Patent Application
20100198311
The present disclosure relates to implantable medical devices (IMDs), in particular to a system and method for use of a cardiac lead that includes a switch responsive to an external field, such as that generated during a magnetic resonance imaging (MRI) procedure.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The human anatomy includes many types of tissue that can either voluntarily or involuntarily, perform certain functions. However, after disease or injury, certain tissues may no longer operate within general anatomical norms. For example, after disease, injury, age, or combinations thereof, the heart muscle may begin to experience certain failures or deficiencies. Some of these failures or deficiencies can be corrected or treated with implantable medical devices (IMDs). These devices can include implantable pulse generator (IPG) devices, pacemakers, implantable cardioverter-defibrillator (ICD) devices, cardiac resynchronization therapy defibrillator devices, or combinations thereof.
One of the main portions of the IMD can include a lead that is directly connected to tissue to be affected by the IMD. The lead can include a tip portion that is directly connected to the anatomical tissue, such as a muscle bundle, and a lead body that connects to the device body or therapeutic driving device. It is generally known that the device body or case portion can be implanted in a selected portion of the anatomical structure, such as in a chest or abdominal wall, and the lead can be inserted through various venous portions so that the tip portion can be positioned at the selected position near or in the muscle group.
The IMD generally remains with the patient during the rest of the patient's natural life. To that end, the IMD 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. In this case, portions of the IMD may act as an antenna and have current and thermal energy induced therein due to the MRI procedure. This induced heat can damage anatomical tissue and cause injury to the patient. Accordingly, reduction or dissipation of the induced current or thermal energy may be useful in certain circumstances.
An implantable medical device (IMD) can include implantable pulse generator (IPG) devices, implantable cardioverter-defibrillators (ICD), cardiac resynchronization therapy defibrillator devices, neurostimulators or combinations thereof. The IMD can be positioned in a selected portion of the anatomical structure, such as a chest wall or abdominal wall, and a lead can be positioned through a vein or transvenously so that a lead tip can be implanted in a portion of the cardiac or heart muscle. Various portions of the IMD, such as a case or device body, the lead body, or the lead tip, can be formed or augmented to reduce or dissipate heat production due to various external environmental factors. For example, a magnetic and/or electric field from a magnetic resonance imager (MRI), diathermy (including shortwave, microwave, ultrasound, or the like) or other energy field producing devices can induce currents in the lead. According to various embodiments, features or portions can be incorporated into the lead body, the lead tip, or the device body to reduce the creation of an induced current, or dissipate or increase the area of dissipation of thermal energy created due to an induced current in the lead.
An implantable medical device operable to provide therapy to an anatomical tissue is provided. The device can include a lead having a body. For a uni-polar lead, the body of the lead can have at least one conductor to transmit the therapy through the body of the lead. The device can further include at least one tip electrode coupled to the body of the lead. The at least one tip electrode can be in electrical communication with the at least one conductor to deliver the therapy to a portion of the anatomical tissue in a first operational state. In a second operational state, the at least one tip electrode can be selectively decoupled from the at least one conductor to reduce heating in the presence of a magnetic and/or electric field (e.g., from a magnetic resonance imaging (MRI) device) and briefly re-coupled to the at least one conductor to deliver a pacing therapy before being decoupled again. In a bipolar lead, the device can also include at least one ring electrode fixedly coupled to the body of the lead. The at least one ring electrode can be in electrical communication with the at least one conductor to provide sensing or to deliver the therapy to the anatomical tissue in the first operational state. In a second operational state, the at least one tip and ring electrodes can be selectively decoupled from their respective conductors to reduce heating in the presence of a magnetic and/or electric field (e.g., from a magnetic resonance imaging (MRI) device) and briefly re-coupled to the conductors to deliver a pacing therapy before being decoupled again. The lead can switch between the first operational state and the second operational state based on whether an external field is present.
In addition, an implantable medical device is also provided that includes a therapy device operable to generate the therapy for the anatomical tissue. The device can include a lead having a proximal end in electrical communication with the therapy device, a distal end and a body. The body of the lead can have at least one conductor to carry the therapy through the body of the lead. The device can further include at least one tip electrode coupled to the distal end of the lead that can be operable to deliver the therapy to a portion of the anatomical tissue. The device can include at least one ring electrode coupled to the lead that can be operable to provide sensing or to deliver the therapy to the anatomical tissue. The device can also include a switch that can electrically couple the at least one conductor to the at least one tip electrode and/or to the at least one ring electrode. The device can include at least one control system that can activate the switch to electrically couple the at least one conductor to the at least one tip electrode (and ring electrode in a bipolar lead) in a first operational state or to selectively electrically decouple the at least one conductor to the at least one ring electrode (and ring electrode in a bipolar lead) in a second operational state in the presence of an external field. The tip (or tip and ring) electrode is briefly re-coupled to the conductor(s) to deliver therapy before being decoupled again.
