or more electrodes may be used to sense, or detect, electrical activity, and one or more motion sensors may be used to sense, or detect, mechanical activity.

The one or more IMD's of the system <NUM> may include leadless or leaded IMDs. As used herein, a "leadless" device refers to a device being free of a lead extending out of the patient's heart <NUM>. In other words, a leadless device may have a lead that does not extend from outside of the patient's heart <NUM> to into the inside of the patient's heart. Some leadless devices may be introduced through a vein, but once implanted, the device is free of, or may not include, any transvenous lead and may be configured to provide cardiac therapy without using any transvenous lead. In one example, a leadless device implanted in the left ventricle (LV), in particular, does not use a lead to operably connect to an electrode in the LV when a housing of the device is positioned in the LV.

The system <NUM> may include one or more intracardiac IMDs. As used herein, an "intracardiac" device refers to a device configured to be implanted entirely within the heart <NUM>. An intracardiac IMD may include a leadlet, which does not extend out of the patient's heart <NUM>.

A first electrode of the system <NUM> may be configured to sense electrical activity of one or both ventricles (left, right, or both) of the patient's heart <NUM> or to deliver cardiac therapy to the particular ventricle of the patient's heart. A second electrode of the system <NUM> may be configured to sense electrical activity of an atrium of the patient's heart <NUM>. In some cases, the second electrode may also be configured to deliver cardiac therapy to the particular atrium of the patient's heart <NUM>.

One or more leadless electrodes may be coupled to the housing of an IMD. An IMD having only leadless electrodes may be described as a leadless IMD. As used herein, a "leadless" electrode refers to an electrode operably coupled to a device being free of a lead, or without using a lead, extending between the electrode and the housing of the device. In some embodiments, the first medical device <NUM> make take the form similar to a leadless MICRA™ available from Medtronic plc, of Dublin, Ireland, implanted in the LV.

A motion sensor of the system <NUM> may be configured to sense mechanical activity of the patient's heart <NUM>. In some cases, the motion sensor may be configured to sense at least mechanical activity of one or both atria (left, right, or both) of the patient's heart <NUM>. The motion sensor used may be the same as or similar to the motion sensor <NUM> described with respect to <FIG>.

A controller of the system <NUM>, which may include processing circuitry, may be operably coupled to one or more of the electrodes and to the motion sensor. The operable coupling may be made using a wired or wireless connection. Using the one or more electrodes and the motion sensor, the controller may be configured to deliver pacing to at least one of the ventricles of the patient's heart <NUM> using the first electrode based on dual-chamber sensing in a dual-chamber sensing mode or single-chamber sensing in a single-chamber sensing mode. The controller may also be configured to determine whether or not the electrical activity of at least one of the atria sensed by the second electrode is indicative of AF. The controller may also be configured to determine whether or not mechanical activity of the patient's heart <NUM> sensed by the motion sensor is indicative of AF, for example, for example, in response to determining that the electrical activity of one or both atria are indicative of AF. The mechanical activity may represent an atrial contraction. The atrial contraction of the patient may be referred to as an "atrial kick. " The absence of the atrial kick may be indicative of AF. Further, the controller may be configured to deliver inhibited pacing using the first electrode based on single-chamber sensing, for example, in response to determining that the mechanical activity of the patient's heart <NUM> is indicative of AF (or does not represent an atrial contraction or atrial kick).

In one embodiment, the system <NUM> may include only one intracardiac or leadless IMD implantable in the right atrium (RA) toward the LV (such as IMD <NUM> of <FIG>). The intracardiac or leadless IMD may include a first electrode implantable to sense near-field electrical activity of the LV of the patient's heart <NUM> or to deliver cardiac therapy to the LV of the patient's heart. The intracardiac or leadless IMD may also include a second electrode implantable to sense near-field electrical activity of the RA of the patient's heart <NUM> or to deliver cardiac therapy to the RA of the patient's heart.

In another embodiment, the system <NUM> may include only one intracardiac or leadless IMD implanted in the LV (such as first medical device <NUM> of <FIG>). The intracardiac or leadless IMD may include a first electrode implantable to sense near-field electrical activity of the LV of the patient's heart <NUM> or to deliver cardiac therapy the LV of the patient's heart. The intracardiac or leadless IMD may also include a second electrode implantable to sense far-field electrical activity of the RA of the patient's heart <NUM>.

In another embodiment, the system <NUM> may include one intracardiac or leadless IMD and one a leaded IMD (such as first medical device <NUM> and second medical device <NUM> of <FIG>). The intracardiac or leadless IMD may be implantable in the LV and include a first electrode to sense electrical activity of the LV of the patient's heart <NUM> or to deliver cardiac therapy to the LV of the patient's heart. The leaded IMD may include a second electrode to sense electrical activity of the RA of the patient's heart <NUM> or to deliver cardiac therapy to the RA of the patient's heart. The leaded IMD may be configured to communicate at least an atrial activation time to the intracardiac or leadless IMD.

