KR20050045847A - Externally applied rf for pulmonary vein isolation - Google Patents

Abstract

A resonant circuit is included in the stent, which can be implanted into the pulmonary vein using known cardiac catheterization. When an external RF field (high frequency field) is generated at the resonant frequency of the stent, the RF energy is re-radiated by the stent toward the conductive tissue of the wall of the pulmonary vein and forms a conduction barrier around it. The stent is made of biodegradable material and can finally be resorbed. After ablation, the stent may be left in place. Repeated ablation can be performed using this inserted stent until it is determined that the desired lesions have been formed. In addition, if the treated arrhythmias recur or new arrhythmias appear after insertion, the same stent can be used over the years, thus reducing the need for future invasive procedures.

Description

Externally applied RF for pulmonary vein isolation

The present invention is directed to an apparatus and method for the medical treatment of heart disease. More specifically, the present invention relates to a method and apparatus for treating cardiac arrhythmias by ablation near pulmonary vein tissue using high frequency energy.

Invasive cardiac ablation techniques are known in the art. For example, US Pat. Nos. 5,443,489, 5,480,422, and 5,954,655 to Ben-Haim describe systems for ablation of heart tissue. U.S. Patent No. 5,807,395 to Muller et al., U.S. Patent No. 6,190,382 to Omssby et al. Describe systems for ablation of body tissue using high frequency. US Pat. Nos. 6,251,109, 6,090,084 to Hassett et al., US Pat. No. 6,117,101 to Diederich et al., And US Pat. No. 5,938,660 to Swartz et al. 6,235,025, US Pat. No. 6,245,064 to Lesh et al., US Pat. Nos. 6,164,283, 6,305,378, and 5,971,983 to Lesh et al., US Patents issued to Crowley et al. 6,000,269 and US Pat. No. 6,064,902 to Haissaguerre et al. Treat tissues that treat atrial arrhythmia, primarily by excision of tissue located in the pulmonary veins or in the ostium of the pulmonary veins. The ablation apparatus will be described. U. S. Patent No. 5,366, 490 to Edwards et al. Describes a method of applying destructive energy to a target tissue using a catheter.

More recently, circumferential lesions have formed near or in the pores of the pulmonary veins to treat atrial arrhythmias. US Pat. Nos. 6,012,457 and 6,024,740, both issued to Lesche, disclose radially expandable ablation apparatuses, including high frequency electrodes. Using such a device, it is proposed to electrically insulate the pulmonary veins from the left atrium by delivering high frequency energy to the pulmonary veins to achieve peripheral conduction blockage.

Radiofrequency ablation using several consecutive circumferential points guided by electro-anatomical mapping was described in 2000, page 102, page 2619-261, pp. Pappone et al., "Circumferential Radiofrequency Ablation of Pulmonary Vein Pores: A New Anatomical Approach to Treat Atrial Fibrillation".

It has also been proposed to create circumferentially removable wounds using ultrasound waves delivered through the balloon. This technique is described, for example, in Natale A et al., Page 2000, page 1879-1882, the first human experiment on pulmonary vein isolation using circumferential ultrasound ablation via ballooning for recurrent atrial fibrillation. Is described in a document called ".

PCT publication WO 02/30331 to Walsh et al describes a stent device having a geometrical configuration that radiates a region primarily confined to the vascular endothelium to remove proliferative tissue growing around the stent. Irradiation with the stent occurs when the stent is placed in a high frequency field formed by an external scanner. Repeated ablation with this device is said to prevent the stent clogging.

In accordance with the disclosed embodiments of the present invention there is provided an improved apparatus and method for electrically insulating the pulmonary vein by circumferential conduction blocking around the pulmonary vein cavities. In particular, the present invention provides an indwelling device for repeating ablation for the treatment of conductive tissue around a pulmonary vein. The intrinsic device may be biodegradable.

In an embodiment of the invention, a resonant circuit is included in the stent, which has a configuration that is implanted in the pulmonary vein near the pores of the left atrium. Implantation is accomplished by known cardiac catheterization techniques. When an external high frequency field is generated at the resonant frequency of the stent, high frequency energy is re-radiated by the stent toward the conductive tissue of the wall of the pulmonary vein. This creates a circumferential conduction block that electrically insulates the pulmonary vein from the left atrium. The stent is made of biodegradable material and finally resorbed.

Advantageously, after the invasive portion of this procedure is completed, repeated ablation may be performed until it is determined that the desired wounds have been formed. Furthermore, if the treated arrhythmias recur or new arrhythmias develop, they can be used for years after the same stent is inserted, eliminating the need for invasive procedures in the future.

