Patent Application
20090024154
The invention relates generally to implantable devices (e.g., embolic coils, stents, and filters) having flexible electrolytic detachment mechanisms.
Implants may be placed in the human body for a wide variety of reasons. For example, stents are placed in a number of different anatomical lumens within the body. They may be placed in blood vessels to cover vascular lesions or to provide patency to the vessels. Stents are also placed in biliary ducts to prevent them from kinking or collapsing. Grafts may be used with stents to promote growth of endothelial tissue within those vessels. As another example, vena cava filters can be implanted in the vena cava to catch thrombus sloughed off from other sites within the body and carried to the implantation site via the blood stream.
As still another example, vaso-occlusive devices are used for a wide variety of reasons, including for the treatment of intravascular aneurysms. An aneurysm is a dilation of a blood vessel that poses a risk to health from the potential for rupture, clotting, or dissecting. Rupture of an aneurysm in the brain causes stroke, and rupture of an aneurysm in the abdomen causes shock. Cerebral aneurysms are usually detected in patients as the result of a seizure or hemorrhage and can result in significant morbidity or mortality. Vaso-occlusive devices can be placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. The embolus seals and fills the aneurysm, thereby preventing the weakened wall of the aneurysm from being exposed to the pulsing blood pressure of the open vascular lumen.
One widely used vaso-occlusive device is a helical wire coil having windings, which may be dimensioned to engage the walls of the vessels. These coils typically take the form of soft and flexible coils having diameters in the range of 10-30 mils. Multiple coils will typically be deployed within a single aneurysm. There are a variety of ways of discharging vaso-occlusive coils into the human vasculature. In addition to a variety of manners of mechanically deploying vaso-occlusive coils into the vasculature of a patient, U.S. Pat. No. 5,122,136, issued to Guglielmi et al., describes an electrolytically detachable vaso-occlusive coil that can be introduced through a microcatheter and deployed at a selected location in the vasculature of a patient.
This vaso-occlusive coil is attached (e.g., via welding) to the distal end of an electrically conductive pusher wire. With the exception of a sacrificial joint just proximal to the attached embolic device, the outer surface of the pusher wire is coated with an ionically non-conductive material. Thus, the sacrificial joint will be exposed to bodily fluids when deployed within the patient. A power supply is used to provide direct current (DC) power to the core wire, with a conductive ground patch or intravenous needle located on or in the patient providing a ground return path. Applying a positive DC voltage to the pusher wire via the power supply relative to the ground return causes an electrolytic reaction between the sacrificial joint and the surrounding bodily fluid (e.g., blood). As a result, the sacrificial joint will dissolve, thereby detaching the vaso-occlusive coil from the pusher wire at the selected site.
While the use of electrolytically detachable vaso-occlusive coils has generally been successful, the period of time needed to detach the vaso-occlusive coils from the pusher wire is relatively long (currently, averaging from 30 to 40 seconds) and variable, resulting in an increase in procedure time. This problem is compounded by the need to deploy multiple vaso-occlusive coils within the patient. The relatively long and varying detachment time is due, in large part, to the relatively large and widely varying tissue impedance between the sacrificial joint and the ground electrode amongst patients. Many factors can affect the impedance at the detachment zone, including the formation of bubbles during the electrolytic process and the aggregation of blood constituents and electrolytic products. In addition, the bodily fluid surrounding the sacrificial joint may not be the optimum electrolyte (compared with saline) for inducing an electrolytic reaction in the detachment zone. It is believed that some blood constituents (proteins, fats, amino acids, etc.) may tend to aggregate into a cloud and/or adhere to the electrically active sacrificial joint which will tend to increase impedance, decrease the rate of electrolysis, thereby increasing the overall detachment time. Blood environment may also introduce variability in detachment time due to variations in blood constituents amongst patients. There, thus, remains a need to provide an improved electrolytic means for deploying implants within a patient.
In accordance with one aspect of the present inventions, a medical system is provided. The medical system comprises an implant assembly including an elongated pusher member, an implantable device (e.g., a vaso-occlusive device) mounted to the distal end of the pusher member, and an electrolytically severable joint disposed on the pusher member. The implantable device detaches from the pusher member when the severable joint is severed. The medical system further comprises an electrical power supply coupled to the implant assembly. The power supply is configured for conveying a time varying signal having net positive electrical energy to the severable joint to detach the implantable device from the pusher member. The medical system may further comprise a delivery catheter configured for slidably receiving the implant assembly.
