WO2011101778A1

WO2011101778A1 - Ablation catheter and a method of performing ablation

Info

Publication number: WO2011101778A1
Application number: PCT/IB2011/050599
Authority: WO
Inventors: Mischa Megens; Jan Frederik Suijver; Godefridus Antonius Harks; Anna Hendrika Van Dusschoten
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-02-19
Filing date: 2011-02-14
Publication date: 2011-08-25

Abstract

The invention relates to an ablation catheter, for performing ablation of a target tissue in a patient, where the ablation catheter comprises an elongate body part with a distal end, and an ablation electrode with a distal part. A tissue abutment part extends to a location distal of the ablation electrode distal part in order to separate the distal part of the ablation electrode spatially from the target tissue. This allows of more efficient irrigation and cooling of the target tissue site and of the ablation electrode, and further allows direct monitoring of the target tissue, e.g. by an ultrasound transducer.

Description

Ablation catheter and a method of performing ablation

FIELD OF THE INVENTION

The present invention relates to an ablation catheter with an ablation electrode, more particularly to an ablation catheter for performing ablation procedures applied to internal body tissues, such as the heart. The invention also concerns a method of performing such ablation procedures.

BACKGROUND OF THE INVENTION

In cardiac ablation procedures, the electrical activity of the heart wall is altered by localized heating of the tissue, thus creating a lesion in a controlled manner. The goal of the ablation procedure is to obtain a lesion that extends throughout the entire thickness of the heart wall. In many known ablation devices this is accomplished by applying energy in the radio frequency (RF) range, i.e. RF heating, RF ablation. To prevent heating of the catheter itself and of the blood surrounding it, ablation devices are commonly cooled by irrigation with saline solution. The saline solution may be distributed to the ablation site through lateral apertures in the catheter tip, where it cools the tip, blood in the vicinity of the tip, and the heart wall tissue.

An advantage of RF ablation over other ablation techniques is that the heating actually takes place inside the tissue, since the tissue surface is cooled by the flow of saline solution at the electrode tip usually formed in metal. This facilitates making lesions that extend over the full thickness of the heart wall; the lesion is then said to be "transmural".

For use in ablation on internal organs it is desirable to monitor the ablation procedure in process. For this purpose there is a need for an ablation catheter with integrated ultrasonic ablation monitoring as well as fluid irrigation. In conventional devices, this requires an ablation electrode window that is substantially transparent for ultrasound.

Polymeric materials may seem especially suited for this, since these provide a good impedance match and hence little acoustic reflection; a thin metal film on the polymer provides a conductive path, functioning as electrode. In conventional ablation catheters, with monitoring capabilities there is no room for a solid cooled metal electrode, since this would obstruct the view of the ultrasound monitoring transducer. Instead, a very thin acoustically transparent metal electrode is used, but such a thin electrode needs mechanical support. A polymer window can provide this support, but its limited thermal conductivity reduces the cooling, and the tissue will be heated less uniformly. In such conventional devices, the hottest point appears directly under the catheter tip, at the surface of the tissue due to the thermal insulation presented by the catheter window. One conventional ablation device having monitoring capability is disclosed in US-20090076390 Al . This document discloses an integrated catheter / imaging system for performing ablations. The ablation is still always done with the ablation electrode in snug contact with the organ tissue, and the devices must be moved between monitoring and performing ablations.

The inventor of the present invention has appreciated that an improved ablation catheter is of benefit, and has in consequence devised the present invention.

SUMMARY OF THE INVENTION

It would be advantageous to achieve an ablation catheter enabling the heating of tissue internally, cooling the tissue surface, while not obstructing the view of an integrated monitoring ultrasound transducer. In general, the invention preferably seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination. In particular, it may be seen as an object of the present invention to provide a method that solves the above mentioned problems, or other problems, of the prior art.

To better address one or more of these concerns, in a first aspect of the invention an ablation catheter for performing ablation of a target tissue in a patient is presented where the ablation catheter comprises:

an elongate body part, having a distal end; and

an ablation electrode having a distal part,

the ablation electrode being provided at the distal end of said elongate body part, where said ablation catheter further comprises a tissue abutment part extending distally of said distal part of the ablation electrode, in order to separate the distal part of the ablation electrode spatially from the target tissue.

Thereby, an ablation catheter is achieved that shows an improved ablation.