The present invention provides a method of electrically insulating the ventricles, which is accomplished by introducing a resonant circuit to an operating position near the pores of the pulmonary vein, generating an electromagnetic field at a location remote from the resonant circuit, the resonant circuit being operable within the electromagnetic field. Included. The electromagnetic field has a frequency substantially the same as the resonant frequency of the resonant circuit, causing the resonant circuit to re-radiate electromagnetic energy to remove target tissue in the walls of the pulmonary veins.

In one feature of the invention, the electromagnetic field is generated until a blocking of the conduction is identified in the target tissue.

In another aspect of the invention, the resonant circuit is included in the stent, the resonant circuit is introduced by circumferentially combining the inner wall and the stent of the pulmonary vein to form a circumferential contact area between the stent and the pulmonary vein, the main axis of the stent Substantially aligned in a coaxial relationship.

One feature of the method of the invention includes automatically calibrating the stent to resonate at the frequency of the electromagnetic field.

In one feature of the method of the invention, the joining of the stent in the circumferential direction is achieved by expanding the stent in the radial direction.

According to an additional feature of the method of the invention, the stent consists of an alloy with shape memory.

Another feature of the method of the present invention involves changing the temperature of the stent to change the structure of the stent.

In another feature of the method of the invention, while changing the temperature, the stent expands radially in response to its shape memory.

According to another feature of the method of the invention, the stent is composed of a biodegradable material.

In one feature of the method of the invention, after generating the electromagnetic field, the stent is left in its working position, after which the step of generating the electromagnetic field is repeated.

The present invention provides a system for electrically insulating a ventricle including a resonant circuit configured to introduce into a working position in the pulmonary vein near the pores of the pulmonary vein. The resonant circuit re-radiates high frequency energy in response to an externally generated electromagnetic field having a frequency substantially the same as the resonant frequency of the resonant circuit, and the electromagnetic field removes the target tissue of the inner wall of the pulmonary vein by re-radiating the high frequency energy. Let's do it.

The system may include a sensor to monitor the electrophysiological characteristics of the patient's heart to determine if a predetermined end point has been reached. The scheduled end point can confirm the blocking of conduction in the target organization.

Another feature of the system includes a stent having dimensions for engaging circumferentially with the inner wall of the pulmonary vein to form a circumferential contact area between the pulmonary vein and the stent, the main axis of the stent being substantially coaxially aligned with the pulmonary vein. . A resonant circuit is included in the stent.

Other features of the system include a plurality of capacitors in the resonant circuit and a control circuit that automatically selects one of the capacitors in response to the frequency of the electromagnetic field to match the frequency of the electromagnetic field with the resonant frequency of the resonant circuit. will be.

According to another feature of the system, the stent is composed of an alloy with shape memory.

According to another feature of the system, the stent is composed of a biodegradable material.

The present invention relates to a resonant circuit configured to introduce into a working position in a patient's pulmonary vein near the pores of the pulmonary vein, a catheter configured to carry the resonant circuit to a working position in the pulmonary vein, and a pulmonary vein to form a circumferential contact area between the pulmonary vein and the stent A system for electrically insulating a ventricle comprising a stent having dimensions circumferentially engaging the inner wall of the chamber. The main axis of the stent is substantially coaxial with the pulmonary vein, and the resonant circuit is included in the stent. The system includes a generator disposed outside the patient to produce an electromagnetic field having a frequency substantially the same as the resonant frequency of the resonant circuit, the electromagnetic field operatively including the resonant circuit such that the resonant circuit is the target of the inner wall of the pulmonary vein. Reradiates electromagnetic energy to remove tissue.

An additional feature of the system is the inclusion of a sensor to monitor the electrophysiological characteristics of the patient's heart to determine if a predetermined endpoint has been reached.

According to another feature of the system, the predetermined endpoint confirms the conduction blocking in the target tissue.

Another feature of the system is a plurality of capacitors in the resonant circuit and a control circuit that automatically selects one of the capacitors in response to the frequency of the electromagnetic field to match the frequency of the electromagnetic field with the resonant frequency of the resonant circuit.

Other features of the system include a plurality of localizing field generators disposed outside the patient, a position sensor on the catheter in response to localizing electromagnetic fields generated by the localizing field generator, and an output of the position sensor. It includes a localizing subsystem to track the position and orientation of the catheter including the responding receiver.

