Abstract:
An apparatus and method for appropriate selection of high energy shocking electrodes based on impedance measurements. In one example, an impedance measurement circuit measures the impedance between different sets of electrodes upon implant. The measured electrode impedance is compared to a predetermined impedance range to detect the presence of a high-energy shocking electrode. If a high-energy shocking electrode is present, a lead electrode status indicator is set. Based on the state of the lead electrode status indicator, a processor prevents or allows the use of various electrode combinations to deliver high energy therapy. Since the increase in automaticity allows the system to change the programmed therapy based on the status of the leads, patient safety is increased.

Description:
TECHNICAL FIELD  
         [0001]    This document relates to pacemakers, defibrillators, and any other devices that are capable of diagnosing and treating cardiac arrhythmia, and in particular, to an apparatus and method for appropriate selection of high energy shocking electrodes based on impedance measurements.  
         BACKGROUND  
         [0002]    Pacemakers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via an intravascular lead (hereinafter referred to as a “lead”). By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its pumping efficiency.  
           [0003]    Defibrillators are devices capable of delivering higher energy electrical stimuli to the heart. A defibrillator is capable of delivering a high energy electrical stimulus that is sometimes referred to as a defibrillation countershock. The countershock interrupts a fibrillation, allowing the heart to reestablish a normal rhythm for efficient pumping of blood.  
           [0004]    As these devices continue to increase in complexity, the number of leads and electrodes used by a single device increases. One problem this causes is the increased complexity in configuring the leads. Another problem is that there is an increased chance that a lead develops a poor connection or the lead becomes compromised. There is a need in the art for an improved system for detection and configuration of leads.  
         SUMMARY OF THE INVENTION  
         [0005]    This document discusses an apparatus and method for appropriate selection of high energy shocking electrodes based on impedance measurements. In one example, an impedance measurement circuit measures the impedance between different sets of electrodes upon implant. The measured electrode impedance is compared to a predetermined impedance range to detect the presence of a high-energy shocking electrode. If a high-energy shocking electrode is present, a lead electrode status indicator is set. Based on the state of the lead electrode status indicator, a processor prevents or allows the use of various electrode combinations to deliver high energy therapy. Since the increase in automaticity allows the system to change the programmed therapy based on the status of the leads, configuring the system is greatly simplified.  
           [0006]    In a second example, impedance measurements, made during high voltage therapy delivery, are used to determine the suitability of various shocking electrodes. Alternate shocking electrodes may be chosen by a processor if the condition of the primary electrodes is compromised. If the alternate electrodes are also compromised, the processor may continue its selection process until a suitable set of electrodes is identified.  
           [0007]    In a third example, daily impedance measurements are used to determine the suitability of various electrodes. Alternate shocking electrodes may be chosen by a processor if the condition of the primary electrodes is compromised. If the alternate electrodes are also compromised, the processor may continue its selection process until a suitable set of electrodes is identified.  
           [0008]    This summary is intended to provide an overview of the subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the subject matter of the present patent application.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    In the drawings, where like numerals refer to like components throughout the several views,  
         [0010]    [0010]FIG. 1 is a general illustration of one embodiment of portions of a system for treating cardiac arrhythmia.  
         [0011]    [0011]FIG. 2 is a block diagram of portions of a device for treating cardiac arrhythmia coupled to a heart.  
         [0012]    [0012]FIGS. 3 through 6 illustrate example embodiments of treating cardiac arrhythmia by disposing leads around selected cardiac regions.  
         [0013]    [0013]FIG. 7 is a flow chart of one example of a method of a device for treating cardiac arrhythmia automatically changing the lead combination used to deliver shock therapy based on lead impedance measurements.  
         [0014]    [0014]FIG. 8 is a flow chart of one example of a method of an external programmer changing the lead combination used to deliver shock therapy based on lead impedance measurements. 
     
    
     DETAILED DESCRIPTION  
       [0015]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. Other embodiments may be used and structural changes may be made without departing from the scope of the present invention.  
