CONTACTLESS INTERCONNECT FOR TRANSD UCERS

BACKGROUND

Implantable medical devices (IMDs) are commonly employed in medical therapies such as acrdiac rhythm management (CRM), neurological monitoring and therapy, and other diagnostics and monitoring. Such CRM devices røay be coupled to a surface of a patient's heart via one or more medical electrical leads. Typically the one or more leads include electrodes for both stimulating the heart and sensing electrical activity of the heart. In order to provide better management of cardiac conditions, one or more leads may also include a physiological sensor such as a transducer, in addition to intracardiac leads, transducers may also be incorporated into leads that are placed in the abdomen, subcutaneously or submuscularly in the thorax or in or around the cranium to measure specific physiologic variables, In many cases, it is desirable that all of the necessary elements, including electrodes and/or transducers, be carried on a single lead body wherein locations of each element along the lead body accommodate proper function to meet the therapeutic objective of the system because it is desirable to maintain a small lead diameter while including multiple lead components, it may be preferable that the size of the transducer be as small as possible

In addition to having a small size, transducers contained within leads must be designed to function well in the environment in which they will be placed. For example, transducers that are exposed to a patient's body are susceptible to corrosion such that integrated circuit chips included in the transducers may degrade over time. To prevent exposure to bodily fluids, transducers may be enclosed in hermetically sealed capsules. The transducer, inside the capsule, is electrically joined to a power source through an electrical feedthrough which may rigidly attach the transducer to the lead. By isolating the transducer, thsi configuration increases corrosion, allowing for long-term implantation. However, when the transducers are disposed in or near a patient's heart, heart contractions may cause force to be repeatedly applied to the rigid connection between the transducer and the lead. This undesirable strain may decrease the structural integrity of the transducer over time. Transducers on leads that are placed subeutaneously or intramuscularly would also be subjected to repeated strain due to patient movements In addition, encasing the transducers in hermetically sealed capsules has the undesirable

effect of increasing their size. Some transducers, such as biochemical sensors, cannot be encased in hermetic capsules because they need to interact with the body fluids.

Accordingly, it is desirable to have a relatively simple and inexpensive transducer that has a corrosion resistant configuration and is capable of being implanted into a patient for long periods of time. In addition, it is desirable that the transducer be small to fit within the circumference of an implanted medical device, such as an intracardiac lead. In addition, it is desirable to have a transducer that is configured to be tolerant Io strain, such as due to repetitive lead movement caused by cardiac activity.

SUMMARY

Embodiments of the invention include implantable medical devices including, for example, pacemakers, cardiac resynchronization devices, implantable defibrillators and physiologic monitors. The implantable medical devices may comprise lead bodies including one or more conductors within the leads and one or more transducers supported by the lead by for detecting physiological data The one or more transducers are electrically coupled to the one or more conductors by a conductive fluid, paste or gel. In some embodiments, the transducer may be media exposed. The conductive fluid, paste, or gel that couples the transducer to the conductor may be contained within a well in the lead body Embodiments of the invention include leads such as intracardiac leads, intravascular leads, subcutaneous leads and submuscular leads.

A variety of transducers are appropriate for embodiments of the invention. In some embodiments, the transducer may be a MEMS chip and/or an integrated circuit. The transducer may perform a variety of functions. For example, the transducer may be a sensor such as a pressure sensor, an acceleroraeter, an acoustic sensor, a flow sensor, a glucose sensor, a biochemical sensor, a pH sensor, and/or a strain gauge. The conductor may provide power to one or more transducers as well as other lead body components and/or may provide data transmission.

BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 is a side view of an exemplary lead.

FlG 2 is a partial cross section of a portion of a lead according to an embodiment.

FIG. 3 is a cross section of a portion of a lead according to another embodiment.

FIG 4 is a portion of a lead with a section of the sheath and backbone cut away.

FIG. 5 is a cross section of a transducer and conductive body in a well including a capacitor plate

FIG. 6 is a cross section of a pressure sensor within a lead.

FIG 7 is a cross section of a pressure sensor within a lead according to another embodiment.

