WO1998022179A2

WO1998022179A2 - Ultrasonically marked catheter for electrotherapy and system for use of the same

Info

Publication number: WO1998022179A2
Application number: PCT/EP1997/006459
Authority: WO
Inventors: Branko Breyer; Bozidar Ferek-Petric; Achim Kitschmann; Wolfgang Geistert
Original assignee: Sulzer Osypka Gmbh
Priority date: 1996-11-20
Filing date: 1997-11-19
Publication date: 1998-05-28
Also published as: WO1998022179A3; EP1039948A2; JP2001505454A

Abstract

Ultrasonically marked catheter for electrotherapy comprising a piezoelectric transducer (21) mounted onto a catheter and electrically connected to its proximal end with longitudinal conductors. The piezoelectric transducer electrodes are of appropriate thickness and conductivity for the ablation energy. The outside electrode (22) is either in direct contact with the tissue or, (for HF systems), covered with electrically insulating layer that does not impede the transmission of high frequency waves for electrosurgery. The same conductor within the catheter is used both for ultrasonic guidance purposes and for conveying energy. Ultrasonically marked catheter for electrotherapy improves the guidance of electrosurgical procedures due to the fact that the position of the ultrasonic marker transducer and electrotherapy member are at identical position. This invention represents an essential simplification and therefore reduction in price of the manufacture of the electrotherapy catheter with ultrasonic marking since one single element represents the therapy and the guiding system.

Description

Ultrasonically marked catheter for electrotherapy and system for use of the same

1. Field of the Invention

This inventions relates to a field of medical technology, and in particular to technology of cardiac electrotherapy catheters guidable by ultrasound. The specific application field is in the ablation of cardiac conductive paths and treatment of cardiac arhytmias. This invention specifically improves ultrasonic marking and other measurements in connection with ablation catheters.

2. Background and Prior Art

A particular problem in electrotherapy is the exact aiming of the delivering of therapeutic amounts of energy to defined points in organs such as heart. The said energy is normally delivered using catheters. The problem in visualization of flexible electrotherapy catheters indwelled into the human body is the fact that these devices are not in their entirety within the ultrasound scanning plane, so that without a specific solution one does not know which part of the catheter is imaged. This is a particular problem when the catheter is within the heart so that it moves and is therefore only discontinuously in the scanning plane. A similar problem of visualization appears when the catheter is only partly visible because it passes through the areas where gasses in lungs or intestines partly prevent ultrasound penetration. The problem of localization is particularly severe when an electrosurgery (cardiac ablation) electrode must be localized. The solution to this problem is particularly important when an electrotherapy aerial or electrode is marked in order to enable the guiding and control of electrotherapy procedures (e.g. cardiac ablation) using ultrasound echoscopy. In this case one must solve the problem of the most accurate localization of the electrode proper.

Tachycardia is the state of increased heart rate. Natural tachycardia occurs during physical exercise and emotional stress due to the tonus of the sympatic nervous system and increased concentration of circulating catecholamines. The most important property of the natural tachycardia is that it increases the heart minute volume (pumping rate) . Pathological tachycardia endangers the heart haemodynamics, i.e. the cardiac output decreases. Electrophysiology distinguishes two large groups of tachycardias: the supraventricular and the ventricular tachycardia as well as two groups of etiologies: ectopic foci and phenomenon of early excitation. The principle of the therapy of tachycardia is to either depress the ectopic centres or interrupt the path of early excitation. The first approach is always drug therapy. In spite of the recent advance of electropharmacology, every antiarhytmic drug is not effective with every patient. The drugs can cause side effects that can be hazardous for the patient. Therefore one must take into consideration invasive procedures such as surgery of permanent implantation of an electrotherapy device. The method of choice is the ablation of the conductive system in the heart. This is a semi invasive procedure. Transvenous ablation of the cardiac conductive system with a catheter is the less risky alternative to the surgical ablation for control of refractery supraventricular arhytmias. Some results have been achieved in the treatment of ventricular tachycardias as well. In order to achieve a control of the size of the lesion precise ablation energy sources have been introduced. One of the problems is the accurate positioning of the ablation electrode within the heart. As an alternative to the X ray imaging of the ablation catheter, ultrasonic imaging is agreeable in conjunction with the use of ultrasonically marked catheters and electrode catheters described in US patents nos. 4,697,595 and 4,706,681. These systems enable ultrasonic guidance of procedures as well as the exact localization of the tip or the electrode catheter. Position of the ablation electrode marked with an ultrasound transducer can exactly be determined. The same system, but with a slightly broader directivity characteristic of the ultrasound transducer has been described in US patent no. 5,076,278 using a curved transducer surface.

