Time domain reflectometer-integrity testing system and method for
Contents
1. LOTTAS Sheet 3 of 8 5 233 986 Aug 10 1993 U S Patent HLINS a sanor T HUNS HUWS HUWS NVIDISAHd 193136 OL 193138 OL 4 553 O00 39Vd SWALSAS 00 OWd9313 SOIGAWYSLNI 00 82 5 0011 199 0001 189 YAYUNLOVANNVW 12213 Sid 194185 193135 1 OL 4 554 4 MO SNDILV4 SLNIVIGWOD 1 26 8 60 MO 4 HLNOW 9 6 10 20 150 26 10 20 0213 0001 SJINOHYLH JL 26 10 10 0001 SOINOH LHOSL 1 14 3 26 10 10 SNiOVaY U S Patent Aug 10 1993 Sheet 4 of 8 5 233 986 Sheet 5 of 8 5 233 986 Aug 10 1993 U S Patent JWL JIJWYS 9 093 901 801 501 25 TWAYELLNI 35 901 201 2 Sheet 6 of 8 5 233 986 Aug 10 1993 U S Patent 081 AlddNS YAMOd 424 Sheet 7 of 8 5 233 986 Aug 10 1993 U S Patent ee SWHO SONVLSISSY Sheet 8 of 8 5 233 986 Aug 10 1993 U S Patent2. tegrity of an implanted electrode comprises the steps of generating a time domain reflectometer TDR reading output signal from the electrode and transmitting the signal to an output device The output signal may be analyzed to determine whether it varies by a predeter 10 20 25 30 35 40 45 50 55 60 65 4 mined threshold or it may be compared to a previously generated signal from the electrode so that differences in the electrical characteristics of the electrode may be identified The invention allows a cardiologist or tech nician to ensure that the electrode is properly implanted and to non invasively determine the integrity of the electrode over patient s life It is desirable to provide a method and device using time domain reflectometry to determine the integrity of electrodes or cables connected to an external device to thereby alert the cardiologist or the technician of a potential or existing problem associated with the elec trode or cable As indicated above time domain reflec tometry may be used with both unipolar or bipolar electrodes The velocity of propagation of any elec trode is necessary for time domain reflectometry mea surements Such a parameter could be stored in the device It is also desirable to provide a method of analyzing the integrity of the electrode or cable connected to the external device Such analysis could be completed in within the device Of course to be u
3. 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 comprises 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 tor As described further below
4. system for the electrodes or cables connected to such external devices which does not require that the patient be connected to the electrodes or cables so that the cables or electrodes may be tested on a routine basis In addition it is desirable to provide a system that not only indicates whether there is an open circuit in a medical electrical system but location of the open circuit e g whether the break occurs where the cables plug into the pulse generating unit the connector between the cables and the pacing pads or in the middle of the wires of any of the cables Many of the electrodes used with these external de vices are disposable A sterilized package containing the electrodes is opened just prior to use Thus it is also desirable to provide an electrode integrity testing sys tem which is time efficient so as to avoid delaying the provision of the assistance necessary Furthermore because physicians will often be utilizing an integrity testing system under stressful circumstances it must be easy to use and the results of the test must lead to quick 5 233 986 3 interpretation of the integrity of the electrodes ca bles It is also possible for a problem to occur with the integrity of the cables or electrodes during their use For example leads may become disconnected from the patient or from the device or the cable to which the lead is connected Therefore it is desirable to provide an integrity testing system whi
5. 233 986 Aug 10 1993 Cordis Corporation 1986 What Do These Pacers Have in Common Tektronix 1520C Metallic Time Domain Reflectometer Operator Manual May 1990 Genesis TM Cardiac Pacing System Model 285 Techni cal Manual Pacesetter Systems Inc 1985 9190420 001 Ventak 8 PAICD Model 1600 Physician s Manual Automatic Implantables Cardioverter Deflator 1991 Hewlett Packard Application Note 1962 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 Technigues May 1990 Primary Examiner William Kamm Attorney Agent or Firm Baker amp Daniels 57 ABSTRACT A device and method for testing the integrity of an electrode wire such as a pacemaker electrode and electrical wires connected thereto 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 electrode comprises the steps of generating a time domain reflectometer TDR reading output signal from the electrode and trans mitting 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 displayed so that differences in the electrical characteristics of the elec trode may be i
6. 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 models with default electrode sam pling and display options for each electrode model The database may be periodically updated by programmer 28 manufacturer via a floppy disk with information concerning new electrodes on the market When the physician first enters the TDR menu the top Read Configuration for Pacemaker option will be high lighted in reverse video To select a default electrode configuration from the database the physician presses down arrow 43 to cause the Select Configuration from Electrode Database option to be highlighted The physician then depresses the Select button 50 on the screen This causes an overlapping window to be dis 10 20 25 30 35 40 45 50 55 60 65 8 played 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 highlighte
