Assessing a lead based on high-frequency response

In general, this disclosure is directed to techniques and circuitry to determine characteristics of an implantable lead associated with an implantable medical device (IMD). The implantable lead may be designed to be MRI-safe by having one or more components that attenuate frequencies associated with an MRI that, if left unreduced, may interfere with the performance of the lead and/or cause harm to the tissue in which the lead is implanted. The circuitry may transmit a signal through the lead and receive a response signal. The device may determine the lead characteristics by comparing the transmitted signal with the received signal. In addition to determining whether the lead is MRI-safe, the techniques of this disclosure may be also utilized to determine whether the lead is faulty.

TECHNICAL FIELD

The invention relates to medical devices, and, more particularly, to detection of medical device states.

BACKGROUND

A variety of medical devices for delivering a therapy and/or monitoring a physiological condition have been used clinically or proposed for clinical use in patients. Examples include medical devices that deliver therapy to and/or monitor conditions associated with the heart, muscle, nerve, brain, stomach or other organs or tissues. Some therapies include the delivery of electrical signals, e.g., stimulation, to such organs or tissues. Some medical devices may employ one or more elongated electrical leads carrying electrodes for the delivery of therapeutic electrical signals to such organs or tissues, electrodes for sensing intrinsic electrical signals within the patient, which may be generated by such organs or tissue, and/or other sensors for sensing physiological parameters of a patient. Other medical devices do not include leads, and instead include electrodes and/or sensors formed on or located within a housing of the device.

In systems that include medical leads, the leads may be configured to allow electrodes or other sensors to be positioned at desired locations for delivery of therapeutic electrical signals or sensing. For example, electrodes or sensors may be carried at a distal portion of a lead. A proximal portion of the lead may be coupled to a medical device housing, which may contain circuitry, such as signal generation and/or sensing circuitry. In some cases, the medical leads and the medical device housing are implantable within the patient. In systems that do not include medical leads, electrodes and/or sensors may be located within the medical device housing, which may be positioned at a location that allows delivery of therapeutic electrical signals or sensing of bioelectrical signals. Medical devices with a housing configured for implantation within the patient may be referred to as implantable medical devices.

SUMMARY

In general, the disclosure describes techniques for determining a characteristic of an implantable medical lead based on a response of the lead to application of a relatively high frequency signal. For example, based on the response, an implantable medical device (IMD) or other device may determine whether a lead coupled to the IMD is designed to be MRI-safe or safe for other imaging modalities, e.g., the lead includes electromagnetic field mitigation circuitry. As another example, based on the response, an IMD or other device may determine whether the electromagnetic field mitigation circuitry is operating properly as to dissipate MRI energy that may damage the lead and/or cause damage in the tissue where the lead is implanted, e.g., whether an MRI-safe lead attached to the IMD is in fact MRI-safe.

A signal generator within the IMD may generate a relatively high frequency signal, and apply the signal to the lead. The frequency of the signal may be on the order of approximately 1 MHz or greater (e.g., approximately 64 MHz). The IMD may additionally include circuitry to measure a response of the lead to the signal. Based on the response, the lead characteristic, e.g., whether the lead includes properly operating electromagnetic field mitigation circuitry, may be determined. Additionally or alternatively, the response of the lead may indicate whether a lead related condition or lead fault, e.g., a fracture, is present in the lead. The measured response of the lead to the relatively high frequency signal may include, for example, impedance during application of the signal, or a characteristic of a reflected signal during application of the relatively high-frequency signal.

In one example, the disclosure is directed to a method comprising transmitting, by a device, a signal through at least one medical lead implanted within at least one anatomical region of a patient, wherein the at least one medical lead is coupled to an electrical component configured to attenuate a frequency of energy, receiving, by the device, a response signal, analyzing the response signal, and determining characteristics of the at least one medical lead based on the analysis, wherein the characteristics include at least one of an indication whether the electrical component attenuates the frequency or a detected fault in the at least one medical lead.

In another example, the disclosure is directed to a medical system comprising a signal generator that transmits a signal through at least one medical lead implanted within at least one anatomical region of a patient, wherein the at least one medical lead is coupled to an electrical component configured to attenuate a frequency of energy, a sensing module that receives a response signal, an analysis module that analyzes the response signal, and at least one processor that determines characteristics of the at least one medical lead based on the analysis, wherein the characteristics include at least one of an indication whether the electrical component attenuates the frequency or a detected fault in the at least one medical lead.

In another example, the disclosure is directed to a medical system comprising means for transmitting, by a device, a signal through at least one medical lead implanted within at least one anatomical region of a patient, wherein the at least one medical lead is coupled to an electrical component configured to attenuate a frequency of energy, means for receiving, by the device, a response signal, means for analyzing the response signal, and means for determining characteristics of the at least one medical lead based on the analysis, wherein the characteristics include at least one of an indication whether the electrical component attenuates the frequency or a detected fault in the at least one medical lead.

In another example, the disclosure is directed to an article of manufacture comprising a computer-readable medium comprising instructions that, upon execution, cause a processor to transmit, by a device, a signal through at least one medical lead implanted within at least one anatomical region of a patient, wherein the at least one medical lead is coupled to an electrical component configured to attenuate a frequency of energy, receive, by the device, a response signal, analyze the response signal, and determine characteristics of the at least one medical lead based on the analysis, wherein the characteristics include at least one of an indication whether the electrical component attenuates the frequency or a detected fault in the at least one medical lead.

In another aspect, the disclosure is directed to an article of manufacture comprising a computer-readable storage medium. The computer-readable storage medium comprises computer-readable instructions for execution by a processor. The instructions cause a programmable processor to perform any part of the techniques described herein. The instructions may be, for example, software instructions, such as those used to define a software or computer program. The computer-readable medium may be a computer-readable storage medium such as a storage device (e.g., a disk drive, or an optical drive), memory (e.g., a Flash memory, read only memory (ROM), or random access memory (RAM)) or any other type of volatile or non-volatile memory that stores instructions (e.g., in the form of a computer program or other executable) to cause a programmable processor to perform the techniques described herein.