In one embodiment, the implant assembly further includes a terminal carried by the proximal end of the pusher member in electrical communication with the severable joint, wherein the terminal of the power supply is electrically coupled to the terminal of the implant assembly. In another embodiment, the power supply has another terminal electrically coupled to a return electrode, with the terminals of the power supply having different electrical potentials. The return electrode may be an external ground electrode or can be a return electrode carried by the pusher member. In one embodiment, the power supply is current-controlled (e.g., conveying the time varying signal in the range of 0.25 mA to 10 mA). In another embodiment, the power supply is voltage-controlled (e.g., conveying the time varying signal in the range of 0.5V to 11V). The time varying signal may have a suitable frequency (e.g., 10 Hz to 20 KHz). Although the present inventions should not be so limited in their broadest aspects, it is believed that the time varying signal allows the cloud of blood constituents that forms around the detachment site to dissipate, thereby decreasing and making the detachment time more consistent.
The time varying signal may take any of a variety forms (e.g., a square wave, a rounded square wave, a sinusoidal wave, or an exponential wave). The time varying signal may be a pulsed signal or a continuous signal. The time varying signal may have no portion that is negatively polarized or may have negatively polarized portions. In the latter case, the negatively polarized portions may additionally prevent buildup of the blood constituents and electrolysis products on the surface of the severable joint by temporarily reversing the electrical current. To the extent that the time varying signal has an effective duty cycle (i.e., the time period that the time varying signal is positively polarized divided by the total time period of the time varying signal), such duty cycle may be in a suitable range; for example, within the range of 5 percent to 95 percent, or within the range of 20 percent to 80 percent. The power supply may optionally be configured for amplitude modulating the time varying signal.
In accordance with another aspect of the present inventions, a method of implanting a medical device (e.g., a vaso-occlusive device) within a patient is provided. The method comprises introducing the medical device within the patient via a pusher member, and conveying a time varying signal having net positive electrical energy to a joint disposed on the pusher member to induce an electrolytic reaction at the joint, thereby severing the joint to detach the medical device from the pusher member at a target site (e.g., an aneurismal sac) within the patient. The method may further comprise introducing a delivery catheter within the patient, wherein the medical device is introduced within the patient via the delivery catheter, and removing the pusher member from the patient after medical device is detached from the pusher member.
In one method, the time varying signal is conveyed from the joint to a return electrode to induce the electrolytic reaction between the joint and the return electrode. The return electrode may be placed externally to the patient or may be carried by the pusher member. The time varying signal may be current-controlled (e.g., in the range of 0.25 mA to 10 mA) or voltage-controlled (e.g., in the range of 0.5V to 11V). The time varying signal may have a suitable frequency (e.g., in the range of 10 Hz to 20 KHz), and may take one of a variety of forms, such as those described above.
In accordance with a yet another aspect of the present inventions, a power supply is provided. The power supply comprises an electrical contact configured for being coupled to an implant assembly having a pusher member and an electrolytically detachable implantable device. The power supply further comprises power delivery circuitry configured for conveying a time varying signal having net positive electrical energy to the electrical contact to electrolytically detach the implantable device from the pusher member.
In one embodiment, the power supply further comprises another electrical contact configured for being coupled to a return electrode, which may be external or may be carried by the pusher member. The power delivery circuitry may be current-controlled (e.g., delivering the time varying signal in the range of 0.25 mA to 10 mA) or may be voltage-controlled (e.g., delivering the time varying signal in the range of 0.5V to 11V). The time varying signal may have a suitable frequency (e.g., in the range of 10 Hz to 20 KHz), and may take one of a variety of forms, such as those described above. The power supply may optionally comprise control circuitry configured for amplitude modulating the time varying signal.
Other and further aspects and features of the invention will be evident from reading the following detailed description of the preferred embodiments, which are intended to illustrate, not limit, the invention.
The drawings illustrate the design and utility of preferred embodiment(s) of the invention, in which similar elements are referred to by common reference numerals. In order to better appreciate the advantages and objects of the invention, reference should be made to the accompanying drawings that illustrate the preferred embodiment(s). The drawings, however, depict the embodiment(s) of the invention, and should not be taken as limiting its scope. With this caveat, the embodiment(s) of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
Referring generally to
To this end, the medical system 10 generally comprises a delivery catheter 12 that can be intravenously introduced within a patient to access a target site within the vasculature, an implant assembly 14 that can be slidably disposed within the delivery catheter 12, and an electrical power supply 16 that can supply electrical energy to the implant assembly 14 to effect the electrolytic detachment process.