The system <NUM> may include one or both of a first medical device <NUM> and a second medical device <NUM>. Any suitable medical devices may be used for the first medical device <NUM> and the second medical device <NUM>. For example, the first medical device <NUM> or the second medical device <NUM> may represent a defibrillator, a cardiac resynchronization pacer/defibrillator, or a pacemaker. The first medical device <NUM> and the second medical device <NUM> may be described as IMDs. In the illustrated embodiment, one or both of the first medical device <NUM> and the second medical device <NUM> may be configured to deliver pacing therapy, such as pacing therapy to the right and left ventricles of heart <NUM>, respectively, to provide CRT pacing.

In general, when two or more medical devices are used, the devices may be implanted in different chambers of the patient's heart <NUM>. As shown, the first medical device <NUM> is a leadless IMD implanted in the LV of the patient <NUM>, and the second medical device <NUM> is a leaded IMD having a leaded electrode implanted in each of the RA and the right ventricle (RV) of the patient's heart.

The first medical device <NUM> may be a leadless IMD internal to the heart <NUM> of the patient. The first medical device <NUM> may also be described as an intracardiac IMD. The first medical device <NUM> may be described as a left-side IMD implanted in the left side of the patient's heart <NUM>. In some embodiments, one or more IMDs similar to the first medical device <NUM> (not shown in <FIG>) may additionally or alternatively be implanted within other chambers of heart <NUM> or attached to the heart epicardially.

The first medical device <NUM> may be configured to sense electrical activity of the heart <NUM> and to deliver pacing therapy, such as CRT to the heart <NUM>. The first medical device <NUM> may be attached to an interior wall of the heart <NUM> via one or more fixation elements that penetrate the tissue. These fixation elements may secure the first medical device <NUM> to the cardiac tissue and retain an electrode (e.g., a cathode or an anode) on the housing of the first medical device in contact with the cardiac tissue, such as the endocardium or the myocardium. In addition to delivering pacing pulses, the first medical device <NUM> may be configured to sense or monitor electrical activity, in the form of one or more electrical signals, using the electrodes carried on the housing of the first medical device <NUM>. The electrical activity may be generated by cardiac muscle and indicative of depolarizations and repolarizations of the heart <NUM> at various times during the cardiac cycle.

The second medical device <NUM> may include a housing coupled to one or both of a ventricular lead <NUM> and an atrial lead <NUM>. In various embodiments, the second medical device <NUM> is an implantable cardioverter-defibrillator (ICD) capable of delivering pacing, cardioversion, and defibrillation therapy to the heart <NUM>. In particular, the second medical device <NUM> may be an extravascular ICD (EVICD) having an extravascular housing. The ventricular lead <NUM> and atrial lead <NUM> may be operably coupled, or electrically coupled, to a housing of the second medical device <NUM> and extend into the patient's heart <NUM>. The ventricular lead <NUM> may include electrodes (not labeled in <FIG>) positioned on the lead in the patient's RV for sensing ventricular electrogram (EGM) signals and pacing in the RV. The atrial lead <NUM> includes electrodes (not labeled in <FIG>) positioned on the lead in the patient's RA for sensing atrial EGM signals and pacing in the RA. The ventricular lead <NUM> or the atrial lead <NUM> may also include coil electrodes used to deliver cardioversion and defibrillation shocks. The second medical device <NUM> may also include one or more electrodes on its housing.

The first medical device <NUM>, the second medical device <NUM>, the ventricular lead <NUM>, or the atrial lead <NUM> may be used to acquire near-field or far-field cardiac EGM signals from the patient <NUM> and to deliver cardiac therapy in response to the acquired data. In some embodiments, the sensed electrical activity of one of the atria may be based on one or more far-field measurements sensed by the one of the electrodes coupled to the first medical device <NUM>, the second medical device <NUM>, the ventricular lead <NUM>, or the atrial lead <NUM>. For example, a housing-based electrode coupled to the first medical device <NUM>, a housing-based electrode coupled to the second medical device <NUM>, or the ventricular lead <NUM> may be used to detect a far-field atrial signal, such as a far-field P-wave signal. In another example, a far-field intrinsic ventricular activation signal may be detected using one or more devices or leads.

The second medical device <NUM> is shown as being configured for a dual-chamber IMD configuration, but other examples may include one or more additional leads, such as a coronary sinus lead extending into the RA, through the coronary sinus and into a cardiac vein to position electrodes along the LV for sensing LV EGM signals and delivering pacing pulses to the LV.

In some embodiments, the second medical device <NUM> may be configured for a single-chamber IMD system, or otherwise not include the atrial lead <NUM>. In such embodiments, near-field EGM signals of one or both atria may not be available to the cardiac therapy system <NUM>. The first medical device <NUM> or the second medical device <NUM> may be used to detect a far-field EGM signal of one or both atria.

Processing circuitry, sensing circuitry, and other circuitry configured for performing the techniques described herein with respect to the first medical device <NUM> and the second medical device <NUM> may be housed within a respective sealed housing. The housing (or a portion thereof) may be conductive so as to serve as an electrode for pacing or sensing, or as an active electrode during defibrillation. As such, the housing of some IMDs may be described as including a housing electrode, or a housing-based electrode.

In some examples, the first medical device <NUM> and the second medical device <NUM> may engage in wireless communication to facilitate such coordinated activity. The communication may be one-way communication or two-way communication. In some embodiments, wireless communication may utilize a distinctive, signaling, or triggering electrical pulse provided by an electrode of the first medical device <NUM> that conducts through the patient's tissue and is detectable by the second medical device <NUM>, or vice versa. Wireless communication may use a communication interface, which may include an antenna to provide electromagnetic radiation that propagates through patient's tissue and is detectable, for example, using a communication interface of the other IMD.