7. 861 UNIVE MENT TT AL 5 233 986 1 TIME DOMAIN REFLECTOMETER INTEGRITY _ TESTING SYSTEM AND METHOD FOR MEDICAL DEVICE ELECTRODE CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation in part of application Ser No 07 866 850 filed Apr 10 1992 FIELD OF THE INVENTION This invention relates to a device system and method used in medical testing and in particular to a technique for testing the integrity of an electrode or cable or combination thereof through which electrical signals such a heart pacing pulses pass BACKGROUND OF THE INVENTION A number of medical devices are available which provide assistance in the performance of various physi ological functions for an individual experiencing diffi culties Some of these devices are implanted within the patient s body while others are external and are typi cally utilized under temporary or emergency situations Whether residing inside or outside of the patient s body many devices include an electrode or cable connected to the patient for the performance of a physiological function or for the receipt of information from the pa tient Cardiac pacemakers defibrillators the Jarvis heart and insulin pumps are a few examples of devices which may be implanted within the patient s body External devices also include cardiac pacemakers and defibrillators and ECG monitors and other diagnostic equipment Exte
8. CPU 120 is programmed through conventional software to monitor a patients heartbeat through ECG connector 130 As the heartbeat occurs on a periodic basis CPU 120 can detect point in time when it is between heart beats and therefore little or no electrical activity on 5 233 986 17 ECG electrodes At such a point CPU causes a signal to be transmitted to ECG 129 to cause its electrical connection to ECG connectors to be disabled and a signal to be transmitted to TDR 131 to cause its output to be connected to ECG connector 130 A TDR read ing is then taken by TDR 131 CPU 120 then transmits a signal to TDR 131 causing it to electrically disconnect from ECG connector 130 and to ECG 129 causing it to reconnect to ECG connector 130 The combination of these components act as an anticoincidence detector to eliminate the possibility of a TDR reading being taken at the same time a signal is transmitted on the ECG electrodes to monitor the heartbeat Due to the short time period needed to take a TDR reading there is no appreciable interruption in ECG readings How ever the TDR reading can be stored in memory and compared to a reference TDR signal for the ECG con nectors as described above If the comparison indicates that a break or short in a ECG electrode has occurred a graphical display showing the location of the break and an audible alarm are generated It will also be ap preciated that the above procedure can also be em ployed
9. 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 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 default values in the pacemaker prior to implantation Storing these parameters into the pacemaker is accomplished using conventional teleme try programming equipment with appropriate software to carry out the functions described herein 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
10. 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 5 233 986 7 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 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
11. 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 1 0 waits the amount of time represented by TDR Base time 105 Normally this amount of time will be selected to represent 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 20 25 30 35 40 45 50 55 60 65 10 to digital converter in TDR I O 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 in
12. embodiment of the invention illustrated in FIGS 1 8 may be used to determine whether patient cable 192 and electrode 194 or connectors 191 and 193 are within desired resistance range or more specifically whether there is a problem of significance with patient cable 192 electrode tip 194 or connectors 191 and 193 However it is desirable to provide a simplistic method of display ing the information to a technician or a physician Re membering that time is of the essence in the use of the external devices the display should be such that a prob lem is quickly discernable by the operator Referring now to FIG 11 there is shown a represen tative computer screen of an external portable tempo rary defibrillator pacemaker in which the patient cable is defective The display is divided into three sections First display section 180 illustrates defibrillator pacemaker 181 having first and second defibrillator cables 184 185 connected to first and second to paddles 186 187 respectively and also connected at first and second defibrillator connectors 182 183 of defibril lator pacemaker 181 Second graphical section 190 illustrates the configuration of defibrillator pacemaker 181 when used in the pacing mode Patient cable 192 is connected to defibrillator pacemaker 181 at cable con nector 191 which may be equivalent to pacer output connector 128 shown in FIG 9 At the other end of patient cable 192 is connector 193 to which first and s