Further provided is a method of controlling a cardiac lead implanted in an anatomical structure during the presence of an external field. The method can include providing a lead having at least one conductor passing through the lead, at least one first electrode in electrical communication with the at least one conductor to deliver a therapy to a portion of the anatomical tissue and at least one second electrode in electrical communication with the another conductor for sensing or to deliver a therapy to the anatomical tissue. The method can also include determining whether the external field is present and selectively electrically decoupling the at least one first electrode (and/or the at least one second electrode) in the presence of the external field and briefly re-couple the at least one first electrode (and/or the at least one second electrode) with the at least one conductor to deliver the therapy before being decoupled again. The method can include electrically re-coupling the at least one first and second electrode with the their respective conductors to deliver the therapy when the external field is no longer present.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As indicated above, the present teachings are directed towards providing a system and method for use of a cardiac lead that includes a switch that is responsive to an external field, such as that generated by a MRI. It should be noted, however, that the present teachings could be applicable to any appropriate procedure in which it is desirable to have a component that is responsive to external fields. Further, as used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable software, firmware programs or components that provide the described functionality. Therefore, it will be understood that the following discussions are not intended to limit the scope of the appended claims.
With reference to
Contained within or associated with the case 22 can be a power device 25 (i.e., battery), a controller assembly 26, and a connector body 27. The controller assembly 26 can include a circuit board having a processor, memory, transmitter, receiver, and other appropriation portions, further discussed herein. The connector body 27 can extend from or be integrated with the case 22. The connector body 27 can include multiple ports 28 that each interconnect with a connector terminal 30 of a lead assembly 32.
A fixation mechanism can also be included with each lead assembly 32a, 32b to affix each tip electrode 36a, 36b relative to or in a selected tissue of the patient. The fixation mechanism can be near each tip electrode 36a, 36b or define a portion of the tip electrode 36a, 36b. Fixation mechanisms can be any appropriate type, including a grapple mechanism, a helical mechanism, a drug-coated connection mechanism, and other appropriate connection mechanisms.
A majority of each lead body 34a, 34b can also be formed in a generally known and selected manner. For example, the various conductors and electrical components can be encased in silicone, polyurethane, and other appropriate materials. For example, at least one inner electrical conductor (identified as 150 in
The IMD 20, including the components discussed above, can be implanted in a patient 40 as illustrated in
The IMD 20, including the case 22 and the lead bodies 34a, 34b, can be implanted using known procedures. For example, an incision can be made in a chest wall or an abdomen wall of the patient 40 and the lead assemblies 32a, 32b can be passed through selected veins to selected portions of the heart 42 of the patient 40. The case 22 can also be positioned through the incision into a chest wall or abdominal wall of the patient 40. In a selected procedure, the leads assemblies 32a, 32b can be passed through a superior vena cava 44 of the patient 40. The lead tips or tip electrodes 36a, 36b can be positioned at various positions in the heart 42, such as at the ventricles or atriums thereof. The position of the lead assemblies 32a, 32b and tip electrodes 36a, 36b can be selected for pacing, defibrillation, sensing, or other appropriate procedures. The specific implantation procedure, position of the tip electrodes 36a, 36b, and the like can depend upon the patient 40, the surgeon performing the procedure, the specifics of the lead assemblies 32a, 32b, or other considerations.
As discussed above, the IMD 20, including the case 22 and the lead assemblies 32a, 32b can include various features or controls to defibrillate or pace the heart 42. The controls can include a processor associated with the controller assembly 26 located within the case 22. The processor can be programmed to control driving a current through the lead bodies 34a, 34b to the tip electrodes 36a, 36b to defibrillate or pace the heart 42.
With continued reference to
Moreover, the IMD 20, including the case 22 and the lead assemblies 32a, 32b, can be formed to counteract or interact with various environmental factors. For example, the lead assemblies 32a, 32b can include features or portions to re-direct or dissipate thermal energy created by an induced current. Induced currents can be created due to an external field, such as an electromagnetic field acting on the conductors of the lead assemblies 32a, 32b.