In various embodiments, one or both of the first medical device <NUM> and the second medical device <NUM> are configured to communicate wirelessly, or by wire, with an external device <NUM>.

The first medical device <NUM> or the second medical device <NUM> may transmit EGM signal data, cardiac rhythm episode data, or data regarding delivery of therapy to the external device <NUM>. In various embodiments, the external device <NUM> may be a computing device, e.g., used in a home, ambulatory, clinic, or hospital setting, to communicate via wireless, or wired, telemetry. The external device <NUM> may be coupled to a remote patient monitoring system, such as Carelink®, available from Medtronic plc, of Dublin, Ireland. The external device <NUM> may be, for example, a programmer, external monitor, or consumer device, such as a smart phone.

The external device <NUM> may be used to program commands or operating parameters into the first medical device <NUM> or the second medical device <NUM> for controlling the functioning of these devices. In general, the external device <NUM> may be used to interrogate these devices to retrieve data, including device operational data as well as physiological or neurological data accumulated in memory in either of these devices. The interrogation may be automatic, e.g., according to a schedule, or in response to a remote or local user command. One or more of these external devices may also be referred to as an "instrument" or as a group of instruments. The external device <NUM> may be included as part of a recharging system configured to recharge the battery or other power source provided within the first medical device <NUM> or the second medical device <NUM>.

The cardiac therapy system <NUM> may also include a transceiver <NUM> coupled to communicate wirelessly, or by wire, with the first medical device <NUM> or the second medical device <NUM>. In some embodiments, the transceiver <NUM> may be described as an access point that provides a communication link between the first medical device <NUM> and the second medical device <NUM>, such as a network. The transceiver <NUM> may use similar communication techniques as the other devices and may be included as part of a recharging system.

The first medical device <NUM> and the second medical device <NUM> may be configured cooperatively to coordinate their cardiac rhythm detection and treatment activities. In some embodiments, the second medical device <NUM> is operably coupled to the first medical device <NUM> to communicate an atrial activation time to the first medical device to deliver pacing from the first medical device based on the atrial activation time.

For example, leadless resynchronization pacing devices, such as the first medical device <NUM> implanted in the LV, may communicate with the second medical device <NUM>, or right-side implanted system or an extravascular system (e.g., EVICD). The second medical device <NUM> may be used to sense atrial electrical activity, which may be used to trigger the first medical device <NUM> to pace at a predetermined AV delay following an intrinsic atrial activation, or atrial sensed event (e.g., P-wave). When the second medical device <NUM> does not sense the atrial electrical activity directly and uses, for example, far-field P-wave sensing techniques, the P-waves may be harder to sense accurately during AF. The cardiac therapy system <NUM> may be configured to mode switch upon detecting AF, for example, from a VDD/DDD mode to a VVI mode. In such a case, concomitant measurements from may help confirm presence or absence of AF and accordingly help cardiac therapy system <NUM> to mode switch properly. In some embodiments, the first medical device <NUM> may include a motion sensor. Mechanical activity detected by the motion sensor may be used as a concomitant measurement to facilitate AF detection.

<FIG> shows one example of an intracardiac or leadless implantable medical device <NUM> and anatomical structures of the patient's heart <NUM> that may be used with cardiac therapy systems of the present disclosure. The device <NUM> may be the same or similar to first medical device <NUM> except that the medical device <NUM> is implanted from the triangle of Koch region in the RA into the LV instead of being implanted within the LV. One or more of the features described with respect to device <NUM> may also be used with the first medical device <NUM> or even a leaded IMD. For example, the device <NUM> may be used alone or in coordination with the second medical device <NUM> instead of, or in addition to, the first device <NUM>.

In other embodiments (not shown), IMD <NUM> may be replaced with a leaded device coupled to an implantable medical lead, which may be similar to lead <NUM> or lead <NUM>, and may be coupled to second IMD, such as device <NUM>, or may be coupled to an external device, such as device <NUM>. One example of a leaded device is described in <CIT>, entitled "Lead-in-lead systems and methods for cardiac therapy," which is incorporated herein by reference. A motion sensor <NUM> may be integrated into, for example, a distal end portion or distal tip, of the lead of the leaded device to detect mechanical activity of the heart instead of extrinsic motion. In some embodiments, the distal end portion or the distal tip of the lead may have a small piezoelectric sensor in the motion sensor <NUM> configured to detect myocardial motion.

The intracardiac IMD <NUM> may include a housing <NUM>. The housing <NUM> may define a hermetically sealed internal cavity in which internal components of the device <NUM> reside, such as a sensing circuit, therapy delivery circuit, control circuit, memory, telemetry circuit (or communication interface), other optional sensors, and a power source. The housing <NUM> may be at least partially formed from electrically conductive material. Additionally, or alternatively, the housing <NUM> may be formed at least partially from non-conductive material.