DETAILED DESCRIPTION

Embodiments of the invention may be used in implantable medical devices having conductive bodies such as lead bodies An example of an implantable medical device appropriate for the invention is an implantable medical electrical lead such as an intracardiac medical lead 100. FIG. 1 is a side view of an exemplary intracardiac medical lead 100 configured to be coupled to an implantable medical device or other monitoring device (not shown) and includes a transducer 108. Lead 100 may be any one of a number of different types of leads, such as a pressure monitoring lead or a therapy lead. Lead 100 includes a connector assembly 102, a lead body 106, and a transducer module 107. Connector assembly 102 is located at a proximal section 104 oflead 100 and may be configured to be coupled to an implantable medical device (not shown) to electrically couple lead 102 thereto. Other examples of transducers on conductive bodies include conductive bodies that connect an implanted medical device to transducers placed in the abdomen or subcutaneously or submuscularly in the thorax or EEG electrodes on or around the cranium. Examples of appropriate implantable medical devices for use in this invention include pacemakers, defibrillators, cardiac resynchronization therapy (CRT) systems, cardiac or pulmonary monitors, glucose and other chemical monitors, neurosti mulators, neurological monitors, neuromuscular sensors and actuators, and drug pumps.

The transducer module 107 may support any type of transducer 108 suitable for incorporation within a conductive body For example, the transducer 108 may be a sensing transducer, an actuating transducer, an 1C only transducer, or a combination of a sensor and an actuator. Examples of sensing transducers include a sensor and an

integrated circuit integrated on a chip (e g.. a silicon substrate or micro -electro-mechanical system (MEMS) device or nano-electro-mechanical system (NEMS) device), a sensor element without an intergated circuit built into a substrate {e.g , glass, ceramic, silicon, or other suitable material), and a sensor element built into a substrate with an. integrated circuit hermetically encapsulated or packaged into a substrate. Sensors which may be used to detect physiologic data include pressure sensors, oxygen sensors., flow sensors, temperature sensors, accelerometers, acoustic sensors, biochemical sensors, optical sensors and sensors which monitor more than one physiological variable Examples of actuating transducers include an actuator and an integrated circuit integrated on a chip (e.g., a silicon substrate or MEMS device or NEMS device), an actuator element without an integrated circuit built into a substrate {e.g., glass, ceramic, silicon, or other suitable material), and an actuator element built into a substrate with an integrated circuit hermetically encapsulated or packaged into a substrate. Such actuating transducers may include a piezoelectric element actuator for vibration. Examples of IC-only transducers include an integrated circuit on a silicon substrate (e.g , an IC-logie multiplexer on a lead or a memory chip for sensor calibration coefficients) and an integrated circuit hermetically encapsulated or packaged into a substrate (e.g., glass, ceramic, silicon, or other suitable material). Alternatively, embodiments of this invention may include components instead of, or in addition to, transducers 108 Examples of other components which may be used in embodiments of this invention include transceivers., pumps, drug delivery devices, thermocouples and other small devices suitable for inclusion in a conductive body. The transducer 108 may be located within a conductive body such as a lead body 106 and does not need to be encased in a hermetically sealed capsule Rather the transducer 108 may be surrounded by a sheath 110, a capsule or other appropriate material or may be made from biocompatible material. In some embodiments, at least a portion of the trasnducer 108 may be media exposed for interacting with the implant environment and sensing one or more physiological variables. ^' Transducers that may require exposure to the physiologic, media include, but are not limited to, pressure sensors, flow sensors, glucose sensors. pH sensors and other chemical sensors, Other transducers that may not require exposure to the physiologic media include, but are not limited to, accelerometers, temperature sensors, and acoustic sensors. These transducers would be made smaller with the elimination of the hermetic capsule.

As shown in FIGS. 2-7, the conductive body such as a lead body may include an outer sheath 1 10 and a backbone 1 12 The outer sheath 1 10 and the backbone 1 12 of the conductive body may surround a portion of the transducer 108. The outer sheath 1 10 and the backbone 1 12 may be made of a nonconductive material such as polymer, glass, ceramic or an inorganic metal oxide. The appropriate material for the sheath 1 10 and/or backbone 1 12 may be choses fo provide the desired stiffness or flesibility of the conductive body.