Electrodes in the form of plates on one side of the catheter generate a directive electromagnetic field, but the problem of radial orientation of the catheter is thereby not solved. Marking is possible in other ways as described in the US patents nos. 5,161,536 and 5,425,370. The characterization of tissues is possible by the system for ablation described in the US patent 5,385,148.

A method for confirmation of the radial orientation is possible as described in our international PCT application no. PCT/EP94/04252 wherein the contact with the endocard and proximity fuse function have been described as well. The basic principle is as follows: Near the position on the catheter which we want to localize (e.g. tip) a piezoelectric transducer is mounted which is connected to the outside electronic circuits using electrical conductors lied longitudinally along the catheter. The signals obtained on the said marker transducer can be used of generating a visible guiding mark on the echoscope screen as described in the said patents and patent applications.

All the described systems use the ultrasonic transducer as an element separate from the ablation electrode. This clearly complicated the mechanical and electrical design and construction of the ablation catheter.

These inventors are unaware of any system that integrates the source of electromagnetic field for ablation with the ultrasound receiver and transmitter used for ultrasonic marking. This integration is the technological problem solved with the present invention.

3. Summary of the invention

The essential base of this invention consists in electrical connection of the outer electrode of a piezoelectric transducer to the source of the electrotherapy energy, e.g. for ablation of electrically conductive tissue in the heart. Thereby the following results are achieved:

a) An essential increase of the accuracy of the ultrasonic marking of the electrotherapy (ablation) electrode. Contrary to the existing solutions mentioned in the paragraph "Background and prior art", here is the position of the marker transducer and the marked ablation electrode identical and not in the vicinity as solved in the said prior art. b) A reduction of the number of leads by at least one third, sometimes one half, since the same conductor is used to take the signal for ultrasonic marking and for the electrotherapy energy.

c) The lead so far described as the lead for ultrasonic marking and electrotherapy can be used for electrodiagnostic procedures during electrotherapy (e.g. for the measurement of the electrocardiogram) .

d) The manufacturing price is decreased since the production of the electrotherapy (ablation) electrode and the ultrasonic marker transducer is done in one step, which reduces time and manpower needed.

Ultrasonically marked catheter for electrotherapy and system for use of the same according to the present invention comprises the piezoelectric transducer mounted onto a catheter and electrically connected to its proximal end with longitudinal conductors an outside localization circuit (transponder or passive system) an ultrasound diagnostic scanner and a source of energy for electrosurgery. The said source of electrosurgery is connected to the outside electrode of the said piezoelectric transducer. The electrodes of the said piezoelectric transducer are of appropriate thickness and conductivity that they can bear the ablation energy without damage. The outside electrode is, depending on the ablation technology used, either in direct contact with the tissue or (for HF systems) covered with electrically insulating layer that does not impede the transmittal of high frequency waves for electrosurgery.

Thus, in addition to the improvement of the flexibility of the technological design and construction the manufacturing price is reduced. 4. Brief description of figures

Fig. 1 is a block diagram of an integrated system for cardiac electrotherapy and ultrasonic guiding of the procedure.

Fig. 2 is a perspective illustrative drawing of the ultrasonically marked catheter for electrotherapy. In order to clarify the details, the catheter is shown much thicker compared to the length then in reality.

Fig. 3 is a cross sectional drawing of an axially symmetrical ultrasonically marked catheter for electrotherapy with the axis of its directivity characteristic approximately perpendicular to the catheter axis.