         [0016]    [0016]FIG. 1 shows one embodiment of portions of a system for treating cardiac arrhythmia  100 . System  100  includes an implantable pulse generator (PG)  105  that is connected by a first cardiac lead  110  and a second cardiac lead  115 , or one or more additional leads, to a heart  120  of a patient  125 . Implantable PG  105  can take the form of a defibrillator, or a defibrillator that includes pacing capability. System  100  also includes an external programmer  140  that provides for wireless communication with the implantable PG  105  using telemetry device  145 . The first cardiac lead  110  and the second cardiac lead  115  each include a proximal end and a distal end, where the distal end of the leads  110  and  115  are implanted in, or on, the heart  120  at a first cardiac region and a second cardiac region, respectively. Each lead includes one or more electrodes that allow for combinations of either unipolar and/or bipolar sensing and delivery of energy to the heart  120  for pacing, and/or defibrillation. In some embodiments, the one or more electrodes include electrodes such as sensing, pacing, and shocking electrodes.  
         [0017]    [0017]FIG. 2 is a schematic diagram of one embodiment of portions of control circuitry  200  of an implantable PG  105  coupled to the heart  120 . The implantable PG  105 , as shown in FIG. 2, includes a sensing circuit  205  and a therapy circuit  220  coupled to shocking leads  110  and  115 . The PG  105  further includes a shocking lead impedance measurement device  260 , a power source  270 , and a controller/processor  225 . In this embodiment, the controller/processor  225  incorporates a cardiac signal analyzer  230 , a comparator  240 , and a memory  250  to control device  105 . In one embodiment, the functions of the analyzer  230  and the comparator  240  are implemented in software within the controller/processor  225 .  
         [0018]    Sensing circuit  205  is connected to implantable leads  110  and  115 . In some embodiments, sensing circuit  205  is connected to multiple leads. Each of the leads includes one or more shocking/pacing electrodes to deliver low/high energy therapy to the heart  120 . The electrodes are disposed in multiple selected cardiac regions of the heart  120 , such as the coronary sinus region, the ventricular region, and the superior vena cava region. The electrodes coupled to leads  110  and  115  can include sensing, pacing, and/or shocking electrodes. Sensing circuit  205  receives cardiac signals from the sensing electrodes and amplifies the received cardiac signals.  
         [0019]    Shocking lead impedance measurement device  260  is connected to the electrodes and measures shocking lead impedances by measuring impedance between each possible set of electrodes including at least one shocking electrode from all of the disposed electrodes. One example of a method for measuring defibrillation lead impedance is to measure the lead voltage resulting from a test current sent through the lead. This method is discussed in Linder et al. U.S. Pat. No. 6,317,628, entitled “Cardiac Rhythm Management System with Painless Lead Impedance Measurement System” and is incorporated by reference herein in its entirety, including its discussion of a lead impedance measurement of a defibrillation lead. Another example of a method for measuring defibrillation lead impedance is to calculate the impedance value from the voltage droop of a capacitively coupled output voltage pulse over a fixed period of time. This method is discussed in Citak U.S. Registered Invention No. H1,929, entitled “Cardiac Rhythm Management System with Lead Impedance Measurement” and is incorporated by reference herein in its entirety.  
         [0020]    Each possible set of electrodes can include two or more shocking electrodes, a shocking electrode and a pacing electrode, a shocking electrode and a sensing electrode, a shocking electrode and two or more pacing/sensing electrodes, and a shocking electrode and the conductive housing that covers part of the PG  105 .  
         [0021]    In some embodiments, shocking lead impedance measurement device  260  measures shocking lead impedances between electrodes at predetermined time periods. The predetermined time period impedance measurements can include measurements performed daily or measurements performed during a programming session.  
         [0022]    Comparator  240  which is connected to the shocking lead impedance measurement device  260 , then compares each of the measured shocking lead impedances to a predetermined range of acceptable shocking lead impedance values. In one embodiment, the predetermined range of values is approximately 20 ohms to 125 ohms.  
         [0023]    If the lead impedance measurement is within the predetermined range, analyzer circuit  230  which is connected to comparator  240  allows shock therapy to be delivered through the set of electrodes. If the measured lead impedance is outside of the predetermined range, analyzer circuit  230  prevents delivery of shock therapy using that electrode set and automatically changes the electrode set combination used to deliver the therapy.  
         [0024]    In one embodiment, analyzer circuit  230  activates a lead electrode status indicator circuit or sets a lead electrode status indicator flag in a location in memory  250  to indicate the presence of the lead or that the integrity of the lead is not compromised. Memory  250  stores the predetermined acceptable range of shocking lead impedance values. The analyzer circuit then polls the lead electrode status indicator before delivering the therapy.  