In some embodiments, the transducer 108 is a pressure sensor 1 14. In such embodiments, the pressure sensor 114 may be configured to sense pressure exerted upon it by a patient's blood or other body fluid The pressure sensor S S 4 may include a pressure transducer The transducer may include a MEMS/I C or a NEMS/1C on a substrate, in some embodiments, a complementary metal oxide semiconductor (CMOS) buffer amplifier may be used in place of, or in addition to, the MEMS/IC or NEMS/IC. The MEMS/IC or NEMS/IC may be configured to convert sensed pressure into representative signals. The transducer may include a flexible diaphragm 120 that, when subjected to fluid pressure, may create a capacitance with a nearby fixed plate. In some embodiments, the transducer may include piezoelectric material that creates an electrical signal when subjected to a force due to surrounding fluid pressure. The pressure tansducer may also include at least, one conductive pad 1 16, which provides an electrical connection to other components Other types of transducers may also have at least one conductive pad 1 16, The transducer 108 may be supplied with power by conductors 1 18 that pass through the conductive body to the transducer 108 These conductors 1 18 may be surrounded by the backbone 1 12 as they pass through the conductive body. In addition, the conductors 1 18 may be surrounded by insulation These conductors 118 may be wire coils, such as single pole coiled wire conductors, and may be made of a suitable biocompatible material such as MP35N In some embodiments, such as MEMS pressure sensors, the conductors provide low voltage power, on the order of microamperes, to the transducers 108. The conductors 1 18 may also transmit data to a device, such as a monitoring device, from the sensors 108. in some embodiments, the conductors 1 18 may be bi-directional and may supply power io the transducer 108 as well as transmit data from the transducers 108 to the monitoring device.

When the conductor 1 18 reaches the transducer 108, there is a gap in a portion of the backbone 1 12 such that the backbone 1 12 no longer surrounds the conductor

1 18. This gap is located along a length of conductor 1 18 which extends adjacent to a conductive pad 1 16 of the transducer 108. The gap extends at least from the conductor ! 18 to the conducive pad 1 16, creating a well 122 which encompasses both components. A portion or all of the conductor 1 18 is without insulation within the well 122, in some embodiments, the well 122 is completely surrounded by insulating material. The well may extend through the backbone 1 12 from the conductive pad 1 16 to the sheath ! 10, or may only extend through a portion of the backbone 1 12. In some embodiments the conductive body may have a backbone 1 12 but no separate sheath 1 10 in such embodiments, the well 122 may not extend through to the outer circumference of the backbone 1 12, but rather the backbone 1 12 may enclose the well 122. Alternatively, the well 122 may extend through the backbone 1 12 and a nonconductive material may cover the well 122, In such embodiments the well 122 is an opening within the conductive body which contains a conductive pad 1 16 and a conductor 118 and which is electrically isolated. inside the well 122, there is no hard wire or other structural connection between the conductor 1 18 and the conductive pad 1 16. Rather, the well contains an electrically conductive material which electrically connects the conductor 1 18 and the conductive pad 116. For example, in one embodiment, the well 122 may be filled with an ionic conductve fluid or gel. Examples of appropriate conductive fluids or gels include physiologic saline, ionic liquid, inorganic salt solution in a hydrogel. organic salt solution in oil or hydrophilio liquid-like polymers. In another embodiment, the well 122 may be tilled with an electrically conductive paste, polymer gel or adhesive. Examples include pastes containing carbon-graphite or silver powder, conductive gaskets, conductive polymers such as poly pyrrole, poly acetylene and poly aniline., conductive carbon or metal nanoparticle filled oil or polymer with a glass transition temperature lower than room temperature, and liquid metals.