Prior art cardiac ablation catheters and ablation devices/catheters in general operates under the common belief or assumption that it is a requirement that an RF electrode must be in contact with the tissue to be ablated. It has even been observed experimentally that no ablation takes place when the electrode of a conventional ablation catheter is retracted a few millimeters from the heart wall. The inventor's experiments have shown that this limitation is not inherent, and that it is possible to perform RF ablations with a slightly retracted electrode, using a suitable design of the catheter tip geometry. The claimed invention provides more design freedom for cooling the catheter tip, and ameliorates the ablation temperature profile. Experiments as well as simulations have been conducted that demonstrate the effect. The present invention enables heating tissue internally, and cooling the tissue surface, while not obstructing the view of an e.g. integrated monitoring ultrasound transducer by windows or electrodes. The invention is based on the insight that it is not necessary for the electrode to establish mechanical contact to the tissue directly, and that the heating of the tissue is produced by confining the current to a small area on the tissue.

Preferably, the ablation catheter further comprises irrigation conduits to supply irrigation in the form of a cooling fluid to the distal part and/or the target tissue.

In particular, the cooling liquid can be used as a conductive path to the target tissue, enabling better cooling of the interface, without intervening heat insulating window material. The electrical current is conducted by the irrigation fluid, which has an electrical conductivity similar to the tissue of the organs to be ablated. The temperature rise of the irrigation fluid is minor, since the fluid can be continually replenished. By confining the electrical current to the front of the ablation catheter, the heating effect is concentrated in the tissue located there, and it is possible to perform an ablation, even when the electrode itself is not in contact with the tissue, challenging common beliefs. The direct cooling by the irrigation fluid promotes a uniform temperature profile in the heart wall.

The functioning of the ablation catheter as outlined above further is indifferent with regard to which angle catheter is applied to the target tissue.

In embodiments, the irrigation conduits are either provided laterally with respect to the elongate body part or they are provided in a distal direction, or preferably both. Experiments show that the combination creates broader and deeper lesions. It turns out that the depth is directly related to the width of the lesion. The diameter of the lesion is determined by the diameter of the region where current is flowing from. Thus, in preferred embodiments additional lateral irrigation conduits or holes are provided.

In combination with any of the above embodiments, the tissue abutment part of the ablation catheter comprises a distally facing tissue abutment surface, the tissue abutment surface being provided with anti-slip properties. Such anti-slip properties of the tissue abutment surface may be provided by undulating. Or they may be provided by the tissue abutment surface being serrated or notched. Thereby, an ablation catheter is achieved that is prevented from sliding during an ablation procedure, due to a rougher and thereby firmer interface with the tissue surface.

In any or all of the above mentioned embodiments, the ablation catheter may further comprise an integrated monitoring ultrasound transducer. Preferably, the tissue abutment part is arranged to provide a viewport for a monitoring ultrasound transducer integrated in the ablation catheter, and preferably a field of view of the ultrasound transducer overlaps with a spatial position of the target tissue during use. Thereby, the ablation process may be performed with improved accuracy, because the process and lesion progression may be monitored in real time and on location.

In embodiments, said viewport may also double as an irrigation conduit.

Preferably the ultrasound transducer is arranged proximally of the tissue abutment part in order to separate the ultrasound transducer spatially from the target tissue.

In addition to any of the embodiments described above, the ultrasound transducer may further be adapted so that it may perform tissue coagulation, thereby doubling the ablation electrode.

In combination with any of the above embodiments the distal end of the body part of the ablation catheter may be configured to confine an electrical current to be emitted from said ablation electrode to the target tissue. Preferably, the confinement is provided in particular in a lateral direction with respect to a longitudinal axis of the elongate body part.

Such a confinement may in an embodiment be provided by a skirt forming a distal extension of the body part of the ablation catheter, the skirt partly or fully surrounding the ablation electrode. The skirt may be formed in an electrically insulating material or it may be provided with an electrical insulation. The skirt may be formed as a tube or tubular part.

The tissue abutment part extends distally of the skirt. The tissue abutment part may be provided as a further extension of the skirt. However, the tissue abutment part may alternatively be provided as one or more legs or distally extending flanges, from the skirt or from distal end of the body part of the ablation catheter.

In all embodiments the ablation electrode may be an RF electrode.

In combination with any of the above described embodiments the ablation catheter may further comprise one or more sensors to measure the local temperature at the electrode, the tip of the catheter or in target tissue, in order to monitor the ablation process.

Further, in combination with any of the above described embodiments the ablation catheter may comprise a sensor to monitor the heat flux through the tip/distal most part of the ablation catheter, i.e. the tissue abutment part. Further, in combination with any of the above described embodiments the ablation catheter may comprise multiple temperature sensors to monitor the heat flux through the tip/distal most part of the ablation catheter, i.e. the tissue abutment part.

In another aspect objects of the invention are achieved by a method of ablating a target tissue at an internal organ of patient, the method comprising:

providing an ablation catheter having an ablation electrode and a tissue abutment part extending distally of said ablation electrode,

bringing the tissue abutment part into physical contact with a surface of an internal organ at a target site, such that a space is maintained between said surface of said organ and a distal-most end of said ablation electrode, and

applying energy from said ablation electrode to said target tissue.

