Apparatus and method for occluding a vessel by RF embolization

An RF ablation system includes an electrode element of elongate form and a cathode pad. A control unit includes a processing unit, a power unit and, optionally, a temperature sensor and/or an impedance sensor. The control unit in one embodiment carries out RF ablation in at least two phases, the first phase at a higher energy level and a second phase, after at least partial retraction of the anode element, at a second lower phase in order to close any remaining lumen within a blood clot formed within the vessel during the first phase. Other embodiments provide for sensing retraction of the anode terminal and effecting RF ablation during and/or after the retraction process in order to create a more effective occlusion barrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119(a) to Great Britain Patent Application No. 1406496.8, filed Apr. 10, 2014, which is incorporated by reference here in its entirety.

TECHNICAL FIELD

The present invention relates to apparatus and a method for occluding or closing a vessel by means of RF embolization.

BACKGROUND ART

There are numerous medical conditions when it is desired or necessary to close a body vessel, including for instance in the treatment of aneurysms, arteriovenous malformations, arteriovenous fistulas, for starving organs of oxygen and nutrients for instance in the treatment or containment of cancerous growths, and so on.

Several techniques are known and in use for closing or occluding such body vessels. Traditionally, vessels have been closed by means of external ligation, which generally must be carried out by an open surgery procedure, with its associated risks, inconvenience and long patient recovery times. Other more recent methods aim to use an endoluminal procedure to insert into the vessel or organ one or more occlusion devices, such as a metal framed occluder, pellets or the like, able to obstruct the flow of blood in the vessel.

It is also known to seek to constrict a vessel by endoluminal ablation, causing contraction of the vessel and/or coagulation of blood to form a blood clot in the vessel. A technique which has been considered suitable is RF ablation, in which an electrical terminal is fed endoluminally into the vessel and an electrical pulse at RF frequencies applied to the electrical terminal. The conductivity of blood and/or the vessel tissues causes localised heating. This heating can be used to cause damage to the tissue (intima) of the vessel wall, resulting in vessel contraction. In other devices RF ablation heats the surrounding blood, causing this to coagulate around the electrical terminal and form a blood clot which blocks the vessel.

Two types of RF ablation apparatus are generally contemplated in the art, the first being a monopolar system having an elongate anode terminal and a cathode pad. The anode terminal is designed to be fed endoluminally into the patient's vessel, while the cathode pad is positioned against the person's outer body, as close as practicable to the anode terminal. Electrical energy applied to the anode terminal will pass by conduction through the patient to the cathode pad. There will be localised heating at the anode terminal, which effects the desired ablation.

A problem with monopolar systems is that it can be difficult to control the extent of damage to surrounding tissues and organs, as well as to the vessel wall. This risks damaging the vessel to the point of rupture, as well as possible irreversible damage to neighbouring organs.

Another RF ablation system uses a bipolar arrangement, in which an elongate electrical element includes both the anode and cathode terminals, which are spaced longitudinally from one another at a distal end of the electrical element. Current passes between the anode and the cathode terminals through the surrounding blood, causing localised heating and coagulation of the blood. A bipolar system has been considered to provide more localised heating and therefore reduced risk of damage to surrounding organs and tissue.

A problem particularly with a bipolar system, but also experienced in a monopolar system, lies with the retraction of the electrical terminal from the vessel at the end of the ablation process. In a system which ablates the vessel wall to cause its contraction, the electrical terminal can become attached to the vessel wall tissue, with the risk of tearing and rupturing the vessel wall. In a system which ablates the surrounding blood to generate a blood clot in the vessel, there is the risk that the blood clot is dragged with the electrical element and that the occlusion of the vessel is as a consequence lost. There is also the risk of leaving an opening in blood clot where the electrical terminal resided, which can result in incomplete occlusion and the risk of recanalization.

Some such devices have attempted to address the above problems by having an electrical element with a detachable terminal end. However, this entails leaving a foreign body in the patient.

SUMMARY OF THE INVENTION

The present invention seeks to provide improved apparatus for occluding or closing a body vessel.