DETAILED DESCRIPTION In order to better understand the present invention, reference is made to the detailed description of the invention, which is read by way of example in conjunction with the drawings, wherein like reference numerals are used for like elements.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known circuits and control logic have not been shown in detail so as not to unnecessarily obscure the present invention.

System structure

Referring now to the drawings, reference is now made to FIG. 1, which is a schematic diagram of an ablation system 10 that is constructed and operated in accordance with a disclosed embodiment of the present invention. The system 10 is configured to ablate a target tissue 12 of a patient and includes a positioning and mapping subsystem 14 that includes a plurality of radio frequency (RF) transmitters 16 coupled to a control unit 18. It includes. The transmitter 16 can operate in a low-power mode for positioning and mapping, and in a high-power mode for target tissue removal. Alternatively, separate transmitters may be provided for position sensing and ablation. A stent 20 having a resonant circuit is disposed in the pulmonary vein 22 near the target tissue 12 to be removed, as shown in more detail below. In some embodiments, stent 20 is dimensioned to engage the pulmonary vein. An outer diameter of 3 cm may be appropriate.

In other embodiments, only to remove the target tissue, not to stent the pulmonary vein, there is no need to physically engage the walls of the pulmonary vein to perform ablation. In such embodiments, the resonant structure only needs to be positioned to include the target tissue within its operating range and can be energized as discussed later. These embodiments provide a relatively small resonant structure for all uses in patients of different ages and sizes, without having the structure required for the resonant structure to function as a stent or having the structure have the correct dimensions for the pulmonary vein. It has the advantage that it can be used as a model.

To help insert the stent in the desired position, a cardiac catheter 24 is used. The catheter 24 has a sensor 26 for determining the position of the distal segment 28 of the catheter, which carries the stent 20 during insertion. In some embodiments, catheter 24 also has one or more monitoring electrodes 30 for sensing electrical characteristics at the location of the heart. The target tissue 12 to be removed can be positioned using the positioning and mapping system disclosed in US Pat. Nos. 5,840,025 and 5,391,199, both of which are hereby incorporated by reference. For the embodiment of US Pat. No. 5,840,025, the monitoring electrode 30 may act as mapping electrodes. The electrodes detect the local electrical activity of the heart 32 as a function of the position provided by the sensor 26. The distal segment 28 of the catheter 24 may be radiopaque to aid its localization by conventional radiographic techniques in addition to or as an alternative to the system disclosed in US Pat. No. 5,840,025. Can be.

In one embodiment of the present invention, sensor 26 is an electromagnetic position and orientation sensor, which receives electromagnetic signals from multiple electromagnetic transmitters 16 disposed outside the patient on or near the body surface. In use, the transmitters 16 transmit an electromagnetic field to establish a frame of reference to track the position and orientation of the distal segment 28 of the catheter 24. Therefore, based on the sensed electromagnetic field, sensor 26 provides five or more dimensions of the position and orientation information ((X, Y, Z, pitch and yawing) in the form of coordinate information. Transmit a position signal to the control unit 18. In some embodiments, six position and orientation information (X, Y, Z, pitch, yawing, and rolling) are provided. Transmitted by leads 34, which are connected to the control unit 18. Alternatively, signal transmission from the sensor 26 to the control unit 18 is provided to a wireless receiver (not shown).

Examples of the present invention may be understood by reading a brief description of the positioning and mapping subsystem 24 used for tracking the distal segment 28, disclosed in US Pat. Nos. 5,840,025 and 5,391,199. will be. The sensor 26 is used to sense the instantaneous position of the distal segment 28 and is typically an alternating current (AC) magnetic field receiver that senses the magnetic field generated by the transmitter 16. These transmitters generate an AC magnetic field to form a fixed frame of reference. Sensors suitable for use as sensor 26 are described in U.S. Patent No. 5,391,199 and PCT Patent WO 96/05768, filed May 14, 1997, the contents of which are incorporated herein by reference. 793,371). Then, the position and orientation coordinates of the distal segment 28 are determined by measuring the position and orientation coordinates of the sensor 26. Sensor 26 may include one or more antennas, for example one or more coils 36. The placement of the transmitters 16 and their size and shape may vary depending upon the application of the present invention. Transmitters useful for medical applications include wound annular coils having an outer diameter of about 2 to 20 cm, a thickness of about 0.5 to 2 cm and a triangular arrangement in the same plane. Bar shaped transmitters, triangular and square coils may all be useful for such medical applications. In addition, in cases where the lying patient is undergoing a procedure according to the example of the present invention, the transmitters 16 are located on or below the surface on which the patient is resting, just below the body part of the patient where the procedure is performed. do. In other applications, the transmitters may be very close to the patient's skin.

