Patent Description:
for left ventricular pacing, a lead may be inserted next to the left ventricle. and an implantable medical device (IMD) may output voltage pacing pulse to capture, e.g. depolarize, the left ventricle. In some examples, an IMD may use a quad-pole lead. e.g. with four electrodes and select one or more of the four electrodes to capture the left ventricle. Selecting which of the electrodes to provide the voltage-controlled pacing pulse may depend on which combination of electrodes provides the best outcome for the patient. <CIT> relates to evaluating therapeutic stimulation electrode configurations based on physiological responses.

In general, the disclosure describes capturing, cardiac tissue, such as the left ventricle (LV) using current steering techniques, and not voltage-controlled pacing, with a multi-pole lead implanted adjacent to the left ventricle. e.g. in a cardiac vein The techniques of this disclosure include current-controlled sources in an IMD to provide current regulation to the electrical current stimulation pulses (e.g., pacing pulses) allowing direct stimulation through multiple electrodes with known current delivery to the tissue, where known current delivery includes stimulation such that a clinician may configure the IMD to direct a desired current amplitude through a desired current path through tissue. Direct stimulation through multiple electrode contacts with known current amplitude may be beneficial because the clinician may achieve a desired medical outcome for the patient with improved control of stimulation therapy and reduced power consumption compared to other techniques.

Direct stimulation through multiple electrode contacts with known current amplitude, which may also be called current steering, may use a delivery current source coupled to a delivery electrode and a receiving current source coupled to a receiving electrode to steer the current to the desired tissue to be stimulated. In some examples, different electrode pairs may be paced sequentially or together. In other examples, two or more electrodes may be considered the "delivery electrodes" and two or more electrodes may be considered the "receiving electrodes.

In one example, the disclosure describes a medical system comprising: an implantable medical device coupled to a cardiac lead and configured to deliver pacing therapy to cardiac tissue of a heart via a plurality of electrodes of the cardiac lead. The implantable medical device comprises a first current source configured to output an electrical current stimulation pulse and a second current source configured to sink the electrical current stimulation pulse to capture a portion of the cardiac tissue as well as processing circuitry configured to: electrically connect the first current source to a first electrode of the plurality of electrodes to output the electrical current stimulation pulse to the cardiac tissue; and electrically connect the second current source to a second electrode of the plurality of electrodes to sink the electrical current stimulation pulse to the cardiac tissue.

In another, however non-claimed example, the disclosure describes a method comprising: electrically connecting a first current source to a first electrode of a cardiac lead comprising a plurality of electrodes configured to be implanted proximate to cardiac tissue to output an electrical current simulation pulse; electrically connecting a second current source to a second electrode of the plurality of electrodes to sink the electrical current simulation pulse; and delivering the electrical current stimulation pulse to tissue of the cardiac tissue via the first electrode and the second electrode to capture a portion of the cardiac tissue.

In another example, the disclosure is directed to a computer-readable medium containing instructions. The instructions may cause processing circuitry, e.g. a programmable processor to electrically connect a first current source to a first electrode of a plurality of electrodes to output an electrical current stimulation pulse to cardiac tissue; and electrically connect a second current source to a second electrode of the plurality of electrodes to sink the electrical current stimulation pulse. A cardiac lead comprising the plurality of electrodes is coupled to the implantable medical device and the implantable medical device is configured to deliver pacing therapy to the cardiac tissue of a heart via the plurality of electrodes of the cardiac lead. The implantable medical device comprises the first current source configured to output an electrical current stimulation pulse and the second current source configured to sink the electrical current stimulation pulse to capture a portion of the cardiac tissue.

The disclosure describes capturing cardiac tissue, for example, the left ventricle (LV), using current steering techniques with a multi-pole lead implanted near the heart, such as in a cardiac vein. Capturing cardiac tissue may refer to applying an electrical current stimulation pulse, or other pacing pulse to the cardiac tissue causing depolarization and contraction.

The techniques of this disclosure include current-controlled sources in an implantable medical device to provide current regulation to the electrical current stimulation pulses (i.e., pacing pulses) allowing direct stimulation through multiple electrodes with known current delivery to the tissue. In accordance with one or more examples described in this disclosure, the electrical stimulation pulses may be current stimulation pulses, and therefore, the pacing pulses may be referred to as electrical current stimulation pulses. For instance, the implantable medical device may include multiple current sources to output (e.g., source) and sink the electrical current stimulation pulses through electrodes, and processing circuity may select which electrodes to output and sink the electrical current stimulation pulses.

Current steering refers to techniques to selectively couple electrodes to different current sources to steer the path of the electrical current, and hence the electrical field generated by the electrical current. Current steering techniques may use a delivery current source coupled to a delivery electrode and a receiving current source coupled to a receiving electrode to steer the current to the desired tissue to be stimulated. In some examples, different electrode pairs may be paced sequentially or together. In other examples, two or more electrodes may be considered the "delivery electrode" and two or more electrodes may be considered the "receiving electrode.

The current steering techniques from within a cardiac vein of this disclosure may provide advantages over other pacing techniques. When compared to voltage-controlled pacing, which use a voltage-controlled source, the impedance of the electrodetissue interface at each active contact will dictate current flow in the tissue. In turn, while these voltage-controlled pacing may allow for simultaneous activation of multiple contacts at a single voltage level, the clinician may not be able to directly control current flow across the contacts. Moreover, using an intracardiac multi-pole (i.e., a multi-electrode) lead, for example within a cardiac vein, may provide precise selection of the cardiac tissue to be stimulated when compared to a current steering lead placed in other locations. In particular, field steering directs the energy to an optimal tissue location while avoiding undesirable areas (e.g. phrenic nerve).

The techniques of this disclosure may allow capture of the cardiac tissue using reduced energy pacing pulses when compared to other techniques. In some examples, by precisely targeting the cardiac tissue to be stimulated, an IMD of this disclosure may use a lower energy electrical current stimulation pulse, e.g. a reduced amplitude and/or pulse width, and cause depolarization and contraction of the targeted cardiac tissue. Reduced energy pulses may provide better outcomes for a patient, including increased battery longevity and therefore longer times between battery replacement or recharging. Battery replacement may require surgery to replace a device, therefore, reducing the number of replaced devices may reduce patient cost, inconvenience, and risk of infection.

<FIG> is a conceptual diagram illustrating an example system <NUM> for monitoring and treating cardiac events, which may include LV pacing using current steering according to the techniques of this disclosure. Example system <NUM> in <FIG>, may include an IMD <NUM>, such as an implantable cardiac pacemaker, implantable cardioverter/defibrillator (ICD), or pacemaker/cardioverter/defibrillator. IMD <NUM> connects to leads <NUM>, <NUM> and <NUM> and is communicatively coupled to external computing device <NUM>. IMD <NUM> senses electrical signals attendant to the depolarization and repolarization of heart <NUM>, e.g., a cardiac electrogram (EGM), via electrodes on one or more leads <NUM>, <NUM> and <NUM> or the housing of IMD <NUM>. IMD <NUM> may also deliver therapy in the form of electrical signals to heart <NUM> via electrodes located on one or more leads <NUM>, <NUM> and <NUM> or a housing of IMD <NUM>. The delivered therapy may be pacing, cardioversion and/or defibrillation pulses. IMD <NUM> may monitor EGM signals collected by electrodes on leads <NUM>, <NUM> or <NUM>, and based on the EGM signal, diagnose, and treat cardiac episodes.

