Abstract:
This document discusses, among other things, techniques for generating and delivering a high voltage defibrillation shock using an implantable cardiac rhythm management device. An output energy delivery bridge can be programmed to provide desired shock vectors or polarities. A bootstrapped fully solid-state switch control voltage generation circuit is described. Automatic polarity or vector reconfiguration embodiments are described, such as in response to an unsuccessful attempt to convert the heart to a normal rhythm.

Description:
CLAIM OF PRIORITY 
     This application is a continuation of and claims the benefit of priority under 35 U.S.C. §120 to U.S. Pat. No. 8,116,865, filed on Dec. 11, 2008, which claims the benefit of priority under 35 U.S.C. §119(e) of U.S. Provisional patent application Ser. No. 61/007,637, filed on Dec. 13, 2007, the benefit of priority of each of which is claimed hereby, and each of which are incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     This patent application pertains generally to implantable cardiac rhythm management devices and more particularly, but not by way of limitation, to a programmable output energy delivery bridge. 
     BACKGROUND 
     Implantable medical devices include, among other things, cardiac rhythm management (CRM) devices such as pacers, cardioverters, defibrillators, cardiac resynchronization therapy (CRT) devices, as well as combination devices that provide more than one of these therapy modalities to a subject. For example, an implantable defibrillator/pacer is typically configured as an implantable defibrillator with backup pacing capability. Such devices are intended to serve patients having a history of previous ventricular or atrial tachyarrhythmia episodes. Ventricular arrhythmias include ventricular tachyarrhythmia (VT) and dangerous and life-threatening ventricular fibrillation (VF), referred to collectively herein as VT/VF. VT/VF is typically treated with antitachyarrhythmia pacing (ATP) therapy or a defibrillation countershock. 
     SUMMARY OF THE DISCLOSURE 
     Examples of techniques for generating and delivering a high voltage defibrillation shock using an implantable CRM device are disclosed herein. An output energy delivery bridge can be programmed to provide desired shock vectors or polarities in some examples. A bootstrapped fully solid-state switch control voltage generation circuit is described. Automatic polarity or vector reconfiguration embodiments are described according to some examples, such as in response to an unsuccessful attempt to convert the heart to a normal rhythm. 
     Example 1 includes an implantable medical device for delivering electric therapy to a heart of a patient comprising a voltage source, a first switch circuit, and a bridge circuit. The first switch circuit comprises a first node and a second node. The first node is coupled to a first terminal of the voltage source. The bridge circuit is coupled to the second node and to a second terminal of the voltage source. The bridge circuit is configured to connect to a first electrode and a second electrode. The first and second electrodes are configured to be implanted in or near the heart. The bridge circuit is also configured to deliver a first polarity energy to the heart using the first and second electrodes in a first mode and an opposite polarity energy to the heart using the first and second electrodes in a second mode. 
     In Example 2, the first switch circuit of Example 1 is optionally configured to control a timing of the delivery of the first polarity energy and the opposite polarity energy. 
     In Example 3, the implantable medical device of any of Examples 1-2 optionally includes the first electrode. The first electrode comprises a can electrode. 
     In Example 4, the implantable medical device of any of Examples 1-2 optionally includes the first electrode. The first electrode comprises an atrial coil electrode. 
     In Example 5, the implantable medical device of any of Examples 1-4 optionally include the second electrode. The second electrode comprises a ventricular coil electrode. 
     In Example 6, the bridge circuit of any of Examples 1-5 optionally includes a second switch circuit, a third switch circuit, a fourth switch circuit, and a fifth switch circuit. The second switch circuit is coupled to the second node and configured to be connected to the first electrode. The third switch circuit is coupled to the second node and configured to be connected to the second electrode. The fourth switch circuit is coupled to the second terminal and configured to be connected to the first electrode. The fifth switch circuit is coupled to the second terminal and configured to be connected to the second electrode. The bridge circuit is configured to deliver the first polarity energy when the third and fourth switch circuits are closed, and to deliver the opposite polarity energy when the second and fifth switch circuits are closed. 
     In Example 7, the second, third, fourth, and fifth switch circuits of Example 6 optionally comprise thyristors. 
     In Example 8, the second and fourth switch circuits of any of Examples 6-7 are optionally stacked substantially adjacent to each other. 