Fig. 4 is a drawing in two projections of an ultrasonically marked catheter for electrotherapy with the transducer and corresponding surface electrode in the form of plate.

5. Description of embodiments

The system in which an ultrasonically marked catheter for electrotherapy functions is shown in figure 1.

The ultrasonically marked catheter for electrotherapy 1 is indwelled into the patient's body 100 for an electrosurgical procedure. On the catheter there is the transducer assembly 2 which essentially consists of a piezoelectric marker transducer and its electrodes. The outer electrode serves to convey and deliver energy for the said medical procedure. The transducer assembly 2 is connected to the outside electronic circuits by the way of electrical conductors laid along the catheter body 1. The whole procedure is guided with the ultrasound scanner 41 using the probe 40 that scans the area 42 within the body. Transponder 30 responds to each incoming ultrasound pulse from the probe 40 with a series of pulses, thus generating a visible mark on the echoscope screen 41. When the transducer assembly 2 is maneuvered into the vicinity of the position for electrosurgery (by delivery of electrical energy) , Generator 200 is activated. This generator thus delivers the necessary energy via the transducer assembly 2. Circuit 210 prevents interference of instruments 200 and 30, i.e. isolates the generator 200 from transponder 30 when necessary.

Echoscope 41 is a normal medical ultrasound scanner normally used in ultrasound diagnostics, e.g. echocardiography. It usually functions at ultrasound frequencies of the order of magnitude 3 - 8 MHz. The generator 200 is an electrosurgical generator normally used in medicine for ablation of conductive tissue in the heart or any other electrosurgical generator. Circuit 210 is essentially a protection circuits (e.g. a diode protective circuit) that prevents the energy from generator 200 from damaging the transponder 30.

According to figure 2 the said transducer assembly is mounted on some position along the catheter 1. This piezoelectric transducer is connected via conductors 3 and 4 laid along the catheter 1 with connectors 5 and 6. The position of the transducer assembly 2 along the catheter 1 is determined by the application need and can be anywhere between the proximal and distal end of the catheter 1. It is possible to use more than one transducer assembly of which each is connected with outside electrical circuits with its own conductors. The transducer assembly can be divided into segments, e.g. incisions 7. On the outside of the transducer assembly there is the electrotherapy electrode or antenna.

In the first embodiment which is shown in figure 3 is the piezoelectric transducer 21 of a cylindrical shape (ring) mounted on the catheter body 1. Figure 3 shows in more detail the transducer assembly 2 from figures 1 and 2. This assembly consists of a piezoelectric transducer 21, outside electrode 22 that us at the same time used for electrotherapy, inside electrode 25 and conductors 3 and 4 which take the corresponding electrical signals. Said outside and inside electrodes are connected to the said conductors with connections 33 and 34 respectively. The connections 33 and 34 can be soldered, conductively glued or mechanical (by pressure) . The said conductors 3 and 4 have on the proximal side connectors 5 and 6. Signals generated by piezoelectric transducer 21 are taken by the said conductors to connectors 5 and 6. Conversely, the electrical signals are taken to the said transducer by the said conductors. This enables the applications of various methods for guidance of medical procedures by ultrasonic echography. A particular feature of the system is the outside electrode 22 connected with connection 34 via a conductor to connector 6, to which the energy for electrotherapy is brought from an appropriate generator (e.g. for high frequency cardiac ablation) . The electrode has dimensions that enable conveying and delivering of electrical energy, current density in particular, needed for the electrosurgical procedure.

This embodiment has a response that is circularly symmetrical about the catheter axis, thus the axis of the directivity characteristic is essentially perpendicular to the same. If the cylindrical transducer consists of segments as shown in figure 2 (cut 7) , then one has to have conductors equivalent to conductors 3 and 4 along with their connectors for each of the said segments. The whole transducer - antenna assembly can be covered with and insulating layer if the energy for electrosurgery is of such a nature that it does not require galvanic contact. This layer can be made as a quarter wavelength matching layer for ultrasound when appropriate. The insulation layer is not shown in figure 2, thus that form of the assembly is appropriate for the case when the ablation system is built to deliver energy galvanically. When high frequency signal (electromagnetic wave) is used for ablation then an insulating layer 47 (figure 4) may be used.