The transmitters 16 are operated by the control unit 18. The signals received by the sensor 26 are amplified and processed along with the representation of actuation signals in a signal processor within the control circuit 18 to indicate the position and orientation of the end segment 28. The transmitters 16 may be placed in any convenient position and orientation as long as they are fixed relative to any reference frame and no two transmitters share the same position, ie position and orientation. When operated by the control unit 18, the transmitters 16 generate a number of distinguishable AC magnetic fields sensed by the sensor 26. Magnetic fields can be distinguished in terms of frequency, phase, or both frequency and phase of the signals in each magnetic field. Time multiplexing of different magnetic fields is also possible.

The sensor 26 may consist of a single coil, but more generally has two or more and even three or more sensor coils 36 wound on a core made of a hollow core or certain material. The coils 36 have axes perpendicular to one another, one of which is conveniently aligned with respect to the longitudinal axis of the catheter 24. The coils 36 may be interconnected as shown in the inset of FIG. 1, or closely spaced along the longitudinal axis of the catheter 24 to reduce the sensor 26 diameter. In many aspects of the invention, a quantitative measure of the position and orientation of the distal segment 28 relative to the reference frame is required. This fixed frame of reference requires two or more non-overlapping transmitters 16 to generate two or more distinguishable AC magnetic fields received by the sensor 26. In order to measure the magnetic field flux due to distinguishable magnetic fields, there must be at least two non-parallel coils 36 in the sensor 26. In order to measure the six position and orientation coordinates (X, Y, Z direction, pitching, yawing and rolling orientation) of the distal segment 28, at least two coils 36 and three transmitters 16 are positioned and It is preferably present in the mapping subsystem 14. Three coils are typically used to improve the accuracy and reliability of the position measurement. In other applications where fewer location and orientation coordinates are required, only one coil may be needed for sensor 26. Certain features and functions of a single axis positioning system having only one coil are described in co-transferred US Pat. No. 6,484,118, which is incorporated herein by reference. In one embodiment, the coil 36 is wound 800 times with a diameter of 16 μm (micrometer) with an internal diameter of 0.5 mm so that the overall coil diameter is 1 to 1.2 mm. The effective capture area of each coil is typically about 400 mm ² . It will be appreciated that these dimensions can vary over a significant range. In particular, the size of the coils 36 may be as small as 0.3 mm (with some loss of sensitivity) and may exceed 2 mm. The wire size of the coils 36 may range from 10 to 31 μm, and the number of turns may vary between 300 and 2600 depending on the maximum allowable size and wire diameter. The effective capture area should be as large as possible, relative to the overall size requirements. Typical sensor coil shapes are cylindrical, but other shapes may be used. For example, barrel-shaped coils may have more turns than cylindrical coils of the same diameter.

Conductor 34 delivers the signal detected by sensor 26 to control unit 18 for processing to generate the required position and orientation information. Conductor 34 may be twisted pairs to reduce pick-up and may further be electrically shielded.

The sensor 26 is useful not only for determining whether the distal segment 28 is in its operating position, but also for determining when the heart 32 is not moving, for example, during relaxation. Alternatively, the sensor 26 may be omitted from the catheter 24 and the position of the distal segment 28 may be measured using other sensing or imaging means known in the art. In such a case, other components of the positioning and mapping subsystem 14 which are unnecessary in this imaging means may also be omitted.

Console 38 allows physician 40 or another user to observe and adjust the functions of catheter 24. The console 38 includes a computer, a keyboard, and a display. The console 38 also includes control circuits to control and operate the catheter 24 and the control unit 18, in particular to start and end data collection.

The signal processor of the control unit 18 has circuits for receiving, amplifying, filtering, and digitizing various signals received from the catheter 24, including signals generated by the sensor 26 and the monitoring electrode 30. . The circuits of the signal processor also calculate the electrical characteristics of the heart 32 portion and the position and orientation of the distal segment 28 from the signals generated by the sensor 26 and the monitoring electrode 30. In addition, the circuits of the signal processor may process ECG signals on the body surface. Digitized signals generated by the circuitry of the signal processor may be used to reconstruct an electrical or electromechanical map of a portion of the heart 32, for example the ventricular wall 42 of the interatrial septum 44. Received by the computer of console 38 for visualization.