Leads <NUM>, <NUM>, <NUM> extend into the heart <NUM> of patient <NUM> to sense electrical activity of heart <NUM> and/or deliver electrical stimulation to heart <NUM>. In the example shown in <FIG>, right ventricular (RV) lead <NUM> extends through one or more veins (not shown), the superior vena cava (not shown), and right atrium <NUM>, and into right ventricle <NUM>. Left ventricular (LV) lead <NUM> extends through one or more veins, the vena cava, right atrium <NUM>, and into the coronary sinus <NUM> to a region adjacent to the free wall of left ventricle <NUM> of heart <NUM>. Right atrial (RA) lead <NUM> extends through one or more veins and the vena cava, and into the right atrium <NUM> of heart <NUM>.

Lead <NUM> may be a multi-electrode, or multi-polar lead. In the example in which lead <NUM> includes four electrodes, lead <NUM> may be referred to as a quadripolar LV lead. To simplify <FIG>, only three electrodes are labeled, electrodes <NUM>, <NUM> and <NUM>. In other examples, lead <NUM> may include more or fewer electrodes. In some examples, LV lead <NUM> comprises segmented electrodes, e.g., in which each of a plurality of longitudinal electrode positions of the lead, includes a plurality of discrete electrodes arranged at respective circumferential positions around the circumference of lead.

In some examples, IMD <NUM> includes one or more housing electrodes, such as housing electrode <NUM>. Housing electrode <NUM> may be formed integrally with an outer surface of hermetically-sealed housing <NUM> of IMD <NUM> or otherwise coupled to housing <NUM>. In some examples, housing electrode <NUM> is defined by an uninsulated portion of an outward facing portion of housing <NUM> of IMD <NUM>. Other divisions between insulated and uninsulated portions of housing <NUM> may be employed to define two or more housing electrodes. In some examples, a housing electrode comprises substantially all of housing <NUM>. In other examples, an electrode may be included in header <NUM> of IMD <NUM> and be referred to as an indifferent electrode.

Housing <NUM> encloses a signal generator that generates therapeutic stimulation, such as cardiac pacing, cardioversion, and defibrillation pulses, as well as a sensing module for sensing electrical signals attendant to the depolarization and repolarization of heart <NUM>. Housing <NUM> may also enclose one or more processors coupled to a memory for storing the sensed electrical signals. Housing <NUM> may also enclose a telemetry module for communication between IMD <NUM> and external computing device <NUM>.

IMD <NUM> may be configured to sense electrical signals attendant to the depolarization and repolarization of heart <NUM> via electrodes of leads <NUM>, <NUM>, <NUM> and housing electrode <NUM>. IMD <NUM> may sense such electrical signals via any bipolar combination of electrodes of leads <NUM>, <NUM>, <NUM>. Furthermore, any of the electrodes may be used for unipolar sensing in combination with housing electrode <NUM>.

The illustrated numbers and configurations of leads <NUM>, <NUM> and <NUM> and electrodes are merely examples. Other configurations, i.e., number and position of leads and electrodes, are possible. In some examples, system <NUM> may include an additional lead or lead segment having one or more electrodes positioned at different locations in the cardiovascular system for sensing and/or delivering therapy to patient <NUM>. For example, instead of or in addition to intracardiac leads <NUM>, <NUM> and <NUM>, system <NUM> may include one or more leads not positioned within heart <NUM>. Some examples of other leads may include an epicardial lead, a subcutaneous lead, a substernal lead, and esophageal lead, and so on. In some examples, a combination of electrodes on an intracardiac lead, along with electrodes in other locations, may provide precise steering of stimulation energy to specific tissue.

In some examples, external computing device <NUM> takes the form of a handheld computing device, computer workstation or networked computing device that includes a user interface for presenting information to and receiving input from a user. A user, such as a physician, technician, surgeon, electro-physiologist, or other clinician, may interact with external computing device <NUM> to retrieve physiological or diagnostic information from IMD <NUM>. A user may also interact with external computing device <NUM> to program IMD <NUM>, e.g., select values for operational parameters of the IMD. External computing device <NUM> may include a processing circuitry configured to evaluate EGM signals transmitted from IMD <NUM> to external computing device <NUM>.

IMD <NUM> and external computing device <NUM> may communicate via wireless communication using any of techniques. Examples of communication techniques may include, for example, low frequency or radiofrequency (RF) telemetry Other techniques, such as BLUETOOTH, Medical Implant Communication System (MICS), and similar techniques. In some examples, external computing device <NUM> may include a programming head that may be placed proximate to the patient's body near the implant site for IMD <NUM> to improve the quality or security of communication between IMD <NUM> and external computing device <NUM>. In some examples, external computing device <NUM> may be located remotely from IMD <NUM> and communicate with IMD <NUM> via a network. External computing device <NUM> may also communicate with one or more other external devices using any one or more communication techniques, both wired and wireless, such as Ethernet, Wi-Fi, and similar techniques.

LV lead <NUM> is an example of an implantable LV lead comprising a plurality of electrodes, wherein the plurality of electrodes includes at least one bipolar electrode pair configured to sense a LV bipolar cardiac electrogram signal of tissue of the left ventricle <NUM> of heart <NUM> proximate the bipolar electrode pair. In some examples, IMD <NUM> comprises a signal generator configured to deliver cardiac pacing pulses to left ventricle <NUM> of heart <NUM> via at least one of the plurality of electrodes of LV lead <NUM>.

Pacing in the left ventricle may be helpful for patients with certain conditions, such as a bundle branch block causing an uncoordinated contraction of the heart or congestive heart failure (CHF) patients. In some examples, IMD <NUM> may deliver voltage-controlled pacing pulses to capture, e.g. depolarize, the left ventricle. The techniques of this disclosure include IMD <NUM> with circuitry and LV lead <NUM> configured to deliver current controlled pacing, e.g. electrical current stimulation pulses, to stimulate and capture the left ventricle. By using electrical current stimulation pulse and current steering techniques, an IMD of this disclosure may more precisely steer the electrical current stimulation pulses to the targeted cardiac tissue to ensure the heart contracts in a coordinated manner to efficiently pump blood for the patient.

In this disclosure, a selected pacing vector, e.g. between two or more electrodes of LV lead <NUM>, may cause a current path through the cardiac tissue between the selected electrodes. When the amplitude, or other characteristics of the pacing pulse, e.g. the electrical current stimulation pulse, satisfy the pacing threshold for the cardiac tissue in contact with the electrodes, the pacing pulse may cause depolarization of the cardiac tissue in and around the current path. In other words, the selected pacing vector may capture the selected portion of the cardiac tissue, which may conduct through the cardiac tissue to the rest of the left ventricle and cause a contraction. During implant, a clinician may select different pacing vectors and observe the results to determine which electrode selections, and which resulting current paths, provide the best outcome for the patient.

Pacing between two LV electrodes, e.g., between electrode <NUM> and <NUM> may be called bipolar pacing. Pacing between any one of the LV electrodes and housing electrode <NUM> may be called unipolar pacing. A bipolar stimulation arrangement, i.e., an arrangement in which an electrode, such as electrode <NUM> acts as an anode delivering current, and a second electrode e.g., <NUM> acts as a cathode receiving current, may provide stimulation fields that are small and have localized shapes. The small stimulation field is caused by the close proximity between the anodes and cathodes as compared to the sphere-like field created by a unipolar stimulation arrangement. A bipolar stimulation arrangement may produce a localized and tightly constrained stimulation. In this manner, a bipolar stimulation arrangement producing such a localized and tightly constrained stimulation field may be useful in specifically targeting one or more stimulation sites of a patient.