The housing <NUM> may be described as extending between a distal end region <NUM> and a proximal end region <NUM> in a generally cylindrical shape to facilitate delivery. The housing <NUM> may include a delivery tool interface member <NUM>, e.g., at the proximal end <NUM>, for engaging with a delivery tool during implantation of the device <NUM>. For example, the delivery tool interface member <NUM> may be used while the device <NUM> is advanced toward a target implant region <NUM> using a delivery catheter.

All or a portion of the housing <NUM> may function as an electrode during cardiac therapy, for example, in sensing and/or pacing. In the example shown, the housing-based electrode <NUM> is shown to circumscribe a proximal portion of the housing <NUM>. When the housing <NUM> includes (e.g., is formed from) an electrically conductive material, portions of the housing <NUM> may be electrically insulated by a non-conductive material, such as a coating, leaving one or more discrete areas of conductive material exposed to define the proximal housing-based electrode <NUM>. When the housing <NUM> includes (e.g., is formed from) a non-conductive material, an electrically conductive coating or layer may be applied to one or more discrete areas of the housing <NUM> to form the proximal housing-based electrode <NUM>. In other examples, the proximal housing-based electrode <NUM> may be a component, such as a ring electrode, that is mounted or assembled onto the housing <NUM>. The proximal housing-based electrode <NUM> may be electrically coupled to internal circuitry of the device <NUM>, e.g., via the electrically-conductive housing <NUM> or an electrical conductor when the housing <NUM> includes a non-conductive material.

In the example shown, the housing-based electrode <NUM> is located nearer to the housing proximal end region <NUM> than the housing distal end region <NUM> and may, therefore, be described as being a proximal housing-based electrode. In other examples, however, the housing-based electrode <NUM> may be located at other positions along the housing <NUM>, for example, relatively more distally than the position shown.

At the distal end region <NUM>, the device <NUM> may include a distal fixation and electrode assembly <NUM>, which may include one or more fixation members <NUM>, in addition to one or more dart electrodes <NUM> of equal or unequal length. The one or more dart electrodes <NUM> of the assembly <NUM> may be described as tissue-piercing electrodes. In other embodiments (not shown), the distal fixation and electrode assembly <NUM> may include a helical or spiral-shaped electrode. A dart electrode or a helix electrode may also be described as a tissue-piercing electrode.

The device <NUM> as depicted includes a single dart electrode <NUM> that may include a shaft <NUM> extending distally away from the housing distal end region <NUM> and may include one or more electrode elements, such as a tip electrode element <NUM> at or near the free, distal end region of the shaft <NUM>. The tip electrode element <NUM> may have a conical or hemispherical distal tip with a relatively narrow tip diameter (e.g., less than about <NUM> millimeter (mm)) for penetrating into and through tissue layers without using a sharpened tip or needle-like tip having sharpened or beveled edges.

The shaft <NUM> of the dart electrode <NUM> may be a normally straight member and may be rigid. In other embodiments, the shaft <NUM> may be described as being relatively stiff but still possessing limited flexibility in lateral directions (e.g., resilient or semi-rigid). The dart electrode <NUM> may be configured to pierce through one or more tissue layers to position the tip electrode element <NUM> within a desired tissue layer, e.g., the ventricular myocardium. As such, the length or height <NUM> of the shaft <NUM> may correspond to the expected pacing site depth. If a second dart electrode <NUM> is employed, its length or height may be unequal to the expected pacing site depth and may be configured to act as an indifferent electrode for delivery of pacing energy to the tissue.

The one or more fixation members <NUM> may be described as one or more "tines" having a normally-curved position. The tines may be held in a distally extended position within a delivery tool. The distal tips of tines may penetrate the heart tissue to a limited depth before elastically curving back proximally into the normally curved position (shown) upon release from the delivery tool.

In some examples, the distal fixation and electrode assembly <NUM> includes a distal housing-based electrode <NUM>. In the case of using the device <NUM> as a pacemaker for multiple-chamber pacing (e.g., dual- or triple-chamber pacing) and sensing, the tip electrode element <NUM> may be used as a cathode electrode paired with the proximal housing-based electrode <NUM> serving as a return anode electrode. Alternatively, the distal housing-based electrode <NUM> may serve as a return anode electrode paired with tip electrode element <NUM> for sensing ventricular signals and delivering ventricular pacing pulses. In other examples, the distal housing-based electrode <NUM> may be a cathode electrode for sensing atrial signals and delivering pacing pulses to the atrial myocardium in the target implant region <NUM>. When the distal housing-based electrode <NUM> serves as an atrial cathode electrode, the proximal housing-based electrode <NUM> may serve as the return anode paired with the tip electrode element <NUM> for ventricular pacing and sensing and as the return anode paired with the distal housing-based electrode <NUM> for atrial pacing and sensing.

As shown in this illustration, the target implant region <NUM> in some pacing applications is along the atrial endocardium <NUM>, generally inferior to the AV node <NUM> and the His bundle <NUM>. The dart electrode <NUM> may define the length or height <NUM> of the shaft <NUM> for penetrating through the atrial endocardium <NUM> in the target implant region <NUM>, through the central fibrous body <NUM>, and into the ventricular myocardium <NUM> without perforating through the ventricular endocardial surface <NUM>. When the length or height <NUM> of the dart electrode <NUM> is fully advanced into the target implant region <NUM>, the tip electrode element <NUM> may rest, or be positioned, within the ventricular myocardium <NUM>, and the distal housing-based electrode <NUM> may be positioned in intimate contact with or close proximity to the atrial endocardium <NUM>.