According to an aspect of the present invention, there is provided apparatus for closing a blood vessel including: an elongate electrode element for being passed endoluminally to a treatment site and having at least one electrical terminal at a distal end thereof; a power supply for supplying energy to the electrode element; a detection unit for detecting at least one operational change at the at least one electrical terminal; a control unit connected to the power supply and to the detection unit; wherein the control unit is operable to control the power supply to supply energy to the electrode element at a first power level to cause a primary blood coagulation, to detect at least one operational change at the at least one electrical terminal and to control the power supply to supply energy to the electrode element at a second power level lower than the first power level to cause a secondary blood coagulation once the operational change has been detected.

The apparatus disclosed herein provides for closing any opening or lumen left by the retracting or retracted electrical element, namely by applying energy through the electrical element, at a power level less than the initial ablation power, which has the effect of causing secondary blood coagulation. Preferably, the second power level is insufficient to cause the creation of a further vessel occluding barrier, that is a second barrier which closes off the vessel in its entirety. Specifically, the application of the power at the second level stops once sufficient blood has coagulated to close any aperture left by the retracted or retracting electrical element. The occluding barrier created by application of power at the first power level will therefore form the total length of effective vessel occlusion, thereby making the method also suitable in vessel zones having short treatment sites, such as in locations with adjacent vessel side branches and the like.

Preferably, the apparatus includes a user notification unit coupled to the control unit, the control unit being operable to generate a notification on detection of the operational change in the at least one electrical terminal. The notification unit could be a visual notification, an acoustic notification, a vibratory notification, a combination of any of these, or any other suitable notification.

Preferably, the control unit is operable to command a partial retraction of the electrode element in a proximal direction on detection of the operational change. Partial retraction may leave a part of the electrode tip within the formed clot, thereby to keep any aperture therein closed and to ensure that the second phase of ablation takes place within the blood clot and able to close off the residual lumen.

In an embodiment, the apparatus may include a positioning, or drive, unit coupled to the control unit, the positioning unit being operable to effect the partial retraction of the electrode element in the proximal direction on detection of the operational change. The control unit may be operable to generate a notification to effect said partial retraction of the electrode element.

There may be provided an electrode position sensor coupled to the control unit, wherein the control unit is operable to control the power supply to supply energy to the electrode element at the or a second power level lower than the first power level when partial retraction of the electrode element has been detected.

In some embodiments the control unit may be operable to command the power supply to supply power to the electrode element until the electrode element has been retracted by a predetermined distance. The predetermined distance may be equivalent to a desired length of closure of the vessel. In other words, the system of this embodiment is able to create an occluding barrier of varying length.

The operational change preferably includes at least one of: change in measured impedance and change in temperature.

There may be provided a temperature sensor at the distal end of the electrode element.

In an embodiment, the electrode element includes an anode terminal, the apparatus including a cathode pad. In other words, the system may be a monopolar system.

In another embodiment, the electrode element includes anode and cathode terminals. In other words, the system may be a bipolar system.

According to another aspect of the present invention, there is provided apparatus for closing a blood vessel including: an elongate electrode element having at least one electrical terminal at a distal end thereof; a power supply for supplying energy to the electrode element; a detection unit for detecting at least one operational change at the at least one electrical terminal; a position sensor arranged to detect the position of the distal end of the electrode in a patient; a control unit connected to the power supply, to the detection unit and to the position sensor; wherein the control unit is operable to control the power supply to supply energy to the electrode element at a first power level, to determine movement of the electrode and to apply power to the electrode when the electrode has been deemed to have been moved by a first predetermined distance.

In this aspect, the system monitors for a change in the position of the electrode and applies ablation energy in a manner which can elongate the occlusive barrier which is produced.

In one embodiment, the control unit is operable to apply power to the electrical terminal continuously when in an initial position and while the electrode element is moved by the predetermined distance. In another embodiment, the control unit is operable to apply power to the electrical terminal discontinuously, when in an initial position and after the electrode element has been moved by the predetermined distance.

Preferably, the control unit is operable to apply power to the electrical terminal up to a second distance greater than the first predetermined distance. The second distance may be equivalent to a desired length of closure of the vessel.

