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Contents
1. age on the electrode to completely drain until the TDR reading process begins Also some sensing electrodes such as those used to monitor heart activity may have a rhythmic voltage on them generated by an internal organ Such electrodes are used for example to moni tor cardiac activity and logic and control unite 11 sec tion of the pacemaker is capable of determining at any point in time the status of the rhythmic activity For such electrodes it is desirable to time each TDR read ing to being at the same time in the rhythmic cycle so that each TDR reading is taken at the same time of the rhythmic cycle and therefore less subject to noise For a cardiac sensing electrode TDR blanking interval 103 may begin after completing of physiological event such as the atrial beat as sensed by logic and control 11 and last for 300 milliseconds After the 300 millisecond blanking interval the TDR reading or readings may be made as further described below and the readings may be completed before the ventricular beat begins This method in combination of the minimal current needed to generate a TDR incident pulse minimizes the likelihood of causing an irregular heartbeat This system constitutes an anti coincidence detector adapted to pre vent a stimulating signal or physiological event from interfering with the incident pulse signal generated by the time domain reflectometer and its reflected wave After the TDR blanking interval has pa2. output warning signal such as a flashing light buzzer or DEFECTIVE screen display is generated High and low limits from the electrode portion of the display waveform may be represented as horizontal lines on the graphical display Specifically minimum warning line 64 and maximum warning line 65 as shown in FIG 67 define the boundaries in which the entire electrode portion of the waveform is expected to fall If a wave form deviates from these limits DEFECTIVE legend 66 may be displayed on the screen preferably in a highly contrasting color and accompanied by an audible alarm FIG 6 shows a representative superimposed TDR reading in which archived reading 61 shows an elec trode in good condition while current reading 62 shows that the electrode has broken Specifically reading 62 includes waveform rise 63 indicating that the impe dance of the electrode has risen This may be caused by for example a filament becoming cracked or com pletely severed Because current reading 62 exceeds maximum alarm level 65 DEFECTIVE legend 66 is displayed on the screen alerting the physician that the electrode may be defective The Current Configuration parameters 40 41 and 42 shown in FIG 2 as mentioned above may be adjusted With regard to Display Options 42 these parameters effect how a particular TDR reading is displayed on the screen In particular different electrodes from different manufacturers and for different purposes will g
3. Rev N C Ventak AICD TM Model 1600 Physician s Manual Automatic Implantable Cardioverter Defibril lator 1991 Cardiac Pacemakers Inc Quantum TM Ii Intermedics TM Cardiac Pulse Gen erator Physician s Manual Models 253 25 and 254 3 0 1990 Pacesetter TM Technical Manual APS II Model 3000 Programmer With Model 3030 Function Pak 1988 Cordis Corporation 1986 Brochure entitled What do these pacers have in common Tektronix 1502C Metallic Time Domain Reflectometer Service Manual Tektronix Inc Ist Prnt Jul 1989 Revised Jul 1991 pp 5 1 to 5 11 Primary Examiner William E Kamm Attorney Agent or Firm Baker amp Daniels 57 ABSTRACT A device system and method is used for testing the integrity of an implantable electrode The electrical device has a receptacle for an electrode and includes a time domain reflectometer comprising an output signal mechanism operatively connected to the electrode re ceptacle The method of analyzing the integrity of an implanted electrode comprises the steps of generating a time domain reflectometer TDR reading output sig nal from the electrode and transmitting the signal to an output device The output signal may be analyzed to determined whether it varies by a predetermined threshold or it may be compared to a previously gener ated signal from the electrode so that differences in the electrical characteristics of the electrode may be identi fied
4. The present device system and method allows a cardiologist or technician to ensure that the electrode is properly implanted and to non invasively determine the integrity of the electrode over a patient s life 64 Claims 5 Drawing Sheets Sheet 1 of 5 5 231 987 Aug 3 1993 U S Patent I hi L 21 NOLLO3S 7TOuLNOO 91901 UXLLINSN WvubSOud ANJI TEEN YOLVTIIOSO YOLVTHIDSO 1 15 HOLIMS 0334 Sc VELL dL 81 8c 5 231 987 Sheet 2 of 5 Aug 3 1993 U S Patent c 9p HOSUfO x 9 HOSuno LV OHY 26 10 01 31 H195N31 1V2UulL0313 NOISIAIQ WI OZ ANOS 1VLNOZIHOH 1 HLONAT 1VOISAHd WW 0 1NIOd 3ONzu3H3H TV LNOZIHOH gt zy NOILISOd HOSHND 1N3uHHn2 NOISIAIQ OHUM 051 AIVOS 1VOLLHJA OHY 00 LNIOd VOLLH3A 24 JONVLSISSY SNOIALdO AV IdSIQ 8 0 NOILVOOdOUd 40 ALIDOTJA SQNOO3SONVN 000 35 SONOOASITIIN 006 SNINNV1E YAL WO SI H1ON31 WOISAHd 113 ON uv IOdINI ALiuvlOd OHH W SE OHHITIIN Ov WO 06 HLON31 7991919913 Ly S S35VU3AV SNIDQV3U JO ON 0001 SOINOU LLO3 13 L SNOILdO 5 L 400819314 6y isnrav 4 063 NOILVHfISIJNOO LNSYHND H3XVW3OVd NI 9NIQV3H LN3HHO JEN SONIQV3H YAL M3IA3H SNIQV3H
5. converted to a digital value by an analog to digital converter and stored in memory The pulse generating wave storing process is repeated except that the time period between the pulse genera tion an when a portion of the reflected wave is stored is increased slightly causing a different slice of the reflected wave to be stored After a sufficient number of samples e g 256 have been collected a compilation of the stored waveform readings a TDR reading pro vides a view of the entire reflected wave representa tive TDR pulse may comprise a 300 mV amplitude into a 50 ohm load with a 25 microsecond pulse duration and the reflected rise may be detected in less than 200 picoseconds In general the present invention operates in the fol lowing manner Logic and control 11 is designed to periodically send pacing signals via output line 24 to output section voltage multiplier 13 Logic and control section 11 is programmed to cause output section volt age multiplier to generate cardiac stimulating pulses of predetermined amplitude duration and frequency ac cording to parameters stored in RAM 22 A typical cardiac pacemaker generates stimulating pulses at fre quencies of 0 5 to 3 per second at amplitudes from 2 5 V to 8 5 V and at durations of 0 15 to 2 3 milliseconds Accordingly there is a substantial time gap of at least 300 milliseconds between pulses As a complete TDR pulse and reflection reading time can be accomplished
6. electrode Connected to logic and control unit 11 is a telemetry system com prised of telemetry transmitter 18 and program receiver 19 both of which on connected to common antenna 20 The telemetry system allows the pacemaker to be inter rogated to determine its operating conditions after it has been implanted and also allows the pacemaker to be reprogrammed without surgery For example the de vice can be reprogrammed to generate stimulating pulses on the pacing electrode at set rate or at a varying rate depending on cardiac activity Other parameters such as the pulse width and pulse amplitude can also be specified after the pacemaker has been implanted These operating parameters are stored in random access mem ory RAM 22 while the control program is stored in read only memory ROM 21 Reprogramming is ac complished through the use of an external system pro grammer 28 having an RF transceiver wand 27 al though a convention serial data port with lead connec tors extending through the skin of the patient may also be used The invention also includes time domain reflectome ter TDR I O control 23 which includes the circuitry necessary to generate a TDR pulse on the electrodes and to detect the resulting voltage A TDR applies a narrow pulse of current typically by a tunnel diode to the electrode and monitors the resulting reflected volt age on the electrode over a period of time A stored reflected voltage waveform comprise