The device <NUM> (as shown) and the devices <NUM>, <NUM> may include a motion sensor <NUM>, or motion detector, which may be contained in the housing <NUM>. The motion sensor <NUM> may be used to monitor mechanical activity, such as atrial mechanical activity (e.g., an atrial contraction) and/or ventricular mechanical activity (e.g., a ventricular contraction). In some embodiments, the motion sensor <NUM> may be used to detect RA mechanical activity. A non-limiting example of a motion sensor <NUM> includes an accelerometer. In some embodiments, the mechanical activity detected by the motion sensor <NUM> may be used to supplement or replace electrical activity detected by one or more of the electrodes of the device <NUM>. For example, the motion sensor <NUM> may be used in addition to, or as an alternative to, the proximal housing-based electrode <NUM>.

The mechanical activity detected by the motion sensor <NUM> may correspond to various heart sounds. In general, heart sounds are associated with mechanical vibrations of a patient's heart and the flow of blood through the heart valves and, thus, may be highly correlated with pressure gradients across heart valves and blood pressure. Heart sounds may be not only due to vibrations of and pressure within the heart, but may also be due to the entire cardiohemic system, e.g., blood, heart, great arteries, etc. Heart sounds may recur with each cardiac cycle and are separated and classified according to the activity associated with the vibration.

The first heart sound is referred to as "S <NUM>," and can be thought of as the vibration sound made by the heart during closure of the atrioventricular, or AV, valves, i.e., the mitral valve and tricuspid valve. The S1 sound can sometimes be broken down into the M1 sound component, from the closing of the mitral valve, and the T1 sound component, from the closing of the tricuspid valve. The second heart sound is referred to as "S2," and results from the closure of the semilunar valves, i.e., the pulmonary and aortic valves. The S2 heart sound can be thought of as marking the beginning of diastole. The S2 sound can also be broken down into component parts. The P2 sound component is from the closing of the pulmonary valve and the A2 sound component is from the closing of the aortic valve. The third and fourth heart sounds are referred to as "S3" and "S4," respectively, and can be conceptualized as related to filling of the ventricles during diastole. S3 is due to rapid filling of the ventricles and can occur when the ventricular wall is not relaxed when a large volume of blood flows into the ventricles from the atria. S4 is caused by blood rapidly filling into the ventricles from the atria due to atrial contraction.

The device <NUM> may be implanted such that the electrode <NUM> is positioned to sense electrical activity or deliver pacing therapy to a specific part of the patient's LV myocardium. For example, the electrode <NUM> may be implanted in the basal, septal, or basal-septal region of the LV.

<FIG> is a two-dimensional (2D) ventricular map <NUM> of a patient's heart (e.g., a top-down view) showing the LV <NUM> in a standard <NUM> segment view and the RV <NUM>. The map <NUM> includes a plurality of areas <NUM> corresponding to different regions of a human heart. As illustrated, the areas <NUM> are numerically labeled <NUM>-<NUM> (which, e.g., correspond to a standard <NUM> segment model of a human heart, correspond to <NUM> segments of the left ventricle of a human heart, etc.). Areas <NUM> of the map <NUM> may include basal anterior area <NUM>, basal anteroseptal area <NUM>, basal inferoseptal area <NUM>, basal inferior area <NUM>, basal inferolateral area <NUM>, basal anterolateral area <NUM>, mid-anterior area <NUM>, mid-anteroseptal area <NUM>, mid-inferoseptal area <NUM>, mid-inferior area <NUM>, mid-inferolateral area <NUM>, mid-anterolateral area <NUM>, apical anterior area <NUM>, apical septal area <NUM>, apical inferior area <NUM>, apical lateral area <NUM>, and apex area <NUM>. The inferoseptal and anteroseptal areas of the right ventricle <NUM> are also illustrated, as well as the right bunch branch (RBB) and left bundle branch (LBB).

In some embodiments, any of the tissue-piercing electrodes of the present disclosure may be implanted in the basal and/or septal region of the LV myocardium of the patient's heart. In particular, the tissue-piercing electrode may be implanted from the triangle of Koch region of the RA through the RA endocardium and central fibrous body.

Once implanted, the tissue-piercing electrode may be positioned in the target implant region <NUM> (<FIG>), such as the basal and/or septal region of the LV myocardium. With reference to map <NUM>, the basal region includes one or more of the basal anterior area <NUM>, basal anteroseptal area <NUM>, basal inferoseptal area <NUM>, basal inferior area <NUM>, mid-anterior area <NUM>, mid-anteroseptal area <NUM>, mid-inferoseptal area <NUM>, and mid-inferior area <NUM>. With reference to map <NUM>, the septal region includes one or more of the basal anteroseptal area <NUM>, basal anteroseptal area <NUM>, mid-anteroseptal area <NUM>, mid-inferoseptal area <NUM>, and apical septal area <NUM>.

In some embodiments, a tissue-piercing electrode of an implantable medical device, such as the device <NUM> of <FIG>, may be positioned in the basal septal region of the LV myocardium when implanted. The basal septal region may include one or more of the basal anteroseptal area <NUM>, basal inferoseptal area <NUM>, mid-anteroseptal area <NUM>, and mid-inferoseptal area <NUM>.