An example unipolar stimulation arrangement may be one in which housing electrode <NUM>, or some other electrode in the header or on the housing is configured as an anode and sources current. An electrode on another lead, such as RV coil, RV ring, RA tip, on RV lead <NUM> or one of electrodes <NUM>, <NUM> or <NUM> on LV lead <NUM> is configured as a cathode and sinks current. A unipolar configuration may be desirable for lower power consumption that results from the low impedance path through the tissue of patient <NUM>, the stimulation field produced by a unipolar stimulation arrangement may resemble a large sphere, in contrast to the localized field for a bipolar arrangement.

In other examples, multiple anodes and/or multiple cathodes on one or more leads may be used to create a stimulation field in multipolar stimulation arrangement. Combining aspects of a bipolar stimulation arrangement, with aspects of a unipolar stimulation arrangement may deliver to a user more localized stimulation while consuming less power than would be achievable using bipolar stimulation. For example, housing electrode <NUM> may be configured as an anode, electrode <NUM> also configured as an anode and electrode <NUM> configured as a cathode, receiving current. In some examples, housing electrode <NUM> and electrode <NUM> may be configured to deliver equal amounts of current, e.g., <NUM>% of the total current, while electrode <NUM> is configured to sink <NUM>% of the current. In other examples, the delivered current from each electrode may be unequal, e.g., <NUM>%-<NUM>%, <NUM>%-<NUM>% or any other combination. Note that processing circuitry of IMD <NUM> may configure any combination of electrodes as sources or sinks and any percentage of current sourced or sunk from each electrode. The above examples are just for illustration.

In this manner a user effectively shapes, focuses or steers a stimulation field. Steering a stimulation field may allow a user to transition between a unipolar stimulation arrangement and a bipolar (or multipolar) stimulation arrangement or between a bipolar (or multipolar) arrangement and a unipolar arrangement, permitting the user to select different weighted combinations of current delivered to one or more lead cathodes by the housing anode and lead anode. The user may stop the transition at a desired point to use both a housing anode and at least one lead anode. In some examples, a user may configure one or more electrodes as anode "shields" on the lead that are in proximity to the cathodes. For example, electrodes <NUM> and <NUM> may be configured as cathodes and electrode <NUM>, between electrodes <NUM> and <NUM>, may be configured as an anode shield.

<FIG> is a conceptual diagram illustrating an example multi-polar lead implanted in a heart. In the example of <FIG>, heart <NUM> and LV lead <NUM> correspond to heart <NUM> and LV lead <NUM> and connected to IMD <NUM> described above in relation to <FIG>. As described above in relation to <FIG>, LV lead <NUM> may include a plurality of electrodes, e.g. electrodes <NUM> - <NUM>, and may be placed in a cardiac vein near or on the left ventricle. Though shown with four electrodes in the example of <FIG>, LV lead <NUM> may include any number of electrodes. Although <FIG> describes a multi-polar lead implanted in a cardiac vein, in other examples, a multi-polar lead of this disclosure may be implanted in other regions proximal to heart <NUM>, such as the right ventricle, right atrium or other locations.

Any one or more of electrodes <NUM> - <NUM> may be configured as the output or high side electrodes, or as the sink or low side electrodes. In some examples, depending on the desired current path, one or more electrodes in RV lead <NUM>, RA lead <NUM>, housing electrode <NUM>, and indifferent electrode, or an electrode on a lead extension (not shown in <FIG>) may be configured as either the output or sink electrodes, in conjunction with any one or more LV lead electrodes, to steer current to the desired tissue to be stimulated. The output current may follow a current path between the output electrode(s) to the sink electrodes(s). The precise current path may depend on the conduction characteristics of the tissue between the output and sink electrodes. The clinician may select a pacing vector, e.g. between LV electrode <NUM> and LV electrode <NUM>, between LV electrode <NUM> and housing electrode <NUM>, or any other combination, such the current path that travels between the output and sink electrodes depolarizes the desired cardiac tissue.

The depolarization of the LV when paced may be different than intrinsic depolarization of the LV. For example, paced depolarization of the LV may generally progress from epicardial to endocardial tissue, and from the pacing site, while intrinsic depolarization may generally progress from endocardial to epicardial tissue, and from the Purkinje fibers.

In this disclosure, electrical capture occurs when a pacing stimulus, e.g. an electrical current stimulation pulse, leads to depolarization of the cardiac tissue and causes a contraction. A capture threshold is the minimum energy required to produce a depolarization of the paced chamber. The amount of energy in an electrical stimulation pulse may be controlled by, for example, a voltage magnitude, a current magnitude, a pulse width, pulse shape, and so on. In some examples, to find this minimum current setting, during initial implant, a clinician may set the pacing output above the patient's native heart rate, so that the chamber of interest (e.g. RV, LV, or atrium) is being paced continuously. The clinician may reduce the pacing amplitude until the pacing pulse no longer causes a contraction, e.g. a loss of capture. In some examples, the capture threshold for a given patient may change over time, e.g. based on the degree of dehydration, taking certain medications, blood sugar levels, and so on. In some examples, IMD <NUM> may be configured to perform a periodic, e.g. daily or weekly, test for the pacing threshold, for example by decreasing the pacing amplitude to a low setting, and stepping up the pacing amplitude until the electrical current stimulation pulse consistently causes depolarization and a contraction.

In some examples, the most distal electrode <NUM> may be placed in a phrenic nerve stimulation (PNS) region <NUM>. In some examples distal electrode <NUM> may be used in combination with one or more other electrodes to sense polarization and depolarization of the left ventricle. Pacing pulses that include electrode <NUM> may result in stimulation of phrenic nerve <NUM>, which may be uncomfortable for a patient because it may cause undesired contraction of the diaphragm, e.g. hiccups.

The current steering techniques of this disclosure may control specific regions of cardiac tissue that may be stimulated, which in turn may avoid causing stimulation in PNS region <NUM>. It should be understood that the example techniques are not limited to avoiding stimulating in PNS region <NUM>. In some examples, heart <NUM> may include a necrotic region <NUM>, that may have been caused by cardiac ischemia that has become a myocardial infarction. Although shown near the apex of the right ventricle in the example of <FIG>, a necrotic region <NUM> may occur in many locations on the heart, depending on where blood flow to the heart was reduced or blocked. Necrotic regions, like necrotic region <NUM>, may affect the ability of pacing stimulation pulses to capture the heart muscle and cause a contraction.

The current steering techniques of this disclosure may provide precise current paths through heart tissue to capture the left ventricle such that the left ventricular contraction efficiently pumps blood to the patient's arteries. For example, a contraction that starts near the apex and works toward the anterior portion of the heart may squeeze blood from the left ventricle more efficiently than a contraction that starts in a different location and works toward the apex. The location of the electrodes in LV lead <NUM> in cardiac vein <NUM> may provide more precise current paths that require less electrical energy when compared to electrodes placed in other locations, such as locations at a distance from the patient's heart, e.g. subcutaneous, internal thoracic vein, external skin electrodes or other locations.

In operation, a first electrode, e.g. electrode <NUM> may act as the delivery electrode and a second electrode, e.g. electrode <NUM>, and third electrode, e.g. electrode <NUM> as the receiving electrodes. In some examples, IMD <NUM> (not shown in <FIG>) may configure electrode <NUM> to output the electrical current stimulation pulse by connecting the delivery current source to electrode <NUM>. IMD <NUM> may connect the receiving (e.g. sink) current source to electrodes <NUM> and <NUM>. In some examples, IMD <NUM> may cause electrode <NUM> to output, e.g. deliver, the electrical current stimulation pulse at the same time, e.g., approximately simultaneously, by causing both electrodes <NUM> and <NUM> to sink the electrical current stimulation pulse. Therefore, the current path in this example will be from electrode <NUM> to electrodes <NUM> and <NUM>.

