WO2019093214A1 - Electrode catheter - Google Patents

Abstract

There is provided an electrode catheter for measuring an electric potential inside a heart of a subject. The electrode catheter includes: a shaft that is inserted into the heart, wherein the shaft comprises a distal end portion that is configured to make contact with an endocardium of the subject, and a guide portion that is connected to the distal end portion; at least one ring electrode that is provided to surround an outer circumferential surface of the distal end portion; and at least one insulator that is provided on the outer circumferential surface so as to cover the ring electrode, wherein the insulator exposes a portion of the ring electrode.

Description

ELECTRODE CATHETER

The present disclosure relates to an electrode catheter. Particularly, the present disclosure relates to an electrode catheter for measuring an electric potential inside a heart of a patent.

JP-A-2002-191571 discloses an electrode catheter for measuring an electric potential inside a heart of a patient. According to the electrode catheter disclosed in JP-A-2002-191571, a plurality of ring electrodes are arranged side by side and provided on a distal end portion of a tube body, and a variation of the electric potential inside the heart can be measured by any of the plurality of ring electrodes. While moving the electrode catheter, a medical worker carefully observes the variation of the electric potential inside the heart acquired from the electrode catheter. In this manner, the medical worker can estimate a place where arrhythmia (e.g. atrial fibrillation etc.) occurred inside the heart (e.g. inside a left atrium).

Each of the ring electrodes has to be in contact with an endocardium of the heart as a precondition for measuring the variation of the electric potential inside the heart using the electrode catheter. This is because an electric signal acquired from a predetermined ring electrode cannot reflect the variation of the electric potential inside the heart when the predetermined ring electrode is not in contact with the endocardium. Therefore, before observing the variation of the electric potential inside the heart (e.g. an electrocardiogram waveform) that is acquired from each of the ring electrodes and displayed on a monitor, the medical worker has to confirm whether the ring electrode is in contact with the endocardium or not. On the other hand, it is difficult for the medical worker to accurately determine whether the ring electrode is in contact with the endocardium or not by use of an X-ray fluoroscopic image of the patient.

To solve this problem, how to determine contact between a ring electrode and the endocardium based on a variation of an impedance value between the ring electrode and an electrode attached to the patient has been under review. In this respect, since electric conductivity of blood is larger than electric conductivity of the endocardium, an impedance value measured by the ring electrode which has already been in contact with the endocardium is larger than an impedance value measured by the ring electrode which has not been in contact with the endocardium yet. It is however difficult to accurately determine the contact between the ring electrode and the endocardium when there is a small variation between the impedance value measured by the ring electrode which has already been in contact with the endocardium and the impedance value measured by the ring electrode which has not been in contact with the endocardium yet. From this viewpoint, there is still room for further improvement of usability of the electrode catheter.

Summary

The present disclosure provides an electrode catheter whose usability is improved.

According to one or more aspects of the present disclosure, there is provided an electrode catheter for measuring an electric potential inside a heart of a subject.
The electrode catheter comprises:
a shaft that is inserted into the heart, wherein the shaft comprises a distal end portion that is configured to make contact with an endocardium of the subject, and a guide portion that is connected to the distal end portion;
at least one ring electrode that is provided to surround an outer circumferential surface of the distal end portion; and
at least one insulator that is provided on the outer circumferential surface so as to cover the ring electrode, wherein the insulator exposes a portion of the ring electrode.

According to one or more aspects of the present disclosure, there is provided an electrode catheter for measuring an electric potential inside a heart of a subject.
The electrode catheter comprises:
a shaft that is inserted into the heart, wherein the shaft comprises a distal end portion that is configured to make contact with an endocardium of the subject, and a guide portion that is connected to the distal end portion; and
at least one chip electrode that is provided on an outer circumferential surface of the distal end portion, and that is configured to make contact with the endocardium.
A dimension of the chip electrode extending along an outer circumference direction of the distal end portion is smaller than a circumferential length of the distal end portion.