In some embodiments, the tissue-piercing electrode may be positioned in the high inferior/posterior basal septal region of the LV myocardium when implanted. The high inferior/posterior basal septal region of the LV myocardium may include a portion of at least one of the basal inferoseptal area <NUM> and mid-inferoseptal area <NUM>. For example, the high inferior/posterior basal septal region may include region <NUM> illustrated generally as a dashed-line boundary. As shown, the dashed line boundary represents an approximation of about where the high inferior/posterior basal septal region and may take somewhat different shape or size depending on the particular application. Without being bound by any particular theory, intraventricular synchronous pacing and/or activation may result from stimulating the high septal ventricular myocardium due to functional electrical coupling between the subendocardial Purkinje fibers and the ventricular myocardium.

Although particular devices are illustrated in <FIG>, such as device <NUM>, device <NUM>, and device <NUM>, the techniques of the present disclosure may be used with any suitable cardiac therapy system. Such suitable cardiac therapy systems generally include a controller.

<FIG> shows one example of cardiac therapy system that includes a controller <NUM> that may be used with various IMDs of the present disclosure. The controller <NUM> is operably coupled to a first electrode <NUM>, a motion sensor <NUM>, and a second electrode <NUM>. In particular, the controller <NUM> may include a processor <NUM>, a memory <NUM> operably coupled to the processor, and a communication interface <NUM>, or input/output interface, operably coupled to the processor and the first electrode <NUM>, the motion sensor <NUM>, and the second electrode <NUM>.

In general, various components of the controller <NUM> may be contained within the first medical device, the second medical device, another medical device, or any combination of these. In some embodiments, the first electrode <NUM> and the motion sensor <NUM> may be coupled to a housing of a first medical device. The second electrode <NUM> may be coupled to a housing of a second medical device that is separate from the first medical device. Although various operable connections are contemplated, in some embodiments, the first electrode <NUM> and the motion sensor <NUM> may be coupled to the communication interface <NUM> using a wired connection. The second electrode <NUM> may be coupled to the communication interface <NUM> using a wireless connection. An electrical signaling pulse delivered through the patient's body may also be used. In other embodiments, the first electrode <NUM>, the motion sensor <NUM>, and the second electrode <NUM> are coupled to the housing of a single IMD and coupled using a wired connection.

One or more of the components of devices described herein, such as controllers, interfaces, or sensors, may include a processor, such as a central processing unit (CPU), computer, logic array, or other device capable of directing data coming into or out of the respective device. In general, the controller may include one or more computing devices having memory, processing, and communication hardware. The controller may include circuitry used to couple various components of the controller together or with other components operably coupled to the controller. The functions of the controller may be performed by hardware and/or as computer instructions on a non-transient computer readable storage medium.

The processor of the controller may include any one or more of a microprocessor, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and/or equivalent discrete or integrated logic circuitry. In some examples, the processor may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, and/or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to the controller or processor herein may be embodied as software, firmware, hardware, or any combination thereof. While described herein as a processor-based system, an alternative controller could utilize other components such as relays and timers to achieve the desired results, either alone or in combination with a microprocessor-based system.

In one or more embodiments, the exemplary systems, devices, methods, and other functionality may be implemented using one or more computer programs using a computing apparatus, which may include one or more processors and/or memory. Program code and/or logic described herein may be applied to input data/information to perform functionality described herein and generate desired output data/information. The output data/information may be applied as an input to one or more other devices and/or methods as described herein or as would be applied in a known fashion. The controller functionality as described herein may be implemented in any manner known to one skilled in the art who has the benefit of this disclosure.

The cardiac therapy systems of the present disclosure may perform various functionality to perform mode switching. For example, cardiac therapy systems may detect AF and mode switch accordingly between or among a plurality of different pacing modes. In some embodiments, cardiac therapy systems may switch between a dual-chamber sensing mode (e.g., VDD or DDD) and a single-chamber sensing mode (e.g., VVI) depending on whether AF has been detected.

<FIG> shows one example of a method <NUM> of mode switching during cardiac therapy delivery that may be used with cardiac therapy systems of the present disclosure. In general, the method <NUM> facilitates mode switching between a VDD or DDD (VDD/DDD) mode and a VVI mode. Switching detection may be performed at any suitable rate. In some embodiments, the method <NUM> is performed for each cardiac cycle. In other embodiments, the method <NUM> is performed periodically (e.g., every <NUM> cardiac cycles, every <NUM> cardiac cycles, every <NUM> second, every <NUM> second, every <NUM> second, etc.).

VDD refers to a mode of the cardiac therapy system that is configured to sense atrial and ventricular activity, such as electrical activations or other events, and paces only one or both ventricles. This mode may be used, for example, for patient's with normal sinus rhythm but with an AV block. DDD refers to a mode of the cardiac therapy system that is configured to both sense activity and deliver pacing to both one or both atria and one or both ventricles as needed. VVI refers to a mode of the cardiac therapy system that is configured to pace one or both ventricles in response to an irregular intrinsic ventricular rhythm (for example, a ventricular rhythm falling below a threshold). The VDD/DDD mode may be described as a pacing mode using dual-chamber sensing. VVI mode may be described as a pacing mode using single-chamber sensing.