7. of a TDR pulse until the amount of time specified by the TDR blanking interval has elapsed after the transmission of a stim ulating pulse or occurance of an identified physio logical event on the electrode 15 The device of claim 1 wherein the device further comprises means for receiving a TDR base time signal to the time domain reflectometer and means for deferring storing of the reflected TDR incident pulse until the amount time specified by the TDR base time signal has elapsed after the generation of a TDR pulse 16 The device of claim 1 wherein the device further comprises means for connecting the device to a second implant able electrode and switch means for selecting whether the time domain reflectometer is operably connected to the means for connecting the first implantable electrode or the means for connecting to the second implantable electrode 17 The device of claim 1 wherein the device further comprises means for storing information regarding an electrode connectable to the device and means for transmitting the stored information through the output signal means 18 A system for displaying a time domain reflectom eter output signal comprising a device of claim 10 and a graphical display means operatively connected to a receiving means for receiving a transmitted output signal from the device of claim 8 19 A method of analyzing the integrity of an elec trode implanted in a body comprising the steps of ge
8. output signal with a time reference indicating when the output signal is generated 9 The device of claim 7 further comprising 14 means for transmitting a specified stored output sig nal through the output signal means 10 The device of claim 1 wherein the time domain reflectometer means comprises means for transmitting 5 an electrical signal to the electrode receiving means 30 5 35 50 40 45 55 60 65 and wherein the device further comprises an anti coincidence detector adapted to prevent a signal generated by the transmitting means from interfering with the signal generated by the time domain reflectometer 11 The device of claim 1 further comprising means for actuating the time domain reflectometer to generate an output signal the actuating means comprising an electromagnetic wave receiver 12 The device of claim 1 further comprising means for transmitting an output signal generated by the time domain reflectometer the transmitting means comprising an electromagnetic wave trans mitter 13 The device of claim 1 wherein the time domain reflectometer further comprises a pulse generator and an array of selectable source resistors through which a pulse generated by the pulse generator may be transmitted 14 The device of claim 1 wherein the device further comprises means for receiving a TDR blanking interval signal to the time domain reflectometer and means for deferring generation
9. selected prop erties 56 The system of claim 37 wherein the system fur ther comprises 20 25 30 35 45 50 55 65 18 means for specifying blanking interval for a TDR reading to be made by the time domain re flectometer of the implanted device and means for transmitting the specified TDR blanking interval to the transceiver means 57 The system of claim 37 wherein the system fur ther comprises means for specifying a TDR base time for a TDR reading to be made by the time domain reflectome ter and means for transmitting the specified TDR base time to the transceiver means 58 The system of claim 37 wherein the transceiver means comprises and RF transceiver 59 The system of claim 37 wherein the transceiver means comprises a serial data port 60 The system of claim 37 wherein the device com prises data storage means and the system further com prises means for transmitting an instruction to the device commanding the device to store a TDR reading 61 The system of claim 37 wherein the device com prises data storage means and the system further com prises means for transmitting an instruction to the device commanding the device transmit to the system a previously stored TDR reading 62 The system of claim 37 wherein the system fur ther comprises means for displaying the amplitude differential be tween the incident pulse and a selected portion of the first TDR read
10. step of associating each stored output signal with a time reference indicating when the TDR reading is gen erated 28 The method of claim 19 further comprising the step of transmitting a previously stored output signal through the output means 29 The method of claim 19 wherein the output means comprises an electromagnetic wave receiver 30 The method of claim 19 further comprising the steps of providing a TDR blanking interval signal and deferring generation of a TDR pulse until the amount of time specified by the TDR blanking interval has elapsed after the transmission of a stimulating pulse or the occurrence of an identified physiolog ical event on the electrode 20 25 35 45 31 The method of claim 19 further comprising the steps of providing a TDR base time signal to the time domain reflectometer and deferring the storing of the reflected TDR incident pulse until the amount time specified by the TDR base time signal has elapsed after the generation of a TDR pulse 32 The method of claim 19 further comprising the steps of graphically displaying the generated TDR reading 33 The method of claim 32 further comprising the steps of providing a reference output signal and superimposing the reference output signal on the graphically displayed generated output signal 55 60 65 16 34 The method of claim 32 further wherein the gen erated output signal is displayed on a screen monit
11. store electrode settings for an electrode other than no 1 the number information may be ignored and the val ues replaced by the received values After this information has been specified and prior to implantation the physician may take an initial TDR reading This is done by using the up and down arrows to highlight the Obtain TDR Reading option the depressing the Select option 50 on the touch screen This action causes programmer 28 to transmit a com mand to the pacemaker commanding the pacemaker to take a TDR reading according to the parameters stored in RAM 22 When the pacemaker receives an instruction to take a TDR reading the pacemaker waits until no stimulating pulse is present on the electrode Referring to FIG 8 normally if stimulating pulses are being generated on a periodic basis logic and control unit 11 will wait until the trailing edge of stimulating pulse 101 has been gen erated Because stimulating pulse 101 may cause noise to be present on the electrode for a short time period after the pulse is generated no action is taken during the time previously specified as TDR Blanking Interval 103 This system comprises means for deferring genera tion of the TDR incident pulse until the amount of time specified by the TDR blanking interval has elapsed after the transmission of a stimulating pulse on the elec trode or the detection of an identified physiological event For stimulating pulse electrodes this allows volt