Referring now to FIG. 2, this is an enlarged schematic view of the distal segment 28 of the catheter 24 (FIG. 1). To perform an ablation procedure, the stent 20 is typically carried by the inflatable balloon 46 by the catheter 24 to the patient's heart position near the target tissue 12. Structurally, stent 20 includes a coil 48, which is included or attached to ring structure 50. The coil has a characteristic resonant frequency, which is used in the ablation process as described below. The ring structure 50 structurally supports the coil 48 and may have a dielectric property. Balloon 46 is shown in an inflated state. However, during the insertion procedure, it is typically at least partially contracted. Stent 20 may be inflated in place at its place of operation by inflating balloon 46 to push stent 20 against the inner wall of pulmonary vein 22 (FIG. 1). Additionally or alternatively, heating by resistance of coil 48 may be used to control the expansion of stent 20 within pulmonary vein 22. Then, to retrieve the catheter 24, the balloon 46 is retracted, at which time it is detached from the stent 20 and the stent 20 remains attached to the pulmonary vein 22.

Alternatively, stent 20 may comprise an elastic material, ie a superelastic material, such as nitirol, which is held by catheter 24 in a compressed state during insertion into heart 32. When the distal segment 28 of the catheter 24 reaches the operating site where the stent 20 is deployed, such as in the pulmonary vein 22, the catheter 24 releases the stent 20. The elastic properties of the stent material cause the stent 20 to expand outwardly to secure the stent 20 against the inner wall of the pulmonary vein 22.

Referring again to FIG. 1, the stent 20 is typically positioned in the pores of the pulmonary veins, or in or near the vesicles. In some applications, stent 20 may need to be placed in several pulmonary veins, or in all pulmonary veins. Placement of the vascular catheter and delivery of the stent on the anchoring balloon are described in US Application No. 10 / 062,698, incorporated herein by reference and entitled “High Frequency Pulmonary Vein Isolation”. Since cardiac catheterization techniques are known in the art, further explanations are omitted for simplicity.

After the stent 20 is inserted, the catheter 24 is typically withdrawn from near the target tissue 12 leaving the stent in place. In general, the catheter 24 is left in the left atrium to monitor the ablation process using the monitoring electrode 30. The control unit 18 then drives the transmitters 16 to generate an electromagnetic field at the resonant frequency f _r of the stent 20. Power output from 50 watt transmitters 16 at a frequency of 13.56 MHz is suitable. Stent 20 is subjected to this electromagnetic field and re-radiates electromagnetic energy at resonant frequency f _r . The target tissue 12 absorbs the re-radiated high frequency energy, raising the temperature of the target tissue 12 to about 50 ° C., which removes the target tissue 12 and makes nonconductive wounds, forming a conductive barrier. do. Alternatively or additionally, the temperature of the stent 20 itself increases in response to the electromagnetic fields of the transmitters 16, which results in ablation by direct conduction of heat from the stent 20 to the target tissue 12.

Typically, wounds made by excision form one or more circumferential conduction barriers around the pulmonary vein at or near the point of contact of the pulmonary vein with the stent. In one application, if the arrhythmias originate from the identified location of the pulmonary vein, a circumferential conduction block is formed along the path of the wall tissue containing the source that causes the arrhythmia to remove the source, or between the source and the left atrium A blocking is formed to prevent the transmission of unwanted signals.

Referring now to FIG. 3, this is an enlarged schematic diagram showing the electrical characteristics of the stent 20 (FIG. 1) constructed and operating in accordance with the disclosed embodiment of the present invention. The stent 20 includes a coil 48 and a capacitor 52, which are electrically connected to the coil 48. The coil 48 may be made of a resistive metal such as nitinol having elasticity and shape memory. Coil 48 is typically wound about 15 times. Because of its geometry, the coil 48 acts as an inductor. In selecting the reactance of the coil 48, a compromise is needed between the desirability of the high quality factor Q, which ensures efficient power delivery, and the resistance train desired to be formed in the stent circuit. This compromise will be apparent to those skilled in the art given the fundamental laws of physics that govern the operation of these circuits.

Preferably, the stent 20 is calibrated at manufacture to determine the correct resonant frequency, which may vary depending on the manufacturing variation of both the inductor and capacitor and the exact geometry of the stent. However, it may be desirable to measure the exact resonant frequency when the stent 20 is in its operating position. This can be done magnetically using a dip meter.