DETAILED DESCRIPTION

This disclosure describes various techniques for verifying characteristics of components of an IMD, including determining whether an implantable medical lead is MRI-safe and whether the lead is functional. Implantable medical leads typically include a lead body containing one or more elongated electrical conductors that extend through the lead body from a connector assembly provided at a proximal lead end to one or more electrodes located at the distal lead end or elsewhere along the length of the lead body. The conductors connect signal generation and/or sensing circuitry within an associated implantable medical device housing to respective electrodes or sensors. Some electrodes may be used for both delivery of therapeutic signals and sensing. Each electrical conductor is typically electrically isolated from other electrical conductors and is encased within an outer sheath that electrically insulates the lead conductors from body tissue and fluids.

Medical lead bodies implanted for cardiac applications tend to be continuously flexed by the beating of the heart. Other stresses may be applied to the lead body, including the conductors therein, during implantation or lead repositioning. Patient movement can cause the route traversed by the lead body to be constricted or otherwise altered, causing stresses on the lead body and conductors. In rare instances, such stresses may fracture a conductor within the lead body. The fracture may be continuously present, or may intermittently manifest as the lead flexes and moves.

Additionally, the electrical connection between medical device connector elements and the lead connector elements can be intermittently or continuously disrupted. For example, connection mechanisms, such as set screws, may be insufficiently tightened at the time of implantation, followed by a gradual loosening of the connection. Also, lead pins may not be completely inserted.

Lead fracture, disrupted connections, or other causes of short circuits or open circuits may be referred to, in general, as lead related conditions or lead faults. In the case of cardiac leads, sensing of an intrinsic heart rhythm through a lead can be altered by lead-related conditions. Identifying lead-related conditions may be challenging, particularly in a clinic, hospital, or operating room setting, due to the often intermittent nature of lead-related conditions. Identification of lead-related conditions may allow modifications of the therapy or sensing, or lead replacement.

Once implanted, an IMD generally remains within the patient for a significant duration of time, and can be exposed to various environmental factors. For example, the patient may undergo a magnetic resonance imaging (MRI) procedure or other high frequency imaging procedures. It is generally desirable to avoid or mitigate certain effects of MRI or other imaging modalities on an IMD, or a patient in which an IMD is implanted.

For example, electromagnetic fields, such as those emitted during an MRI or other imaging procedure may induce currents or energy in the conductors of a lead coupled to an IMD. The sensing circuitry within an IMD may be sensitive to the currents or energy induced in the conductors. Moreover, the currents or energy could lead to heating of the lead, which could in turn cause tissue necrosis of the patient in which the lead is implanted.

For these reasons, it has been proposed to include components that alter the characteristics of leads or IMDs (e.g., high-frequency electromagnetic field mitigation circuitry within leads or IMDs) to make such leads or IMDs “MRI-safe.” Generally, such circuitry is designed to dissipate energy or current on the lead at or above a certain frequency, e.g., radio frequency (RF) energy. Furthermore, it has been proposed to place the operational circuitry of the IMD in an MRI or imaging mode, which generally reduces the functionality of the IMD to avoid any undesired behavior that may occur due to electromagnetic interference emitted by the MRI or other imaging system.

As implantable device and lead technology improves, the devices and leads become more sophisticated and capable of tolerating many conditions and activities in the surrounding environment. One such example is MRI-safe leads, designed to dissipate MRI RF energy (e.g., 64 MHz RF energy for a 1.5 T MRI scanner) that, if left unreduced, can cause lead tip heating. Lead tip heating may result in increased pacing capture threshold and/or heart tissue necrosis.

Therefore, prior to an MRI or other imaging procedure, it may be desirable to safely confirm that an implanted device and/or leads are MRI-safe and that the RF mitigation circuitry is functioning properly. Using the techniques of this disclosure, e.g., prior to a procedure that requires using an MRI machine, or other source of electromagnetic energy or interference, pulses with a specific, relatively high frequency may be applied to the lead. A response of the lead to the applied signal, such as an impedance or a reflected signal, may then be determined. Based on the response, a determination is made regarding a characteristic of the lead, e.g., whether the lead is MRI-safe. In addition to the MRI-safe determination, another characteristic of the lead that may be determined based on the response may be whether any faults are present in the lead, or in its contact with patient tissue or connection to the IMD. In this manner, the same techniques may be used to detect whether an implantable electric lead is not faulty and confirm that the lead is also MRI-safe.

FIG. 1is a conceptual diagram of an implantable medical device. More particularly,FIG. 1is a conceptual diagram illustrating an example system10that may be used to monitor and/or provide therapy to heart12of patient14. Patient14ordinarily, but not necessarily, will be a human.

System10includes IMD16, which is coupled to leads18,20, and22, and programmer24. IMD16may be, for example, an implantable pacemaker, cardioverter, and/or defibrillator that provides electrical signals to heart12via electrodes coupled to one or more of leads18,20, and22. In accordance with certain techniques of this disclosure, IMD16may include circuitry to detect and confirm whether one or more leads18,20, and22are operating as expected, as will be described in more detail below. For example, IMD16may transmit one or more signals through one of leads18,20, and22, and measure impedance or a reflected signal during transmittal of the signal through one or more leads18,20, and22. IMD16may then analyze the impedance or reflected signal to determine a characteristic of the lead through which IMD16transmitted the signal. Based on the analysis, IMD16may determine whether the lead is operating as expected.