The delivery catheter 12 includes an elongate, flexible, tubular member 28 composed of a suitable polymeric material and optionally reinforced with a coil or braid to provide strength or obviate kinking propensities. The delivery catheter 12 further includes a lumen (not shown) through which the implant assembly 14 can be selectively located. The delivery catheter 12 further includes a pair of radiopaque markers 24 disposed on the distal end 20 of the tubular member 28 to allow visualization of the delivery catheter 12 relative to the vaso-occlusive implant 22. The delivery catheter 12 further includes a proximal fitting 26 disposed on the proximal end 22 of the tubular member 28 for introduction of the implant assembly 14, as well as for the optional introduction of dyes or treatment materials.
The implant assembly 14 includes a pusher member 28, an electrolytically severable joint 30, and a vaso-occlusive device 32 that detaches from the distal end 34 of the pusher member 28 when the joint 30 is electrolytically severed. The pusher member 28 typically includes an electrically conductive core (not shown) that provides the pusher member 28 with the necessary tensile and columnar strength, an electrically insulative covering (not shown), and flexible coils (shown) that increase the flexibility of the pusher member 28 at its distal end. Two types of implant assemblies 14 are illustrated: (1) a monopolar implant assembly 14(1) (shown in
The monopolar implant assembly 14(1) includes a positive terminal 38 (shown mated with the power supply 16) disposed on the proximal end 36 of the pusher member 28. The positive terminal 38 may simply be formed on the proximal end 36 of the pusher member 28 by exposing the underlying core wire. The positive terminal 38 serves as a positive terminal that is electrically coupled to the severable joint 30. In this case, the system 10 includes an external return electrode 40 in the form of a ground patch electrode or a ground needle, which can be placed into contact with the patient's tissue remote from the implant assembly 14(1). Thus, a monopolar patient circuit can be formed between the severable joint 30 at the distal end of the pusher member 28 and the return electrode 32 remotely located from the severable joint 30. An optional intermediate return electrode (not shown) can be carried by the distal end 34 of the pusher member 28 to enhance the monopolar patient circuit.
In contrast, the bipolar implant assembly 14(2) includes positive and negative terminals 42, 44 disposed on the proximal end 36 of the pusher member 28 (shown mated with the power supply 16), and a return (ground) electrode 46 carried by the distal end 34 of the pusher member 28 adjacent to the severable joint 30. The positive terminal 42 is electrically coupled to the severable joint 30, whereas the negative terminal 44 is electrically coupled to the return electrode 46. Thus, a bipolar patient circuit can be formed between the severable joint 30 and the return electrode 46 at the distal end 34 of the pusher member 28. In an optional embodiment, the power supply includes a third electrode (not shown), which is configured at the distal end 34 of the pusher member 28 near and preferably physically between the severable joint 30 and the return electrode 46. The third electrode is in electrical communication with terminal (not shown) on the proximal end of the pusher member 28. The third electrode has a high input impedance, so negligible amount of current flows through it, and can be used to monitor and maintain a specific voltage potential level between the severable joint 30 and the electrolyte solution in a voltage-controlled configuration (this third electrode is not necessary in current-controlled configurations). Current- and voltage-controlled configurations will be described in further detail below. Additionally, the third electrode may not be desired for voltage control if the system is electrochemically stable and predictable.
In either of the monopolar or bipolar arrangements, the severable joint 30 serves as an anode, and the external ground electrode 40 or return electrode 46 serves as a cathode. In both of the monopolar and bipolar arrangements, the positive terminals 38, 42 are typically electrically coupled to the severable joint 30 via a stainless steel, or otherwise electrically conductive, core wire (not shown) that extends within and provides the necessary tensile and columnar strength for the pusher member 28. In the monopolar arrangement, however, the entire proximal end of the pusher member 28 will typically be uninsulated to expose the underlying core wire, which will serve at the positive terminal 38. Further details discussing various exemplary constructions of monopolar and bipolar implant assemblies are disclosed in U.S. Provisional Patent No. 60/939,032, entitled “Electrolytically Detachable Implantable Device With Return Electrode,” which is expressly incorporated herein by reference.