The method <NUM> may include delivering cardiac therapy in a VDD/DDD mode <NUM>. In some embodiments, sensing of P-waves and/or an atrial kick may be used to trigger pacing in a VDD/DDD mode. The P-wave may be indicative of an atrial activation or other event.

The method <NUM> may include determining whether the patient's heart is experiencing atrial fibrillation (AF) <NUM>. The determination may be made using monitored electrical or mechanical activity of the patient's heart or some combination of these measurements. In some embodiments, at least one measurement of electrical activity and at least one measurement of mechanical activity are used to determine whether the patient's heart is experiencing AF. The determination <NUM> may be made one or more times periodically or when triggered, for example, by detecting the absence of a near-field or far-field P-wave.

The method <NUM> may also include delivering cardiac therapy in a VVI mode <NUM> in response to determining that the patient's heart is experiencing AF. In response to determining that the patient's heart is not experiencing AF, the method <NUM> may return, or continue, to deliver cardiac therapy in a VDD/DDD mode <NUM>.

Far-field sensing of P-waves may be challenging for use in VDD/DDD modes because the P-wave amplitudes are small. The issue may be further complicated when the patient goes into AF as P-waves can become even smaller and may be even harder to pick up. Utilizing mechanical activity may facilitate confirmation of whether atrial activation has occurred. In particular, an atrial kick typically follows normal or paced atrial activation. The atrial kick may manifest as a distinguishable amplitude change on mechanical activity sensed, for example, by an integrated accelerometer.

<FIG> shows one example of a particular method that may be used to implement the method <NUM> of <FIG> to determine whether to deliver cardiac therapy in a VDD/DDD mode <NUM> or in a VVI mode <NUM>, especially when using far-field P-waves. As illustrated, the method <NUM> may include determining whether atrial activation has been detected <NUM>, which may provide an indication of whether AF may be present, while delivering cardiac therapy in a VDD/DDD mode <NUM> using dual-chamber sensing. One example of detecting atrial activation includes detecting the P-wave. The method <NUM> may continue to deliver cardiac therapy in a VDD/DDD mode <NUM>, for example, in response to a P-wave being detected in sensed electrical activity.

When a P-wave is not detected, there may be possible AF. In other words, the absence of a P-wave may be indicative of AF. The method <NUM> may withhold, or inhibit, pacing and detect intrinsic ventricular electrical activity <NUM>, for example, detecting intrinsic ventricular activation in response to determining that no P-wave has been detected.

Without detecting the P-wave, the system may determine whether a mechanical artifact of atrial activation is present, such as an atrial kick. The method <NUM> may determine a peak in a motion sensor signal within a time window <NUM>, for example, in response to determining the intrinsic ventricular electrical activity. In some embodiments, the peak in the motion sensor signal may indicate mechanical activity that corresponds to the S4 heart sound, which may be described as an A4 signal. Then, the method <NUM> may include determining whether an atrial kick has been detected <NUM>, for example, based on the peak and a threshold value. For example, the magnitude of the peak may be compared to the threshold value. In some embodiments, a small peak below a threshold value indicates that the P-wave was not, or was unlikely, to have been present in the far-field signal, for example, due to the patient's heart being in AF.

Without an atrial kick, the system may be able to determine that AF is not present. The method <NUM> may include switching to a VVI mode <NUM> using single-chamber sensing, for example, in response to determining that no atrial kick is detected. The next cardiac cycle may be paced in the VVI mode <NUM>. The method <NUM> may return, or continue, to determine whether a P-wave has been detected <NUM>. If a P-wave has returned, the method <NUM> may switch back to a VDD/DDD mode <NUM>.

When the atrial kick is detected without detecting the P-wave, the system may adjust P-wave detection techniques to facilitate fewer "false negatives" of P-wave detection or fewer "false positives" of possible AF detection. The method <NUM> may adjust a P-wave detection sensitivity or a blanking period <NUM>, for example, in response to determining that an atrial kick is detected. The P-wave detection sensitivity may also be described as an atrial activation threshold, such as based on magnitude of a peak where the P-wave is expected, to detect the P-wave. Sensitivities may be based off amplitudes of the electrical activity or differences in amplitude within a sensing time-window or time-gradients of amplitudes (e.g., a slope threshold). The method <NUM> may return, or continue, to deliver cardiac therapy in a VDD/DDD mode <NUM> using the adjusted sensitivity or blanking period. These adjustments to sensitivity or blanking may facilitate more accurate detection of a P-wave and, therefore, more accurate detection of AF using sensed electrical activity.

As used herein, the term "blanking period" refers to a time period or mode in which the device does not sense any electrical or mechanical activity, which may facilitate avoiding cross-interference or over sensing.

With various techniques being described, <FIG> shows one example of a plot <NUM> of an electrical activity signal and a mechanical activity signal upon which the various techniques may be used. The electrical activity signal <NUM> may be acquired in any suitable manner. In some embodiments the electrical activity signal <NUM> is an EGM signal. The mechanical activity signal <NUM> may be acquired in any suitable manner. In some embodiments, the mechanical activity signal <NUM> is an accelerometer signal from a motion sensor coupled to the patient's heart. In one example, the mechanical activity signal <NUM> is obtained from a motion sensor implanted in a ventricle or an atrium. The motion sensor may be coupled to a leadless or intracardiac IMD.