In some examples, leads18,20, and22may be modified to operate in environments that may be otherwise detrimental to the operation of IMD16and/or leads18,20and22, e.g., in the presence of MRI or other electromagnetic fields. For example, one or more of leads18,20and22may include electromagnetic field mitigation circuitry. IMD16may apply the relatively high-frequency signal to one or more of the leads in order to determine whether the lead18,20or22includes electromagnetic field mitigation circuitry and/or whether the electromagnetic field mitigation circuitry is operating properly to mitigate the effect(s) of electromagnetic fields on the lead. Thus, in some examples, IMD16may transmit a signal with a particular frequency (e.g., a relatively high frequency) to confirm whether a lead designed to be MRI-safe is operating accordingly.

Additionally, IMD16may utilize the results of the same analysis to detect any lead faults, e.g., lead fractures. In one example, IMD16may periodically apply a signal, to a lead, e.g., automatically or in response to a user command, for testing lead operability. IMD16may test whether a lead includes properly-operating electromagnetic field mitigation circuitry in response to a user command, e.g., a command for the IMD to enter a MRI-safe mode of operation. In some examples, IMD16may alert a user (e.g., a clinician via a programmer24or a computing network) if a fault is detected in lead operation.

Leads18,20,22extend into the heart12of patient14to sense electrical activity of heart12and/or deliver electrical stimulation to heart12. In the example shown inFIG. 1, right ventricular (RV) lead18extends through one or more veins (not shown), the superior vena cava (not shown), and right atrium26, and into right ventricle28. Left ventricular (LV) coronary sinus lead20extends through one or more veins, the vena cava, right atrium26, and into the coronary sinus30to a region adjacent to the free wall of left ventricle32of heart12. Right atrial (RA) lead22extends through one or more veins and the vena cava, and into the right atrium26of heart12. Leads18,20, and22may include electrical components designed to reduce the effects of electromagnetic fields on leads18,20and22or IMD16, e.g., electromagnetic field mitigation circuitry (not shown inFIG. 1). Some examples of electromagnetic field mitigation circuitry that can reduce or dissipate the effects of electromagnetic fields, e.g., MRI RF fields, include inductive chokes, capacitive shunts, traps, shields, and higher inductance lead bodies. In general, such electromagnetic field mitigation circuitry works to prevent current at certain, relatively high, frequencies, e.g., RF or other frequencies associated with MRI or other imaging procedures, on the conductors within the leads.

IMD16may sense electrical signals attendant to the depolarization and repolarization of heart12via electrodes (not shown inFIG. 1) coupled to at least one of the leads18,20,22. In some examples, IMD16provides pacing pulses to heart12based on the electrical signals sensed within heart12. The configurations of electrodes used by IMD16for sensing and pacing may be unipolar or bipolar. IMD16may also provide defibrillation therapy and/or cardioversion therapy via electrodes located on at least one of the leads18,20,22. IMD16may detect arrhythmia of heart12, such as fibrillation of ventricles28and32, and deliver defibrillation therapy to heart12in the form of electrical pulses. In some examples, IMD16may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation of heart12is stopped. IMD16detects fibrillation employing one or more fibrillation detection techniques known in the art.

In some examples, programmer24may be a handheld computing device or a computer workstation. A user, such as a physician, technician, or other clinician, may interact with programmer24to communicate with IMD16. For example, the user may interact with programmer24to retrieve physiological or diagnostic information from IMD16. A user may also interact with programmer24to program IMD16, e.g., select values for operational parameters of IMD16.

For example, the user may use programmer24to retrieve information from IMD16regarding the rhythm of heart12, trends therein over time, or arrhythmic episodes. As another example, the user may use programmer24to retrieve information from IMD16regarding other sensed physiological parameters of patient14, such as intracardiac or intravascular pressure, activity, posture, respiration, or thoracic impedance. As another example, the user may use programmer24to retrieve information from IMD16regarding the performance or integrity of IMD16or other components of system10, such as leads18, and22, or a power source of IMD16. The user may use programmer24to program a therapy progression, select electrodes used to deliver defibrillation pulses, select waveforms for the defibrillation pulse, or select or configure a fibrillation detection algorithm for IMD16. The user may also use programmer24to program aspects of other therapies provided by IMD14, such as cardioversion or pacing therapies.

In one example in accordance with techniques of this disclosure, the user may use programmer24to verify operability of leads18,20, and22generally or in certain environments. For example, the user may use programmer24to control IMD16to apply a signal of a particular frequency to one or more of leads18,20, and22and determine, based on a response of the leads during application of the signal, whether leads18,20, and22are operating in an expected manner, e.g., are fault-free and/or MRI safe. The user may also use programmer24to receive visual indications of the functionality of IMD16and the leads.

IMD16and programmer24may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, for example, low frequency or radiofrequency (RF) telemetry, but other techniques are also contemplated. In some examples, programmer24may include a programming head that may be placed proximate to the patient's body near the IMD16implant site in order to improve the quality or security of communication between IMD16and programmer24.

FIG. 2is a conceptual diagram further illustrating the IMD ofFIG. 1in conjunction with the heart. Leads18,20,22may be electrically coupled to a signal generator and a sensing module of IMD16via connector block34.

Each of the leads18,20,22includes an elongated insulative lead body carrying one or more conductors. Bipolar electrodes40and42are located adjacent to a distal end of lead18. In addition, bipolar electrodes44and46are located adjacent to a distal end of lead20and bipolar electrodes48and50are located adjacent to a distal end of lead22. Electrodes40,44and48may take the form of ring electrodes, and electrodes42,46and50may take the form of extendable helix tip electrodes mounted retractably within insulative electrode heads52,54and56, respectively.