Advantageously, the electrical terminal has a conductive length and the first predetermined distance is less than said conductive length.

In an embodiment, the control unit is operable to control the power supply to supply energy to the electrode element at a second power level lower than the first power level once the operational change has been detected. This is not essential though, and in other embodiments the control unit may be operable to apply power at the first power level or near the first power level so as to produce an occlusive barrier of radial dimensions at least as significant as that produced prior to movement of the electrode.

There may be provided a positioning unit coupled to the control unit, the positioning unit being operable to move the electrode element in at least a proximal direction. Such a positioning unit can therefore provide an automated ablation system.

There is also described herein a method of closing a blood vessel by means of apparatus including an elongate electrode element having at least one electrical terminal at a distal end thereof and a power supply for supplying energy to the electrode element; the method including the steps of: supplying energy to the electrode element at a first power level; detecting at least one operational change at the at least one electrical terminal; when said operational change has been detected supplying energy to the electrode element at a second power level lower than the first power level.

The method may include steps appropriate for effecting the functionality disclosed herein.

Other features of the apparatus and method disclosed herein will become apparent from the following specific description of preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

There are described below various embodiments of apparatus and methods for effecting RF ablation of a body vessel, in particular a blood vessel. The preferred embodiments are designed to create blood clotting, that is to ablate the blood surrounding the electrical element. This can be achieved by selecting an ablation energy level and an ablation time duration suitable to heat surrounding blood, which in some circumstances can be expected to be less than the energy required to ablate the vessel tunica, although there may be experienced some contraction of the vessel as a result of the heating of the blood. The skilled person will be able to determine suitable ablation parameters from common general knowledge in the art. Moreover, the preferred embodiment uses a thin, that is narrow diameter, electrode which minimises the surface area contact with the vessel wall in circumstances where the distal end of the electrode is not deployed in the centre of the vessel.

It is to be appreciated that the level of power applied through the electrode and the time of application will be dependent upon factors including the size of the vessel, the amount and speed blood flow through the vessel, pulsation and turbulence of blood at the point of ablation, and so on.

Although the preferred embodiment is a monopolar system, it is to be understood that the teachings herein can apply also to a bipolar system.

Referring first toFIG. 1, this shows in schematic form an embodiment of monopolar RF ablation system10having an elongate electrode element12and a cathode pad14. The elongate electrode element12is designed to be passed endoluminally through the vasculature of a patient up to a treatment site16of a vessel18, that is to the position in a vessel as which it is desired to close or occlude the vessel18.

The electrode element12includes a distal end20which in this embodiment has an exposed electrode terminal22acting as the anode of the circuit. The electrode element12in some embodiments also includes a temperature sensor24for measuring temperature at the anode terminal22, useful in determining the progress of ablation of the vessel.

The electrode element12also includes a sheath26of electrically insulating material which in practice covers the remainder of the electrode22, such that a current path in use exists solely from the exposed terminal22at the distal end20of the electrode element12.

The electrode element12is coupled electrically to a control unit40, as is the cathode pad14. As explained below, the control unit40is operable to provide energy to the electrode element12, specifically current at RF frequencies. The anode terminal22and cathode pad14form a circuit for the RF energy, which will conduct through a patient's body between the anode terminal22and the cathode pad14. It will be appreciated that the cathode pad14will be applied against the patient's skin, preferably at a position which is practicably as close as possible to the anode terminal22, in order to provide this conduction path. There will be localised heating around the anode terminal22, as a result of its significantly smaller surface area and as a result consequential heating of blood in the vicinity of the anode terminal22, as explained in further detail below.

The control unit40typically includes a processing unit42, a power delivery circuit44coupled to the anode and cathode elements of the system10, typically one or more sensors including a temperature sensor unit40coupled to the temperature probe24and/or an impedance sensor unit48for measuring impedance between the anode22and cathode14of the system10. In some embodiments both of types of sensor units46and48may be provided.