Eliminating the hard conductor interconnection between the transducer and the conductors allows the conductive pad 1 16 and the conductor 1 18 to move relative to each other without interfering with their electrical connection. Such a flexible system is ideal for an environment in which the transducer 108 will undergo repeated stresses over a long period of time, such as a permanent intracardiac lead As a result of this improved flexibility, the system may have less stress or strain induced failures relative to systems with rigid interconnections, making the connection more reliable At the same lime.

elimination of the feedthrough has the additional advantage of making the system smaller

This allows the lead 100 or other conductive body to be small and isodiametric.

The conductor 1 18 which supplies power to the transducer 108 may terminate inside the well 122. Alternatively, the conductor 1 18 may pass through the well 122 and reenter the backbone 112. The conductor 1 18 may then continue distally through the conductive body and supply power to and/or receive data from other conductive body components such as one or more additional transducers 108, pumps, pacing tips., defibrillation coils or other devices. In this way a single conductor 1 18 is able to supply power to and/or receive data from multiple transducers 108 or a combination of components

In some embodiments, the transducer 108 has two conductive pads 1 16, each on the same side of the transducer as shown in FlG. 2. Half of the backbone 1 12 has been cut away in this view to reveal the well 122 surrounding the lower conductor 1 18 and conductive pad 1 16 The conductor 1 18 which is electrically connected to the upper conductive pad J 16 is not shown. The conductive pads 1 16 on the trasnducer 108 are spaced such that the wells 122 in which they are contained are separated by the backbone 1 12 and the wells 122 are electrically isolated from each other. Alternatively, a different insulative material other than the backbone 1 12 could separate and electrically isolate the wells 122

In other embodiments, the transducer 108 has conductive pads 1 16 on opposite sides of the transducer 108, as shown in FIGS. 3 - 4. FlG. 3 is a cross section of a segment of a conductive body in which one well 122 encloses a conductor 118 and conductive pad 1 16 above the transducer 108 and another well 122 encloses the other conductor 1 ! S and other conductive pad 116 below the transducer 108. The conductors 1 18 pass through the wells 122 and continue through the conductive body A seal 124, such as an adhesive or silicone, may be provided around the well 122, as shown in FlG 3. The wells 122 are electrically isolated from each other. In FIG. 4, the portion of the sheath 1 10 and backbone 1 12 above the transducer 108 are cut away to show the conductor 1 18 passing above the conductive pad 1 16

In some embodiments, such as the one shown in FIG 5, the conductive fluid or gel is capacitively coupled to the conductive pad. In the embodiment shown in FIG 5, upper and lower capacitor plates 126 separated by a dielectric layer 128 form a

capacitor. The upper capacitor plate 126 (as shown in FlG 5} forms an inner plate while the lower capacitor plate 126 is positioned within the well 122 and acts as the conductive pad 1 16. Capacitive couplings, such as that shown in FIG. 5, allow the entire pressure module and/or ICs that are susceptible to corrosion from body fluids to be coaled in the dielectric 128 to help isolate the module from the sourrunding media yet provide electrical coupling via a fluid gel in well 122 to conductor 1 18. That is, the dielectric 128 in FlG 5 may be applied over upper plate 126 for capacitive pruposes and over the remainder of the module for media isolations purposes. Appropriate transducers for use in these embodiments include silicon MEMS pressure sensors and accelerometers. The dielectric 128 may be formed by atomic layer deposition or other coating processes. Other transducers, such as optical based or electrochemical sensors, may he coated with a thin layer of silicone or other polymer. Additionally, the capacitor may act with an adhesive layer sea! 124 to seal off well 122 In an alternative embodiment, the upper capacitive plate may he coated with a dielectric without a lower capacitive plate such that the capacitor is formed by the upper capacitive plate and the conductive media. In some capacitive embodiments, enhancements can be made to the capacitor plates to increase the capacitance and, thereby, lower the impedance of the connection. For example, by increasing the surface area of the plates 126, the capacitance may be increased. This may be done, for example, by making the surface of one or both of plates 126 irregular, such as by using jagged or undulated surface. In this way the active surface area of the plates 126 may be increased without increasing the size of the plates 126, thus maintaining the desired small sixe of the connection. Such surfaces may be created using materials such as titanium nitrate, which may be applied using a sputtering process, or plantinum black, which may be applied by an electroplating or electrodeposition process, in some embodiments, such as embodiments having a single capacitive plate, porous silicone with a high dielectric constant may be used as a film to increase the surface area and capacitance of the plate. This embodiment may be appropriate, for example, when the transducer and electronics are a single piece of silicon. The back side of the silicon chip may he processed to make it porous such that it may be coated with a suitable insulating film.

