the embodiments herein are directed to the diagnosis of lead or conductor anomalies , such as insulation failures , in an implantable medical device , such as pacemakers , vagal nerve stimulators , pain stimulators , neurostimulators , and implantable cardioverter defibrillators ( icds ). however , for clarity , discussion of lead or conductor anomalies will be made in reference to icds . however , those with skill in the art are cognizant of the fact that the methods and apparatus as disclosed herein are suitable for use with any one of the various implantable medical devices . fig2 a , 2b , and 3 depict known multi - lumen icd defibrillation electrodes or leads that have been diagnosed with lead conductor anomalies . while these are indicative of the type of leads that can be diagnosed , anomalies in any type of defibrillation electrodes or leads are capable of being diagnosed with the methods and apparatus as disclosed herein . fig2 a depicts the medtronic quattro secure ® lead . fig2 b depicts the medtronic sprint fidelis ® lead . fig3 depicts the st . jude medical riata ® lead . the leads 10 , while having various constructions , have similar features . these similar features are identified with the same reference numbers in the figures . the implantable cardiac lead 10 is comprised of a lumen 12 and center inner pacing coil 14 surrounded by ptfe insulation 16 , a plurality of lumens 18 each containing at least one conductor 20 with each conductor 20 surrounded by etfe insulation 22 , an outer insulating layer 24 , and a silicone insulation 26 disposed between the lumen 12 and the outer insulating layer 24 . the conductors 20 include a sense conductor 21 , a high voltage rv conductor 23 , and a high voltage svc conductor 25 . the plurality of lumens 18 are disposed in the silicone insulation 26 . the conductors 20 carry electric current to the pace - sense electrodes 66 , 68 high voltage rv coil 64 , and high voltage svc coil 62 . as discussed above , and shown in fig4 , insulation failures most commonly occur at three regions along the course of a pacemaker or icd lead 10 . the first region 42 is proximate the pocket , caused either by abrasion of the lead 10 insulation 24 by pressure from the housing (“ can ”) of the pulse generator or twisting of the lead 10 within the pocket . the second region 44 is that between the clavicle and first rib , where the lead 10 is subject to “ clavicular crush .” the third region 46 is the intracardiac region near the tricuspid valve . this third region 46 is a particularly common site of insulation 24 failure for the st . jude riata ® lead 10 which is subject to “ inside - out ” insulation failure due to motion of the internal conductors 20 relative to the outer insulation 24 . fig5 depicts on icd 52 implanted in the chest of a patient . the icd 52 has an outer housing 54 , commonly referred to as a “ can ,” inner circuitry 56 and a battery 58 . connection is made to the heart 60 via the lead 10 . the lead 10 can have an optional proximal defibrillation coil 62 which is near the superior vena cava ( svc ) and is commonly referred to as the svc coil 62 . the lead 10 also has a distal defibrillation coil 64 which is commonly referred to as the right . ventricular coil or rv coil 64 . also shown is the optional “ ring ” pacing - sensing electrode 66 . located at the distal end of the lead 10 is the “ tip ” pacing - sensing electrode 68 . the outer insulating layer 24 of the leads 10 is generally a polymer such as silicone , polyurethane , or a copolymer of silicone and polyurethane . stress on the insulation 24 from anchoring sutures , outside - in abrasion from contact with the housing , or inside - out abrasion from movement of the cables within the lead 10 may result in insulation 24 breaches or failures . in addition , the insulation 24 can fail due to chemical reactions such as metal ion oxidation . fig6 depicts a lead 10 insulation 24 failure at location 70 . when pulses are delivered to the affected conductor 20 the local electrical equi - potential lines appear approximately as those shown at 72 . this results in a disturbance of local potentials recorded within the body or on the body surface via electrodes on the skin . fig7 depicts an example of a detection method for pacing conductors 14 . in this embodiment , an insulation failure is checked for in either the tip pacing - sensing electrode 68 or the ring pace - sense electrode 66 . low amplitude (& lt ; 1 v ) test pulses with duration & lt ; 1 . 