Leads18,20,22also include elongated intracardiac electrodes62,64and66respectively, which may take the form of a coil. In addition, one of leads18,20,22, e.g., lead22as seen inFIG. 2, may include a superior vena cava (SVC) coil67for delivery of electrical stimulation, e.g., transvenous defibrillation. For example, lead22may be inserted through the superior vena cava and SVC coil67may be placed, for example, at the right atrial/SVC junction (low SVC) or in the left subclavian vein (high SVC). Each of the electrodes40,42,44,46,48,50,62,64,66and67may be electrically coupled to a respective one of the conductors within the lead body of its associated lead18,20,22, and thereby individually coupled to the signal generator and sensing module of IMD16. In some examples, as illustrated inFIG. 2, IMD16includes one or more housing electrodes, such as housing electrode58, which may be formed integrally with an outer surface of hermetically-sealed housing60of IMD16or otherwise coupled to housing60.

IMD16may sense electrical signals attendant to the depolarization and repolarization of heart12via electrodes40,42,44,46,48,50,58,62,64,66and67. The electrical signals are conducted to IMD16via the respective leads18,20,22, or in the case of housing electrode58, a conductor coupled to the housing electrode. IMD16may sense such electrical signals via any bipolar combination of electrodes40,42,44,46,48,50,58,62,64,66and67. Furthermore, any of the electrodes40,42,44,46,48,50,58,62,64,66and67may be used for unipolar sensing in combination with housing electrode58.

In some examples, IMD16delivers pacing pulses via bipolar combinations of electrodes40,42,44,46,48and50to produce depolarization of cardiac tissue of heart12. In some examples, IMD16delivers pacing pulses via any of electrodes40,42,44,46,48and50in combination with housing electrode58in a unipolar configuration. For example, electrodes40,42, and/or58may be used to deliver RV pacing to heart12. Additionally or alternatively, electrodes44,46, and/or58may be used to deliver LV pacing to heart12, and electrodes48,50and/or58may be used to deliver RA pacing to heart12.

Furthermore, IMD16may deliver defibrillation pulses to heart12via any combination of elongated electrodes62,64,66and67, and housing electrode58. Electrodes58,62,64,66may also be used to deliver cardioversion pulses to heart12. Electrodes62,64,66and67may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy or other materials known to be usable in implantable defibrillation electrodes.

The configuration of therapy system10illustrated inFIGS. 1 and 2is merely one example. In other examples, a therapy system may include epicardial leads and/or patch electrodes instead of or in addition to the transvenous leads18,20,22illustrated inFIGS. 1 and 2. Further, IMD16need not be implanted within patient14. In examples in which IMD16is not implanted in patient14, IMD16may deliver defibrillation pulses and other therapies to heart12via percutaneous leads that extend through the skin of patient14to a variety of positions within or outside of heart12.

In addition, in other examples, a therapy system may include any suitable number of leads coupled to IMD16, and each of the leads may extend to any location within or proximate to heart12. For example, other examples of therapy systems may include three transvenous leads located as illustrated inFIGS. 1 and 2, and an additional lead located within or proximate to left atrium36. Other examples of therapy systems may include a single lead that extends from IMD16into right atrium26or right ventricle28, or two leads that extend into a respective one of the right ventricle28and right atrium26(not shown). The example ofFIGS. 1 and 2includes a single electrode per chamber of heart12engaged with the wall of heart12, e.g., free wall, for that chamber. Other examples may include multiple electrodes per chamber, at a variety of different locations on the wall of heart. The multiple electrodes may be carried by one lead or multiple leads per chamber.

In accordance with certain aspects of this disclosure, IMD16may include circuitry for monitoring specific functionality and operability of different components such as, for example, leads associated with IMD16. For example, IMD16and leads may be designed for compatibility with different environments, such that operability of IMD16and the leads and safety to the patient are maintained. In one example, IMD16and leads18,20, and22may be compatible with MRI energies, such that, when in an MRI environment, the leads and/or IMD16continue functioning properly and safely. The modifications to the leads to ensure MRI-safety, e.g., inclusion of magnetic field mitigation circuitry, may change the electrical characteristics of the leads relative to standard leads (non MRI-safe). The monitoring circuitry in IMD16may utilize knowledge of these characteristics to determine whether the MRI-safe leads are functioning properly. In one example, IMD16may transmit signals through one or more of the leads and analyze a received response signal to determine the characteristics of the lead, and verify that the leads are still MRI-safe. In one example, IMD16may periodically monitor the lead functionality. In another example, IMD16may perform testing of the leads during preparation time for an MRI scan.

The disclosure generally refers to IMD16as performing monitoring of the leads and initiating testing, but the disclosure is not so limited. In other examples, a user may initiate testing of the leads using programmer24. In response, IMD16may perform the testing to confirm operability of the leads and send a signal to programmer24indicating the results of the testing. Additionally, while the techniques of this disclosure are discussed in terms of MRI-related activities, it should be understood that these techniques may be modified to test for other types of activities that may affect the operation of implantable devices.

FIG. 3Ais a functional block diagram illustrating an example configuration of IMD16that may be used to implement certain techniques of this disclosure. In the illustrated example, IMD16includes a processor80, memory82, signal generator84, sensing module86, telemetry module88, and lead analysis module90. AsFIG. 3Aillustrates, signal generator84may include a high frequency (HF) signal generator92. HF signal generator92may generate signals with frequencies that may be similar to electromagnetic fields generated during imaging, e.g., RF or other frequencies associated with MRI or other imaging procedures. HF signal generator92may generate relatively high frequencies that IMD16may utilize to monitor operation of different IMD components, e.g., leads or electrodes. IMD16may transmit signals generated by HF signal generator92and measure a response, which may include receiving a response signal via sensing module86. Lead analysis module90analyzes the received response signal data to determine characteristics of the leads on which IMD16transmitted the signals. Lead analysis module90may be implemented as software, firmware, hardware or any combination thereof. In some example implementations, lead analysis module90may be a software process implemented in or executed by processor80. Memory82is one example of a non-transitory, computer-readable storage medium that includes computer-readable instructions that, when executed by processor80, cause IMD16and processor80to perform various functions attributed to IMD16and processor80in this disclosure. Memory82may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital or analog media.