12. United States Patent Robson HART US005231987A 11 Patent Number 43 Date of Patent 5 231 987 Aug 3 1993 54 TIME DOMAIN REFLECTOMETER INTEGRITY TESTING SYSTEM AND METHOD FOR IMPLANTABLE ELECTRODE 75 inventor Jack Robson Beech Grove Ind 73 Assignee Random Technologies Inc Indianapolis Ind 21 Appl No 866 850 22 Filed Apr 10 1992 51 Int anciens A61N 1 362 52 US CE 607 29 58 Field of Search 128 419 419 PG 56 References Cited U S PATENT DOCUMENTS 3 922 914 12 1975 Fuchs 73 290 R 4 466 288 8 1984 Grynberg 73 654 4 786 857 11 1988 Mohr et al 324 585 X 4 843 234 7 1989 Berthold et al 250 227 4 893 895 1 1990 Berthold et al 350 96 29 4 960 989 10 1990 Liebenrood et al 250 227 5 033 826 7 1991 Kolner SAC AM 350 355 OTHER PUBLICATIONS Hewlett Packard Application Note 62 TDR Funda mentals Apr 1988 Hewlett Packard Application Note 62 1 Improving Time Domain Network Analysis Measurements Apr 1988 Hewlett Packard Application Note 62 3 Advanced TDR Techniques May 1990 Tektronix 1502C Metallic Time Domain Reflectometer Operator Manual 1st Prn Mar 1989 Revised May 1990 Genesis Cardiac Pacing System Model 285 Tech nical Manual Pacesetter Systems Inc 1985 91904 20 001
13. YAL 2199198 H3XVW3OVd OL 3401 OS ASIGOW 40135 WM asvaviva 300419313 103 HS vy NOLLVHDISIHNOO AYAH 5 231 987 Sheet 3 of 5 Aug 3 1993 U S Patent HLINS a S3NOf HLINS HUWS HUWS NVIDISAHd v 109135 OL 123146 1H9i1H9IH OL 3 000 30Vd ONI SW31SAS H3 113S3O0 Vd 001 OUudO313 ONI SOIG3WH3ANI LOO0 vSC SOIGAWYALNI 0011 199 SuxxvW3OVd OvIOHVO 0001 142 ONI Su3viW3Ovd OVIGHYVO 1330N u3uniov3nNvNW 3380812313 103135 OL 1231136 LHDNHDIH OL 4 SS3ud XO SXO3HO 31911 V3 SO SLNIV IdWOO LNAILWd 26 51 60 d 19403HO HLNOW 9 26 10 40 dN MOSHO 3ALLVH3dO 1SOd 26 10 20 300810313 0001 SOINOYU LHOAL M 26 40 10 000 SOINOUu1H23L M SONIGVAY 1NY IdWI 3Hd 26 10 10 SIN3NWOO 3LV DSNIOQVSY U S Patent Aug 3 1993 Sheet 4 of 5 5 231 987 Sheet 5 of 5 5 231 987 Aug 3 1993 U S Patent 8 AL 3 1dWVS ANOJIS 901 901 a Set 3Sva M T M 801 101 T ADVLIOA 5 231 987 1 TIME DOMAIN REFLECTOMETER INTEGRITY TESTING SYSTEM AND METHOD FOR IMPLANTABLE ELECTRODE FIELD OF THE INVENTION This invention relates to a device system and method used in medical testing and in particular to a non inva sive technique for testing th
14. ated through wand antenna 27 to antenna 20 of the pacemaker accompanied by a command instructing the pacemaker logic and control 11 to store the information in RAM 22 This stored reading may be used as a base line TDR reading against which future TDR readings may be compared to assist in evaluating electrode integ rity In one embodiment RAM 22 has sufficient capac ity to store up to 512 TDR readings and associated information Logic and control 11 stores in RAM 22 an incremental counter indicating the total number of read ings that have been stored in RAM 22 and the address of the next subsequent reading to be stored Assuming the initial TDR reading is acceptable the physician may proceed with implantation of the pace maker and electrode Following implantation but prior to closing the surgical incision in the patient the physi cian may take a second TDR reading to ensure that no damage to the pacemaker or electrode occurred during implantation Assuming the TDR reading is acceptable the physician may close the incision Following implantation the patient can be expected to have numerous follow up visits with the physician during which the integrity of the implanted electrode may be evaluated This may be done using the same programmer 28 described above After the programmer is turned on wand 27 is positioned over the patient s pacemaker and the TDR option is selected the screen shown in FIG 2 may appear The physician cho
15. ators currently available Specifically with regard to an electrode con 10 2 nected to such devices little information with the ex ception of type of electrode used is available through an external programming system Various types of problems can occur with such electrodes including lead fracture lead displacement body reaction to the lead interface migration of the lead through body tissue unsatisfactory electrode position and faulty connection with the implantable device For example the electrode may be improperly fastened to the pacemaker resulting in an ohmic or loose junction or after the electrode is implanted it may rub against a bone within the patient s body and strip the electrode s insulation Thus it is desireable to develop an implantable device having an electrode which is capable of providing information about the integrity of the electrode in a non invasive manner both at the time the device is implanted and throughout the time the electrode remains implanted 25 30 35 40 45 50 55 60 65 One known method used to attempt to determine the integrity of an implanted electrode is an X ray radio graph However X ray radiographs are not adequate for integrity testing as they are unable to provide infor mation about the connection between the device and the electrode or the condition of the electrode in reliable manner For example an X ray radiograph may in some cases indicate
16. ause graphical cursor 5 231 987 11 48 to move left or right At the point where cursor 48 intersects waveform 49 the distance of the electrode circuit and impedance of the waveform are shown in displays 54 and 55 Thus cursor 48 and displays 54 and 55 comprise means for superimposing a distance scale measurement corresponding to the length of the im planted electrode on the graphical display After the physician has obtained and displayed the composite TDR reading the reading may be transmit ted back to the pacemaker and stored in RAM 22 which comprises means for storing multiple TDR out put signals As shown in FIG 2 this may be done by depressing the down arrow until the Archive Current TDR Reading in Pacemaker menu option is high lighted The Select button is then depressed This causes programmer 28 display a dialog box on the screen in which the physician may type a short descriptive sum mary of the reading using a keyboard connected to programmer 28 such as Pre implant readings w Tech nitronics 1000 and in which the physician may enter his or her name After this option information has been entered the Select button is again depressed causing programmer 28 to transmit the TDR waveform along with the Sampling Options Display Options and textual information including the date which comprises a means for associating each stored output signal with a time reference indicating when the output signal is gen er
17. be used to test the integrity of both unipolar and bipolar electrodes Electrodes for many applications are insulated so as to avoid affecting or being affected by the surrounding tissue However the electrodes can deteriorate over time Thus it is desirable to develop an integrity testing system for an implanted electrode which is not signifi cantly affected by the natural deterioration of the elec trode It is also desirable to develop a method for testing the integrity of the electrode which does not interfere with the normal operation of the implanted device pace maker for example must send pulses to the heart at a specified rate such as 60 pulses per second For the pacemaker to continue to operate during the testing 5 231 987 3 procedure the integrity test must be performed without interfering with those pulses Additionally most implantable devices require little power to operate Because little power is required to perform the desired function of the device a battery may be utilized for a lengthy period of time without requiring replacement Therefore it is desirable to de velop an integrity testing system which does not require significant power to operate so as to avoid reducing the life of the battery used in the device Time domain reflectometers such as the 1502C Me talic Time Domain Reflectometer manufactured by Tektronix Inc of Beaverton Oreg are used to test the integrity of cable such as co axial