The piezoelectric transducer 21 is built of piezoelectric material, e.g. piezoelectric ceramics with the resonant frequency in the range of the frequencies used by the ultrasound scanner used in ablation guidance. A particular technological request, in the present case, is that the material be chosen such that the electrosurgical energy flowing through its electrode does not damage it. This is reflected in request for a high Curie point and low dielectric loss. The additional mechanical loading of the piezoelectric transducer by the mass of the thickened electrode lowers the mechanical resonance quality factor (Q) and thus broadens the frequency band and lower the sensitivity. Optimum relation of the thickness and surface area is a matter of technological compromise for each combination of electrode material, piezoelectric material, amount of energy delivered and its type.

The second embodiment of the present invention is shown in figure 4. In this case a piezoelectric plate 41 is used for ultrasound reception and transmission. Electrodes 42 and 45 are deposited on the sides of plate 41 and connected with connections 43 and 44 via longitudinal electrical conductors 3 and 4 to connectors 5 and 6. Electrode 42 serves double purpose, i.e. for electrosurgery and as electrode of the piezoelectric marker transducer. It is possible to use more than one plate in the way of plate 41 and connect each of such plates to outside electrical circuits via their own conductors. The insulating layer is here indicated with number 47. In this embodiment the ablation

(electrosurgery) energy can not be transferred galvanically, but in the form of high frequency electromagnetic fields with electrode 42 as antenna.

This embodiment costs less to manufacture and has an inherently narrower directivity characteristics compared to the embodiment shown in figure 3.

Claims

1. Ultrasonically marked catheter for electrotherapy and system for use of the same characterized by comprising:

- an ultrasonically marked catheter that has piezoelectric transducer mounted on the body adjusted for the use in conjunction with an ultrasound scanner whose signal frequency spectra overlaps with the frequency spectrum of the said piezoelectric transducer having outside electrode thickened for cardiac ablation energy bearing and an electrotherapy/electrosurgery generator.

- where the said piezoelectric transducer is of a form that can be mounted onto the said catheter having the outside electrode of sufficient thickness and conductivity to convey the energy generated by the said electrotherapy/electrosurgery source without increase of its temperature above 90 degrees Celsius.

- where the said transducer's electrodes are connected to the outside electric circuits with electrical conductors running along the said catheter,

- where one of the said outside electronic circuits is an ultrasonic localization circuit in the form of a transponder or passive localization circuit, where an outside ultrasound scanner, as a part of the system is used for scanning of the body interior, - source of electrosurgery (ablation) energy for treatment of human tissues by delivering the energy through the said outside electrode of the said piezoelectric transducer.

2. Ultrasonically marked catheter for electrotherapy and system for use of the same according to claim 1, characterized by the transducer according to claim 1 is built as a whole or segmented ring (tube) .

3. Ultrasonically marked catheter for electrotherapy and system for use of the same according to claim 1, characterized by the transducer according to claim 1 is built as one or a multitude of plates.

4. Ultrasonically marked catheter for electrotherapy and system for use of the same according to claim 1, 2 and 3 characterized by the said transducer having electrodes on its outside and inside connected to the proximal side of the catheter from claim 1.

5. Ultrasonically marked catheter for electrotherapy and system for use of the same according to claim 1,

2 or 3 characterized by having the said outside electrode from claim 1 and 4 thickened and made maximally conductive.

6. Ultrasonically marked catheter for electrotherapy and system for use of the same according to claims

1, 2, 3, 4 or 5 characterized by having the outside localization electronic circuits from claim 1 and the electrosurgery (ablation) energy source connected to the same outside electrode of the piezoelectric transducer from claim 5. Ultrasonically marked catheter for electrotherapy and system for use of the same according to claims 1, 2, 3, 4 or 5 characterized by having a single lead leading from the said outside electrode from claim 1 and 5 to the outside localization circuit from claim 1 and outside electrosurgery circuit from claim 1.