13. invention when used in connec tion with a programmable cardiac pacemaker FIG 2 a representative computer touch screen user interface for configuring and testing 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 5 233 986 5 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 FIG 9 shows a block representative diagram of one embodiment of the device of the present invention when used in connection with a portable external defi brillator pacemaker FIG 10 is a representative graphically displayed baseline T
14. DR reading and a corresponding representa tive diagram a patient cable connected to an electrode both of which are in good condition FIG 11 is a representative computer screen of a defibrillator pacemaker in which the patient cable is defective SUMMARY OF THE INVENTION The invention comprises a device and method for testing the integrity of an electrode The electrical de vice 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 electrode comprises the steps of generating a time do main reflectometer TDR reading output signal from the electrode and transmitting the signal to an output device The output signal may be analyzed to deter mined whether it varies by a predetermined threshold or it may be displayed so that differences in the electri cal characteristics of the electrode may be identified The present invention allows a cardiologist or techni cian to ensure that the electrode is properly engaged and to determine the integrity of the electrode 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 carr
15. United States Patent 9 Robson 54 TIME DOMAIN REFLECTOMETER INTEGRITY TESTING SYSTEM AND METHOD FOR MEDICAL DEVICE ELECTRODE 75 Inventor Jack R Robson Beech Grove Ind Random Technologies Inc Indianapolis Ind 21 Appl 971 415 22 Filed Nov 4 1992 73 Assignee Related U S Application Data 63 Continuation in part of Ser No 866 850 Apr 10 1992 51 Int CIS AGIN 1 362 52 U S 607 4 607 27 607 29 58 Field of Search 128 419 046 56 References Cited U S PATENT DOCUMENTS 3 922 914 12 1975 Fuchs 73 290 R 4 466 288 8 1984 Grynberg et al 73 654 4 786 857 11 1988 Mohr et al 324 58 5 BO 4 843 234 7 1989 Berthold et al 250 227 4 893 895 1 1990 Berthold et al 350 96 4 960 989 10 1990 Liebenrood et al 250 227 5 033 826 7 1991 350 355 OTHER PUBLICATIONS Tektronix 1520C Metallic Time Domain Reflectometer Service Manual Tektronix Inc Jul 1991 pp 5 1 to 5 11 Quantum lII Intermedics Cardiac Pulse Generator Physician s Manual Models 253 25 and 254 30 Jan 1990 Pacesetter Technical Manual APSII Model 3000 Programmed with Model 3030 Function Pak 1988 US005233986A 11 Patent Number 45 Date of Patent 5
16. 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 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 reading a TDR reading pro vides a view of the entire reflected wave A 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 To test for an open circuit the system may merely measure the time between the incident pulse and the beginning of the reflected waveform In general the present invention operates in the fol lowing manner Logic and
17. ar rate sensing mor phology 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 insulin pumps and such wires are within the scope of the term electrode as used herein and in the claims In addition in instances where a tube or stint is implanted in a patient a tube configured with an embedded electrical conductor run ning the length of the tube and connectable to a TDR and which will break if the tube breaks is also included within the definition of an electrode as used herein Electrodes as used herein also include electrical con ductors that are external to a patient used to send or receive electrical signals such as for example ECG electrodes or external pacemaker or defibrillator leads It will also be appreciated that although the in the embodiment described above a TDR reading is output through 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 fa
18. ating 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 5 233 986 9 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 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 begin 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
19. cceptable 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 choose to first retrieve a copy of the archived TDR reading 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 readin