18. cables For such in tegrity testing time domain reflectometers send electri cal pulses down the cable and detect any reflections made by any discontinuities in the cable Specifically time domain reflectometers send out successive pulses and measure the respective reflected pulses at times corresponding to points along the cable Measurements are provided in terms of voltage versus time which can then be converted to resistance over the length of the cable Time domain reflectometers can locate shorts opens defects in the shield of the cable foreign sub stances in the cable kinks and more Generally only one parameter is required for the proper operation of the time domain reflectometer in determining the integ rity of a cable That parameter is the velocity of propa gation or the speed of the signal down the cable which varies for different cable dielectric materials Time do main reflectometers may operate on either a closed or an open circuit For an open circuit the signal continues to be reflected through the air or other medium and returns to the instrument In general variations in the resistance measured by the time domain reflectometer indicates a fault such as a bad connection the stripping of insulation pressure on the cable or a break in the cable Time domain reflectometry has been used for a vari ety of applications In U S Pat No 4 466 288 time domain reflectometry is used to evaluate vibrations The level o
19. com prises means for generating the first TDR reading by forming a composite reading from multiple TDR read ings 50 The system of claim 49 wherein the system fur ther comprises means for transmitting a signal to the device trans ceiver means indicating the number of TDR read ings to use to form the composite signal 51 The system of claim 37 wherein the system fur ther comprises means for storing multiple received TDR readings means for generating a TDR reading comprising a composite of individual TDR readings 52 The device of claim 51 wherein the composite TDR reading comprises an average of the multiple readings based upon a user designated number of read ings from the time domain reflectometer 53 The system of claim 37 wherein the time domain reflectometer further comprises an incident pulse gener ator and wherein the system further comprises means for selecting a value indicating the source resistance of an incident pulse to be generated by the time domain reflectometer and means for transmitting the selected value to the de vice 54 The system of claim 37 wherein the system fur ther comprises means for specifying a propagation velocity factor for the first TDR reading 55 The system of claim 37 wherein the system fur ther comprises means for selecting a set of properties for the im planted electrode from a database of electrode properties and means for displaying at least one of the
20. d The physician may then depress the left 48 and or right 49 arrows which will cause the highlighted values to be decremented or incremented respectively After the has specified the desired elec trode configuration values the physician may store them in the pacemaker so that they do not have to be reprogrammed each time a TDR reading is taken This is done by depressing the up or down arrows until the Store Configuration to Pacemaker option is selected The Select button is then depressed which causes all of 20 25 30 40 50 55 60 the displayed electrode information to be transmitted to the pacemaker by RF transceiver 27 and stored in RAM 22 If the pacemaker provides means for connecting to a second electrode such as for multiple leads or in cludes two leads for single electrode i e a pulse and a ground then the pacemaker RAM 22 may be config 65 8 ured with sufficient memory to store a separate setting for each electrode or lead In addition pulse selector wil include switch means for selecting whether the time domain reflectometer is operably connected to the means for connecting the first implantable electrode or the means for connecting to the second implantable electrode The location for each storage will be desig nated by the Electrode No option in FIG 2 If a pacemaker having capability for storing only one set of electrode readings receives an instruction and data to
21. e integrity of an electrode implanted within a patient s body BACKGROUND OF THE INVENTION Advances in technology together with an increased understanding of physiological functions has led to the development of a variety of devices which may be im planted into the body to assist or to perform specific functions Cardiac pacemakers defibrillators the Jarvis heart and insulin pumps are just a few examples of these implantable devices Generally implantable devices are usually comprised of a power source coupled with elec trical and or mechanical components necessary to per form the desired function The power source and the other components may require replacement or repair over the life of the patient Therefore many implantable devices provide a mechanism for non invasively pro viding vital information regarding the device s perfor mance In this manner it may be determined without surgery whether the device is in need of repair or re placement or whether the device is approaching a threshold thereby indicating the need for replacement or repair A number of cardiac pacemakers available on the market today are capable of being both programmed and evaluated non invasively These pacemakers in clude for example the Model 402B Multicor II man ufactured by Cordis Corporation of Miami Fla the Quantum 8 Model 254 09 manufactured by Interme dics Inc of Freeport Tex the Chorus DDD manufac tured by ELA Medical Inc
22. enerate TDR readings have different impedance baselines and lengths In order to scale a TDR reading on the graphi cal display the Vertical and Horizontal reference points and scales may be adjusted These values will also be stored along with an archived TDR reading so that when the reading is retrieved it will be initially dis played using the same viewing parameters as when it was stored It will be appreciated to those of skill in the art that may changes could be made in the foregoing represen tative embodiment without departing from the spirit and scope of the invention For example the present invention may be used with virtually any type of im plantable electrode such as ventricular rate sensing morphology high voltage mapping sensor temporary ablation and angio artheretomy electrodes The inven tion may also be used in connection with wires used in connection with devices such as implanted insulin pumps and such wires are within the scope of the term electrode as used herein and in the claims In addi tion in instances where a tube or stint is implanted in a patient a tube configured with an embedded electrical conductor running the length of the tube and connect able to a and which will break if the tube breaks 5 231 987 13 is also included within the definition of an electrode as used herein It will also be appreciated that although the in the embodiment described above a TDR reading is output th