     In Example 9, the implantable medical device of any of Examples 6-8 optionally comprises a sixth switch circuit and a seventh switch circuit. The sixth switch circuit is coupled to the second node and configured to be connected to a third electrode. The third electrode is configured to be implanted in or near the heart. The seventh switch circuit is coupled to the second terminal and is configured to be connected to the third electrode. The bridge circuit is configured to deliver a third energy to the heart when the fourth and sixth switch circuits are closed, and to deliver a fourth energy to the heart when the second and seventh switch circuits are closed. 
     In Example 10, the bridge circuit of Example 9 is optionally configured to deliver the first polarity energy concurrently with the third energy. 
     In Example 11, the system of any of Examples 9-10 is optionally configured to deliver the opposite polarity energy concurrently with the fourth energy. 
     In Example 12, the switch circuit of any of Examples 1-11 optionally comprises a bipolar junction transistor (BJT). 
     In Example 13, the switch circuit of Example 12 optionally comprises a first control terminal, a drive voltage capacitor, a resistive element, a second diode, and a firing circuit. The first control terminal is coupled to a first diode, the first diode coupled to a third node. The drive voltage capacitor is coupled to the third node and to the second node. The resistive element is coupled to the third node and to a fourth node. The second diode is coupled to the second node and the fourth node. The firing circuit is coupled to the fourth node. A base of the BJT is coupled to the fourth node, a collector of the BJT is coupled to the first node, and an emitter of the BJT is coupled to the second node. The first control terminal is configured to provide a first controlled voltage to charge the drive voltage capacitor in a first stage. 
     In Example 14, the firing circuit of Example 13 optionally includes a second control terminal coupled to a second capacitor and to a gate of a field effect transistor (FET). The second capacitor is coupled to a drain of the FET and to the fourth node. A source of the FET is coupled to a ground voltage. The second control terminal is configured to provide a second controlled voltage to activate the BJT in a second stage. 
     Example 15 includes a method of delivering defibrillation energy to a heart of a patient using an implanted medical device including providing a voltage source, controlling a bridge circuit, and closing a switch circuit. The bridge circuit is coupled to a first terminal of the voltage source such that the bridge circuit is in a first mode. The switch circuit is coupled to a second terminal of the voltage source and to the bridge circuit, such that a first polarity energy is provided to the heart through the bridge circuit. 
     In Example 16, closing the switch circuit in Example 15 optionally includes comprises charging a drive voltage capacitor coupled to a gate and an emitter of a transistor. The transistor comprises a collector coupled to the second terminal of the voltage source and the emitter coupled to the bridge circuit. Closing the switch circuit also includes causing the drive voltage capacitor to provide a voltage to turn on the transistor. 
     In Example 17, the method of Example 15 optionally includes the switch circuit is a first switch circuit. Controlling a bridge circuit such that the bridge circuit is in a first mode in Example 15 optionally includes closing a second switch circuit coupled to the first terminal and to a first electrode implanted in or near the heart, and closing a third switch circuit coupled to a second electrode implanted in or near the heart and coupled to the first switch circuit. 
     In Example 18, controlling a bridge circuit such that the bridge circuit is in a first mode in Example 17 optionally includes closing a fourth switch circuit coupled to a third electrode implanted in or near the heart and coupled to the first switch circuit, 
     In Example 19, the method of any of Examples 15-18 optionally include opening the switch circuit, controlling the bridge circuit such that the bridge circuit is in a second mode, and closing the switch circuit such that an opposite polarity energy is provided to the heart through the bridge circuit. 
     In Example 20, the method of Example 19 optionally includes determining whether an arrhythmia is present in the heart before delivering the first polarity energy, and determining whether the arrhythmia remains present before delivering the opposite polarity energy. 
     Example 21 includes an implantable medical device. The implantable medical device includes a voltage source, means for controlling a bridge circuit. coupled to the voltage source, and means for closing a first switch circuit coupled to the voltage source and to the bridge circuit such that a first polarity energy is provided through the bridge circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
         FIG. 1  is an example of a high voltage charging circuit for generating a high defibrillation voltage in an implantable cardiac function management device. 
         FIG. 2  is a drawing of an example of an II-bridge output bridge approach for delivering energy from the high voltage capacitor to the desired defibrillation electrodes, which are implanted within the patient receiving the defibrillation therapy. 
         FIG. 3  is a schematic drawing illustrating generally an example of an alternative approach for delivering energy from the high voltage capacitor to the desired defibrillation electrodes, which are implanted within the patient receiving the defibrillation therapy. 