In other examples, IMD <NUM> may sequentially activate one or more electrodes. IMD <NUM> may cause electrode <NUM> to output the electrical current stimulation pulse simultaneously with causing electrode <NUM> to sink the electrical current stimulation pulse but pause before activating electrode <NUM> to also sink the electrical current stimulation pulse. In this manner, IMD <NUM> may direct the electrical current stimulation pulse through a current path through tissue between electrode <NUM> and electrode <NUM>, then redirect some electrical energy to a current path between electrode <NUM> and electrode <NUM>.

In other examples, IMD <NUM> may, at a first time, configure electrode <NUM> to output the electrical current stimulation pulse and the RV tip electrode (not shown in <FIG>) to sink the electrical current stimulation pulse. At a second time, e.g. within a few milliseconds of the first time, IMD <NUM> may configure electrode <NUM> to output the electrical current stimulation pulse and the can of IMD <NUM> (e.g. housing electrode <NUM>, not shown in <FIG>) to sink the electrical current stimulation pulse. In this manner IMD <NUM>, e.g. as configured by a clinician, may sequentially stimulate the LV cardiac tissue in two separate current paths, which for a particular patient, may efficiently capture the LV cardiac tissue and cause the desired depolarization and contraction. In a similar manner, any set of electrodes, e.g. the indifferent electrode, RV coil, RV ring, RA tip, epicardial or other leads not positioned within heart and so on, may be configured to either output or sink the electrical current stimulation pulse to select the desired current path with the desired current amplitude, pulse width, or other parameters to capture the LV cardiac tissue.

<FIG> is a two-dimensional (2D) ventricular map <NUM> of a patient's heart (e.g., a top-down view) showing the left ventricle <NUM> in a standard seventeen segment view and the right ventricle <NUM>. Ventricle-from-atrium (VfA) cardiac therapy uses an implantable medical device or system, as shown and described in <CIT>. The implantable medical device may include a tissue-piercing electrode implanted in the basal and/or septal region of the left ventricular myocardium of the patient's heart from the triangle of Koch region of the right atrium through the right atrial endocardium and central fibrous body. The device may include a right atrial electrode, a right atrial motion detector, or both. The device may be implanted completely within the patient's heart or may use one or more leads to implant electrodes in the patient's heart. The device may be used to provide cardiac therapy, including single or multiple chamber pacing, atrioventricular synchronous pacing, asynchronous pacing, triggered pacing, cardiac resynchronization pacing, tachycardia-related therapy, or conduction system pacing (e.g. left bundle branch pacing, right bundle branch pacing, Bundle of His pacing). A separate medical device may be used to provide some functionality for cardiac therapy, such as sensing, pacing, or shock therapy. Vfa pacing may be combined with the current steering techniques described above in relation to <FIG> and <FIG>.

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 left ventricular myocardium of the patient's heart. In particular, the tissue-piercing electrode may be implanted from the triangle of Koch region of the right atrium through the right atrial endocardium and central fibrous body.

Once implanted, the tissue-piercing electrode may be positioned in the target implant region, such as the basal and/or septal region of the left ventricular 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, the tissue-piercing electrode may be positioned in the basal septal region of the left ventricular 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 left ventricular myocardium when implanted. The high inferior/posterior basal septal region of the left ventricular 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.

<FIG> is a conceptual diagram illustrating an example configuration of a multi-polar cardiac lead. In the example of <FIG>, LV lead <NUM> includes electrodes <NUM>, <NUM>, <NUM> and <NUM> located proximate to a distal end of LV lead <NUM>. LV lead <NUM> includes electrodes <NUM>, <NUM>, <NUM> and <NUM> correspond to LV lead <NUM> and electrodes <NUM> - <NUM> described above in relation to <FIG> and <FIG>. As noted above, though the example of <FIG> illustrates a quadripolar lead to simplify the description, LV lead <NUM> may have any number of electrodes. The distal end of LV lead <NUM>, including electrodes <NUM>, <NUM>, <NUM> and <NUM>, is configured to be placed in or near LV tissue, e.g., within the coronary sinus or a cardiac vein reachable via the coronary sinus, the right ventricle, in subcutaneous tissue, in the esophagus, or other locations proximal to the heart, as described above in relation to <FIG>.

In the example of <FIG>, electrodes <NUM> and <NUM> are separated by an inter-electrode spacing 68A, electrodes <NUM> and <NUM> are separate by an inter-electrode spacing <NUM>. and electrodes <NUM> and <NUM> are separated by an inter-electrode spacing 68B. Inter-electrode spacings refer to the distance, e.g., measured in a direction substantially parallel to a longitudinal axis of lead <NUM>, from one electrode to another, e.g., center-to-center or edge-to-edge. In some examples, electrodes <NUM> and <NUM> may act as a bipolar electrode pair configured to sense a LV bipolar cardiac electrogram signal of tissue of the left ventricle <NUM> of heart <NUM> near electrodes <NUM> and <NUM>. The bipolar electrode pair may be referred to as a short-spacing bipolar electrode pair because of a relatively smaller inter-electrode spacing <NUM> between electrodes <NUM> and <NUM>. e.g., relative to a larger inter-electrode spacings 68A and 68B.

In the example of <FIG>, inter-electrode spacings 68A and 68B (collectively "inter-electrode spacings <NUM>") are relatively larger than inter-electrode spacing <NUM>. Inter-electrode spacings <NUM> may be the same as, or different than, each other.

The arrangement of electrodes <NUM> - <NUM> and the inter-electrode spacings <NUM> and <NUM> illustrated in <FIG> are one example. Other example LV leads that may be included in a system according to this disclosure may include a different arrangement of electrodes and inter-electrode spacings. For example, on some LV leads that may be included in a system according to this disclosure, a most proximal pair of electrodes, e.g., electrodes <NUM> and <NUM>, or a most distal pair of electrodes, e.g., electrode <NUM> and <NUM>, may have an inter-electrode spacing <NUM> and act as a bipolar pair of electrodes configured to sense a LV bipolar cardiac electrogram signal of tissue of the left ventricle <NUM> of heart <NUM> proximate the bipolar electrode pair. Some LV leads may include a plurality of electrodes having an inter-electrode spacing <NUM>, and thus configured to act as a bipolar pair of electrodes configured to sense a LV bipolar cardiac electrogram signal of tissue of the left ventricle <NUM> of heart <NUM> proximate the bipolar electrode pair. IMD <NUM>, described above in relation to <FIG>, may also be configured to sense LV activity using one or more of LV electrodes <NUM> - <NUM> in conjunction with housing electrode <NUM>, or any other electrode connected to IMD <NUM> (not shown in <FIG>). IMD <NUM> may also be configured to send current-controlled pacing pulses through any combination of electrodes to capture the left ventricle.

In some examples, the current regulated pacing approach of this disclosure may also be applied to other lead configurations and implant locations. For example, IMD <NUM> may target the His bundle or left bundle branch with a current regulated/steered field from a multiple pole lead (not shown in <FIG>). Other lead configurations such as a segmented lead may could provide additional field steering ability for cardiac pacing (not shown in <FIG>).

<FIG> is a block diagram illustrating an example configuration of an IMD, according to the techniques of this disclosure. IMD <NUM>, leads <NUM> - <NUM>, and housing electrode <NUM> of <FIG> correspond to IMD <NUM>, leads <NUM> - <NUM>, and housing electrode <NUM> described above in relation to <FIG>.

In the example of <FIG>, IMD <NUM> includes a processor <NUM>, memory <NUM>, signal generator <NUM>, sensing module <NUM>, telemetry module <NUM>. and one or more sensors <NUM>. Memory <NUM> may store computer-readable instructions that, when executed by processor <NUM>, cause IMD <NUM> and processor <NUM> to perform various functions attributed to IMD <NUM> and processor <NUM> herein. Memory <NUM> may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital or analog media.