The control unit40may also include an electrode drive unit50for moving the electrode12within the patient's vessel18. In some embodiments, the control unit40may be provided with a position sensor for measuring the position of the electrode12within a patient and in particular for measuring the retraction of the electrode12from within the vessel18. Some embodiments may include both a drive unit59and a position sensor.

The processing unit40also includes a user interface60coupled to the control unit40and operable to provide data to a user and for input of user commands to the control unit40. The user interface60may, in its simplest embodiment, include an on/off switch for operating the control unit40and therefore the RF ablation, with the control unit40then effecting the desired ablation process under the command of the unit40solely. In other embodiments, the user interface60may be more sophisticated and enable, for example, a user to select different modes of ablation and also to produce, for instance, occluding barriers of different lengths, as described in further detail below.

The user interface60preferably also includes an output for providing ablation feedback and/or warning signals to a user. It may, for example, provide an indication of measured temperature and/or impedance, an indication of progress of ablation of the vessel and so on. For such purposes, the user interface60may include a visual unit, for example a display to display quantitative data such as graphs, measures of temperature and impedance, determined length of occlusion and so on. In other embodiments the display may be simpler, having for instance simple visual indicators such as one or more illuminated lamps. The output could also be an acoustic output and/or, as appropriate, a tactile output such as a vibration generator and so on. Any combination of user feedback devices may be provided.

The apparatus10ofFIG. 1is intended to cause heating of blood within the vessel18so as to occlude the vessel by the formation of a blood clot, rather than by ablation and damage of the tunica (tissues) of the vessel wall.FIGS. 2A to 2Dshow in schematic form the preferred mode of operation of the apparatus10ofFIG. 1and method of ablating a vessel18.

Referring first toFIG. 2A, once the electrode element12has been positioned at the desired location in the vessel18, the control unit40commands the power unit44to supply RF energy to the electrode12, as a result of which current passes from the exposed terminal tip22into the volume of the vessel18, passing through the body of the patient to the cathode pad14. The energy concentration at the electrode22causes local heating of blood and as a result coagulation of the blood to form a clot70around the exposed terminal tip22. This phase of the operation of the apparatus10preferably occurs at first power level which is relatively high, indicated as such in the depiction of the meter display62inFIG. 2A.

The progress of ablation in this phase is preferably controlled by one or more sensors, for instance by means of a temperature probe24and temperature sensor unit46in the control unit50and/or by measuring the impedance of the circuit formed by the apparatus10when in operation. In practice, sensing temperature will aim to detect an increase in temperature indicative of passing a threshold at which blood will coagulate to form a clot70, whereas measurement of impedance will determine when a sufficient amount of blood has clotted around the anode tip22to cause a drop in measured current and consequential increase in impedance.

It is not to be excluded that the control unit50could be operated without sensors, for example for a predetermined period of time at a predetermined energy which is considered sufficient to create a blood clot of the required dimensions. This is, though, not preferred as it is preferable to have as precise as possible an indication of the actual state of clotting of blood within the vessel18and therefore of the occlusion which is formed.

Referring now toFIG. 2B, at the end of the first phase ofFIG. 2A, that is once a clot70is determined to have been formed in the vessel18, the electrode element12is partially retracted, such that the anode tip22is at least partially exposed outside the blood clot70. The withdrawal of the anode tip22will generally leave an aperture or lumen72within the blood clot70. In the example shown inFIG. 2A, the anode tip22is only partially removed from within the volume of the blood clot70, although in other embodiments the anode tip22may be fully retracted from the blood clot70so that the distal end of the anode tip22lies close to the blood clot70but not therewithin. In one example, a cathode tip of around 10 mm or so may be retracted by 2 to 10 mm at the end of the first phase of the process.

In this embodiment, during this second phase the control unit50commands the power unit44to apply energy at a second power level lower than the first power level applied during the phase ofFIG. 2A. In some embodiments, during the retraction process, the control unit50may command the power unit44to apply no power at, that is until after the partial retraction of the anode tip22.

It will be appreciated that the retraction of the anode tip22, by means of retraction of the electrode element12, may be effected manually by the medical practioner or automatically by means of a drive unit50provided in or coupled to the control unit40. A suitable drive unit will be apparent to someone of average skill in the art.