In some embodiments, the stent 20 comprising the coil 48 may be made of a biodegradable material, such as polymer polylactide and trimethylene carbonate polymer. After insertion, the stent 20 remains firmly circumferentially coupled to the inner lining of the pulmonary vein due to its elasticity and shape memory. In these embodiments, the stent 20 retains its original position in subsequent ablation procedures and eventually reabsorbs. Stent 20 can continue to function as a re-radiator of high frequency energy from transmitters 16, in the event that a repetitive ablation procedure is needed while remaining intact. In such embodiments, the continued stent 20 in the pulmonary vein may have the added benefit of reducing the risk of stenosis and contracture of the pulmonary vein. In another embodiment, in addition to remaining in that position, as disclosed in 10 / 062,698, the delivery of another desired therapeutic agent or stent 20 is coated with a drug, which is a narrowing of the blood vessels. Acts locally to prevent

Although the capacitor 52 is shown in FIG. 3 as a separate component, the inherent capacitance of the material of the stent itself is important for measuring the resonant frequency of the stent 20. In some applications, this inherent capacitance is sufficient to give the desired resonance, in which case no separate capacitor is needed.

Referring now to FIG. 5, this is a schematic electrical circuit diagram of a parallel LC resonant circuit 54. Circuit 54 is an equivalent circuit of stent 20 (FIG. 3). The circuit 54 comprises a capacitor 58 and an inductor 56 connected across it, the values of which are the frequencies of the high frequency electromagnetic field to which the resonant frequency f _r of the circuit 54 is applied by the transmitters 16. Is selected to correspond to. In embodiments of the invention with a single capacitor as shown in FIGS. 3 and 5, the resonant frequency f _r is given by Equation 1 below.

Where L is the inductance of inductor 56 and C is the capacitance of capacitor 58.

A resonant frequency, 13.56 MHz, which does not correspond to any frequencies or harmonics of clinical relevance should be used. For example, if the capacitor 58 has a capacitance C of 60 pF and the inductor 56 has an inductance L of 2.30 μH, a resonance frequency f _r of 13.56 MHz is obtained. Inductor 56 is designed and manufactured to have a quality factor of at least 100 or greater at 13.56 MHz.

Referring to FIG. 4, this schematically illustrates a stent circuit 60 that is constructed and operated in accordance with another embodiment of the present invention. The resonant frequency of the stent circuit 60 may be selected to match the output of the transmitter. Stent circuit 60 may be used as stent 20 (FIG. 1) in system 10. Stent circuit 60 includes one or more loops of wire made of a resistive alloy such as nitinol or a nickel-chromium alloy. The control chip 64 is included in the stent circuit 60 and reacts to the current flowing through the stent circuit 60. The control chip 64 automatically operates the switch 71 to sequentially switch capacitors 66, 68, and 70 into the circuit, and locks the capacitor to the circuit such that the resonance frequency is closest to the resonant frequency of the transmitter. This embodiment has the advantage of adaptively changing the resonant frequency of the stent, which is useful when the size and / or shape of the stent must be adjusted during implantation into the pulmonary vein, for example when inflating the stent using a balloon. Do. This change in size changes the inductance of the coil and thus affects the resonant frequency of the circuit, which can be adjusted by selecting the appropriate capacitor. The possibility of adjusting the resonant frequency by the choice of capacitor is also useful when more than one stent is implanted and needs to be selectively excited within the same patient. The transmitter can then be tuned to the operating frequency required by the stent.

work

Referring now to FIG. 6, this illustrates a method of electrically insulating a pulmonary vein in accordance with a disclosed embodiment of the present invention. The procedure begins at an early stage 72 where a catheter insertion of the heart takes place. The resonant stent is removably attached to the intravascular catheter. The venous system can be accessed using known Seldinger technology, where the introducer sheath is located in the peripheral vein, typically the femoral vein. The intraocular sheath is introduced through the introductory sheath and advanced through the inferior vena cava to the right atrium. Then, using a Brockenbrough needle, the fossa ovalis of the septum of the heart is pierced, which is expanded if necessary. The Brockenbrow needle is retrieved and the intraocular envelope is placed in the left atrium. Alternatively, other methods known in the art can be used to access the left atrium, with or without assistance of the guide sheath and the guide wire, as described below.

Next, in step 74, the pulmonary vein is selected and the guide wire is advanced through the intraocular envelope and through the left ventricle to the selected pulmonary vein. The order in which specific pulmonary veins are visited and treated is arbitrary, but it may be desirable to focus first on the two upper pulmonary veins, where the muscular sleeve is more pronounced than in the lower pulmonary vein. Thereafter, the lower pulmonary veins may be insulated. Typically, an ablation procedure involves isolating all four pulmonary veins.