Processor <NUM> may include processing circuitry such as any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discrete or analog logic circuitry. In some examples, processor <NUM> 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, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to processor <NUM> herein may be embodied as software, firmware, hardware, or any combination thereof Generally, processor <NUM> controls signal generator <NUM> to deliver stimulation therapy to heart <NUM> of patient <NUM> described above in relation to <FIG> according to a selected one or more of therapy programs or parameters, which may be stored in memory <NUM>. As an example, processor <NUM> may control signal generator <NUM> to deliver electrical pulses with the amplitudes, pulse widths, frequency, or electrode polarities specified by the selected one or more therapy programs or parameters.

Signal generator <NUM> is configured to generate and deliver electrical stimulation therapy to patient <NUM>. As shown in <FIG>, signal generator <NUM> is electrically coupled to electrodes <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM>, <NUM>, and <NUM>, e.g., via conductors of the respective leads <NUM>, <NUM>, and <NUM> and, in the case of housing electrode <NUM>, within housing <NUM>. described above in relation to <FIG>. For example, signal generator <NUM> may deliver pacing, defibrillation or cardioversion pulses to heart <NUM> via at least two of electrodes <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM>, <NUM> and <NUM>. In some examples, signal generator <NUM> delivers stimulation in the form of signals other than pulses such as sine waves, square waves, or other substantially continuous time signals. In some examples, the electrical stimulation therapy may be in the form of voltage-controlled pacing pulses. In other examples, signal generator <NUM> may also be configured to control which electrodes are configured to output the electrical current stimulation pulse, e.g. current controlled pacing, and which electrodes are configured to sink the electrical current stimulation pulse.

In some examples, signal generator <NUM> includes a switch module (not shown) and processor <NUM> may use the switch module to select, e.g., via a data/address bus, which of the available electrodes are used to deliver the electrical stimulation. The switch module may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple stimulation energy to selected electrodes. Electrical sensing module <NUM> monitors electrical cardiac signals from any combination of electrodes <NUM>, <NUM>, <NUM>, <NUM>-<NUM>, <NUM>, <NUM> and <NUM>. In some examples, sensing module <NUM> also includes a switch module which processor <NUM> may control to select which of the available electrodes are used to sense the heart activity, depending upon which electrode combination is used in the current sensing configuration.

As described above in relation to <FIG> and <FIG>, IMD <NUM> may include current controlled circuitry to deliver electrical current stimulation pulse using current steering techniques. In the example of <FIG>, signal generator <NUM> includes voltage pacing circuitry <NUM> and current pacing circuitry <NUM>. In some examples, processor <NUM> may control voltage pacing circuitry <NUM> of signal generator <NUM> to deliver voltage-controlled pacing pulses via RV lead <NUM>, RA lead <NUM>, housing electrode <NUM>, and/or an indifferent electrode (not shown in <FIG>). In some examples, processor <NUM> may control current pacing circuitry <NUM> of signal generator <NUM> to deliver current pulses using current steering techniques via one or more electrodes, e.g. electrodes <NUM> - <NUM> of LV lead <NUM>. In some examples, IMD <NUM> may be configured to deliver only voltage-controlled pacing pulses via RV lead <NUM> and RA lead <NUM>, and current-controlled pacing pulses via LV lead <NUM>. In other examples, signal generator <NUM>, e.g. using the switch module, may be configured to deliver current controlled pacing stimulation via any combination of electrodes.

In some examples, processor <NUM> or external computing device <NUM>, described above in relation to <FIG>, may execute one or more algorithms configured to map responses of the cardiac tissue of heart <NUM> to current controlled pacing stimulation, e.g. in the form of electrical current stimulation pulses. The one or more algorithms may be stored, for example at memory <NUM>, or a memory device at external computing device <NUM> and may provide information to a clinician on selecting electrode combinations and electrical current settings, such as amplitude, pulse width etc. that can capture the LV cardiac tissue with the least amount of electrical energy. One example algorithm may include VectorExpress™ LV automated test available from Medtronic, Inc. , of Minneapolis, MN. VectorExpress is programmer-based algorithm that may allow automated testing of clinician-selected pacing. The clinician may test a variety of LV pacing vectors, then choose the LV pacing vector with the appropriate capture threshold and impedance to ensure capture and maximize device longevity while avoiding phrenic nerve stimulation (PNS). Processor <NUM> or external computing device <NUM> may execute similar algorithms. In some examples, IMD <NUM> may store selected pacing vectors <NUM> at memory <NUM>.

In some examples, IMD <NUM> may pace electrode combinations together, e.g., approximately simultaneously. In other examples, IMD <NUM> may pace electrode combinations in sequence. In other words, some pacing vectors may be stimulated at the same time to capture the desired portion of the left ventricle. In other examples, some pacing vectors may be paced in sequence, e.g., separated in time by an interval. The interval of separation may be fractions of a second.

Sensing module <NUM> may include one or more detection channels, each of which may comprise an amplifier. The detection channels may be used to sense cardiac signals. Some detection channels may detect events, such as R-waves or P-waves, and provide indications of the occurrences of such events to processor <NUM>. One or more other detection channels may provide the signals to an analog-to-digital converter, for conversion into a digital signal for processing or analysis by processor <NUM> or external computing device <NUM>.

For example, sensing module <NUM> may comprise one or more narrow band channels, each of which may include a narrow band filtered sense-amplifier that compares the detected signal to a threshold. If the filtered and amplified signal is greater than the threshold, the narrow band channel indicates that a certain electrical cardiac event, e.g., depolarization, has occurred. Processor <NUM> may then use that detection in measuring frequencies of the sensed events.

In some examples, processor <NUM> may determine whether the patient's heart is contracting as expected based on the sensed events, or lack of a sensed event. For example, IMD <NUM> may be configured to sense a left ventricular contraction based on sensing whether or not the left ventricle depolarized at the expected time in the cardiac cycle. For example, the left ventricle of patient with a partial left bundle branch block (LBBB) may depolarize at the correct time in the cardiac cycle to indicate a coordinated heart contraction. When the signals from sensing module <NUM> indicated that the left ventricle fails to depolarize within the expected time window, processor <NUM> may cause signal generator <NUM> to deliver an electrical current stimulation pulse between two or more electrodes, based on the programmed configuration for a left ventricular pacing pulse, as described above in relation to <FIG>.

In one example, at least one narrow band channel may include an R-wave or P-wave amplifier. In some examples, the R-wave and P-wave amplifiers may take the form of an automatic gain controlled amplifier that provides an adjustable sensing threshold as a function of the measured R-wave or P-wave amplitude. Examples of R-wave and P-wave amplifiers are described in <CIT> and is entitled, "APPARATUS FOR MONITORING ELECTRICAL PHYSIOLOGIC SIGNALS," and is incorporated herein by reference in its entirety.

In some examples, sensing module <NUM> includes a wide band channel which may comprise an amplifier with a relatively wider pass band than the narrow band channels. Signals from the electrodes that are selected for coupling to the wide-band amplifier may be converted to multi-bit digital signals by an analog-to-digital converter (ADC) provided by, for example, sensing module <NUM> or processor <NUM>. Processor <NUM> may analyze the digitized version of signals from the wide band channel. Processor <NUM> may employ digital signal analysis techniques to characterize the digitized signals from the wide band channel to, for example, detect and classify the patient's heart rhythm.