Referring now toFIG. 2C, during a subsequent phase of the RF ablation process, the control unit40commands the power unit44to apply energy at the second, lower, power level, which causes further ablation of blood within the vessel18. In particular, this phase of operation of the apparatus10causes blood within the lumen72to coagulate and thereby form an additional blood clot80within the lumen70so as to close off the lumen70, as well as further relatively minor blood coagulation around the exposed part of the anode tip22to form clotted blood82therearound. As the system is operated at a lower power level than the first power level, in this embodiment, the volume of the blood which is clotted is substantially less and preferably such as not to alter notably the length of the blood clot70produced in the first phase of the process shown inFIG. 2A. Therefore, the occluding barrier70preferably remains substantially the same length even in this second phase of RF ablation process. Specifically, the secondary blood clotting82is insufficient to fill the width of the vessel18and in practice will not obstruct any side vessels. The effective length of the blood clot will remain the length of the primary blood clot70.

The degree of clotting during the second phase of the ablation process ofFIG. 2Ccan again be sensed by the temperature probe24and temperature sensor unit46and/or by the impedance unit48. It will be appreciated that the temperature reached during this second phase of and/or the impedance change may very well differ from those experienced during the first phase of the process, depicted inFIG. 2A. The person skilled in the art will be able to determine suitable thresholds for achieving such secondary clotting80,82.

The process of partial retraction and RF ablation at a lower power level depicted inFIG. 2Ccan be carried out a plurality of times during the process. In one example, the anode tip22may be retracted only a small distance from within the blood clot70, the second phase carried out, the anode tip22retracted a little further, the second ablation phase operated again and so on, until it has been deemed that a sufficient secondary barrier80has been produced within the lumen72of the first formed blood clot70. In other examples, the second phase may be carried only once.

At the end of the second RF ablation phase, the electrode and consequently the anode tip22are completely retracted from the treatment site and the vessel18, thereby to leave a blood clot formed of a first blood clot70and secondary blood clots80,82. At this stage the control unit50will have commanded the power unit44to cut all power to the electrodes22,14. As can be seen, there is produced a blood clot formation70-82which is completely sealed and which, moreover, is not unduly long.

FIGS. 3 to 5are flow charts depicting three different modes of operation of the apparatus10ofFIG. 1, carried out by the control unit40. The skilled person will appreciate that the apparatus10can be operated also in modes other than those described in connection withFIGS. 3 to 5. The skilled person will also appreciate that the control unit40may be set up to operate in a single mode of operation, but that in other embodiments may be programmed to operate in one of a plurality of modes of operation, as desired by the practitioner or required for the medical indication.

Referring first toFIG. 3, in this mode of operation, the electrode element12is, at step100, inserted endoluminally into a patient's vessel up to the treatment site. Once positioned as necessary, at step102, RF energy is applied to the anode tip22while measuring the temperature of the tip22and/or impedance through the circuit. At step104, the control unit40and in particular the processing unit42, by continuous monitoring of temperature and/or impedance, determines whether the temperature and/or impedance has reached a first threshold indicative of generation of blood clot70. If the threshold has not been reached, the control unit40continues commanding the power unit44to apply energy to the anode tip at the first energy level. On the other hand, if at step104it is determined that the first threshold has been reached, the anode tip is retracted, either to remain partially within the clot formation70or to be fully withdrawn therefrom as described above, and the processing unit42then commands at step108the power unit44to apply RF energy to the anode tip22at reduced power, while continuing to measure temperature and/or impedance. The processing unit44continues monitoring the temperature and/or impedance at step110to determine therefrom whether this has reached a second threshold level. If the second threshold is deemed not to have been reached at step110, the system continues operating in accordance with step108, that is to apply energy at the reduced power level. On the other hand, if it is determined at step110that the second threshold has been reached, the processing unit42switches off power at step112, on the basis that the condition atFIG. 2Cis deemed to have been reached. At step114, the electrode element12and therefore the anode tip, is removed from the vessel.