Next, at step 76, the guide sheath is recovered and the ablation catheter is able to slide on the guide wire, using the catheter's guidewire lumen. The catheter advances to the left atrium. While manipulating the catheter in the heart, its location can be monitored by a positioning and mapping system as disclosed in US Pat. No. 5,840,025, or alternatively by conventional imaging techniques. During deployment, the catheter's stationary balloon remains in a contracted state and the stent is radially folded around the outer wall of the stationary balloon. The diameter of the folded stent is smaller than the diameter of the pulmonary vein, allowing the stent to move within the lumen of the vein. The stent is located in or in the pores of the selected pulmonary vein. The stent expands radially to engage the surrounding area of the inner layer of the pulmonary vein where the target tissue is located.

The expansion of the stent is accomplished by the expansion of the balloon, which pushes the stent radially outward toward the inner wall of the pulmonary vein. In some embodiments, the shape memory of the coil alloy is used to heat the coil by resistance to cause the stent to expand, or to spontaneously expand when the coil has sufficient elasticity to release from the catheter. The radially inflated stent engages the pulmonary vein in a continuous line extending around the circumferential circumference of the pulmonary vein near its pores so that the main axis of the stent is substantially coaxial with the pulmonary vein. Perfusion of the area through the catheter port may also be used for minimizing stasis of blood in that area, particularly in embodiments where heating by the stent's resistance has a great effect. If not selectively supported, the coil does not expand.

Next, in step 78, once the coil is positioned, the catheter is withdrawn. If the stent is carried on the balloon, the balloon is retracted. The catheter can be rearranged in the left atrium so that signals from its monitoring electrodes can inform the operator of the progress of ablation. If there is no need for support, the catheter is not recovered.

Next, in step 80, the outer high frequency transmitter is excited and high frequency energy is transferred from the transmitter to the stent. A stent that resonates at the frequency of the transmitter re-radiates high frequency energy. High frequency energy transfer from the stent to the pulmonary veins is relatively short at a time. The external high frequency generator is configured such that the reradiated high frequency energy heats the target tissue to about 50 ° C. The application of energy can be controlled according to continuous electrophysiological monitoring and the end point is reached when conduction cutoff is identified across the ablation line. Alternatively, the endpoint may be the delivery of a predetermined amount of energy to the target tissue, or the expiration of a time period. The stent is usually left in place for subsequent procedures. Optionally it may be removed.

Control now passes to decision step 82, where it is determined whether there are more pulmonary veins remaining to be treated. If the determination at decision step 82 is affirmative, control returns to step 74. Thereafter, steps 74 to 80 are repeated, and in order to individualize energy transfer to each pulmonary vein without affecting other pulmonary veins, it is preferred that each stent placed in different pulmonary veins have a different frequency. Alternatively, if only one resonant frequency is used for several stents, step 80 should be delayed until the stent insertion of all lung veins is complete to prevent reheating of previously ablation regions.

If the determination at decision step 82 is negative, the process ends at final step 84.

It will be understood by those skilled in the art that the present invention is not limited to those specifically shown and described above. Rather, the scope of the present invention includes all combinations and subcombinations of the various features described above, as well as modifications and variations which are not in the prior art to which those skilled in the art will be able to read.

The present invention provides an improved apparatus and method for electrically insulating the pulmonary vein by making a circumferential conduction block around the pulmonary vein cavities.

1 is a schematic diagram of an ablation system constructed and operative in accordance with a disclosed embodiment of the present invention.

FIG. 2 is an enlarged schematic view of the distal segment of the catheter used in the ablation system shown in FIG. 1. FIG.

3 is an enlarged schematic view of a stent that resonates with respect to the electromagnetic field used in the system of FIG. 1 in accordance with a disclosed embodiment of the present invention.

4 is a schematic diagram of a stent circuit having an automatic calibration circuit constructed and operative in accordance with another embodiment of the present invention.

5 is a schematic circuit diagram of an equivalent circuit of the stent shown in FIG.

6 is a flow chart illustrating a method of electrical isolation of pulmonary veins in accordance with a disclosed embodiment of the present invention.