Processor <NUM> may detect and classify the patient's heart rhythm based on the cardiac electrical signals sensed by sensing module <NUM> employing any of a variety of signal processing methodologies. For example, processor <NUM> may maintain escape interval counters that may be reset upon sensing of R-waves by sensing module <NUM>. The value of the count present in the escape interval counters when reset by sensed depolarizations may be used by processor <NUM> to measure the durations of R-R intervals, which are measurements that may be stored in memory <NUM>. Processor <NUM> may use the count in the interval counters to detect a tachyarrhythmia, such as ventricular fibrillation or ventricular tachycardia. A portion of memory <NUM> may be configured as a plurality of recirculating buffers, capable of holding series of measured intervals, which may be analyzed by processor <NUM> to determine whether the patient's heart <NUM> is presently exhibiting atrial or ventricular tachyarrhythmia.

In some examples, processor <NUM> may determine that tachyarrhythmia has occurred by identification of shortened R-R interval lengths. In some examples, processor <NUM> may detect a tachycardia rhythm when the interval length falls below <NUM> milliseconds (ms) and fibrillation when the interval length falls below <NUM>. These interval lengths are merely examples, and a user may define the interval lengths as desired, which may then be stored within memory <NUM>. In some examples, processor <NUM> may determine whether the shortened interval length is detected for a certain number of consecutive cycles, for a certain percentage of cycles within a running window, or a running average for a certain number of cardiac cycles.

In some examples, an arrhythmia detection method may include any suitable tachyarrhythmia detection algorithms. In one example, processor <NUM> may utilize all or a subset of the rule-based detection methods described in <CIT>, or in <CIT>et al. , entitled, "PRIORITIZED.

OF ARRHYTHMIAS," which issued on May <NUM>, <NUM>. <CIT>et al. and <CIT>et al. are incorporated herein by reference in their entireties. However, other arrhythmia detection methodologies may also be employed by processor 70in some examples. For example, EGM morphology may be considered in addition to or instead of interval length for detecting tachyarrhythmias.

In some examples, processor <NUM> may detect a treatable tachyarrhythmia, such as ventricular fibrillation (VF), based on the EGM, e.g., the R-R intervals and/or morphology (shape) of the EGM, and selects which therapy to deliver via, for example, signal generator <NUM>, to terminate the tachyarrhythmia. An example of therapy may include a defibrillation pulse of a specified magnitude. The detection of the tachyarrhythmia may include a number of phases or steps prior to delivery of the therapy, such as first phase, sometimes referred to as detection, in which a number of consecutive or proximate R-R intervals satisfies a first number of intervals to detect (NID) criterion, a second phase, sometimes referred to as confirmation, in which a number of consecutive or proximate R-R intervals satisfies a second, more restrictive NID criterion. Tachyarrhythmia detection may also include confirmation based on EGM morphology or other sensors subsequent to or during the second phase.

One or more sensors <NUM> may be optionally included in some examples of IMD <NUM>. Sensor <NUM> may include one or more accelerometers in some examples. Sensors <NUM> may additionally or alternatively include other sensors such as a heart sounds sensor, a pressure sensor, a temperature sensor, a flow sensor, or an O<NUM> saturation sensor. In some examples, sensors <NUM> may detect respiration via one or more electrodes.

Processor <NUM> may use the information obtained from activity sensor <NUM> to determine activity level, posture, blood pressure, blood flow, blood oxygen level, or respiratory rate, as examples. In some examples, this information may be used by IMD <NUM> to aid in the classification of an abnormal heart rhythm. In some examples, this information may be used by IMD <NUM>, or a user of external computing device <NUM>, to determine desired LV pacing locations and timings for delivery of cardiac resynchronization therapy (CRT). For example, blood pressure or flow metrics may indicate the effectiveness LV pacing locations, electrode selection, electrical current polarity, and timings in improving the performance of heart <NUM>.

In some examples, sensors <NUM> are located outside of the housing <NUM> of IMD <NUM>. Sensors <NUM> may be located on a lead that is coupled to IMD <NUM> or may be implemented in a remote sensor that wirelessly communicates with IMD <NUM> via telemetry module <NUM>. In any case, sensors <NUM> are electrically or wirelessly coupled to circuitry contained within housing <NUM> of IMD <NUM>.

Sensing module <NUM> may be configured to sense the LV bipolar electrogram signal during LV pacing, e.g., at times when the heart is paced, and depolarizes in response to the pacing rather than intrinsic conduction. Under the control of processor <NUM>, signal generator <NUM> delivers LV pacing to left ventricle <NUM> via one or more of the electrodes, e.g., electrode <NUM> or <NUM>, of LV lead <NUM>, or another implantable LV lead. In some examples, sensing module <NUM>, processor <NUM>, may digitize the LV bipolar electrogram signal.

The locations of the electrodes may be determined using various techniques, such as fluoroscopy or other imaging, or through measuring electrical potentials on the electrodes when exposed to an electrical field, e.g., generated by surface electrodes on patient <NUM>. As examples, the locations of the electrodes may be determined using the LocaLisa® system commercially available from Medtronic, Inc. , of Minneapolis, MN, or the EnSite NavX® system commercially available from St. Jude Medical, Inc. Processor <NUM> may receive such electrode location information, e.g., from such systems, via telemetry module <NUM>. In some examples, electrode location information <NUM> may be stored at memory <NUM>.

Telemetry module <NUM> includes any suitable hardware, firmware, software, or any combination thereof for communicating with another device, such as external computing device <NUM> (<FIG>). Under the control of processor <NUM>, telemetry module <NUM> may receive downlink telemetry from and send uplink telemetry to external computing device <NUM> with the aid of an antenna, which may be internal and/or external. In some examples, processor <NUM> may transmit cardiac signals, e.g., EGM signals produced by sensing module <NUM>. For example, processor <NUM> may transmit an LV bipolar cardiac electrogram signal to external computing device <NUM> or another external computing device via telemetry module <NUM>, e.g., to facilitate analysis of the signal by the external computing device.

<FIG> is a schematic diagram illustrating an example implementation of current-controlled pacing circuitry, according to one or more techniques of this disclosure. The example of <FIG> depicts LV pacing channels: channel A <NUM>, channel B <NUM>, channel C <NUM>, and channel N <NUM>. Each of the channels may connect to an electrode of LV lead <NUM>, described above in relation to <FIG>. For example, LV1 <NUM> may connect to electrode <NUM>, LV2 <NUM> may connect to electrode <NUM>, and so on. Although the example of <FIG> only depicts LV electrode channels, in other examples, similar current controlled pacing circuitry may connect to other electrodes of system <NUM>, described above in relation to <FIG>, such has housing electrode <NUM> or one or more electrodes of RV lead <NUM> (not shown in <FIG>). In some examples, IMD <NUM> may be configured to connect either current controlled pacing circuitry or voltage-controlled pacing circuitry to an electrode of system <NUM>, e.g. via a switching network. In some examples the IMD may be configured to bypass the current regulation portion of the circuit and deliver voltage controlled electrical stimulation pulses, e.g. generated by voltage pacing circuitry <NUM> of signal generator <NUM> includes as described above in relation to <FIG>. Current pacing circuitry <NUM>, described above in relation to <FIG>, may correspond to channels A- N depicted in <FIG>.

<FIG> also includes controller <NUM>, which is shown as operatively coupled to current sources Ihigh <NUM> and Ilow <NUM>. However, controller <NUM> may be considered as operatively coupled to each of the current sources, as well as all the switches in <FIG>, though only shown connected to current sources Ihigh <NUM> and Ilow <NUM> to simplify <FIG>. In some examples, controller <NUM> may also receive indications from a current source or a switch of <FIG>, such as switch status (open or closed), temperature of the current source, or some other status or indicator from the current source.