For example, according to various embodiments, the patient 40 which has the implanted IMD 20 may receive a certain therapy or diagnostic technique, such as a magnetic resonance image (MRI) scan. Although not illustrated, a MRI, generally understood by one skilled in the art, uses high frequency radio frequency (RF) pulses and strong magnetic fields to create image data regarding the patient 40. Generally, a MRI will have a frequency of about 42 MHz per tesla. Many common MRI systems use about 1.5 tesla magnetic fields and have a corresponding RF frequency of about 64 MHz. Without being bound by the theory, the strong magnetic fields in a MRI can induce aligned spins of sub-atomic particles and the high frequency RF pulses can be used to change the alignment or otherwise affect the sub-atomic particles within the patient 40.
The strong magnetic fields and RF pulses may induce currents within the lead assemblies 32a, 32b of the IMD 20. The current induced in the lead assemblies 32a, 32b may cause certain affects, including heating, of the various lead components or tissue of the patient undergoing the MRI scan. According to various embodiments, such as those discussed herein, components, controls and/or mechanisms can be provided to reduce or eliminate the amount of current or thermal energy induced within each tip electrode 36a, 36b, or increase an area over which the current or thermal energy can be dissipated.
According to various embodiments, and with reference to
The IPG 120 can include a control system 122 and at least one IPG stimulation lead 124 which can be implanted into an anatomical structure, similar to the placement of the IMD 20 relative to the heart 42, as shown in
The controller 122a can be in communication with and responsive to the programmer 50 to receive a desired treatment plan for the heart 42, such as a desired voltage for the electrical stimulation of the heart 42. The controller 122a can also be in communication with the lead 124 to receive the sensed electrical activity of the heart 42, as will be discussed. The pulse generator 122b can be in communication with and responsive to the controller 122a to generate the desired therapy (i.e., electrical stimulation or pulse) for the heart 42. The pulse generator 122b can be in electrical communication with the lead 124 to supply the lead 124 with the desired therapy.
The field sensor 122c can be responsive to an external field, such as that generated by a MRI scan. In this regard, the field sensor 122c can be capable of detecting multi-level field strengths and/or can be capable of discriminating between different field ranges. For example, the field sensor 122c can comprise a Hall effect sensor or the magnetic field sensor 60 disclosed in commonly assigned U.S. Pat. No. 7,050,855, incorporated herein by reference. The field sensor 122c can also be an RF field sensor, as known in the art or can comprise another suitable field sensor used to detect an external field. The field sensor 122c can be in communication with the controller 122a to transmit a signal indicative of the surrounding field, such as whether the patient 40 is undergoing a MRI scan. Based on the signal received from the field sensor 122c, the controller 122a can adjust the voltage and location of the electrical therapy provided by the lead 124 to the heart 42, and optionally can also communicate the presence of the field to an optional field control system 132 of the lead 124, if employed, as will be discussed.
With reference to
The distal end 136 can terminate within the anatomical structure adjacent to the desired location for the delivery of the therapy to the heart 42, as generally known, and illustrated in
The pacing conductor 150 and the sensing/control conductor 152 can each be insulated to conduct or carry electrical signals along the body 138 of the lead 124. As best shown in
The ring electrode 140 can be disposed near the distal end 136 of the lead 124 (
The inner surface 140b of the ring electrode 140 can be in electrical communication with the switch assembly 144 via a ring contact 144a. As will be discussed, the switch assembly 144 can selectively electrically decouple the ring electrode 140 from the IPG 120 in a second operational state, briefly re-coupling to sense or deliver therapy as further discussed herein.
With reference to
With reference to
With continued reference to
The optional field control system 132 includes a controller 132a and a field sensor 132b. As the field control system 132 can be optional, the controller 132a and field sensor 132b will be illustrated herein in phantom. If employed, the controller 132a can be in communication with and responsive to the controller 122a of the IPG 120 to receive a signal that indicates whether an external field is present, based on data received from the field sensor 122c.
Further, if employed, the controller 132a can be in communication with and responsive to the field sensor 132b, and can be in communication with the switch assembly 144. Based on the data received from the field sensor 132b, the controller 132a can transmit a signal to the controller 122a of the IPG 120, via the sensing/control conductor 152d, which can indicate that an external field is present. In addition, based on the data received from the field sensor 132b, and the controller 122a, the controller 132a can transmit a signal to the switch assembly 144 to electrically couple either the ring electrode 140 or the tip electrode assembly 142 to the pacing conductor 150 to receive the therapy from the IPG 120.