※ Explanation of symbols about main part of drawing ※

10: Ablation System 12: Target Organization

14: Positioning and Mapping Subsystem

16: high frequency (RF) transmitter 18: control unit

20: stent 22: pulmonary vein

24: cardiac catheter 26: sensor

28 terminal segment 30 monitoring electrode

Claims (24)

Introducing a resonant circuit having a resonant frequency into an operating position in the pulmonary vein near the ostium of the pulmonary vein; Generating an electromagnetic field at a location remote from said resonant circuit; The resonant circuit is operably included within the electromagnetic field, the electromagnetic field having a frequency substantially the same as the resonant frequency of the resonant circuit, the electromagnetic field causing the resonant circuit to re-radiate electromagnetic energy to A method of electrical insulation of the ventricles that ablate the target tissue in the wall. The method of claim 1, Generating the electromagnetic field is performed until a conduction block in the target tissue is identified. The method of claim 1, The resonant circuit is included in the stent, wherein the step of introducing the resonant circuit includes circumferentially coupling the inner wall of the pulmonary vein and the stent to form a circumferential contact area between the stent and the pulmonary vein, Wherein the major axis is aligned substantially coaxially with the pulmonary vein. The method of claim 3, wherein And automatically calibrating the stent to resonate at the frequency of the electromagnetic field. The method of claim 3, wherein Coupling the stent in the circumferential direction is performed by expanding the stent in a radial direction. The method of claim 5, wherein And said stent is comprised of a shape memory alloy. The method of claim 6, Further comprising varying the temperature of the stent to alter the structure of the stent. The method of claim 7, wherein During the step of changing the temperature, the stent expands radially in response to the shape memory. The method of claim 3, wherein And the stent is comprised of a biodegradable material. The method of claim 3, wherein Leaving the stent in the working position after performing the steps of generating an electromagnetic field; And subsequently repeating the above steps of generating an electromagnetic field. A resonant circuit having a resonant frequency configured to be introduced into an operating position in the closed vein near the pores of the pulmonary vein, the resonant circuit having a high frequency in response to an externally generated electromagnetic field having a frequency substantially the same as the resonant frequency of the resonant circuit; Re-radiating energy, wherein the electromagnetic field causes the resonant circuit to re-radiate the high frequency energy to ablate target tissue in the wall of the pulmonary vein. The method of claim 11, And a sensor for monitoring the electrophysiological characteristics of the patient's heart to determine if a predetermined endpoint has been reached. The method of claim 12, The predetermined endpoint comprises confirmation of conduction interruption in the target tissue. The method of claim 11, And further comprising a stent having dimensions that circumferentially engage the inner wall of the pulmonary vein to form a circumferential contact area between the stent and the pulmonary vein, the major axis of the stent being substantially coaxially aligned with the pulmonary vein, The resonant circuit is included in the stent. The method of claim 14, A plurality of capacitors in the resonant circuit; And a control circuit for automatically selecting one of the capacitors in response to the frequency of the electromagnetic field to match the frequency of the electromagnetic field with the resonant frequency of the resonant circuit. The method of claim 14, The stent is comprised of a shape memory alloy. The method of claim 14, The stent is comprised of a biodegradable material. A resonant circuit having a resonant frequency configured to be introduced into an operating position in a pulmonary vein of a patient near the pores of the pulmonary vein; A catheter configured to carry the resonant circuit to an operating position within the pulmonary vein; A stent having dimensions that circumferentially engage the inner wall of the pulmonary vein to form a circumferential contact area between the stent and the pulmonary vein; A generator disposed outside of the patient to form an electromagnetic field having a frequency substantially the same as the resonant frequency of the resonant circuit, A major axis of the stent is aligned substantially coaxially with the pulmonary vein, and the resonant circuit is included in the stent; The electromagnetic field operatively comprising the resonant circuit, the resonant circuit causing the re-radiating electromagnetic energy to ablate a target tissue in the wall of the pulmonary vein. The method of claim 18, And a sensor for monitoring the electrophysiological characteristics of the patient's heart to determine if a predetermined endpoint has been reached. The method of claim 19, The predetermined endpoint comprises confirmation of conduction interruption in the target tissue. The method of claim 18, A plurality of capacitors in the resonant circuit; And a control circuit for automatically selecting one of the capacitors in response to the frequency of the electromagnetic field to match the frequency of the electromagnetic field with the resonant frequency of the resonant circuit. The method of claim 18, The stent is comprised of a shape memory alloy. The method of claim 18, The stent is comprised of a biodegradable material. The method of claim 18, A plurality of localizing field generators disposed outside the patient; A position sensor on the catheter responsive to a localizing electromagnetic field generated by the localizing field generator; And a localizing subsystem for tracking the position and orientation of the catheter, the receiver including a receiver responsive to the output of the position sensor.