         FIG. 4  shows an example of the timing for a RV coil to RA coil shock. 
         FIG. 5  is a schematic drawing illustrating generally an example of a switch circuit, such as for implementing switch  305 G of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an example of a high voltage charging circuit 100 for generating a high defibrillation voltage (e.g., 40V-780V) in an implantable cardiac function management device. In this example, the high defibrillation voltage is stored on at least one high voltage capacitor  110  (“HV Cap”), and the particular defibrillation voltage depends on the desired shock energy (e.g., 0.1 J to 41 J).  FIG. 1  shows an example of how this can be accomplished by using a flyback converter to transfer energy from the battery  105  (e.g., at about 3V) to the high voltage capacitor. 
     In  FIG. 1 , when the switch  125  (e.g., n-channel MOSFET) is closed, the current through the primary winding of the flyback transformer ramps up to a maximum value (e.g., about 9 amps). While this current is building, the diode  115  is reverse-biased, so no current flows in the secondary winding of the transformer  120 . When the current reaches its desired peak value, the switch  125  is opened. When the switch  125  is opened, the output of the transformer  120  reverses, and the diode  115  becomes forward biased. The energy that was stored in the transformer  120  is then transferred to the high voltage capacitor  110 . This can be repeated (e.g., at 10 microsecond cycles) until the capacitor  110  is charged to the desired voltage. 
     In certain examples, one or more bypass capacitors can be placed in parallel with the battery  105  to help source the peak current when the switch  125  is closed In certain examples, the high voltage capacitor can be implemented as two separate capacitors in series, and each such series capacitor can be given its own secondary transformer winding. In certain examples, additional windings can be used, such as to supply the current used to meet the current demands associated with switching the switch in the primary winding path. 
       FIG. 2  is a drawing of an example of an H-bridge output bridge approach for delivering energy from the high voltage capacitor to the desired defibrillation electrodes, which are implanted within the patient receiving the defibrillation therapy. Examples of such defibrillation electrodes are denoted as “atrial coil”  220  and “ventricular coil”  225  in  FIG. 2 . If it is desired that the atrial coil  220  be positive during a first phase of a two-phase (biphasic) defibrillation waveform, then the switches labeled  205 A and  210 A can be closed for phase  1 . After phase  1 , the switches labeled  205 A and  210 A can be opened. Then, the switches labeled  205 B and  210 B can be closed for phase  2 , and then opened after phase  2 , In a “hot can” configuration, the implantable defibrillator housing (which is sometimes referred to as the “can”) provides a “can” electrode that is electrically connected (e.g., “shorted”) to the atrial electrode  220 . This can be accomplished, in certain examples, via a hard electrical connection (e.g., provided at manufacturing) in a header feed-through portion of the implantable defibrillator, where the atrial and ventricular coil electrodes are disposed on an intravascular leadwire that is electrically connected to the implantable defibrillator at the header. In a “cold can” configuration, the implantable defibrillator housing is not electrically connected to the atrial or ventricular coil electrodes. 
     One potential issue with the H-bridge configuration of  FIG. 2  occurs when, for a particular one of phase  1  or phase  2 , the top (“high side”) switch is implemented as a thyristor, and the bottom switch is implemented as a field-effect transistor. In such an example, the transistor switch is essentially used for electrode selection, and the high side thyristor switching characteristic determines the rise and fall times of the switching. However, because the thyristor switches abruptly, the switching rise and fall times are not necessarily well-controlled by the high-side thyristor, and this could lead to complicated secondary circuit design or layout considerations, such as to avoid or deal with the effect of parasitic reactances during such abrupt switching. 
       FIG. 3  is a schematic drawing illustrating generally an example of an alternative approach for delivering energy from the high voltage capacitor to the desired defibrillation electrodes, which are implanted within the patient receiving the defibrillation therapy. Examples of such defibrillation electrodes are denoted as “atrial coil  220 ,” “ventricular coil  225 ,” and “can  330 ” in  FIG. 3 , Unlike the “hot can” example described above, with respect to  FIG. 2 , in the example of  FIG. 3 , that “can” electrode  330  can be selectively utilized (via switches  305 C and  305 F) rather than “hard-wired” (or not “hard-wired”) at manufacturing. 
     In certain examples, the shock delivery circuit  300  of  FIG. 3  can be used to provide at least three different defibrillation shock vectors: (1) Right Ventricular Coil  225  to Right Atrial Coil  220 ; (2) Right Ventricular Coil  225  to Right Atrial Coil  220  and Can  330 ; or (3) Right Ventricular Coil  225  to Can  330 . An example of such shock vectors and corresponding switching configurations is described in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Example of Shock Vectors and Switch Operation 
               