As indicated above, the techniques described in this disclosure may be implemented by IMD16to determine whether the operation of the leads is consistent with their design. Specifically, the leads associated with IMD16may be designed to withstand conditions in environments that present factors, which when left unaccounted for, may cause harm to the IMD, leads, and/or the patient. In one example, the leads may be designed to function safely in environments that may be otherwise harmful to IMD16and/or to tissue or organs receiving therapy from IMD16. For example, the leads may include mitigation circuitry70that ensures tolerance and continued operability in environments such as, for example, an MRI environment, which introduce energy levels that can cause overheating of lead tips, resulting in damage to tissue in which the leads are implanted or to which the leads supply therapy. Components70may be, for example, electromagnetic field mitigation circuitry, which may include, for example, inductive chokes, capacitive shunts, traps, shields, and higher inductance lead bodies. HF signal generator92may generate signals at a relatively high frequency that is suppressed or otherwise mitigated by mitigation circuitry70.

Periodically or prior to entering an MRI environment, IMD16may utilize HF signal generator92to generate and transmit signals at relatively high frequency over one or more leads or electrodes, and may utilize one or more leads or electrodes to sense a response signal. Data associated with the transmitted and received signals may be stored in a signal data memory96. Lead data94may include data associated with the leads indicating expected lead characteristics according to the lead design, e.g., signal characteristics for a lead designed to be MRI-safe, lead length, and the like. Lead analysis module90may utilize the signal data and lead data to determine the characteristics of the lead and whether the leads are operating as expected.

In some examples, processor80controls signal generator84to deliver stimulation therapy to heart12according to a selected one or more of therapy programs, which may be stored in memory82. For example, processor80may control signal generator84to deliver electrical pulses with the amplitudes, pulse widths, frequency, or electrode polarities specified by the selected one or more therapy programs.

Signal generator84is electrically coupled to electrodes40,42,44,46,48,50,58,62,64,66, and67e.g., via conductors of the respective leads18,20,22, or, in the case of housing electrode58, via an electrical conductor disposed within housing60of IMD16. In some examples, signal generator84is configured to generate and deliver electrical stimulation therapy to heart12. For example, signal generator84may deliver defibrillation shocks as therapy to heart12via at least two electrodes58,62,64,66. Signal generator84may deliver pacing pulses via ring electrodes40,44,48coupled to leads18,20, and22, respectively, and/or helical electrodes42,46, and50of leads18,20, and22, respectively. In some examples, signal generator84delivers pacing, cardioversion, or defibrillation stimulation in the form of electrical pulses. In other examples, signal generator84may deliver one or more of these types of stimulation in the form of other signals, such as sine waves, square waves, or other substantially continuous time signals.

Signal generator84may include a switch module, and processor80may use the switch module to select which of the available electrodes are used to deliver such stimulation. The switch module may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple stimulation energy to selected electrodes.

As discussed above, signal generator84may include HF signal generator92, which is capable of generating signals at relatively high frequencies intended for testing and monitoring purposes, in accordance with techniques of this disclosure. In one example, a high frequency signal may be generated to test whether leads18,20, and22or electrodes associated with IMD16are configured for operation in certain environments (e.g., MRI scan environment) that may be otherwise harmful to the device, leads or electrodes, and/or patient. Processor80may use the switch module in signal generator84to select leads for testing by selecting the appropriate electrodes and transmitting generated HF signals on the selected electrodes.

In some examples, sensing module86monitors signals from at least one of electrodes40,42,44,46,48,50,58,62,64,66or67in order to monitor electrical activity of heart12. Sensing module86may also include a switch module. In some examples, processor80may select the electrodes that function as sense electrodes via the switch module within sensing module86.

Sensing module86may include one or more detection channels (not shown), each of which may comprise an amplifier. The detection channels may be used to sense the cardiac signals. Some detection channels may detect cardiac events, such as R- or P-waves, and provide indications of the occurrences of such events to processor80. One or more other detection channels may provide the signals to an analog-to-digital converter, for processing or analysis by processor80. In some examples, processor80may store the digitized versions of signals from one or more selected detection channels in memory82as EGM signals. In response to the signals from processor80, the switch module within sensing module86may couple selected electrodes to selected detection channels, e.g., for detecting events or acquiring an EGM in a particular chamber of heart12.

In one example, signals received in response to transmitted HF signals for testing or monitoring purposes may be processed by processor80. Processor80may utilize lead analysis module90to determine lead characteristics based on the received response signal, relative to the transmitted HF signal. In one example, based on the analysis, processor80may determine whether the tested lead is operating in accordance with its design, e.g., MRI-safe. Additionally, processor80may detect faults in the tested lead based on the analysis of the received response signal. In this manner, processor80may determine based on the same analysis results whether there is a fault in a tested lead (e.g., breakage, shifting, or other flaws that may alter electrical properties of leads) and/or whether the lead is behaving in a manner consistent with its design (e.g., MRI-safe). In some examples, processor80may determine based on the analysis results whether a lead is MRI-safe without having prior knowledge whether the lead is designed to be MRI-safe.

AsFIG. 3Aillustrates, in addition to program instructions, memory82may store lead data94and signal data96. Lead data94may be data associated with leads18,20, and22such as, for example, electrical characteristics of the leads resulting from altering their design (e.g., by adding mitigation circuitry70) to make them effectively and safely operable in conditions that may otherwise have adverse effects on the operation of the leads and/or the patient. In some examples, an IMD may be modified to reduce harmful effects in an environment such as, for example, during an MRI scan, where leads can become harmful from MRI RF energy. For example, the MRI RF energy can cause heating of the tip of the leads, resulting in damage to surrounding tissue. As another example, the MRI signals may affect the operation of the leads and/or the IMD resulting in delivery of unnecessary stimulation, which can damage the target organ (e.g., heart). Therefore, electrical components70(electromagnetic field mitigation circuitry, e.g., chokes, shunts, traps, and the like) may be added to leads to dissipate and reduce harmful effects of MRI RF energy. The added components may change electrical properties of the associated leads, and the characteristics of the modified leads may be known (e.g., expected impedance, effect on frequency and amplitude of a waveform, and the like). The expected characteristics may be stored as lead data94in memory82.