If employed, the field sensor 132b can be responsive to an external field, such as that generated by a MRI scan, and can be capable of detecting multi-level field strengths and/or can be capable of discriminating between different field ranges. Thus, if desired, the field sensor 132b can be substantially similar to the field sensor 122c.
With reference to
In one example, the switch assembly 144 can be activated by the IPG 120. In this regard, based on only the receipt of the signal from the field sensor 122c, the controller 122a can determine if the external field is present. If the external field is present, then the controller 122a can output a signal to activate the switch assembly 144 to switch from the first operational state to the second operational state.
In another example, the switch assembly 144 can be activated by the IPG 120 and the field sensor 132b. In this regard, based on the receipt of the signal from the field sensor 122c and the signal from the field sensor 132b, the controller 122a can determine if the external field is present. If the external field is present, then the controller 122a can output a signal to activate the switch assembly 144 to switch from the first operational state to the second operational state. The controller 122a can also determine if the signal from the field sensor 122c and the signal from the field sensor 132b are about equal. If the signal from the field sensor 122c and the signal from the field sensor 132b are not about equal, then the controller 122a can output error data for the programmer 50 that can indicate that one of the field sensor 122c and field sensor 132b has failed.
In another example, the switch assembly 144 can be activated by the control system 122 of the IPG 120 and the field control system 132 of the lead 124. In this regard, based on the signal from the field sensor 122c, the controller 122a can output a signal for the controller 132a that can indicate if an external field is present. If the external field is present, then the controller 122a can output a signal to activate the switch assembly 144 to switch from the first operational state to the second operational state where the tip electrode 142 and the ring electrode 140 and selectively and briefly re-coupled to delivery therapy and then decoupled again from the IPG 120 so reduce heating of components or tissue. The field controller 132a can receive the signal from the controller 122a that indicates if the external field is present, and can receive the signal from the field sensor 132b that indicates if the external field is present. The controller 132a can determine if the signal from the field sensor 122c and the signal from the field sensor 132b are about equal. If the signal from the field sensor 122c and the signal from the field sensor 132b are not about equal, then the controller 132a can output a signal for the controller 122a such that the controller 122a can output error data for the programmer 50. If, based on at least one of the signal from the field sensor 122c and the field sensor 132b, the external field is present, then the controller 132a can also output a signal for the drive circuit 144c to activate the switch assembly 144 to electrically decouple and re-couple tip electrode 142 and the ring electrode 140 to the IPG 120 in the second operational state such that therapy can continue to be delivered during an MRI scan.
In yet another example, if the lead 124 is not in the presence of an external field or in a normal operating state, then the switch assembly 144 can be in contact with the tip contact 144b, such that the current from the IPG 120 can flow to the tip electrode 142b, via the transmission coil 142a, in the first operational state (i.e., no external field detected). If the lead 124 is in the presence of the external field, then the switch assembly 144 can decouple the tip electrode 142 while allowing the ring electrode 140 to remain connected for sensing purposes, in the second operational state. Thus, in the presence of an external field, the tip electrode 142b can be electrically decoupled from the lead 124, which thereby reduces the effective length of the lead 124. In this regard, the amount of current or thermal energy induced in the lead 124 can depend upon a length of the lead 124. In the normal operating state, the length of the lead 124 can be illustrated as L1 (
With reference now to
The IPG field control module 204 can receive as input IPG field sensor data 212. The IPG field sensor data 212 can comprise a signal from the field sensor 122c and optionally, the field sensor 132b if employed, that can be used to determine whether or not an external field is present. Based on the IPG field sensor data 212, the IPG field control module 204 sets field data 214 for the pacing control module 206 and the lead control module 202. The field data 214 can comprise data that indicates whether an external field, such as that generated by a MRI scan, is present.
The pacing control module 206 can receive as input the field data 214, heart rhythm data 216 and programmer data 218. The heart rhythm data 216 can comprise the electrical activity of the anatomical tissue, such as the heart 42, as sensed by the ring electrode 140. The programmer data 218 can comprise data received from the programmer 50, such as a desired therapy to be output by the IPG 120 based on the presence of an external field, such as that generated by a MRI scan. Generally, the IPG 120 produces a pacing therapy at about 0.01 volts (V), however, this voltage value is programmable to achieve capture of the patient's heart muscle so that the pacing therapy can be effectively delivered.