Controller <NUM> may configure each current source according to programmed pacing settings, which may be set up by the clinician during an initial implant of a medical device, such as IMD <NUM> described above in relation to <FIG> and <FIG>. Programmed pacing settings may include current pulse amplitude, pulse width, pulse shape, electrode configuration and other settings. In the example of <FIG>, controller <NUM> may correspond to a combination of processor <NUM> and signal generator <NUM>, described above in relation to <FIG>, but shown as a single block to simplify <FIG>.

For channel A <NUM>, in the example of <FIG>, input voltage from a pacing power supply of IMD <NUM>, Vsup 170A, connects to an input terminal of a first current source, Ihigh <NUM>. The output terminal of Ihigh <NUM> connects to electrode LV1 <NUM> via a lead, such as LV lead <NUM> through switch S1P <NUM>. Electrode LV1 <NUM> also connects to ground through recharge switch S1R <NUM> and to switch S2P <NUM> and recharge switch S2R <NUM> through capacitor <NUM>. Recharge switch S2R <NUM> connects to a reference voltage level, shown as ground in the example of <FIG>. Switch S2P <NUM> connects capacitor <NUM> to an input terminal of current source Ilow <NUM> and the output terminal of current source Ilow <NUM> connects to the same reference voltage level, which is shown as ground in <FIG>.

The circuit arrangement in the example of <FIG> is just one example implementation of a current controlled pacing source. In other examples, the recharge switches, e.g. recharge switch S1R <NUM> and S2R <NUM> may be replaced with current sources. In some examples, the circuits of each channel may have additional blocking capacitors or other components. As described above in relation to <FIG>, IMD <NUM> may include any number of channels that drive any number of electrodes on LV lead <NUM>.

In other examples, the circuit arrangement of <FIG> may include more or fewer components. For example, channel A <NUM> may include one or more additional switches, not shown in <FIG>, between electrode LV1 <NUM> and capacitor <NUM> to isolate the current controlled circuitry in examples in which an IMD is programmed to deliver voltage controlled pacing pulses through electrode LV1 <NUM>. In some examples, an IMD, such as IMD <NUM> may be configured to deliver current controlled electrical current stimulation pulses via an electrode such as electrode LV1 <NUM> at a first time and deliver a voltage controlled pulse via electrode LV1 <NUM> at a second time.

For channel B <NUM>, the input voltage from the pacing power supply, Vsup <NUM> connects to an input terminal of current source, Thigh <NUM>. The output terminal of Ihigh <NUM> connects to electrode LV2 <NUM> via a lead through switch S1P <NUM>. Electrode LV2 <NUM> also connects to ground through recharge switch S1R <NUM> as well as to switch S2P <NUM> and recharge switch S2R <NUM> through capacitor <NUM>. Recharge switch S2R <NUM> connects to the reference voltage level, shown as ground. Switch S2P <NUM> connects capacitor <NUM> to an input terminal of current source Ilow <NUM> and the output terminal of current source Ilow <NUM> connects to ground.

For channel C <NUM>, the input voltage from the pacing power supply, Vsup 170C connects to an input terminal of current source, Thigh <NUM>. The output terminal of Ihigh <NUM> connects to electrode LV3 <NUM> via a lead through switch S1P <NUM>. Electrode LV3 <NUM> also connects to ground through recharge switch S1R <NUM> as well as to switch S2P <NUM> and recharge switch S2R <NUM> through capacitor <NUM>. Recharge switch S2R <NUM> connects to the reference voltage level, shown as ground. Switch S2P <NUM> connects capacitor <NUM> to an input terminal of current source Ilow <NUM> and the output terminal of current source Ilow <NUM> connects to ground.

For channel N <NUM>, the input voltage from the pacing power supply, Vsup 170N connects to an input terminal of current source, Thigh <NUM>. The output terminal of Thigh <NUM> connects to electrode LV3 <NUM> via a lead through switch S1P <NUM>. Electrode LV3 <NUM> also connects to ground through recharge switch S1R <NUM> as well as to switch S2P <NUM> and recharge switch S2R <NUM> through capacitor <NUM>. Recharge switch S2R <NUM> connects to the reference voltage level, shown as ground. Switch S2P <NUM> connects capacitor <NUM> to an input terminal of current source Ilow <NUM> and the output terminal of current source Ilow <NUM> connects to ground. In some examples Vsup 170A- 170N may have the same magnitude. In other examples, each of Vsup 170A - 170N may be configured with a different voltage magnitude.

In operation, as described above in relation to <FIG>, processing circuitry of controller <NUM>, such as processor <NUM>, may control current pacing circuitry <NUM> of signal generator <NUM>, e.g. any one or more of channels A <NUM> to channel N <NUM>. In the example of <FIG>, channel N <NUM> is selected as the delivery, or high side channel. Channels A <NUM> and B <NUM> are selected as the receiving or low side channels. In this manner, IMD <NUM> may steer current to apply a stimulation pulse to only selected tissue of heart <NUM>, e.g. as selected by a clinician for a particular patient's condition and anatomy.

Controller <NUM> may configure the selected current sources to output or sink the electrical current stimulation pulse according to the programmed pacing settings. For example, as described above in relation to <FIG>, processor <NUM> may retrieve the programmed pacing settings from memory <NUM>, which may include a current amplitude, pulse width, and other settings, and cause thigh <NUM> to generate a current-controlled pacing pulse according to the settings. Controller <NUM> may close switch S1P <NUM> at the appropriate time, based on, for example, the timing of other pacing pulses delivered through RA lead <NUM> and RV lead <NUM>, or based on measured activity of heart <NUM> sensed by sensing module <NUM>.

Controller <NUM> may cause switches S2P <NUM> and S2P <NUM> to close and set flow <NUM> and Ilow <NUM> to receive a portion of the energy delivered by Thigh <NUM>. In some examples, Ilow <NUM> and Ilow <NUM> may be configured to receive half of the current delivered by Ihigh <NUM>. In other examples, Ilow <NUM> and Ilow <NUM> may be configured to receive an unequal portion of the current to steer the current through the desired cardiac tissue. In other words, the various current sources and sinks of this disclosure are regulated (e.g. controlled). The regulated current sources and sinks forces the current to specifically split and/or combine between the electrodes, e.g. current steering. For example, Ilow <NUM> may be configured to receive <NUM>% of the delivered current and Ilow <NUM> may be configured to receive <NUM>% of the current delivered by Thigh <NUM>. In other examples, current may be split among other electrodes, e.g. <NUM>/<NUM>/<NUM>, or any other desired current split. In some examples, controller <NUM> may control the circuitry of <FIG> to deliver a biphasic pacing pulse, e.g. by delivering a first portion of the pulse in a first direction and a second portion of the pulse in a second direction.

<FIG> is a schematic diagram illustrating an example implementation of a current source according to one or more techniques of this disclosure. Circuit <NUM> may correspond to any of Thigh <NUM> - <NUM> and Ilow <NUM> - <NUM> described above in relation to <FIG>. Circuit <NUM> may also replace any of recharge switches S1R <NUM> - <NUM> or S2R <NUM> - <NUM> to provide current steering for the recharge portion of the pacing cycle. In other examples, a different configuration of a current regulation circuit may correspond to Thigh <NUM> -<NUM> and Ilow <NUM> -<NUM>.