20. ce D2 to D3 patient cable resistance 155 is shown Patient cable resistance 155 is substantially constant and is expected to be be tween minimum patient cable resistance value R1 and maximum patient cable resistance value R2 Should patient cable resistance 155 achieve a value outside of 5 233 986 15 predetermined thresholds namely the minimum and maximum values R1 and R2 respectively it is known that there is a short break or other discontinuity in patient cable 192 Second connector 193 connects pa tient cable 192 to electrode tip 194 and is represented by the distance D3 to D4 In the range between distance D3 and distance D4 second connector resistance 159 rises as indicated From the beginning of the electrode 194 to the end of the electrode tip 194 represented by distance D4 to 15 electrode resistance 161 is substan tially constant and should reside within the predefined threshold range between minimum electrode resistance value R3 to maximum electrode resistance value R4 At the termination of electrode 194 at a distance 105 the value of resistance rises as shown if electrode 194 is not connected to a patient i e if there is an open circuit In one embodiment the upper and lower resistance thresh olds are plus or minus ten percent 10 of the expected resistance at any distance along the completed circuit It will be appreciated by those of skill in the art that much of the analysis discussed herein with regard to the
21. ch can be operated during the device s operation and which does not interfere with the device s other functions Time domain reflectometers such as the 1502C Me tallic Time Domain Reflectometer manufactured by Tektronix Inc of Beaverton Oreg are used to test the integrity of cable such as co axial cables For such in tegrity testing time domain reflectometers send electri cal pulses down the cable and detect any reflections may 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 from the wire and returns to the instru ment In general variations in the resistance measured by the time domain reflectometer i
22. d then de press 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 elec trode 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 A 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 highlighted The physi cian may then depress the left 48 and or right 49 ar rows which will cause the highlighted values to be decremented or incremented respectively After the physician 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 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 el
23. d in FIGS 1 8 TDR circuitry 131 includes the circuitry necessary to generate a TDR pulse and to detect the resulting voltage Such a pulse may be caused to travel to individual defibrillator pad dles connector 126 and the paddles connected thereto or through an electrode connected to pacer output connector 128 or ECG connector 130 Circuitry for time domain reflectometers is well known and in isola tion does not form the present invention FIG 10 is a representative graphically displayed baseline TDR reading and a corresponding representa tive diagram of a patient cable connected to an elec trode tip both of which are in good condition Such a configuration may be such as connected to pacer output connector 128 see FIG 9 wherein a patient cable is connected to the pacer output connector and an elec trode tip is connected to the patient cable In the display of resistance versus distance over which the TDR pulse travels the distance from the origin of the graph to distance D1 represents the internal circuitry of medical device 171 and the resistance of internal circuitry 151 is shown to be substantially constant First connector 191 connecting patient cable 192 to device 171 is repre sented by first connector resistance curve 153 between distances D1 and D2 A rise in resistance occurs over the distance comprising first connector 191 From the beginning of patient cable 192 to the end of the patient cable 192 represented by distan
24. dentified The present invention allows a cardiologist or technician to ensure that the electrode is properly engaged and to determine the integrity of the electrode 23 Claims 8 Drawing Sheets Sheet 1 of 8 5 233 986 10 1993 U S Patent AG Sheet 2 of 8 5 233 986 Aug 10 1993 U S Patent 26 10 01 YOSYND LV OHY LNSYYND NOISIAIG WW 31 05 MINOZIHOH i HL NIT IWOISAHd WW LNIOd MWINOZIHOH gt 5 HOSUNA 051 W 001 WOLLYSA SWHO 24 JONYISISIH JOUNOS SNOILLdO 14510 82 0 30 ALIDO TSA 5 0001 ASVE YAL 006 GL IWOISAHd YVIOdINN ALINV10d W SE WH 06 121919313 5 SNIDGVAY 000 SOINOYLOATSL 5 L 3008190314 isnrav 55 NOLLVYUNDIANOD LNSYYHND NI ONIGVAY go SONIGVSY NIVLGO _ 1909195 OL 38015 lt 40138
25. econd pacing electrodes 194 195 are connected Thereafter electrodes 194 195 are connected to first and second pacing electrode pads 196 197 respec tively which are placed on the patient It should be noted that pacing electrodes 194 195 need not be con nected to pacing electrodes pads 196 197 for integrity testing of electrodes 194 195 to be performed Third graphical display section 200 shows defibril lator pacemaker 181 when used is connection with first and second monitoring electrodes 204 205 for the pur pose of monitoring ECG signals In the ECG monitor ing configuration patient cable 202 is connected to defibrillator pacemaker 181 by connector 201 and to monitoring electrodes 204 205 at its other end As dis cussed above monitoring electrodes 204 205 may be connected to monitoring electrode pads 206 207 re spectively which are then in turn placed on the patient It will be appreciated by those of skill in the art that the display actions are dependent on the device and connec tors employed For example third graphical display 10 15 20 25 30 35 40 45 50 55 60 65 16 function 200 may not be necessary should the ECG monitoring function operate through the same connec tors and cables wires as are used for the pacing function of defibrillator pacemaker 181 In FIG 11 second graphical display section 190 is highlighted indicating defibrillator pacemaker 181 is in its pacing configu