Signal data96may include transmitted signal and received response signal data. When processor80causes the generation and transmission of a high frequency signal from HF signal generator92, processor80may store properties of the transmitted signal (e.g., frequency, wavelength, amplitude, and the like) in signal data96. Subsequently, when processor80receives a response signal via sensing module86, processor80may store properties of the received signal in signal data96. Processor80may also store additional data related to the received signal, e.g., timing information. Processor80may then utilize lead analysis module90to analyze signal data96, including transmitted signal data and received signal data and characterize the lead(s) used to transmit the signal.

Processor80may determine based on the analysis and lead data94whether the lead(s) is operating properly. The analysis may allow processor80to detect faults with the lead(s), and verify the lead's ability to operate without causing harm or damage to the IMD and/or patient. In some examples, IMD16may perform this testing periodically or during a preparation period prior to an MRI scan. In some examples, processor80may provide an indication regarding the operation of the lead(s). For example, processor80may communicate the indication to a remote associated device (e.g., a programmer) via telemetry module88. In one example, a user (e.g., clinician) may receive an indication on the programmer associated with IMD16(e.g., programmer24ofFIG. 1) indicating that the leads are operating properly and that it would be safe to perform an MRI scan. In another example, the user may receive an indication on the programmer that there are problems with the leads and that an MRI scan may be harmful to the IMD and/or patient. In this example, processor80may indicate whether the problem with the lead indicates detection that the lead is not operating as expected (e.g., not MRI-safe) or if the lead is faulty (e.g., breakage or shifting of the lead, or other flaws that may alter electrical properties of leads).

FIG. 3Bis a functional block diagram illustrating an example configuration of an external programmer that facilitates user communication with an IMD. As shown inFIG. 3B, programmer24may include a processor140, memory142, user interface144, telemetry module146, power source148, and lead analysis module190. Programmer24may be a dedicated hardware device with dedicated software for programming of IMDs16. Alternatively, programmer24may be an off-the-shelf computing device running an application that enables programmer24to program IMDs16.

A user may use programmer24to select therapy programs (e.g., sets of stimulation parameters), generate new therapy programs, modify therapy programs through individual or global adjustments or transmit the new programs to a medical device, such as IMDs16. The clinician may interact with programmer24via user interface144, which may include display to present graphical user interface to a user, and a keypad or another mechanism for receiving input from a user. In addition, the user may receive data from IMDs16indicating operating conditions of IMD16and/or leads connected to IMD16via programmer24.

Processor140can take the form of one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, and the functions attributed to processor140herein may be embodied as hardware, firmware, software or any combination thereof. Memory142may store instructions that cause processor140to provide the functionality ascribed to programmer24herein, and information used by processor140to provide the functionality ascribed to programmer24herein. Memory142may include any fixed or removable magnetic, optical, or electrical media, such as RAM, ROM, CD-ROM, hard or floppy magnetic disks, EEPROM, or the like. Memory142may also include a removable memory portion that may be used to provide memory updates or increases in memory capacities. A removable memory may also allow patient data to be easily transferred to another computing device, or to be removed before programmer24is used to program therapy for another patient.

Programmer24may communicate wirelessly with IMDs16, such as using RF communication or proximal inductive interaction. This wireless communication is possible through the use of telemetry module146, which may be coupled to an internal antenna or an external antenna. An external antenna that is coupled to programmer24may correspond to the programming head that may be placed over heart12. Telemetry module146may be similar to telemetry module88of IMD16(FIG. 3A).

Telemetry module146may also be configured to communicate with another computing device via wireless communication techniques, or direct communication through a wired connection. Examples of local wireless communication techniques that may be employed to facilitate communication between programmer24and another computing device include RF communication according to the 802.11 or Bluetooth specification sets, infrared communication, e.g., according to the IrDA standard, or other standard or proprietary telemetry protocols. In this manner, other external devices may be capable of communicating with programmer24without needing to establish a secure wireless connection. An additional computing device in communication with programmer24may be a networked device such as a server capable of processing information retrieved from IMD16.

In some examples, processor140of programmer24and/or one or more processors of one or more networked computers may perform all or a portion of the techniques described herein with respect to processor80and IMD16. For example, processor140or another processor may receive lead data and signal data from IMD16, and utilize lead analysis module190to determine lead characteristics to determine whether a test lead of IMD16is operating correctly, e.g., MRI-safe and/or presence of lead faults, as described above. Processor140may utilize user interface144to display to a user results of the lead analysis. In one example, lead analysis may be performed in IMD16, and results of the analysis may be communicated to programmer24, which may display the results to the user.

FIG. 4is a block diagram illustrating an example system400that includes an external device, such as a server402, and one or more computing devices404A-404N, that are coupled to the IMD16and programmer24ofFIG. 1via a network406. In this example, IMD16may use its telemetry module88to communicate with programmer24via a first wireless connection, and to communication with an access point608via a second wireless connection. In the example ofFIG. 4, access point408, programmer24, server402, and computing devices404A-404N are interconnected, and able to communicate with each other, through network406. In some cases, one or more of access point408, programmer24, server402, and computing devices404A-404N may be coupled to network406through one or more wireless connections. IMD16, programmer24, server402, and computing devices404A-404N may each comprise one or more processors, such as one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, that may perform various functions and operations, such as those described herein.