5 ms are delivered in a “ bipolar ” fashion between the “ tip ” sense conductors 21 and the “ ring ” sense conductors 21 . pulses may be delivered in the absolute refractory period after a paced or conducted beat . the test pulse may be delivered , under sedation in a surgical suite , using a higher output at pulse generator change with background electrical noise . due to the dipole effect of the closely - spaced “ tip ” pacing - sensing electrode 68 and “ ring ” pacing - sensing electrode 66 , the electrical potential lines are tightly located near these electrodes 66 , 68 if the insulation around the conductors is intact , as shown by the smaller ovals 74 . note that these ovals in fig7 represent a simplification of the actual equi - potential lines which are typically positive (+) around the “ ring ” pacing - sensing electrode 66 and negative (−) around the “ tip ” pacing - sensing electrode 68 . the amplitude of the skin - surface potential during bipolar pacing is on the order of approximately 1 mv in a conventional lead and much weaker in other locations with high - fidelity ecg units . an example of a high - fidelity ecg unit is the ge mac 5500 hd . due to the high - frequency nature of the pacing pulse it is typically invisible on older ecg units due to their low - pass filtering . fig8 depicts an embodiment of a method for detecting an insulation failure in either the tip or ring conductor 20 . note that this method is able to be used for any pacing conductor such as endocardial electrodes in the right atrium , coronary sinus , or the left ventricle , as well as epicardial or subcutaneous electrodes . in operation , a single recording electrode is moved along the surface of the body parallel to the path of the implanted lead 10 . visual confirmation of the path can be provided by , for example , radiographic methods , such as an x - ray taken in one or more views , or by ct scan . another embodiment can utilize multiple simultaneous recordings on the surface of the body , e . g ., one over the surgical pocket and intravascular / intracardiac course of the lead 10 . another embodiment can utilize an array of electrodes deployed in fixed positions over the surface of the body . further , although the embodiments described utilize the icd &# 39 ; s 52 electronics 56 as the source of test pulses , test pulses may also be delivered at pulse generator change using an external test device such as a programmer . the method shown in fig8 connects the patient to a high - fidelity ecg unit 80 . the high - fidelity ecg unit reliably displays bipolar transvenous pacing pulses , in order to detect the pacing pulses . the test pulse voltage is reduced below the pacing threshold 81 to minimize pacing . the pacing rate is set to a rate faster than the spontaneous ventricular rate 82 in the asynchronous ( voo mode ) to provide more pulses to detect and to avoid most qrs complexes . a cutaneous electrode is moved along the surface of the body parallel to the path of the implanted lead 83 . visual confirmation of the path can be provided by , for example , radiographic methods , such as an x - ray taken in one or more views , or by ct scan . the cutaneous electrode movement includes the loops of lead in the pocket which is a common site of insulation breach . a local maximum voltage spike is searched for 85 . if a local spike , of sufficient amplitude ( e . g . & gt ; 1 mv ) is located sufficiently far away from the tip of the lead then an insulation break is detected 86 . else , an insulation break is not detected 87 . if the patient cannot tolerate a brief absence of pacing , then pacing is performed at a rate between the lower and upper rate limits ( inclusive ) with the voltage set to the maximum . fig9 depicts an embodiment of a method for detecting an insulation failure in defibrillation conductors in dual - coil systems . the method can detect a possible insulation break in either one of the defibrillation conductors . the icd is modified to deliver a continuous high - frequency ac impedance test between the svc and rv electrodes with the icd housing turned off 91 . the patient is connected to a high - fidelity ecg unit 92 such as a ge mac 5500 hd in order to detect the pacing pulses . the impedance testing high - frequency signal is turned on by initiating an impedance test 93 . an electrode is moved along the surface of the body parallel to the path of the implanted lead 94 . visual confirmation of the path can be provided by , for example , radiographic methods , such as an x - ray taken in one or more views , or by ct scan . the electrode movement includes the loops of lead in the pocket which is a common site of insulation breach . a local maximum voltage spike is searched for as shown at 95 . if a local spike , of sufficient amplitude is located sufficiently far away from the tip of the lead then an insulation break is detected as shown at 97 . else , an insulation break is not detected as shown at 98 . fig1 depicts an embodiment of a method for detecting an insulation failure in defibrillation conductors in single - coil systems . the method can detect a possible insulation break in either one of the defibrillation conductors . the icd is modified to deliver a continuous high - frequency ac impedance test between the rv electrodes and the icd housing 101 . the patient is connected to a high - fidelity ecg