23. es generated by output section 13 Thereafter the generation of stimu lating pulses may resume If the number of readings averaged parameter is greater than one then the TDR reading process may be repeated either immediately if the time until the next stimulating pulse to be generated is sufficiently long or else after the next stimulating pulse is generated Taking multiple TDR readings and averaging them reduces any noise that may be inherent in a single reading For averaged readings instead of storing the each set of individual TDR waveform readings to the same RAM address the digital values may be added to the previ ously stored values After the total number of TDR readings specified by the No of Readings Averaged parameter has been completed the each sum may be 15 20 25 30 40 45 50 55 65 10 divided by the number of readings comprising the sum to obtain a composite reading namely the average Alternatively it is envisioned that merely the raw TDR readings may be transmitted to programmer 28 as de scribed below and programmer 28 perform the averag ing of the readings It will be appreciated from the description of the foregoing embodiment that the time domain reflectome ter ie the system for generating incident pulses and storing the reflected wave form comprises a logic and control system as is already found in conventional pace makers as well as TDR I O circuitry After the raw or comp
24. f claim 39 wherein the first TDR reading is graphically displayed using an axis indicating the time distance of the output signal and wherein the system further comprises means for se lecting the time distance scale at which the first TDR reading is graphically displayed 42 The system of claim 39 wherein the system fur ther comprises means for superimposing a distance scale measurement corresponding to the length of the im planted electrode on the graphical display 43 The system of claim 37 wherein the system fur ther comprises means for storing a second TDR reading and graphi cally displaying it superimposed over the first TDR reading 44 The system of claim 37 wherein the system fur ther comprises means for storing a second TDR reading means for comparing the first and second TDR read ings and means for indicating whether the compared TDR readings vary by a predefined threshold 45 The system of claim 37 wherein the system fur ther comprises means for adjusting the a vertical reference point for the graphical display 46 The system of claim 37 wherein the system fur ther comprises means for adjusting the vertical sensitiv ity of the graphical display 5 231 987 17 47 The system of claim 37 wherein the graphical display means comprises a screen monitor 48 The system of claim 37 wherein the graphical display means comprises a printer 49 The system of claim 37 wherein the device
25. f fluid in a vessel may be determined by time domain reflectometry as disclosed in U S Pat No 3 922 914 Also the constituents of a multi phased fluid system have been evaluated as disclosed in U S Pat No 4 786 857 In addition time domain reflectometry has been used for optical systems as well For example optical time domain reflectometers such as that disclosed in U S Pat No 4 960 989 may be used to determine the tip location of a consumable electrode within an electric furnace as disclosed in U S Pat No 4 843 234 Simi larly optical time domain reflectometry is used in U S Pat No 5 033 826 to determine which surface of a photographic lens is impairing transmissivity It is desirable to provide a method and device using time domain reflectometry to determine the integrity of an implanted electrode to thereby alert the cardiologist or the technician of a potential or existing problem associated with the electrode As indicated above time domain reflectometry may be used with both unipolar or bipolar electrodes The velocity of propagation of any electrode is necessary for time domain reflectome try measurements Such information could be stored in the implanted device It is also desirable to provide a method of analyzing the integrity of the electrode connected to the implant able device Such analysis could be completed in a pro 5 10 20 25 30 35 40 45 50 55 60 65 4 grammer suc
26. g an implantable electrode according to the invention FIG 3 is a representative computer screen list win dow displaying an index of previous TDR readings which have been stored in the device FIG 4 is a representative computer screen list win dow displaying a partial index of electrode manufactur ers and models one of which may be selected to pro vide a set of default electrode sampling and display options for a particular electrode FIG 5 is a representative graphically displayed base line TDR reading for an electrode in good condition FIG 6 is a representative graphically displayed base line TDR reading having superimposed over it a more recent TDR reading for the same electrode showing that a break has occurred in the electrode and that the electrode is now defective FIG 7 is a representative graphically displayed TDR reading for an electrode have a short in it FIG 8 is a representative time graph showing the trailing end of a stimulating pulse on the electrode a TDR incident pulse and reflective pulse SUMMARY OF THE INVENTION The invention comprises a device system and method for testing the integrity of an implantable elec trode The electrical device has a receptacle for an electrode and includes a time domain reflectometer comprising an output signal mechanism operatively connected to the electrode receptacle The method of analyzing the integrity of an implanted electrode com prises the steps of generati
27. h as those used for the analysis of presently available data OBJECTS OF THE INVENTION Accordingly it is one object of the present invention to provide non invasive method to establish that an electrode is properly implanted and to determine the integrity of the implanted electrode over a patient s life It is another object of the present invention to pro vide a system whereby the integrity of an implanted electrode may be telemetered to an external analysis unit which may in turn provide comparative informa tion to the patient s cardiologist or technician to iden tify potential or existing problems It is still another object of the present invention to provide an electrode integrity testing system in which the test procedure does not interfere with the normal operation of the implanted device It is another object of the present invention to pro vide an integrity testing system which requires little power to operate It is still another object of the present invention to provide a testing system which is neither affected by the normal deterioration of the implanted electrode nor affected by physiological changes within the tissue sur rounding the electrode BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 shows a block diagram of one embodiment of a device of the present invention when used in connec tion with a programmable cardiac pacemaker FIG 2 a representative computer touch screen user interface for configuring and testin
28. ing 63 The system of claim 37 wherein the device is connected to a plurality of implanted electrodes and includes switch means for selecting which of the im plantable electrodes the time domain reflectometer is connected to further comprising means for commanding the device for operably con nect the time domain reflectometer to a designated implanted electrode 64 The system of claim 37 further comprising means for commanding the device for operably con nected to the time domain reflectometer to transmit stored information regarding an electrode con nected to the device to the system