In the embodiment ofFIG. 4, a different mode of operation is shown. At step200, the electrode element12, and therefore anode tip, are inserted endoluminally into the vessel, as in step100of the embodiment ofFIG. 3. At step202the processing unit42detects the position of the anode tip within the vessel. If at step204it is determined that the anode tip is being retracted, operation proceeds to step206. On the other hand, if it is not detected that the anode tip is being retracted, the process returns to step202to continue applying RF energy while continuing to monitor the position of the anode tip. When it is determined that the anode tip is being retracted, the process proceeds to step206at which energy continues to be applied to close the thrombus formation. This energy is in the preferred embodiment applied at the lower energy level in order to create secondary thrombus formations as shown inFIG. 2C. In other embodiments energy can be applied at the first power level or a power level sufficient to cause greater, that is larger, thrombus formation and further occlusion of the vessel.

The processing unit42continues to monitor the position of the anode tip22and when it is determined that it has been retracted by a predetermined distance deemed sufficient to close the thrombus formation70, the processing unit42moves to step210, at which it commands the power unit44to switch off power to the terminals22. Then, at step212, the electrode element12and therefore the anode tip22are removed from the vessel.

In its simplest form, the embodiment ofFIG. 4does not measure changes in temperature and/or impedance during the RF ablation process and the system continues applying RF energy where it is determined that the anode tip is being retracted. This embodiment, therefore, in its simplest form avoids leaving an open lumen72within the formed blood clot70, which could as a result lead to incomplete occlusion of the vessel18and risk of recanalization. It is to be understood that the embodiment ofFIG. 4could also include steps to measure temperature and/or impedance and to determine whether these have reached the first and/or the second thresholds disclosed above in connection with the embodiment ofFIG. 3.

Another embodiment of mode of operation of the apparatus10ofFIG. 1is shown inFIG. 5. In this embodiment, as in with the previous embodiments, at step300electrode element12and therefore anode tip22are introduced into the vessel to the location at which treatment is to be carried out.

At step302the control unit42commands the power unit44to apply RF energy to the anode tip22, whilst at the same time measuring temperature and/or impedance at the anode tip22. At step304, the processing unit42determines whether the temperature and/or impedance has reached the first threshold and if it has not, step302continues to operate. On the other hand, when it is determined at step304that the first threshold has been reached, operation passes to step306, at which the control unit commands retraction of the anode tip22by a given distance. This may be by operating the drive unit50shown inFIG. 1or by displaying on a user interface a command instructing the user to effect the necessary withdrawal (the user can equally be warned by an acoustic and/or vibratory command). At step308the processing unit42determines whether the anode tip22has been retracted by a desired distance. This distance is deemed to be the desired total length of the occluding barrier formed by the blood clot70. If it is deemed that the anode tip has not been retracted by the desired distance, the process returns to step302to continue applying RF energy. It is to be understood that in returning to step302a blood clot of the type shown inFIG. 2Awill be generated, but more proximally, in effect to extend the length of the blood clot70to create a longer occluding barrier extending radially all the way to the vessel walls. Once, at step308, it has been determined that the anode tip has been retracted by the desired distance, typically equivalent to the desired length of the blood clot70, the process passes to step310, at which power is switched off and then, at step312, the electrode element12and anode tip22are removed from the patient.

It is to be understood that between steps308to310, the control unit40and in particular the processing unit42may command a process equivalent to steps108and110in the embodiment ofFIG. 3in order to create a secondary occlusive barrier80,82in order to close off any lumen in the formed blood clot70. It is also to be understood that a phase of reduced power may be effected between steps306and308of the embodiment ofFIG. 5, to create a progressive barrier80within the lumen72of the formed blood clot70. In such an event, the embodiment ofFIG. 5will then apply power at a higher power level over a longer period of time in order, in effect, to grow the blood clot82at the exposed end of the anode tip22until the latter is deemed to have filled the volume of the vessel18, that is grown into abutment with the vessel walls.

Thus, the embodiment ofFIG. 5can be used to create an occlusion of varying lengths as well as ensuring closure of the lumen left by the retracting anode tip22.

All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.