Based on the field data 214, the heart rhythm data 216 and the programmer data 218, the pacing control module 206 outputs pacing data 220. The pacing data 220 comprises a desired therapy for the anatomical tissue, such as to enter the second operational state where the tip electrode 142 and ring electrode 140 are first decoupled from the IPG 120 and then selectively and briefly re-coupled to the IPG 120 for the delivery of therapy during the MRI scan. When the patient is no longer in the presence of the MRI field, then the pacing data 220 can re-couple the tip electrode 142 and ring electrode 140 to resume normal pacing operation in the first operational state.
Based on the field data 214, the heart rhythm data 216 and the programmer data 218, the pacing control module 206 outputs pacing data 220. The pacing data 220 comprises a desired therapy for the anatomical tissue, such as a desired electrical pulse to stimulate the heart 42. Thus, if based on the heart rhythm data 216, the pacing control module 206 determines that the heart 42 requires a pacing therapy, then, based on whether the patient 40 is undergoing a MRI scan, as indicated by the field data 214 and/or the programmer data 218, the pacing control module 206 outputs the appropriate level of therapy as pacing data 220. The pacing data 220 can instruct the pulse generator 122c to generate the desired therapy for the anatomical tissue.
The lead control module 202 can receive as input lead field sensor data 224, heart rhythm data 216 and field data 214. The lead field sensor data 224 can be optional, and can comprise a signal from the field sensor 132b that can be used to determine whether or not an external field is present, such as that generated during a MRI scan. Based on the lead field sensor data 224, heart rhythm data 216 and field data 214, the lead control module 202 can output switch data 226 and, optionally, error data 228. The switch data 226 can comprise a signal to the switch assembly 144 to drive the drive circuit 144c to electrically decouple or re-couple either the ring electrode 140 and/or the tip electrode assembly 142 to the IPG 120 based on whether an external field is present. If it is determined that an external field is present, based on the lead field sensor data 224 and/or field data 214, then the switch data 226 can comprise a signal to electrically decouple the ring electrode 140 and/or the ring electrode to the IPG 120 in the second operational state as described above. If it is determined that an external field is not present, then the switch data 226 can comprise a signal to electrically re-couple the tip electrode assembly 142 and the ring electrode 140 to the to the IPG 120 to return to the normal first operational state.
The error data 228 can comprise a signal transmitted to the programmer 50 that there is an error associated with either the field sensor 122c of the IPG 120 or the field sensor 132b of the lead 124, if employed. In this regard, if the field data 214 does not match the lead field sensor data 224, the lead control module 202 can output the error data 228 to indicate that there is a problem with either the field sensor 122c of the IPG 120 or the field sensor 132b of the lead 124.
With reference now to
At decision block 306, the method determines if the field present is greater than a threshold field. The threshold field can be equivalent to a field generated during a MRI procedure, and thus, can comprise a threshold value for a magnetic field or a threshold value for an electrical field. Further, the threshold field can be a value programmed into the IPG 120 by the programmer 50. If the field present is greater than the threshold field, then the method can go to block 310. Otherwise, the method can go to block 312.
At block 312, the method re-couples the tip electrode 142 and ring electrode 130 to the IPG 120 if they had been previously decoupled in block 310. Then, the method can loop to block 300.
At block 310, the method can activate the switch assembly 144 to electrically decouple the IPG 120 from the tip electrode assembly 142 and ring electrode 140 such that the tip electrode assembly 142 cannot deliver the desired therapy to the heart 42 and the ring electrode 140 is not sensing the heart. Then, at block 316, the method can briefly re-couple the tip electrode 142 and the ring electrode 140 to deliver therapy from the IPG to the patient. Then, at block 318, the method can again decouple the tip electrode 142 and the ring electrode 140 and loop to block 300 to again determine whether the patient remains in the external field; that is in one embodiment, having an MRI scan performed.
In a one preferred embodiment regard, the method can adjust decouple/re-couple timing so that the tip electrode 142 and the ring electrode 140 are decoupled approximately 95% of the time to reduce heating of the IPG components as well as the tissue adjacent to the tip electrode 142.
While specific examples have been described in the specification and illustrated in the drawings, it will be understood by those of ordinary skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various examples is expressly contemplated herein so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise, above. Moreover, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular examples illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this disclosure, but that the scope of the present disclosure will include any embodiments falling within the foregoing description and the appended claims.