             
          
           
               
                   
                 Switches closed 
                 Switches closed 
               
               
                 Shock Vector 
                 during phase 1 
                 during phase 2 
               
               
                   
               
               
                 RV coil to RA coil 
                 305A, E, G 
                 305B, D, G 
               
               
                 RV coil to RA coil and CAN 
                 305A, C, E, G 
                 305B, D, F, G 
               
               
                 RV coil to CAN 
                 305C, E, G 
                 305B, F, G 
               
               
                   
               
             
          
         
       
     
     In certain examples, when a defibrillation shock is delivered, switches  305 A-F are configured as desired at brief time period (e.g., 250 microseconds) before closing switch  305 G.  FIG. 4  shows an example of this timing for a ‘RV coil  225  to RA coil  220 ’ shock. 
     In  FIG. 3 , in certain examples, the switches  305 A-F can be implemented as thyristors (such as by using remote gate thyristors (RGTs) or silicon controlled rectifiers (SCRs)), and the switch  305 G is implemented as a transistor (such as an insulated gate bipolar transistor (IGBT). In certain examples, the topology shown in  FIG. 3  permits the switches  305 A and  305 D to be stacked (e.g., switch  305 A, which can include an RGT, stacked with switch  305 D, which can include an SCR), also permits the switches  305 B and  305 E to be stacked (e.g., switch  305 B, which can include an RGT, stacked with switch  305 E, which can include an SCR), and also permits the switches  305 C and  305 F to be stacked (e.g., switch  305 C, which can include an RGT, stacked with switch  305 F, which can include an SCR), thereby saving space and reducing the size of the implantable cardiac function management device. 
       FIG. 5  is a schematic drawing illustrating generally an example of a switch circuit  500 , such as for implementing switch  305 G of  FIG. 3 . In this example, a node  502  represents the connection between switch  305 G of  FIG. 3  to a terminal of the HV capacitor, as shown in  FIG. 3 . A node  504  represents the connection between the switch  305 G of  FIG. 3 , and the common node of switches  305 A,  305 B, and  305 C of  FIG. 3 . 
     Control of the switch  305 G of  FIG. 3  can be implemented, in  FIG. 5 , by three separate control signal inputs: (1) HVS_ENBLE at node  505 , (2) HVS_FIRE_N at node  506 , and (3) HVGMEAS at node  507 . In an “idle” state, HVS_ENBLE is held “low” at 0V, HVS_FIRE_N is held “high” at 12V, and HVS_GMEAS is held “low” at 0V. 
     Turning “on” the switch  305 G of  FIG. 3  corresponds to turning “on” the corresponding n-channel insulating gate npn bipolar junction transistor (IGBT)  508  in  FIG. 5 . To prepare for turning on IGBT  508 , a gate-emitter drive voltage can be stored across a capacitor  520  (e.g., 1.5 microFarads), This can be accomplished by transitioning HVS_ENBLE at node  505  to a “high” voltage of 12V. This forward-biases and turns-on a diode  510 , thereby allowing current to flow through and charge up the capacitor  520 . This same current also flows through a diode  512 , which is forward-biased “on.” This same current also flows through the drain-source conduction path of an n-channel field effect transistor (FET)  540 , which is “on.” This same current is then sunk at node  507  by the circuit providing the “low” 0V ground voltage at HV_GMEAS. During this time period, since the FET  540  is “on”, there is a voltage of about 12V stored across a capacitor  522  (e.g., 10 pF, rated for 1000V), which is located between the gate and drain terminals of the FET  540  (since the drain terminal of the FET  540  is at 0V and the gate terminal of the FET  540  is at 12V). 