In one embodiment of the above described method, the method further comprises irrigating the distal end of the ablation electrode and/or the target tissue.

In another embodiment of the above described method, the method further comprises monitoring the ablation at said target site via an ultrasound transducer integrated in said ablation catheter.

In general the various aspects of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 shows a section through the distal end of an ablation catheter according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of the invention is illustrated in FIG 1 showing, in section, the distal end of an ablation catheter 1. The ablation catheter 1 has an elongate body part 10, of which only the distal end 11 is shown in the drawing. The body part 10 serves as a shaft for introducing the other functional elements for ablation (to be described below) into a patient's body and bring said functional elements close to an internal organ of the patient, such as a heart or liver. Consequently, the length of the body part 10 may be adapted to with respect to how deep into the body it may be desired to reach. The body part preferably has a circular or oval cross section.

Extending distally of the distal end 11 of the body part 10, is a pin 25. The pin 25 has a body part and a proximal end, where it is connected to the distal end of the 11 of the body part 10 of the ablation catheter. At the distal-most tip of the pin 25 an ablation electrode 20 is provided. The ablation electrode 20 is configured to emit energy to tissue at a target site. The ablation electrode 20 is preferably configured to emit energy in the radio frequency, RF, range. The ablation electrode 20 is connected to a source of energy, through electric conductors (not shown) provided through the length of the body part of the pin 25 and the body part 10 of the ablation catheter 1 in a suitable manner. The body part 10 of the catheter 1 is preferably formed in and electrically insulation material or at least being provided with an electrical insulation at its outer surface, and with respect to the ablation electrode 20 and the electric conductors thereto.

Also, extending distally of the distal end 11 of the body part 10, is a skirt 12, in the form of a tubular flange. The skirt 12 is preferably formed in an electrically insulating material. Alternatively, it may be provided with a layer of electrically insulating material.

Extending distal of the distal end 21 of the ablation electrode 20 is a tissue abutment part 30, having a distal-most i.e. distally facing surface 31. The tissue abutment part 30 in the shown embodiment is simply an extension of the skirt 12, described above. The extension forming the abutment part 30, at its distal-most end extends or bends slightly towards the centre (or towards a longitudinal axis (not shown) of the catheter 1) of the ablation catheter 1. In other embodiments (not shown) the tissue abutment part 30 may take other forms. It may e.g. be a tubular extension (without the bending at the distal-most end). In yet other embodiments the tissue abutment part 30 may be provided by one or more distally extending legs, pins or flanges (not shown). These may extend distally from a skirt 12, or they may extend directly from the distal end 11 of the body part 10 of the ablation catheter 1. In the case that the tissue abutment part 30 is provided by legs, pins or flanges these may support a circular flange with a central hole (not shown), the circular structure forming a distalmost tissue abutment surface 31 that may reduce the risk of the legs, pins or flanges causing stress of damage to the tissue, during use (abutment).

In the embodiment shown in Fig. 1, a tissue abutment surface 31 is formed by the inward "bending" of the tissue abutment part 30 in the distal-most end thereof. The skirt 12 and/or the tissue abutment part 30 defines a space 70 separating the distal end 21 of the ablation electrode 20 from the tissue abutment surface 31 and thereby the target tissue during use.

A cooling fluid, preferably in the form of a saline solution, may irrigate the distal part 21 and the target tissue (during use), through one or more fluid conduits 15 formed in and through the elongate body part 10 of the ablation catheter 1. The fluid conduits 15 are connectable to a reservoir of cooling fluid. Thereby the space 70 and the area surrounding the distal part 21 of the ablation electrode 20 may be irrigated by cooling fluid. Further, lateral fluid conduits 33 are formed in the distal end of the skirt 12, and/or in the tissue abutment part 30, to irrigate the area surrounding the target tissue during use. Further, distally directed fluid conduits 32, 34 are formed to irrigate the surface of the target tissue during use. A central opening/fluid conduit 34 also provides a "window" or viewport for the electrical energy from the ablation electrode distal part 21 to the target tissue.

The ablation catheter 1 may further be provided with an ultrasound

transducer 40. The ultrasound transducer may e.g. be provided at a distally facing surface 11 of the body part 10 of the ablation catheter 1. The ultrasound transducer is connectable via a connection 41 formed through the body part 10 of the ablation catheter 1, to an external power supply and control means (not shown).