         [0025]    In another embodiment, processor  225  communicates the status of the lead electrodes to the external programmer  140 . External programmer  140  then either allows or disallows selection of the electrode set by the programmer operator for use in shock therapy. In one example of this embodiment, when the external programmer  140  does not allow the selection of the electrode set, the external programmer  140  does not display to the programmer operator the choice of the shock therapy combination that includes the electrode set. In another embodiment, the electrode set choice is highlighted, for example by graying of the display, to indicate to the programmer operator that the choice of the electrode set is not allowed.  
         [0026]    In another embodiment, if an impedance measurement indicates the presence of a set of electrodes, analyzer circuit  230  includes the electrode set in the periodic impedance measurements. If subsequent impedance measurements indicate that the lead has become compromised, the analyzer circuit  230  does not allow the electrode set to be used to deliver shock therapy.  
         [0027]    [0027]FIG. 3 illustrates one example of an embodiment  300  of treating cardiac arrhythmias by disposing leads around selected regions of the heart  120 . In this embodiment leads and electrodes are shaped and sized to be disposed in the right ventricle  310  with the conductive housing covering a part of the PG  105  as the second electrode.  
         [0028]    [0028]FIG. 4 illustrates another example of an embodiment  400  of treating cardiac arrhythmias by disposing leads around selected regions of the heart  120 . In this embodiment leads and electrodes are shaped and sized to be disposed in the coronary sinus  330  and the superior vena cava  320 , and the third electrode is the conductive housing covering a part of the PG  105  adapted to be an electrode.  
         [0029]    [0029]FIGS. 5 and 6 illustrate further embodiments of treating cardiac arrhythmias by disposing leads and electrodes around selected regions of the heart  120 . In these embodiments leads and electrodes are shaped and sized to be disposed in the right ventricle  310 , superior vena cava  320 , and the coronary sinus  330 . In FIG. 5, shock therapy originates from the right ventricle electrode  310 . In FIG. 6, shock therapy originates from the coronary sinus  330 .  
         [0030]    [0030]FIG. 7 is a flow chart of a method  700  of a device automatically changing the electrode set combination used to deliver shock therapy based on lead impedance measurements. At step  710  the impedance measurement is initiated. In one embodiment, the external programmer  140  initiates the impedance measurement of the electrode set. In another embodiment, the PG  105  automatically measures the impedance of the electrode set. At step  720  it is determined if the impedance measurement falls within the predetermined range. If it does fall within the range, at step  730  analyzer circuit  230  activates the lead electrode status indicator. At step  740  the analyzer enables shock therapy using that electrode set. At step  750 , the analyzer adds the electrode set to the list of leads included in the periodic impedance measurements.  
         [0031]    If the lead impedance does not fall within the range, at step  760  analyzer circuit  230  clears the lead electrode status indicator. At step  770 , the analyzer circuit  230  disables shock therapy using that electrode set. At step  780 , the analyzer circuit  230  chooses an alternate electrode set to deliver the shock therapy.  
         [0032]    [0032]FIG. 8 is a flow chart of a method  800  of a device automatically changing the lead combination used to deliver shock therapy based on impedance measurements of the electrode set made during therapy delivery. At step  810  the impedance measurement is initiated. At step  820  it is determined if the lead impedance measurement falls within the predetermined range. If it does fall within the range, at step  830  analyzer circuit  230  activates the lead electrode status indicator. At step  840  the analyzer  230  communicates the status of the electrode set to the external programmer  140 . At step  850 , the external programmer  140  allows the programmer operator to select the electrode set, or a combination of leads that includes that electrode set, to deliver shock therapy.  
         [0033]    If the measured impedance does not fall within the range, at step  860  analyzer circuit  230  clears the lead electrode status indicator. At step  870 , the analyzer circuit  230  communicates the status of the electrode set to the external programmer  140 . At step  880 , the external programmer disallows the programmer operator from selecting the electrode set, or a combination of leads that includes that electrode set, to deliver the shock therapy.  
         [0034]    In one embodiment, the analyzer  230  communicates the status of the electrode set to the external programmer  140  when the external programmer  140  interrogates the lead electrode status indicator and allows use of the electrode set if the status indication is that the electrode set is present or not compromised, and disallows use of the electrode set if the status indication is that the electrode set is not present or compromised.  
         [0035]    Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any other embodiment that exists that is calculated to achieve the same purpose may be substituted for the specific example shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is intended that this invention be limited only by the claims and their equivalents.  
         [0036]    In the following claims, the terms “first,” “second,” “third,” etc. are used merely as labels, and are not intended to impose numeric requirements on their objects.