     Next, turning “on” switch  305 G of  FIG. 3  corresponds to turning “on” the IGBT  508  in  FIG. 5 . Initially, the gate-emitter voltage of the IGBT  508  is close to 0V, such that the IGBT  508  is “off”. To turn on the IGBT  508 , a control signal HVS_FIRE_N at node  506  is transitioned from a logic “high” at 12V to a logic “low” at 0V. Because of the voltage that was previously stored across the capacitor  522  during the above-described preparation phase, the voltage at the gate terminal of the IGBT  508  is at a voltage that is more negative than the about 11.5V at the node between  520  and  510  (e.g., the HVS_ENBLE voltage of 12V less a diode drop of about 0.5 V). This causes a current to flow in a resistor  530  (e.g., 18 Kohms) to charge the capacitor  522  and to reverse-bias the diode  512  to be “off”. The drive voltage that was previously stored across the capacitor  520  now effectively appears across the gate and emitter terminals of the IGBT  508 . This turns the IGBT  508  “on.” When the IGBT  508  turns on, the voltage at node  504  begins to rise toward the high voltage delivered by the high voltage capacitor at node  502 . As the voltage at node  504  begins to rise, the voltage at the node between the capacitor  520  and the diode  510  follows suit, thereby reverse-biasing the diode  510 . In this manner, a “bootstrap” voltage is provided at the node between  520  and  510  to provide sufficient drive voltage to the gate of IGBT  508  even as its emitter voltage rises toward the high voltage provided by the HV capacitor at node  502 . 
     Moreover, in the above example, a well-controlled rise or fall time of the switching of the IGBT  508  can be established. The rise or fall time of the switching of the IGBT  508  can be established by delivering a controlled current at HVS_FIRE_N to charge the capacitor  522  as the gate voltage of the IGBJT  508  is driven high by the voltage-follower like arrangement of the IGBT  508  described above. Moreover, since  522  is configured as a “Miller” capacitor between the fixed gate voltage and the widely swinging drain voltage of the FET  540 , this can advantageously be used to provide a larger effective capacitance for controlling the switching rise or fall time of the IGBT  508 , if desired. The switching time of the IGBT  508  will also be affected by the RC time constant formed by  530  and the gate capacitance of the IGBT  508 . 
     The configuration described above with respect to  FIGS. 3 and 5  also provides all solid-state control for performing the switching without requiring any opticoupler, triggering transformer, floating supply, or transformer-coupled supply, as may be required by certain other approaches. This can reduce expense, circuit volume, and complications that may arise from such other approaches. 
     The configuration described above with respect to  FIGS. 3 and 5  also has advantages over hard-wired “hot can” or “cold can” configurations described above since it allows flexibility in defibrillation waveforms. For example, Table 1 illustrates a shock vector from RV coil to RA coil by closing switches  305 A,  305 E, and  305 G during phase  1 , and then closing switches  305 B,  305 D, and  305 G during phase  2 . In another example, the polarity of this shock vector could be reversed by closing switches  305 B,  305 D, and  305 G during phase  1 , and then closing switches  305 A,  305 E, and  305 G during phase  2 . Similarly, the other waveform polarities can also be reversed by interchanging the switches closed in phase  1  with the switches closed in phase  2 . 
     In a further example, automatic polarity reversal is implemented. For example, after each shock delivery, sensing circuits are used to determine whether the rhythm has successfully been converted from a tachyarrhythmia or fibrillation waveform to a normal waveform. If, after a specified number of attempts (e.g., 3 shocks), the heart has not been converted to a normal rhythm, then at least one subsequent attempt (e.g., the 4th shock) is performed using the opposite waveform polarity of the same shock vector. In other examples, different shock vectors or polarities are automatically used, such as when initial defibrillation shock attempts for that particular episode have been unsuccessful at obtaining a normal heart rhythm. 
     Additional Notes 
     The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as “examples,” Such examples can include elements in addition to those shown and described. However, the present inventors also contemplate examples in which only those elements shown and described are provided, 
     All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls. 
     In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. 
     Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, the code may be tangibly stored on one or more volatile or non-volatile computer-readable media during execution or at other times. These computer-readable media may include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like. 
     The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure, This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.