Circuit <NUM>, in the example of <FIG>, is voltage to current conversion circuit using source degeneration on a metal oxide semiconductor field effect transistor (MOSFET). The drain of N-channel transistor M1 <NUM> connects to a supply voltage, Vsup <NUM>, which may correspond to Vsup <NUM> described above in relation to <FIG>. Resistor R1 <NUM> provides source degeneration by connecting the source of transistor M1 <NUM> to a reference voltage, such as ground. The output of amplifier <NUM> connects to the gate of transistor M1 <NUM> to control the magnitude and duration of lout <NUM>. Processor <NUM> controls Iout <NUM> by controlling input voltage Vin <NUM>, which is connected to the noninverting input of amplifier <NUM>. The inverting input connects to the source of transistor <NUM>. Processor <NUM> may control current pulse amplitude, pulse width, pulse shape, e.g., an increasing pulse, a decaying pulse or other pulse shape or other aspects of the stimulation therapy delivered to the cardiac tissue.

<FIG> is a flow chart illustrating an example mode of operation of the medical system of this disclosure. The blocks of <FIG> will be described in terms of <FIG>.

Processing circuitry, such as processor <NUM>, depicted in <FIG>, may cause a first current source to electrically connect to a first electrode of a ventricular lead comprising a plurality of electrodes. The ventricular lead may be configured to be implanted proximate to a left ventricle to output an electrical current simulation pulse (<NUM>). As described above in relation to <FIG>, signal generator <NUM> may close switch S1P <NUM> to electrically connect Thigh <NUM> to electrode LV-N <NUM>. In other examples, signal generator <NUM> may electrically connect a current source to an electrode separate from the electrodes on LV lead <NUM>, e.g. housing electrode <NUM>, an electrode on a lead extension, or some other electrode.

In some examples, processing circuitry <NUM>, may configure settings for the first current source to output the electrical current stimulation pulse. For example, processing circuitry <NUM> may adjust the voltage of Vsup <NUM>, shown in <FIG> and <FIG> and configure any control circuitry for Vin <NUM> to output an electrical current stimulation current pulse with a selected amplitude, pulse shape, pulse width and other characteristics. Processing circuitry <NUM> may select the first current source, e.g. any of current sources Ihigh <NUM> - <NUM> based on the desired pacing vector, e.g. as set by a clinician during the implant procedure for IMD <NUM>, or later office visit. For example, the clinician may set the pacing vector to avoid a necrotic region, e.g. necrotic region <NUM>, or to avoid stimulating phrenic nerve <NUM>, as described above in relation to <FIG>. In other examples, the clinician may place LV lead <NUM> to capture other tissue of heart <NUM>, such as the bundle of His or other portions of the bundle branches, Purkinje fibers, or other cardiac tissue to deliver a current-controlled pacing pulse and capture the left ventricle.

In other examples, the current steering techniques of this disclosure may deliver electrical stimulation therapy to, for example, atrial tissue, the right ventricle, or other cardiac tissue. In other words, the techniques of this disclosure may include the ability to stimulate various portions of the heart and from various intra- and extra-cardiac locations, as described above in relation to <FIG>. For example, a multiple electrode lead in the right ventricle may be configured to steer current towards the Bundle of His. In some examples, pacing stimulations from this location may provide an improved physiologic cardiac response than traditional right ventricle apex pacing. In other examples, the techniques of this disclosure may steer pacing current to cardiac tissue from electrode placements, such as temporary pacing from a lead placed in the esophagus to provide pacing and avoid unwanted nerve stimulation.

Processor <NUM> may cause signal generator <NUM> to electrically connect the other one or more current sources to the associated electrode (<NUM>). For example, signal generator <NUM> may close switch S2P <NUM> to electrically connect Ilow <NUM> to electrode LV2 <NUM>, e.g. through capacitor <NUM>. In this manner, medical system <NUM> may deliver the electrical current stimulation pulse to tissue of the left ventricle via at least the first electrode and the second electrode to capture, e.g., cause depolarization of, a portion of the left ventricle (<NUM>).

As described above in relation to <FIG>, processor <NUM> may configure one or more additional current sources to sink the electrical current stimulation pulse. In the example of a single current source, the second current source may be configured to receive all of the electrical energy delivered in the electrical current stimulation pulse. In the example of multiple current sources, the current sources may be configured to receive a portion of the electrical current stimulation pulse such that the stimulation pulse travels through the desired cardiac tissue using current steering.

In this manner the techniques of this disclosure provide advantages that those skilled in the art may not have appreciated. As described above in relation to <FIG>, current steering techniques using a plurality of electrodes, including electrodes in contact with left ventricular cardiac tissue, may provide more precise control of electrical stimulation pulses, when compared to other techniques. The more precise control may also provide an advantage in requiring less electrical energy in each pulse to reach the capture threshold for the target tissue and thus may extend the battery life for a device. By applying precise control to cardiac pacing, the techniques of this disclosure may provide a solution to a long-felt, but unsolved need.

The current steering techniques of this disclosure applied to left ventricular chamber pacing may represent an incremental improvement in a crowded art field. Incremental improvements may serve the public interest, e.g. in the example of this disclosure may result in improved coordinated contraction of a patient's heart, which may lead to more efficient blood flow. Also, reduced battery consumption and longer battery life may result in fewer surgeries for a patient to replace a device, and therefore reduced risk of infection or complications. For a rechargeable device, longer battery life may result in improved quality of life for a patient by reducing the amount of time spent recharging the device. In addition, current steering techniques applied to cardiac pacing, may not have been implemented, despite the advantages, which may indicate that the techniques of this disclosure may not have been obvious to those skilled in the art.

In one or more examples, the functions described above may be implemented in hardware, software, firmware, or any combination thereof. For example, the various components of <FIG> and <FIG>, such as controller <NUM>, ECS controller <NUM> and ADC <NUM> may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardwarebased processing unit.

The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in RAM or cache). By way of example, and not limitation, such computer-readable storage media, may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a compact disc ROM (CD-ROM), a floppy disk, a cassette, magnetic media, optical media, or other computer readable media. In some examples, an article of manufacture may include one or more computer-readable storage media.

Instructions may be executed by one or more processors, such as one or more DSPs, general purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry. Accordingly, the term "processor," as used herein, such as ECS controller <NUM>, may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein.

Claim 1:
A medical system comprising:
an implantable medical device coupled to a cardiac lead (<NUM>) and configured to deliver pacing therapy to cardiac tissue of a heart via a plurality of electrodes (<NUM>-<NUM>) of the cardiac lead, wherein the implantable medical device comprises a first current source (Ihigh, <NUM>) configured to output an electrical current stimulation pulse and a second current source (Ilow, <NUM>) configured to sink the electrical current stimulation pulse to capture a portion of the cardiac tissue; and
processing circuitry (<NUM>) configured to:
electrically connect the first current source to a first electrode (<NUM>, <NUM>) of the plurality of electrodes to output the electrical current stimulation pulse to the cardiac tissue; and
electrically connect the second current source to a second electrode (<NUM>, <NUM>) of the plurality of electrodes to sink the electrical current stimulation pulse to the cardiac tissue,
wherein a first channel of implantable medical device comprises the first current source, the first channel further comprising:
a first switch (S1P, <NUM>) configured to connect an output terminal of the first current source (Ihigh, <NUM>) to the first electrode (LV1, <NUM>, <NUM>);
a first recharge switch (S1R, <NUM>) configured to connect the first electrode to a reference voltage;
a second recharge switch (S2R, <NUM>) configured to connect the first electrode to the reference voltage through a capacitor (<NUM>);
a further current source (Ilow, <NUM>) comprising an input terminal and an output terminal wherein:
the output terminal of the further current source connects to the reference voltage,
the input terminal of the further current source is configured to connect to the first electrode through the capacitor and a second switch (S2P, <NUM>), and
the further current source is configured to sink current from the first electrode when the second switch is closed for conducting current.