Access point408may comprise a device that connects to network406via any of a variety of connections, such as telephone dial-up, digital subscriber line (DSL), or cable modem connections. In other examples, access point408may be coupled to network406through different forms of connections, including wired or wireless connections. In some examples, access point408may be co-located with patient14and may comprise one or more programming units and/or computing devices (e.g., one or more monitoring units) that may perform various functions and operations described herein. For example, access point408may include a home-monitoring unit that is co-located with patient14and that may monitor the activity of IMD16.

In some cases, server402may be configured to provide a secure storage site for data that has been collected from IMD16and/or programmer24. Network406may comprise a local area network, wide area network, or global network, such as the Internet. In some cases, programmer24or server402may assemble data in web pages or other documents for viewing by trained professionals, such as clinicians, via viewing terminals associated with computing devices404A-404N. The illustrated system ofFIG. 4may be implemented, in some aspects, with general network technology and functionality similar to that provided by the Medtronic CareLink® Network developed by Medtronic, Inc., of Minneapolis, Minn.

In some examples, processor410of server402may be configured to receive signal and lead information from IMD16for processing by lead analysis module412in the manner described throughout this disclosure. In other examples, processor410may receive data processed by a lead analysis module, e.g., data processed by lead analysis module90of IMD16. Lead analysis module412may determine characteristics of leads associated with IMD16and determine whether the leads are operating as designed (e.g., MRI-safe) and detect faults with the leads using any of the techniques described in this disclosure. Processor410may provide alerts to users, e.g., to the patient via access point408or to a clinician via one of computing devices404, identifying conditions, e.g., leads are or are not MRI-safe, or leads have faults like breakage. Processor410may suggest to a clinician, e.g., via programmer24or a computing device404, a solution to a faulty lead or a lead that is not MRI-safe, such as replacing the identified lead, or not proceeding with a scheduled imaging operation or other procedure. Processor410may also adjust or control the delivery of therapy by IMD16, e.g., electrical stimulation therapy and/or a therapeutic substance, via network406.

FIG. 5is a flow diagram of an example method of determining characteristics of a lead in accordance with this disclosure. As noted above, lead analysis module90of IMD16(FIG. 3) or lead analysis module412of external device402(FIG. 4) may be used to perform some or all of the calculations and decisions in order to detect the condition or characteristics of an implantable electrical element (e.g., lead).

Implantable electrical elements such as, for example, leads associated with IMDs may be affected by their surrounding environment (e.g., imaging devices and other sources of electromagnetic fields). In some situations, the effect of the surrounding environment may be minimal and may not change the characteristics of a lead or the leads operability. However, in some environments, such as within or proximate to MRI scanners, a lead's characteristics and operation may be greatly altered, and if not detected and/or changed, the consequences may be detrimental (e.g., cause damage to lead, IMD, and/or patient). Therefore, it may be important to ensure that implantable devices and leads are protected against harm that can be caused by different environments, e.g., MRI scanners. While the techniques of this disclosure are discussed in terms of MRI scanners, it should be understood that these techniques may be modified for or applied to determining the operability of leads in other environments that may present harmful conditions to the device and/or patient, such as other imaging devices and other sources of electromagnetic fields, e.g., electrosurgical equipment, such as electrocautery or ablation equipment.

As discussed above, leads coupled to IMDs may be made MRI-safe by including electrical components (e.g., electromagnetic field mitigation circuitry) that reduce or dissipate MRI RF energy (e.g., 64 MHz range for a 1.5 T MRI scanner). Some example electrical components that can be added to the leads may be inductive chokes, capacitive shunts, traps, shields, and higher inductance lead bodies, and the like. Adding such components changes the electrical characteristics (e.g., impedance) of the leads at different frequencies, and with proper tuning, specific harmful high frequencies, such as those associated with MRI scanner, may be attenuated. In some examples, the components may be added at any location on the lead and used to determine MRI-safety conditions. In other examples, components may be added at the distal end of a lead, which changes the characteristics of the distal end of the lead, and which may be beneficial in detecting whether the lead is MRI-safe and to detect lead faults (e.g., breakage). In other examples, components may be added to the tip of the lead. Examples of some of the electrical components listed above are described in U.S. patent application Ser. No. 11/555,111 filed on Oct. 31, 2006 and entitled “RADIOFREQUENCY (RF)-SHUNTED SLEEVE HEAD AND USE IN ELECTRICAL STIMULATION LEADS,” U.S. patent application Ser. No. 11/741,568 filed on Apr. 27, 2007 and is entitled “MEDICAL ELECTRICAL LEAD BODY DESIGNS INCORPORATING ENERGY DISSIPATING SHUNT,” and U.S. patent application Ser. No. 10/059,598 filed on Jan. 29, 2002 and is entitled “ELECTROMAGNETIC TRAP FOR A LEAD,” each of which is incorporated herein in its entirety.

However, simply implementing the electrical components on the leads may not be sufficient. Leads can become faulted (e.g., breakage, shifting, insulation breaches, degradation, or other flaws that may alter electrical properties of leads), electrical components may shift or stop working overtime affecting the desired characteristics, for example. Therefore, it is important to determine, especially prior to an MRI scan, whether the leads are MRI-safe. In some situations, it may be desirable to monitor the leads and periodically check lead conditions. In accordance with techniques of this disclosure, a circuitry in the IMD may be used to monitor lead conditions and determine whether a lead is MRI-safe, in addition to detecting lead faults (e.g., shifting, breakage, or other flaws that may alter electrical properties of leads).