29. nal teleme tery programming equipment with appropriate soft ware to carry out the functions described herein 5 231 987 7 To program the default electrode sampling and dis play options into the pacemaker external programmer 28 is first turned on and the telemetry head of wand antenna 27 is positioned over the pacemaker The telem etry head generates a magnetic field which activates reed switch 25 inside the pacemaker This switch causes logic and control unit 11 to activate program receiver 19 and to receive instructions from programmer 28 In one embodiment of the invention programmer 28 has a touch screen and various options are selected by touch ing the indicated portion of the screen The physician will initially step through the prompts displayed on programmer 28 to transmit the desired pacemaker set tings e g stimulation rate pulse amplitudes sensitivi ties and mode into the pacemaker The physician may then select a TDR option on programmer 28 which will cause programmer 28 permit the TDR parameters to be specified and displayed such as through the TDR options screen shown in FIG 2 The physician will initially wish to specify the default TDR values to be stored in the pacemaker Ideally programmer 28 will include a database of electrode manufacturers and mod els with default electrode sampling and display options for each electrode model The database may be periodi cally updated by programmer 28 manufacturer
30. nerating a first time domain reflectometer TDR reading from the implanted electrode and 5 231 987 15 transmitting the generated TDR reading to an output means 20 The method of claim 19 further comprising the step of providing a reference time domain reflectometer reading and comparing the first and reference time domain reflec tometer readings and generating an indicating output based on whether the first and reference output signals vary by a prede fined threshold 21 The method of claim 19 wherein the implanted electrode comprises a pacemaker electrode 22 The method of claim 19 wherein the implanted electrode comprises an automatic implantable cardio verter defibrillator electrode 23 The method of claim 19 further comprising the step of generating multiple output signals from the time do main reflectometer and combining the multiple output signals to form a com posite output signal 24 The method of claim 23 wherein the composite reading from multiple readings comprises an average of the multiple readings based upon a user designated number of TDR readings from the time domain reflec tometer 25 The method of claim 19 further comprising the step of selecting a source resistance for the incident pulse generated by the time domain reflectometer 26 The method of claim 19 further comprising the step of storing the generated TDR reading 27 The method of claim 26 further comprising the
31. ng a time domain reflectome ter TDR reading output signal from the electrode and transmitting the signal to an output device The output signal may be analyzed to determined whether it varies by a predetermined threshold or it may be com 5 231 987 5 pared to a previously generated signal from the elec trode so that differences in the electrical characteristics of the electrode may be identified The present inven tion allows a cardiologist or technician to ensure that the electrode is properly implanted and to non inva sively determine the integrity of the electrode over a patient s life DETAILED DESCRIPTION Referring to FIG 1 there is shown a representative block diagram of one embodiment of the present inven tion In this embodiment the invention is located in an implantable multi programmable pacemaker which includes logic and control unit 11 which includes a CPU and appropriate software to carry out the func tions described herein rate limit section 12 and output section voltage multiplier 13 Conventional microcir cuitry and preferably and application specific inte grated circuit is used to package the TDR and other components in the implantable case The pacemaker is designed to provide periodic pulse to two implantable pacing electrodes through electrode receiving means namely connectors 14 and 15 and 16 and 17 respec tively However the invention may also be used with a device connected to a single
32. nt the amount of time it will take for a reflected pulse to be detected by TDR I O 23 and may be on the order of 1 10 000 nanoseconds depending on the elec trical characteristics and length of the electrode After TDR Base Time 105 passes the TDR stores analog voltage detected 106 on the electrode in an analog time base Voltage 106 represents only a small portion of the entire reflected waveform 107 This analog voltage value is then converted to digital format by an analog to digital converter in TDR 1 0 23 and then transmit ted to logic and control section 11 for storage in output device such as RAM 22 After a predetermined amount of time such as 200 microseconds from the initiation of the first incident pulse TDR I O 23 generates second TDR pulse 108 The atove process is repeated numer ous e g 256 times except the time at which an analog voltage reading is stored in the analog timebase is incre mented slightly with each cycle As a result RAM 22 has stored in it a raw TDR reading representing the reflected waveform After the TDR reading has been generated logic and control section 11 sends a signal to pulse selector 26 causing the electrode connectors 14 15 and or 16 17 to be electrically reconnected to the output section 13 and electrically disconnected from TDR I O 23 The isola tion of TDR I O 23 from output section 13 by pulse selector 26 guards against any damage to the circuitry of TDR I O 23 from stimulating puls
33. nvertible into impedance Thus a rise in the waveform represents increased resistance along the electrode while a fall in the waveform represents a short circuit between the electrode and the pacemaker ground Accordingly for the representative waveform shown in FIG 7 waveform rise 52 represents an increase in resistance which in this representative case is attributa ble to the internal pacemaker wiring connection be tween the application specific integrated circuit on which pacemaker circuitry is connected and the wires connected to the pacing leads 14 15 and 16 and 17 Second waveform rise 53 is attributable to the intercon nection between electrode receptacle and the electrode plug Thereafter the waveform is flat indicating a con stant impedance throughout the length of the electrode with no breaks or shorts FIG 5 shows a representative reading in which the electrode has a partial short and is in need of re placement Such a short may be caused for example by defective insulation between the leads of a bipolar elec trode or by the exterior insulation of the electrode becoming worn by for example excessive rubbing against a bone pacemaker case or other structure The short is evident by waveform fall 60 indicating the impedance of the electrode that point has fallen At anytime while a TDR Reading is displayed the physician may depress the cursor left 45 or cursor right 46 arrows below the display to c