In a further embodiment, not shown, electrode 20 constitutes the entire pin 25. In yet further embodiments, an electrode 20' may alternatively or additionally to the electrode 20 be located at the distally facing surface 11 of the body part 10 of the ablation catheter 1, the electrode 20' having a distal part 21 ', being flush with the distally facing surface 11 of the body part 10, or it may extend slightly distally of the distally facing surface 11 of the body part 10. When an electrode 20' is located at the distally facing surface 11 of the body part 10, an ultrasound transducer 40 may, in a further embodiment be arranged at the distally facing surface 11 of the body part 10 as shown in Fig. 1. In this case there may not be pin 25. In other embodiments, where an electrode 20' is arranged at the distally facing surface 11 of the body part 10, an ultrasound transducer, may alternatively or additionally be located on the distal-most part the pin 25 at the place where the electrode 20 is shown in Fig. 1.

In other embodiments, an electrode 20" may alternatively be provided at the sidewall of the pin 25. In this case an ultrasound transducer may alternatively or additionally (to the ultrasound transducer 40 shown in Fig 1) be located on the distal-most part the pin 25 at the place where the electrode 20 is shown in Fig. 1. In the case, where an electrode 20" is provided at the sidewall of the pin 25, the electrode 20" will have a distal-most part 21 ".

In all embodiments the abutment part 30 extends distally with respect to the distal-most part 21, 21 ', 21 " of the electrode 20, 20', 20".

In all embodiments, the ultrasound transducer may be substituted by or combined with another device suitable for obtaining information about the target site or target tissue in front (distally of) the ablation device 1, e.g. a lens for visual inspection.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless

telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An ablation catheter (1), for performing ablation of a target tissue in a patient, said ablation catheter comprising:

an elongate body part (10), having a distal end (11); and

an ablation electrode (20, 20', 20") having a distal part (21, 2 , 21 "),

said ablation electrode (20, 20', 20") being provided at the distal end

(11) of said elongate body part (10),

wherein said ablation catheter (1) further comprises a tissue abutment part (30) extending distally of said distal part (21, 2 Γ, 21 ") in order to separate the distal part (21, 21 ',

21 ") of the ablation electrode (20) spatially from the target tissue.

2. An ablation catheter (1) according to claim 1, further comprising irrigation conduits (15, 32, 33) to supply irrigation in the form of a cooling fluid to the distal part (21, 21 ', 21 ") and/or the target tissue.

3. An ablation catheter (1) according to claim 2, wherein the irrigation conduits

(33) are provided laterally with respect to the elongate body part (10) and /or the irrigation conduits (32) are provided in a distal direction.

4. An ablation catheter (1) according to claim 1, wherein the tissue abutment part (30) comprises a distally facing tissue abutment surface (31), and wherein said tissue abutment surface (31) is provided with an anti-slip properties, e.g. by an undulation, serration or notches.

5. An ablation catheter (1) according to claim 1, further comprising an integrated monitoring ultrasound transducer (40).

6. An ablation catheter (1) according to claim 1, wherein the tissue abutment part (30) is arranged to provide a viewport (50) for a monitoring ultrasound transducer (40) integrated in the ablation catheter (1).

7. An ablation catheter (1) according to claim 6, wherein a field of view of the ultrasound transducer (40) overlaps with a spatial position of the target tissue during use.

8. An ablation catheter (1) according to claim 5, wherein the ultrasound transducer (40) is arranged proximally of the tissue abutment part (30) in order to separate the ultrasound transducer (40) spatially from the target tissue.

9. An ablation catheter (1) according to claim 1, wherein the distal end (11) of the body part (10) is configured to confine an electrical current to be emitted from said ablation electrode (20, 20', 20") to the target tissue.

10. An ablation catheter (1) according to claim 1, wherein a skirt (12) forming a distal extension of the body part (10) of the ablation catheter (1) partly or fully surrounds the ablation electrode (20, 20', 20").

11. An ablation catheter (1) according to claim 10, wherein the skirt (12) provides an electrical insulation.

12. A method of ablating a target tissue at an internal organ of patient, the method comprising:

providing an ablation catheter (1) having an ablation electrode (20, 20', 20") and a tissue abutment part (30) extending distally of said ablation electrode (20, 20', 20"), bringing the tissue abutment part into physical contact with a surface of an internal organ at a target site, such that a space (70) is maintained between said surface of said organ and a distal-most end (21, 21 ', 21 ") of said ablation electrode (20, 20', 20"), and applying energy from said ablation electrode (20, 20', 20") to said target tissue.

13. A method according to claim 12, further comprising irrigating the distal end (21) of the ablation electrode (20, 20', 20") and/or the target tissue.

14. A method according to claim 12, further comprising monitoring the ablation at said target site via an ultrasound transducer (40) integrated in said ablation catheter.