26. ection with a portable external defibrillator pacemaker The defibril lator pacemaker includes a central processing unit CPU 120 which includes appropriate memory and software to carry out the functions described herein power supply 121 battery 122 charging circuitry 123 and display 124 The device is powered by battery 122 and may be recharged by charger circuitry 123 Display 124 may comprise a computer screen LCD display plotter or other such similar device In this embodi ment three primary functions are provided by the defi brillator pacemaker First the device may serve as a defibrillator through defibrillator circuitry 125 which is responsible for the delivery of energy to defibrillator paddles connector 126 connected to defibrillator cir cuitry 125 The second function of the defibrillator pacemaker is as a pacemaker Pacing circuitry 127 connected to pacer output connector 128 delivers pulses to electrodes see FIG 11 connected to pacer output connector 128 Third the defibrillator pacemaker includes the capability to monitor the ECG signal of a patient through ECG circuitry 129 con nected to ECG connector 130 In addition to these conventional functions of the defibrillator pacemaker the device also includes TDR circuitry 131 connected to CPU 120 and to defibrillator paddles connector 126 pacer output connector 128 and ECG connector 130 As discussed in detail for the embodiment of the in vention illustrate
27. ectrode 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 ured with sufficient memory to store a separate setting for each electrode or lead In addition pulse selector will 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 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 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 stimul
28. for the defibrillator output and pacing outputs so the integrity of the entire system may be tested As it is contemplated that the TDR circuitry may be reduced to a smal and inexpensive application specific integrated circuit it is also within the spirit and scope of the invention that separate TDR s be provided for each electrode circuit instead of providing a single TDR with switch means which may be used to connect the TDR to different electrodes It is also contemplated that different types of TDR readings may be taken for differ ent types of electrodes For example for longer elec trodes it may be desirable to take a TDR reading con sisting of 1 024 time divisions instead of 256 divisions In addition the gain and resolution at which TDR reading may be graphically displayed may very depending on the electrode being tested It is contemplated that such parameters may be separately stored for each electrode in a system and automatically recalled and used to take a particular TDR reading It will further be appreciated that the system of the present invention may include an integral graphical printer and a test mode switch When the test mode switch is activated CPU 120 automatically cycles through each electrode in the system and conducts an integrity test the results of which may be printed out with a date and time stamp Such a system allows its integrity to be checked on a routine basis and before a medical emergency In addi
29. g archived after implanta 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 Millirho Alarm option the physician may specify a millirho value predetermined threshold by which if a TDR reading deviates in a relevant portion an indicating 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 whi
30. gs specified by the No of Readings Averaged parameter has been completed the each sum may be 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 reflectorm eter i e 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 composite 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 i
31. ignal to a stored reference TDR signal means for indicating whether the TDR output signal varies from the stored reference TDR signal by a predefined threshold 7 The device of claim 6 wherein the means for indi cating comprises a graphical display of an electrode 8 The device of claim 7 further comprising means for graphically displaying the relative point on the graphi cally displayed electrode where the TDR output signals varies from the stored reference TDR signal by the predefined threshold 9 The device of claim 1 further comprising means for receiving at least one additional electrode the time domain reflectometer means being operatively con nected to the at least one additional electrode receiving means such that at a time domain reflectometer pulse may be transmitted to the at least one additional elec trode receiving means 10 The device of claim 9 further comprising at least one ECG reading electrode connected to at least one of the electrode receiving means 11 The device of claim 9 further comprising means for automatically causing a TDR reading to be taken on each electrode receiving means 12 A method of analyzing the integrity of a first medical electrode for transmitting an electrical signal comprising the steps of providing means for transmitting an electrical signal on the first electrode the transmitting means being capable of being selectively enabled and disabled providing a time domain reflectomete