unit 102 such as a ge mac 5500 hd in order to detect the pacing pulses . the impedance testing high - frequency signal is turned on by initiating an impedance test 103 . an electrode is moved along the path of the implanted lead 104 . visual confirmation of the path can be provided by , for example , radiographic methods , such as an x - ray taken in one or more views , or by ct scan . a local voltage null is searched for at 105 . without any insulation break , there should be a large signal near the icd can and a large signal near the rv coil 108 . the voltage of this signal is expected to gradually decrease when moving from the can to the rv coil with a polarity inversion ( and now voltage null ) in between . if a local spike ( away from the coil ) is located then an insulation break is detected at 107 . else , an insulation break is not detected at 108 . in the case of an insulation 24 failure adjacent to the icd &# 39 ; s 52 housing 54 , it is sometimes difficult to localize the failure using the above techniques of detecting a surface potential . in this type of scenario , pulses , or a continuous high - frequency alternating current are delivered over the three current paths corresponding to the three electrodes on the lead which include the pace - sense ( tip - ring ) dipole , the ring - rv coil dipole , and the tip - rv coil dipole . in no case should there be evidence of current flow near the pocket 42 or directly under the clavicle ( clavicular crush ) 44 . by determining which dipole or dipoles do not result in an anomalous potential near the housing , identification of the remaining conductor can be made as having failed insulation 24 . fig1 depicts a method of localizing an insulation break . once an insulation break is detected or indicated , localization of the break can be accomplished via a high - resolution inverse - ecg system such as the cardio - insight mapping system . the method requires that the system be modified to provide potentials along the path of the lead with the suspected insulation break . the method is performed by modifying inverse - ecg system to calculate potentials along the lead 110 . the next step is connecting the patient to the inverse - ecg system 112 and then delivering pacing or ac impedance test stimuli . the steps further include locating maximum signals that are not at an electrode 116 and localizing the insulation break to the region of maximum signal that are not adjacent to a stimulated electrode . additionally , for the embodiments as disclosed herein , a baseline recording ( or set of recordings ) can be completed when the lead system becomes stable , which is typically between one and three months after implant . the sites of maximum potential in subsequent testing may then be compared with sites of maximum potential during subsequent testing either by the operator or by using custom software . the above descriptions depict the duration of the testing process as an embodiment of a single test setting ( e . g . at pulse generator change or in outpatient follow up ). however , in other embodiments , the methods can be practiced with a 24 hour to one week ambulatory recording period thus providing an extended time period that can be used to effectively identify intermittent lead insulation failure . in embodiments , the recording system may be activated by telemetry signals delivered by the pulse generator . in an embodiment , the test signals as generated in the embodiments of the methods about are generated from an implantable pulse generator . in another embodiment , as shown in fig1 , an apparatus including an external test device , such as programmer module , is utilized at implant and measurements from the cutaneous electrodes are analyzed in near real time using the external test device . the apparatus 120 has an ac amplifier 122 , an ac generator 124 , a filter 126 , a modulator 128 , and a digital meter 130 . one input of the ac amplifier is connected to the roving ecg electrode and the other input is connected to the reference ecg electrode . the ac amplifier output is fed into the filter 126 , which is depicted as a 10 khz filter but it is not so limited . the filter 126 is output to the modulator 128 and to the digital meter 130 . the ac generator 124 is connected to the implanted leads . the ac generator 124 is depicted as a 10 khz ac generator but it is not so limited . additionally the ac generator 124 is connected to the filter 126 . in an embodiment , the test pulses are delivered through the implanted pulse generator . measurements from the cutaneous electrodes are then stored in an ambulatory recording device or long - term electrocardiographic event recorder . in some embodiments , the recording device can be equipped with a larger electrode array as described herein with respect to other embodiments . after a specified monitoring period , e . g ., 24 hour to one week to one month or longer ambulatory