In one example, the electrical activity signal <NUM> may be obtained from a near-field signal detected by an electrode implanted in an atrium. In another example, the electrical activity signal <NUM> may be obtained from a far-field signal detected by an electrode implanted in a ventricle. The electrode used to detect the electrical activity signal <NUM> may be coupled to a leaded or leadless IMD, which may or may not be an intracardiac IMD.

The electrical activity signal <NUM> may or may not contain a P-wave <NUM>. If the P-wave <NUM> is present, the implantable medical system may continue to pace using VDD/DDD pacing or may switch to VDD/DDD pacing. If the P-wave <NUM> is not present, the implantable medical system may check to confirm whether the patient has AF. The P-wave may be detected using any suitable technique, such as detecting a peak and comparing the peak to a minimum magnitude threshold. Any suitable technique for P-wave sensing and detection may be used, for example, including techniques described in <CIT>, entitled "Far-field P-wave sensing in near real-time for timing delivery of pacing therapy in a cardiac medical device and medical device system.

In one example, if the P-wave <NUM> is not present, the system may inhibit pacing and, instead of pacing, may detect an intrinsic ventricular activation <NUM>, which may be represented as the start of a QRS complex on the electrical activity signal <NUM>. A timestamp of the intrinsic ventricular activation may be noted with a timestamp.

A corresponding mechanical activity signal <NUM> may be examined in a time window <NUM> that starts earlier than the intrinsic ventricular activation, which may immediately precede the timestamp. For example, a time window <NUM> may have a duration less than or equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In one example, the time window <NUM> is equal to <NUM>. The system may determine whether an atrial kick <NUM> (or an A4 signal corresponding to an S4 heart sound) is present in the mechanical activity signal <NUM> within the time window <NUM>.

The atrial kick <NUM> may be detected, for example, when the mechanical activity signal <NUM> exceeds a minimum magnitude threshold. The minimum magnitude threshold may be set, for example, based on a log of previous amplitudes of the atrial kick during VDD/DDD pacing. The minimum magnitude threshold may be based on a mean atrial kick amplitude and the standard deviation of the logged, or historical, amplitudes. In one example, the minimum magnitude threshold may be equal to the mean atrial kick amplitude minus <NUM> standard deviations.

If the atrial kick <NUM> is present, the system may continue to pace using VDD/DDD pacing or may switch to VDD/DDD pacing. In addition, one or both the sensitivity of P-wave detection or a blanking period associated with P-wave detection may be adjusted, for example, to facilitate minimizing false negative detections of the P-wave <NUM>. If the atrial kick <NUM> is not present, the system may switch to VVI pacing for the next cardiac cycle until, for example, one or both of the P-wave and the atrial kick are present in the respective signals.

Thus, various embodiments of the CARDIAC RESYNCHRONIZATION THERAPY MODE SWITCHING USING MECHANICAL ACTIVITY are disclosed.

The terms "coupled" or "connected" refer to elements being attached to each other either directly (in direct contact with each other) or indirectly (having one or more elements between and attaching the two elements). Either term may be modified by "operatively" and "operably," which may be used interchangeably, to describe that the coupling or connection is configured to allow the components to interact to carry out functionality.

As used herein, the term "configured to" may be used interchangeably with the terms "adapted to" or "structured to" unless the content of this disclosure clearly dictates otherwise.

Th singular forms "a," "an," and "the" encompass embodiments having plural referents unless its context clearly dictates otherwise.

The phrases "at least one of," "comprises at least one of," and "one or more of" followed by a list refers to any one of the items in the list and any combination of two or more items in the list.

As used herein, "have," "having," "include," "including," "comprise," "comprising" or the like are used in their open-ended sense, and generally mean "including, but not limited to. " It will be understood that "consisting essentially of," "consisting of," and the like are subsumed in "comprising," and the like.

Claim 1:
An implantable medical system comprising:
a first electrode (<NUM>, <NUM>, <NUM>) to sense electrical activity of one or both ventricles of a patient's heart (<NUM>) or to deliver cardiac therapy to one or both ventricles of the patient's heart;
a second electrode (<NUM>, <NUM>) to sense electrical activity of one or both atria of the patient's heart;
a motion sensor (<NUM>) to sense mechanical activity of the patient's heart; and
a controller operably coupled to the first electrode, second electrode, and the motion sensor, the controller configured to:
switch between a dual-chamber sensing mode to deliver pacing based on sensing electrical activity of at least one atrium and at least one ventricle of the patient's heart and a single-chamber sensing mode to deliver pacing based on sensing electrical activity of only one or both ventricles of the patient's heart;
deliver pacing to at least one of the ventricles of the patient's heart using the first electrode in the dual-chamber sensing mode;
determine whether the electrical activity of one or both atria sensed by the second electrode is indicative of atrial fibrillation;
in response to determining that the electrical activity of one or both atria is indicative of atrial fibrillation, determine whether mechanical activity of the patient's heart sensed by the motion sensor represents atrial contraction; and
in response to determining that the mechanical activity of the patient's heart does not represent the atrial contraction, deliver inhibited pacing using the first electrode in the single-chamber sensing mode.