Signal generator84of IMD16may transmit a signal at a high frequency through the lead that is being monitored (502). Signal generator84may include a HF signal generator92, which may generate signals at high frequencies, e.g., 1 Mhz or 64 MHz. Using signals with lower frequencies may allow detection of faults in a lead. However, signals with lower frequencies may yield results for MRI-safe leads that may not be clearly distinct from results associated with non-MRI-safe leads. Particularly, MRI-safe leads may be designed to have some impedance at low frequencies but go to open or short at high frequencies, depending on the type of component used (e.g., choke or trap tend to go to open impedance at higher frequencies). Therefore, for example, when a choke or trap is used to make a lead MRI-safe, higher frequencies result in making the choke or trap act like an open circuit, resulting in higher impedance, e.g., impedance goes from ˜10Ω to a high impedance range ˜500-3000Ω at 64 MHz. A processor (e.g., processor80ofFIG. 3) may determine the characteristics (e.g., frequency, amplitude, timing, etc.) of the transmitted signals and store them in a memory (e.g., signal data96).

In one example, the transmitted high frequency signal may be a burst, a pulse, or a continuous signal. In response to the transmitted high frequency signal, IMD16may receive a response signal (504). In some examples, the response signal may be a signal reflected in response to the transmitted signal, and may be received on the same lead on which the high frequency signal was transmitted. In other examples, the response signal may be received through another path, e.g., through another lead, or the case. In other examples, impedance of a lead may be measured while the signal is traveling in the lead. It should be noted that the signal transmission and reception may be done tip-to-ring, tip-to-case, or from any one electrode on any lead to any other electrode on another lead.

The characteristics (e.g., amplitude, frequency, timing, etc.) of the response signal may then be determined (506). The processor80may utilize lead analysis module90to analyze the received response signal (508). In analyzing the received response signal, load analysis module90may compare the received signal to the transmitted signal, and based on the comparison, determine the characteristics of the lead on which the high frequency signal was transmitted. For example, analysis of the signals may involve looking at the amplitude or frequency shift of the reflection response signal relative to the transmitted signal. Having knowledge of the amplitude of the transmitted signal and the amplitude of the received signal may be used to determine the amount of attenuation in the amplitude, which may be proportional to the impedance of the lead. For example, if the reflection is perfect, that may indicate an open or short at the distal end, which may be the expected behavior for some components. If, in another example, the response signal is heavily reduced in amplitude, then it may indicate attenuation along the lead, which may be expected behavior for other components. Therefore, once the received signal is analyzed, the characteristics may be compared to the expected characteristics of the lead, based on the type of component used to make the lead MRI-safe (510).

In some examples, as noted above, the comparison may be based on signal characteristics. In other examples, the impedance of the lead may be directly measured at the high frequency conditions. Impedance may be also determined proportionally by determining the lead impedance mismatch, for example. In this example, if the source has an impedance of 50Ω and the signal is nearly perfectly transmitted, then the load also had an impedance of 50Ω, whereas a load with impedance of 10Ω will transmit some of the signal and reflect most of it, and the reflected portion will be inversely proportional to lead impedance mismatch. In this example, the lead impedance mismatch may be a known characteristic for a lead that is operating properly, and a comparison between the measured mismatch and the expected mismatch may allow determination as to whether the lead is operating as expected, i.e., the lead is MRI-safe. By using a high frequency, the expected mismatch in impedance may be greater for MRI-safe leads relative to non-MRI-safe leads.

In addition to determining the impedance of the lead based on the reflected signal or during transmission of the high frequency signal through the lead, to determine whether the lead is MRI-safe, the time between the transmission of the high frequency signal and the reception of the response signal may be measured. Having knowledge of the characteristics of the lead and the signal, may allow determining the distance the signal traveled, therefore, determining the distance to the end of the lead. By comparing the calculated length of the lead with the known length of the lead, the processor may be able to determine whether there is a fault in the lead (e.g., breakage) if the calculated distance is shorter than the known length of the lead. In this manner, the same techniques used to confirm whether the lead is MRI-safe, may be also used to determine whether there is a fault in the lead. In the examples discussed in this disclosure, it should be understood that signals may be transmitted and received on leads or electrodes. For example, a signal may be transmitted and received on the same electrode, i.e., conductor coupled to the electrode, or a signal may be transmitted on one electrode and received on another electrode, where the two electrodes may be on the same lead or on two different leads.

If the processor determines that the lead is MRI-safe (512) and there are no detected faults in the lead (514), the processor may send an indication that the device is MRI-safe and to proceed with MRI scanning (516). If one of the conditions is detected as being abnormal, lead is not MRI-safe and/or the lead has faults, the processor may transmit an indication that the device/lead is not MRI-safe or is faulty (518). In some examples, the processor may determine whether the lead is MRI-safe or whether there are faults in the lead, without necessarily making a determination regarding the other condition.

The techniques of this disclosure may be performed periodically (e.g., once a day), or in response to user command (e.g., via a programmer and/or a command for an IMD to enter MRI-safe mode). In some examples, the techniques of this disclosure determine whether leads are MRI-safe and/or whether the leads have faults. The two determinations may be performed together or individually. For example, the MRI-safe determination may be performed in response to user command or upon indication of entering MRI-safe mode. In another example, lead fault detection may be performed periodically or automatically, and the periodicity of the fault detection may be set to a default value or by a user as to ensure lead integrity and functionality.

Although the disclosure is described with respect to systems that employ sensing and monitoring of cardiac activity, such techniques may be applicable to other systems in which sensing integrity is important, such as, e.g., spinal cord stimulation, deep brain stimulation, pelvic floor stimulation, gastric stimulation, occipital stimulation, functional electrical stimulation, and the like.

The techniques described in this disclosure, including those attributed to image IMD16, programmer24, or various constituent components, may be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the techniques may be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components, embodied in programmers, such as physician or patient programmers, stimulators, image processing devices or other devices. The term “processor” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry.

When implemented in software, the functionality ascribed to the systems, devices and techniques described in this disclosure may be embodied as instructions on a computer-readable medium such as random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, magnetic data storage media, optical data storage media, or the like. The instructions may be executed to support one or more aspects of the functionality described in this disclosure.

Various examples of the invention have been described. These and other examples are within the scope of the following claims.