32. ims may encompass defibrillator cables patient ca bles electrodes or other wires or to any combination thereof extending from such a medical device Also the term medical device as used in the claims may encompass any electrical device used in the medical profession wherein an electrode as defined herein is connected to the device It will be further appreciated that the TDR technol is not limited to a single wire connected to medi cal device Rather the technology may be used for any and all wires cables sensors or pads extending from the medical device In this manner the technician may check the system prior to its use to insure that the com ponents are all operational Accordingly as used herein and in the claims the term electrode includes all of the components used to carry an electrical signal from the instrumentation to the patient and back even where this consists of discrete pieces electrically connected together It will further be appreciated that the system of the present invention can not only test for electrode integ rity prior to use but during operation of the medical device Such a feature is desirable because with the frantic pace at which medical technicians operate dur ing a medical emergency it is possible for electrical cables to become inadvertently pulled and thereby re duce the integrity of the electrical connections between them Thus in one embodiment of the invention
33. itiation of the first incident pulse TDR 1 0 23 generates second TDR pulse 108 The above 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 pulses 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 readin
34. le 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 5 233 986 13 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 generate 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 medi cal electrode such as ventricul
35. n is high lighted The Select button is then depressed This causes programmer 28 display a dialogue 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 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 erated 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 10 20 25 30 35 40 45 50 55 60 65 12 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 a
36. ncludes 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 5 233 986 11 information may be supplied by the electrode manufac turer or manually programmed into the programmer With a known Vy 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 convertible 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 wavefo
37. ndicates 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 of 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 U S patent application Ser No 07 866 850 filed Apr 10 1992 discloses an integrity testing system for implantable electrodes such as may be utilized with implanted pacemakers or defibrillators The electrical device disclosed in U S patent application Ser No 07 866 850 has a receptacle for an electrode and in cludes a time domain reflectometer comprising an out put signal mechanism operatively connected to the electrode receptacle The method of analyzing the in
38. 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 passed 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 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 elec trode receiving means commanding the TDR to gener ate an incident pulse 104 see FIG 8 on the selected electrode lead In one
39. pads of such sys tems may become loose or bent resulting in a poor or open circuit For such systems there may be no appar ent indication that the equipment is faulty causing the defective equipment to be used on patients in critical condition The only way to detect such an equipment failure is for an astute medical technician to notice that all of the patients on which the defective equipment had been recently used had died and to have the equipment thoroughly inspected by an advanced medical techni cian Some external devices such as the Code Master De fibrillators and the Zoll PD 1200 Pacemaker Defi brillator provide information to the operator or techni cian regarding the integrity of the electrode Specifi cally these systems provide a warning when a complete circuit is not provided A complete circuit is one in which there is current flow between the electrodes and there are no severe discontinuities in the electrodes Thus the electrodes must be place against a patient s body to complete an electrical circuit in order to deter mine whether a break exists in the cables electrodes or the connectors of either Because the cables or elec trodes must contact the patient before a test may be performed does not allow a fault in the system to be identified until the system must be used Furthermore because time is of the essence when the device is utilized on a patient it is desirable to provide an integrity testing