In addition, it may be desirable to minimize the distance between the conductive pad 116 and the conductor 1 18, thus mini mixing the resistance as well as providing a small size While the conductive pad 1 16 and the conductor 1 18 may be so

close that they touch, physical contact is not necessary using the conductive fluid or gel according to embodiments of the invention. Thus, by eliminating a hard physical connection, the design accommodates flexion and movement of the conductive pad i 16 relative to the conductor ! 18 while maintaining an electrical connection

At least a portion of the transducer 118 may be media exposed to allow communication with the environment. The conductive body which contains the transducer 108 may include an opening over a portion of the transducer In some embodiments, the transducer 108 may be a pressure sensor 1 14 for detecting pressure, such as the pressure exerted upon the pressure sensor 1 14 by a patient's blood flowing around the pressure sensor 1 14. Such pressure sensors 1 14 may have diaphragms 120 or membranes on their surface, which may be exposed to the environment In embodiments which include a pressure sensor 1 14 within a lead 100 or other conductive body, the diaphragm 120 of the pressure sensor 1 14 may be media exposed through an opening in the sheath 1 10. For example, as shown in FIG. 6, the sheath 1 10 may form an opening by being completely absent over the exposed portion of the pressure sensor 1 14, in this case over a diaphragm 120. The exposed portion of the transducer 108 may be partially sheltered by being located somewhat centrally within the circumference of the lead, such as inside an indentation in the sheath 1 10 and backbone 1 12 as shown in FlG. 6 Alternatively, as shown in FIG'. 7, the sheath 1 10 may form an opening by having one or more small holes or pores 128 over the exposed portion of the transducer 108. The use of pores 128 may- shelter the exposed portion of the transducer 108. If may also allow for selective filtration of the bodily fluids to which the transducer 108 is exposed. For example, for conductive bodies placed in the circulatory system, the pores 128 may filter the blood cellular components such that the transducer 108 is only exposed to plasma Alternatively, such as in the case of biochemical sensors, the pores 128 may be a semi-permeable membrane that allow entry of the substance of interest, such as a chemical, but minimize or exclude diffusion of other substances which may be sources or error. Such arrangements may prevent encapsulation and/or minimize the formation of fibrotic tissue. Prevention of cell adhesion directly on the sensing materia! may reduce or prevent biocorrosion and/or biofouling. It may also improve transducer performance by reducing sensor drift In another embodiment, the transducer 108 may not be media exposed. For example, the transducer 108 may be a pressure sensor 114 including a diaphragm 120. The diaphragm 120 may be contained within a well 122 in the backbone 1 12 which also contains the

conductor 1 18 and the conductive pad 1 16. Thus the diaphragm 120 may be contained within the well 122 and surrounded by a conductive fluid or gel The well 122 may be encased by the sheath 1 10 which may be sufficiently flexible to allow transmission of pressure through the fluid or gel of the well 122 to the diaphragm 120. Alternatively, a flexible capsule may surround the well 122 in addition to or instead of the sheath 1 i 0. Thus fhe same fluid or gel that provides conduction between the pad 1 16 and the conductor 1 18 may also transmit pressure to the sensor diaphragm 120.

In some mebodiments, the conductive body such as a lead body may include one or more optional conductors 1 18, in addition to the conductors 1 18 which supply power to and/or transmit data from the transducer 108. These conductors 1 18 pass through the back bone 1 12 but do not enter the wells 122. The cross section of a conductive body shown in FIG. 6 contains conductors 1 18 which supply power to a transducer 108 within wells. 122 as well as two additional conductors 1 18 In some embodiments, these additional conductors 1 18 may be at a higher voltage than the conductors 1 18 which power the transducer 108, making them appropriate for providing power to applications such as electrodes for cardiac pacing.