The power supply 16 conveys electrical energy to the implant assembly 14 (and in particular, the severable joint 30) and returns electrical energy either from the ground electrode 40 or the implant assembly 14 (and in particular, the return electrode 46), to effect the electrolytic detachment of the vaso-occlusive implant 22. To the end, the power supply 16 has a positive electrical contact 48 configured to mate with the positive terminal 38 of the monopolar implant assembly 14(1) or the positive terminal 42 of the bipolar implant assembly 14(2) via a cable 52, and a negative electrical contact 50 configured to mate with the external ground electrode 40 or the negative terminal 44 of the bipolar implant assembly 14(2) via a cable 54. Notably, for the purposes of this specification, the terms “positive” and “negative” with respect to a terminal or electrical contact is relative and merely means that the positive terminal or electrical contact has a greater voltage potential than that of the negative terminal or electrical contact
In alternative embodiments, the positive terminal 38 of the monopolar implant assembly 14(1) is mated directly to the positive electrical contact 48 of the power supply 16 in the case of a monopolar arrangement, and the positive and negative terminals 42, 44 of the bipolar implant assembly 14(2) are mated directly to the respective positive and negative electrical contacts 48, 50 of the power supply 16. In an optional embodiment, the power supply 16 can be configured as a hybrid power supply that can be selectively operated either in a monopolar energy delivery mode by conveying electrical energy between the severable joint 30 of the monopolar implant assembly 14(1) and the external ground electrode 40 to detach the vaso-occlusive device 32 from the pusher member 28, and in a bipolar energy delivery mode by conveying electrical energy between the severable joint 30 and return electrode 46 of the bipolar implant assembly 14(2) to detach the vaso-occlusive device 32 from the pusher member 28. Further details on this hybrid power supply are disclosed in U.S. Patent Application Ser. No. 60/949,830, entitled Hybrid Power Supply for Electrolytically Detaching Implantable Device from Monopolar/Bipolar Pusher Wire, which is expressly incorporated herein by reference.
Significantly, rather than conveying the electrical energy to the implant assembly 14 in the form of a direct current (DC) electrical signal as done in prior art embodiments, the power supply 16 conveys electrical energy in the form of a time varying signal with net positive energy (i.e., the integral of the time varying signal is positive). By varying the signal conveyed from the power supply 16 to the implant assembly 14, it has been shown that the time required to effect electrolytic detachment of the vaso-occlusive device 32 is decreased and more consistent. It is believed that the lulls between the peaks of the time varying signal allow dissipation of the cloud formed by the blood constituents during the electrolytic process, thereby decreasing and making the detachment time more consistent. Of course, the net positive energy contained within the time varying signal ensures that a net electrical current will flow from the severable joint 30 to the external ground electrode 40 or return electrode 46 via the blood, thereby ensuring that an electrolytic reaction occurs to dissolve the severable joint 30.
In certain embodiments, the time varying signal may be a pulsed signal (i.e., a signal that is alternately pulsed “on” and “off”) at a specific frequency and duty cycle. The “on” periods of the time varying signal induce the electrolytic process to gradually dissolve the severable joint 30 on the pusher member 28, while the “off” periods of the time varying signal allow the high impedance cloud of blood constituents within the detachment zone to dissipate.
As one example, the time varying signal can take the form of a square wave 100(1), as illustrated in
Although the time varying signals have been described as being pulsed, as illustrated in
Although the previously described time varying signals have been described as having no negatively polarized portions, the time varying signal may have negatively polarized portions as long as the net energy of the time varying signal remains positive. For example, the time varying signal can take the form of an offset square wave 100(5) having positively polarized portions 116 and negatively polarized portions 118, as illustrated in
As shown in
With the exception of the offset sinusoidal wave 100(4) illustrated in
In an optional embodiment, the power supply 16 is configured for amplitude modulating the time varying signal. For example, as illustrated in
Having described the function of the power supply 16, its components will now be described. The power supply 16 comprises a power source 60 configured for supplying power at the necessary voltage levels to the components of the power supply 16 and power delivery circuitry 62 configured for delivering the electrical energy necessary to electrolytically detach the vaso-occlusive device 32 of the implant assembly 14 coupled to the power supply 16.
The power source 60 may comprise conventional components, such as one or more batteries (e.g., standard 9V alkaline batteries or a AAA battery), and one or more voltage regulators (not shown) for converting the voltage provided by the output of the battery or batteries to different voltages that can be utilized by the components of the power supply 16.