40. r TDR opera tively connected to the first electrode disabling the transmission of electrical signals on the first electrode generating a first TDR reading from the first elec trode and outputting the TDR reading reenabling the transmission of electrical signals on the first electrode 13 The method of claim 12 wherein the means for transmitting comprises a means for transmitting pace maker pulses 14 The method of claim 12 wherein the means for transmitting comprises a means for transmitting a defib rillator pulse 15 The method of claim 12 wherein the means for transmitting comprises a means for transmitting an ECG reading signal 16 The method of claim 12 wherein the disabling of the transmission of electrical signals on the first elec trode occurs based on the timing of heartbeats of a patient to whom the electrode is connected 17 The method of claim 12 further comprising the steps of 5 233 986 19 storing a reference TDR signa representative of a TDR signal from a working electrode connected to the electrode receiving means comparing the outputted TDR signal to the stored reference TDR signal and indicating whether the outputted TDR signal varies from the stored reference TDR signal by a prede fined threshold 18 The method of claim 17 wherein the indicating step includes graphically displaying an electrode 19 The method of claim 17 wherein the indicating step further includes if the output
41. ration Along patient cable 192 is a marked or highlighted trouble area 198 Also at the top right of the display is message 199 BREAK IN CA BLE which is also highlighted or marked This simple display which may be accompanied by an audible alarm immediately informs the physician or technician that there is a discontinuity of significance in patient cable 192 which requires replacement of patient cable 192 for the proper operation of defibrillator pacemaker 181 It will be appreciated by those of skill in the art that there may be discontinuities or breaks in either first electrode 194 or second electrode 195 in this configura tion One of the advantages of the use of TDR technol ogy is that more than one problem can be identified and displayed to the physician or technician Moreover the system may be easily tested by for example intention ally unplugging an electrode from the system and deter mining whether a BREAK IN CABLE message is dis played It will also be appreciated by those with skill in the art that TDR technology may be used in connection with a variety of types of wires cables or electrodes extending from such a medical device The technology need not be limited to a particular type of cabling nor should the requirement of the device to use a successive connections of various cable types preclude the use of the technology to determine defects in the attached cabling Thus the term electrode as used in the cla
42. rm is flat indicating a con stant impedance throughout the length of the electrode with no breaks or shorts FIG 5 shows a representative TDR 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 at 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 cause graphical cursor 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 optio
43. rnal pacemakers defibrillators and the like are usually portable devices which are battery powered and capable of being recharged The device s portabil ity is important because it is typically used in emergency situations or as a temporary resolution to a patient s problems before a more permanent solution can be ren dered For example defibrillators may be carried in an ambulance or used in hospital emergency rooms to revive a patient or to restore a normal heart rhythm An external pacemaker may be used to provide assistance to a patient who has not yet had an internal pacemaker implanted or to provide pacing while the patient is in surgery to implant or replace an implantable pace maker To provide signals to the medical electrodes or to receive signals from the patient as is necessary for moni toring diagnostic or other functions of the device ca bles electrodes or wires extend from the device to the patient For example the Medtronic Model 5345 Tem porary Pulse Generator available from Medtronic Inc of Minneapolis Minn is a temporary pacemaker such as may be used by a patient prior to implanting a perma nent pacemaker A patient cable is connected to the device and unipolar or bipolar pacing leads contacting the patient are connected to the patient cable The Med tronic model 5311 pacing system analyzer is used to test sensing and pacing thresholds of heart electrodes The Code Master Defibrillators available from He
44. sed in conjunction with the portable devices the integrity testing system must be able to be integrated within the device and must not consume a great deal of power OBJECTS OF THE INVENTION Accordingly it is one object of the present invention is to provide a method and apparatus for testing the integrity of cables leads and or electrodes connected to external medical devices such as defibrillators tempo rary pacemakers or pacing system analyzers to thereby alert the physician or a technician of potential for exist ing problems associated with the electrode or cable that may be detrimental to the patient It is another object of the present invention to pro vide a method for testing the integrity of such cables and or electrodes which does not require that the elec trode be in contact with a patient during such testing and therefore may be performed on a routine basis It is yet another object of the present invention to provide a testing system which is easy to use and time efficient to avoid any delay in the operation of the medi cal device s norma functions It is still another object of the present invention to provide an integrity testing system which does interfere with the normal operation of the medical device may be integrated into the medical device and does not con sume a great deal of power to operate BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 shows a block diagram of one embodiment of a device of the present