34. of Minnetonka Minn and the DDD and Genesis pacemakers from Pacesetter Inc The Ventak Q P Mode 1600 automatic implantable cardioverter defibrillator is another example of an im plantable device providing remote programming and evaluation capabilities These devices typically include an RF transceiver to communicate with an external user interface system which includes a programming wand The external system such as the Pacesetter APS II Model 3000 Programmer with Model 3030 Function Pack available from Pacesetter Systems Inc of Sylmar Calif includes controls to allow physician or medical technician program the diagnostic functions of the device and evaluate its operating parameters The types of information which may be telemetered from for example a pacemaker to such an external system include the device s model number serial number mode in which the pacemaker is programmed magnet rate lead impedance and electrode lead information such as the type of electrode implanted in the patient Also battery life one of the vital characteristics affect ing the performance of the pacemaker may also be telemetered Similarly defibrillators such as the Ven tak P AICD TM Model 1600 manufactured by Car diac Pacemakers Inc of St Paul Minn also are ble of telemetering performance information to such a programming system Some types of problems are not readily discernable with the pacemakers and the defibrill
35. or 35 The method of claim 32 further wherein the gen erated output signal is displayed on a printer 36 The method of claim 19 further comprising the steps of selecting a portion of the generated TDR reading and graphically displaying the selected portion of the TDR reading 37 A system for testing the integrity of an implanted electrode the implanted electrode being connected to device comprising a transceiver means and a time do main reflectometer connected to the electrode the time domain reflectometer being capable of generating an output signal comprising means for transmitting a signal to the device trans ceiver means commanding the time domain reflec tometer to generate a first TDR reading from the implanted electrode and transmit TDR reading through the transceiver and means for receiving the transmitted first TDR read ing 38 The system of claim 37 wherein the system fur ther comprises means for storing multiple received TDR readings means for comparing at least two of the transmitted TDR readings and means for indicating whether the compared TDR readings vary by a predefined threshold 39 The system of claim 37 wherein the system fur ther comprises means for graphically displaying the received first TDR reading 40 The system of claim 39 wherein the system fur ther comprises means for selecting a portion of the first TDR reading to be graphically displayed 41 The system o
36. ose to first retrieve a copy of the archived TDR readin from when the electrode was first implanted This may be done by using up 44 and down 43 arrows to highlight the Review Archived TDR Readings option and depressing Select This will cause programmer 28 to send a signal to the pacemaker instructing logic and control section 11 to transmit the archive number date comment and physician portions of each archived TDR reading to the programmer An archived TDR display window as shown in FIG 3 is then displayed Using up 44 and down 43 arrows the physician may highlight an archived TDR reading which will normally be the baseline reading or first reading archived after implanta 20 25 30 35 40 45 55 60 65 12 tion Depressing the Select portion of the screen causes programmer 28 close the widow and to command the pacemaker to transmit the selected archived TDR read ing including the electrode sampling and display op tions to the programmer where they are displayed The physician may then depress the up arrow to high light the Obtain TDR Reading menu option then press Select 50 This will cause a TDR reading to be generated as described above and superimposed over the archived TDR reading By highlighting and adjusting the Max Mlllirho Alarm option the physician may specify a millirho value predetermined threshold by which if TDR reading deviates in a relevant portion an indicating
37. osite TDR reading has been stored in RAM 22 logic and control section 11 trans mits the stored raw or composite waveform through TDR reading output signal means such as transceiver means comprised of telemetry transmitter 18 and an tenna 20 to wand 27 of programmer 28 In addition in the preferred embodiment logic and control section 11 will also transmit to programmer 28 the stored sam pling values used to take the TDR reading to program mer 28 This transmission assures that the correct pa rameter values may be displayed in association with the TDR reading Programmer 28 then displays the re ceived TDR reading in graphical form on a monitor in graphical display window 411 or a printer or both Preferably programmer 28 includes a Print button which when depressed causes the displayed graph and current configuration information to be printed A rep resentative TDR waveform for a working electrode is shown in FIG 7 The horizontal axis represents the time or sequential samples of the TDR reading which can be directly converted into electrode distance if the of the electrode is known As discussed above this information may be supplied by the electrode manufac turer or manually programmed into the programmer With a known the vertical gridlines or divisions represent a specific length from the TDR I O output to the end of the electrode The vertical axis of the wave form represents millirhos which is directly co
38. rough RAM and an RF antenna other transceiver or output means are within the spirit and scope of the invention For example virtually any other electromag netic wave communication means may be used at any desired frequency including optical frequencies or wire leads may be used to transmit a TDR reading Moreover the TDR reading described above is ob tained by generating multiple incident pulses and stor ing a small portion of each reflected pulse It is contem plated that with the development of faster electronic and CPU circuitry that a TDR reading may possibly be generated by storing the reflected wave from a single incident pulse and such systems included within the definition of a TDR It will also be appreciated that in the embodiment described above a user selected num ber of multiple raw TDR readings may be averaged to produce a composite reading to eliminate noise associ ated with individual readings The averaging function could easily be transferred from the internal implantable device to external programmer 28 Moreover other manipulations of raw TDR readings such as by averag ing multiple readings would not necessarily alter their definition as being a TDR reading Other functions contemplated to be performed by the pacemaker could also be performed by external programmer 28 For example the storage of TDR readings could be per formed on external programmer 28 and optionally may be indexed by a unique key such a
39. s a raw TDR reading If the electrode has a known propagation ve locity the time delay to a particular reflection may be interpreted in distance from the pulse generator This would include the pacemaker s internal wiring to the pacing electrode connectors the electrical connection between the connectors and the pacing electrode and the entire length of the pacing electrode terminating in the portion placed in heart tissue The amplitude of the reflected voltage is a function of the electrode impe dance and the applied pulse and therefore can be inter preted in dB or in rho which is a function of impe dance Circuitry for time domain reflectometers is well known and in isolation do not form the present inven tion In general a TDR comprises an I O controller a digital timebase an analog timebase and a pulse genera 20 25 30 35 45 50 55 65 6 tor As described further below and shown in FIG 8 the TDR generates a short square output pulse After a predetermined amount of time has passed the TDR base time the pulse as reflected back by the electrode is monitored This comprises means for deferring the storing of the TDR signal until the amount time speci fied by the TDR base time signal has elapsed after the generation of a TDR incident pulse At a specific time as determined by the digital timebase a portion or slice of the reflected wave is stored in an analog timebase This value is then