recording period , the stored measurements are downloaded to an external analysis unit . in embodiments , the recording system may be activated by telemetry signals delivered by the pulse generator . it is apparent to those skilled in the art that the ambulatory recording period can be any timeframe as specified by the physician that is sufficient to accomplish the purposes herein . in an embodiment , the 10 khz ac generator 124 is configured to deliver a 10 v sine wave to the implanted leads 10 during a procedure that involves disconnecting the leads 10 from the pulse generator . typically , this occurs for a device change due to battery depletion or infection . the 10 khz frequency is chosen as it is above the frequencies that affect cardiac cells . in certain embodiments , frequencies of 5 to 25 khz are used but , in other embodiments , frequencies of 1 to 250 khz can be used . care should be taken at lower frequencies because cardiac capture or collapse can occur with sufficient amplitudes . in embodiments , a voltage of 5 v ac is delivered to give a strong signal at the skin surface . in other embodiments , voltages of 1 to 20 v ac are provided . in an embodiment , the signal from the recording electrode or electrodes is fed thru the amplifier 122 and then filtered by a narrow - band filter 126 . the filter 126 can be either an analog or digital notch filter . on another embodiment , the filter can be a synchronous filter using the signal 132 for synchronization from the generator 124 . extremely high signal - to - noise ratios are thus achieved . the generator frequency and the filter frequency should be the same . in this embodiment , the roving electrode would not be physically moved . rather , a number of ecg adhesive electrodes would be placed in the region of the implantable lead 10 and be connected to a switch - box . the operator or a computerized system would then select the desired electrode , one at a time . the “ reference ” electrode would be a subcutaneous electrode in the device pocket 42 . the amplified signal is then modulated down to a lower frequency , e . g ., 100 hz , so that the signal can be readily processed by a conventional ecg unit . the digital meter 130 displays the amplified signal amplitude . as the clinician moves the roving electrode , via the switch - box , the digital meter 130 displays the signal at each skin location and is thus able to find the skin location with the strongest signal . additionally , an ecg unit is not required as the digital meter 130 displays the signals . in an alternative embodiment , the signal generator generates a 90 hz sine wave which is easy to differentiate from utility 50 / 60 hz interference and has the advantage of passing readily thru any ecg unit . it does have the disadvantage of limited driving voltage as such frequencies can easily cause cardiac collapse . the following patents and applications , the disclosures of which are incorporated by reference in this case ( other than claims and express definitions ), are prior art attempts by common inventors to solve the problem at issue : u . s . pat . no . 8 , 352 , 033 (&# 39 ; 033 ) to kroll , issued jan . 8 , 2013 ; u . s . patent application ser . no . 13 / 735 , 599 to kroll , filed on jan . 7 , 2013 which is a continuation of &# 39 ; 033 ; and u . s . patent application ser . no . 12 / 868 , 056 to swerdlow , filed on aug . 25 , 2010 . the following provisional applications , the disclosures of which are incorporated by reference in this case ( other than claims and express definitions ), are related to each other : u . s . patent application 61 / 689 , 191 to kroll and swerdlow , filed on jun . 1 , 2012 ; u . s . patent application 61 / 689 , 189 to kroll and swerdlow , filed on jun . 1 , 2012 ; and u . s . patent application 61 / 733 , 713 to kroll and swerdlow , filed on dec . 5 , 2012 . the values noted above are example embodiments and should not be read as limiting the scope of this invention . those skilled in the art will recognize that the above values may be adjusted to practice the invention as necessary depending on the electrode implantable cardiac lead technology used and the physical characteristics of the patient . while the present invention has been described with reference to certain embodiments , those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of the present invention without departing from the spirit and scope of the invention as defined by the appended claims .
the invention relates to a method and apparatus for diagnosis of conductor anomalies , such as insulation failures , in an implantable medical device , such as an implantable cardioverter defibrillator , a pacemaker , or a neurostimulator . insulation failures are detected and localized by identifying changes in electrical fields via surface potentials . small variations in potential are detected along the course of the electrode near the site of insulation failure .