45. ster 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 as patient social secu 10 20 25 30 35 40 45 50 55 60 65 14 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 differential between the incident pulse and a selected portion of a TDR reading Referring now to FIG 9 there is shown a representa tive block diagram of one embodiment of the device of the present invention when used in conn
46. ted TDR signal varies from the stored reference TDR signal by a predefined threshold graphically displaying the relative point on the graphically displayed electrode where the TDR output signals varies from the stored reference TDR signal by the predefined threshold 20 The method of claim 12 further comprising the steps of 10 15 20 25 30 35 45 50 55 65 20 providing at least one second medical electrode and providing means for operatively connecting the TDR to the at least one second medical electrode such that a time domain reflectometer pulse may be transmitted thereto and providing means for selecting which of the electrodes the TDR may be operatively connected to 21 The method of claim 20 wherein the means for selecting comprises automatic means for automatically causing a TDR reading to be taken on each medical electrode 22 The method of claim 12 further comprising the step of graphically displaying the outputted TDR read ing 23 The method of claim 12 further comprising the steps of selecting a portion of the generated TDR reading and graphically displaying the selected portion of the TDR reading lt
47. tion the printout can pro vide written documentation that the system was checked at the designated time What is claimed is 1 An electrical medical device comprising means for receiving a first electrode means for transmitting a first electrical signal to the electrode receiving means time domain reflectometer means operatively con nected to the electrode receiving means such that at a time domain reflectometer pulse may be trans mitted to the electrode receiving means the time domain reflectometer means comprising output signal means and anti coincidence means preventing a time domain reflectometer pulse from being transmitted to the electrode receiving means when a first electrical signal is being transmitted to the electrode receiv ing means 10 15 20 25 30 35 40 45 50 55 60 65 18 2 The device of claim 1 wherein the device com prises a pacemaker 3 The device of claim 1 wherein the device com prises a defibrillator 4 The device of claim 1 wherein the output signal of the means comprises a TDR reading from the time domain reflectometer 5 The device of claim 1 wherein the output signal means comprises means for graphically displaying a TDR output signal 6 The device of claim 1 further comprising means for storing a reference TDR signal representa tive of a TDR signal from a working electrode connected to the electrode receiving means means for comparing a TDR output s
48. wlett Packard of Andover Mass provide the capabilities of defibrillation and ECG monitoring Both integral defib rillator paddies and optional gel electrodes may be used with the device to accomplish these functions Similarly the Lifepak 6 Cardiac Care System available from Physio Control Corporation of Redmond Wash 10 15 20 30 35 40 45 50 55 60 65 2 uses paddles for defibrillation and patient cables for monitoring ECG A combination pacemaker and defib rillator such as the 201 PD 1200 Pacemaker Defi brillator available from ZMI Corporation of Woburn Mass uses paddles or gel electrodes for defibrillation and gel electrodes for pacing and for monitoring ECG signals In all instances the integrity of the defibrillator patient cable or electrode is of utmost importance for the proper operation of the external device Presently most portable pacemakers and defibrilla tors are periodically checked by hospital staff to deter mine only whether the most basic functionality exists For example a nurse may check such a unit to deter mine whether it is plugged in whether the proper dis play appears when the unit is switched on and whether an appropriate quantity of ancillary supplies such as pacing pads are readily available However other as pects of the system do not lend themselves to being readily checked For example many connectors be tween the cables leads electrodes or
49. y out the func tions described herein rate limit section 12 and output section voltage multiplier 13 Conventional microcir cuitry and preferably an application specific integrated circuit is used to package the TDR and other compo nents in the implantable case The pacemaker is de signed 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 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 10 20 25 35 45 55 60 65 6 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
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