40. s patient social secu rity number or pacemaker serial number to distinguish between stored readings from different patients Also graphical display of programmer 28 may include means for displaying the amplitude differentia between the incident pulse and a selected portion of a TDR reading What is claimed is 1 An electrical device implantable in a body the device comprising means for receiving a first electrode comprising time domain reflectometer means operatively con nected to the means for receiving the electrode the time domain reflectometer means comprising out put signal means 2 The device of claim 1 wherein the device com prises a pacemaker 3 The device of claim 1 wherein the device com prises an automatic implantable cardioverter defibrilla tor 4 The device of claim 1 wherein the output signal of the means comprises a single TDR reading from the time domain reflectometer 5 The device of claim 1 wherein the output signal of the device comprises a composite reading from multiple readings from the time domain reflectometer 6 The device of claim 5 wherein the composite read ing from multiple readings comprises an average of the multiple readings based upon a user designated number of TDR readings from the time domain reflectometer 7 The device of claim 1 further comprising means for storing multiple output signal means 8 The device of claim 7 further comprising means for associating each stored
41. ssed logic and control system 11 sends an signal to pulse selector unit 26 which causes the electrode leads to be switched from an electrical connection with output section 13 to 5 231 987 9 the TDR I O and control section 23 During normal pacemaker operation TDR I O and control 23 is insu lated by pulse selector 26 from the stimulating pulses to minimize the possibility that the relatively large cur rents and voltages of the stimulating pulses will harm the TDR circuitry Logic and control 11 then sends a signal to TDR I O and control 23 which comprises means for transmitting an electrical signal to the electrode receiving means commanding the TDR to generate an incident pulse 104 see FIG 8 on the selected electrode lead In one embodiment of the invention logic and con trol section 11 may include in the signal it sends to TDR I O 23 a signal representing a impedance through which the TDR pulse should be sent Ideally the impe dance equals the impedance of the electrode Accord ingly TDR I O 23 may include an internal array of source resistors of various impedances through which an incident pulse may be transmitted and be connected to a multiplexor to select which resistor the pulse should be transmitted This provides a preferred TDR reflection waveform After generation of incident pulse 104 TDR I O waits the amount of time represented by TDR Base time 105 Normally this amount of time will be selected to represe
42. that a fault is located at the point where the electrode is connected to the pace maker However the performance of other tests or examination of the electrode during a surgical proceed ing may reveal a pseudofracture i e no actual fracture is present such as is caused by the excessive tightening of a suture at that point Thus X ray radiographs can lead to unnecessary surgery intended to correct a non existent problem Therefore it is desireable to deter mine the integrity of an implanted electrode through the performance of a single reliable test Additionally such a test should not be as susceptible to interpretation or to patient conditions as is X ray radiography Various pacemakers and defibrillators can accommo date various types of electrodes Generally there are two types of electrodes Unipolar electrodes are defined as those in which the anode is the case of the planted device and the cathode is the electrical lead Bipolar electrodes are those in which the anode is the proximal lead electrode and the cathode is the lead electrode Examples of bipolar electrodes include the VS1 Bipolar Tined Electrode manufactured by Oscor Medical Inc of Palm Harbor Fla Some devices such as defibrilla tors require the utilization of bipolar electrodes so that the defibrillator may deliver shocks to the heart as well as simultaneously monitor the heart s function Thus it is desireable to develop an integrity testing system which may
43. via a floppy disk with information concerning new elec trodes on the market When the physician first enters the TDR menu the top Read Configuration for Pace maker option will be highlighted in reverse video To select a default electrode configuration from the data base the physician presses down arrow 43 to cause the Select Configuration from Electrode Database op tion to be highlighted The physician then depresses the Select button 50 on the screen This causes an overlap ping window to be displayed on the screen as shown in FIG 4 displaying a list of electrode manufacturers and model numbers The physician may repeatedly depress the down arrow until the electrode to be implanted is highlighted then depress the Select option 50 on the touch screen This will close the display window and cause the Electrode Sampling and Display options to be set to the default values recorded in the database for the particular electrode While in this window or any other window which may be opened at any time prior to depressing the Select option 50 the physician may depress the Escape 47 portion on the screen which will close the window and cause the display to revert to its previous status representative window and set of electrode default information values is shown in FIG 1 Should the physician desire to change any of the default values the physician may repeatedly depress the down arrow until the value to be changed is highlighte
44. with a pulse repetition rate of 200 microseconds it is possible to take an entire set of 256 readings in well under 60 milliseconds Thus a complete TDR reading can be generated between the stimulating pulses period ically provided to the pacing electrode However it is also within the scope of the invention to space out the TDR pulses between multiple stimulating pulses Prior to implantation of the device in body the de vice will be programmed with various default parame ters Conventional pacemakers are programmed for example to specify the stimulating pulse repetition rate pulse amplitude positive and negative sensitivities and control mode Prior to implantation one or more pac ing electrodes will be selected and connected to pacing leads 14 15 and 16 17 of the pacemaker Each model of electrode has its own characteristics including a textual model number polarity number of filaments electrical length physical length V and source resistance Rep resentative electrode parameters to assist in taking later TDR readings are shown as electrode menu options 40 in FIG 2 In addition each electrode will ideally have a set of default sampling 41 and display 42 options Preferably the electrode parameters sampling and dis play options may be specified by the electrode manufac turer and used to set defa lt values in the pacemaker prior to implantation Storing these parameters into the pacemaker is accomplished using conventio
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