The power delivery circuitry 62 may comprise an output drive circuit (not shown), which may take the form of a constant current source that will apply as much voltage as necessary to maintain the required current, a current-enable circuit (not shown) for turning the output drive circuit on, a current adjustment circuit (not shown) for adjusting the magnitude of the current output by the output drive circuit, and a patient isolation relay (not shown) that can be energized to decouple the implant assembly 14 from the output drive circuit during the power up diagnostics, after the vaso-occlusive device 32 is detached, or if a failure occurs during a procedure. In the illustrated embodiment, the current output by the power delivery circuitry 62 is a constant direct current (DC) waveform, although other waveforms that induce electrolysis can be used. The electrical energy conveyed from the power delivery circuitry 62 is preferably within the range of 0.1-10 milliamperes. If, alternatively, a voltage source is used, the electrical energy conveyed from the power delivery circuitry 62 is preferably within the range of 0.5-11 volts, preferably in the range of 4-8 volts.
The power supply 16 further comprises a power on/off actuator 64 configured for alternately activating and deactivating the power supply 16, and status indicators 66 for providing the status of the power supply 16 and electrolytic detachment process. The on/off actuator 64 may take the form of a conventional push button toggle switch that a user can alternately depress to activate and deactivate the power delivery circuitry 62. That is, initial actuation of the on/off actuator 64 will cause the power delivery circuitry 62 to deliver electrical energy to the mated implant assembly 14, and subsequent actuation of the on/off actuator 64 will cause the power delivery circuitry 62 to cease delivering electrical energy to the mated implant assembly 14. The status indicators 66 may take the form of any visible and/or audible indicators that provides status, such as low battery, power delivery state, detachment of the vaso-occlusive device 32, and misconnection within the patient circuit.
The power supply 16 further comprises detection circuitry 68 configured for detecting an electrical parameter indicative of a detachment event between the vaso-occlusive device 32 and the pusher member 28. In performing these functions, the detection circuitry 68 may comprises an alternating current (AC) signal generator (not shown) that superimposes or otherwise generates an AC signal in conjunction with the DC current generated the power delivery circuitry 62, and an AC-to-DC rectifier and peak detector (not shown) that measures the magnitude of the AC signal and outputs a DC signal. The detection circuitry 68 may also comprise a DC monitor for measuring the magnitude of the DC signal output by the power delivery circuitry 62.
The power supply 16 further comprises control circuitry 70 configured for monitoring and controlling the vital functions of the power supply 16. The control circuitry 70 may comprise a microcontroller that performs such functions, as controlling the current enable circuit of the power delivery circuitry in response to user operation of the on/off actuator 64, controlling the current adjust circuit and patient isolation relay of the power delivery circuitry under various conditions, determining detachment of the vaso-occlusive device 32 based on the feedback from the detection circuitry 68, managing the status indicators, running self-diagnostics, etc. The control circuitry 70 may be implemented in firmware, hardware, software, or in combination thereof. Alternatively, rather than using feedback to determine detachment, it can be assumed that the vaso-occlusive device 32 will predictably detach in a predetermined period of time in light of the improved detachment consistency provided by the previously described waveforms. In this case, the power supply can be verified/validated to effect detachment in a given period of time (e.g., 95% chance of detachment within 10 seconds).
With respect to the conventional functions performed by the power supply 16, much of the functional details of the foregoing components are described in U.S. Pat. Nos. 5,669,905 and 6,397,850, which are expressly incorporated herein by reference. However, as discussed above, the power supply 16 has the capability of delivering a time varying signal, which is optionally amplitude modulated, that minimizes and/or makes the electrolytic detachment time more consistent. The physical features of the power supply 16 may be similar to those described in U.S. Patent Application Ser. No. 60/949,830, entitled “Hybrid Power Supply for Electrolytically Detaching Implantable Device From Monopolar/Bipolar Pusher Wire,” which has been previously been expressly incorporated herein by reference.
Having described the function and structure of the medical system 10, its operation in performing a medical procedure, and in particular implanting the vaso-occlusive device 32 within an aneurysm 150 of a patient, will now be described with reference to
With reference to
With reference to
In the case of a monopolar implant assembly 14(1) (shown in
Although particular embodiments of the present inventions have been shown and described, it should be understood that the above discussion is not intended to limit the present inventions to these embodiments. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the scope thereof as defined by the claims.
The present application claims the benefit under 35 U.S.C. §119 to U.S. Provisional Application No. 60/951,138, filed Jul. 20, 2007, the contents of which are incorporated herein by reference as though set forth in full.
| Number | Date | Country | |
|---|---|---|---|
| 60951138 | Jul 2007 | US |