Fig. 1 is an overall view of an electrode catheter according to an embodiment of the present invention (hereinafter referred to as present embodiment simply).Fig. 2 is a perspective view showing a distal end portion and a guide portion of a shaft.Fig. 3A is a side view showing a part of the distal end portion of the shaft of the electrode catheter according to the present embodiment in an enlarged manner.Fig. 3B is a plan view of the part of the distal end portion of the shaft of the electrode catheter according to the present embodiment in the enlarged manner.Fig. 3C is a sectional view of the distal end portion of the shaft of the electrode catheter according to the present embodiment cut along a line A-A shown in Fig. 3A.(a) of Fig. 4 is a view showing a state in which a ring electrode is not in contact with an endocardium in an electrode catheter according to a background art. (b) of Fig. 4 is a view showing a state in which the ring electrode is in contact with the endocardium in the electrode catheter according to the background art. (c) of Fig. 4 is a graph showing a variation between an impedance value measured between the ring electrode and an impedance measuring electrode when the ring electrode is not in contact with the endocardium and an impedance value measured between the ring electrode and the impedance measuring electrode when the ring electrode is in contact with the endocardium in the electrode catheter according to the background art.(a) of Fig. 5 is a view showing a state in which a ring electrode is not in contact with an endocardium in the electrode catheter according to the present embodiment. (b) of Fig. 5 is a view showing a state in which the ring electrode is in contact with the endocardium in the electrode catheter according to the present embodiment. (c) of Fig. 5 is a graph showing a variation between an impedance value measured between the ring electrode and an impedance measuring electrode when the ring electrode is not in contact with the endocardium and an impedance value measured between the ring electrode and the impedance measuring electrode when the ring electrode is in contact with the endocardium in the electrode catheter according to the present embodiment.Fig. 6A is a side view showing a part of a distal end portion of a shaft of an electrode catheter according to a first modification of the present embodiment in an enlarged manner.Fig. 6B is a plan view showing the part of the distal end portion of the shaft of the electrode catheter according to the first modification of the present embodiment in the enlarged manner.Fig. 6C is a sectional view showing the distal end portion of the shaft of the electrode catheter according to the first modification of the present embodiment cut along a line B-B shown in Fig. 6A.Fig. 7A is a side view showing a part of a distal end portion of a shaft of an electrode catheter according to a second modification of the present embodiment in an enlarged manner.Fig. 7B is a plan view showing the part of the distal end portion of the shaft of the electrode catheter according to the second modification in the enlarged manner.Fig. 7C is a sectional view of the distal end portion of the shaft of the electrode catheter according to the second modification cut along a line C-C shown in Fig. 7A.Fig. 8 is a view showing a modification of the ring electrode.

Description of Embodiment

An embodiment of the present invention (hereinafter referred to as present embodiment) will be described below with reference to the drawings. Incidentally, description about members having the same reference signs as those of members that have already been described in description of the present embodiment will be omitted for convenience of explanation. In addition, in some cases, dimensions of each member shown in the drawings may be different from actual dimensions of the member for convenience of explanation.

Fig. 1 shows an overall view of anelectrode catheter 1 according to the present embodiment. As shown in Fig. 1, theelectrode catheter 1 is provided with ashaft 2, ahandle 3, and a connector 4. Theelectrode catheter 1 is configured to measure an electric potential (particularly a variation of an electric potential) inside a heart of a subject (e.g. a patient). After inserting theshaft 2 of theelectrode catheter 1 into the heart of the subject, a medical worker carefully observes the variation of the electric potential inside the heart acquired from theelectrode catheter 1 while moving theshaft 2 inside the heart. In this manner, the medical worker can estimate a place where arrhythmia (e.g. atrial fibrillation etc.) occurred inside the heart (e.g. inside a left atrium). Here, an electrocardiogram waveform indicating the variation of the electric potential inside the heart over time is generated based on an electric signal acquired from theshaft 2, and displayed on a not-shown display device.

Theshaft 2 is configured to be inserted into the heart. Theshaft 2 is configured, for example, by a hollow flexible tube, and has adistal end portion 7 and aguide portion 8. Theshaft 2 is formed, for example, out of a resin material. Thedistal end portion 7 is configured to make contact with an endocardium of the subject. Particularly, thedistal end portion 7 is substantially formed into a planar shape (e.g. a ring shape) in order to configure a contact surface for making contact with the endocardium (see Fig. 2). Theguide portion 8 is connected to thedistal end portion 7 and configured integrally with thedistal end portion 7. An extension direction of thedistal end portion 7 and an extension direction of theguide portion 8 are different from each other. In this respect, thedistal end portion 7 and theguide portion 8 may be perpendicular to each other, or an angle formed by thedistal end portion 7 and theguide portion 8 may be set within a range of from 70° to 110° in a used state in which thedistal end portion 7 contacts the endocardium. In addition, the extension direction of thedistal end portion 7 and the extension direction of theguide portion 8 may be the same as each other in a state before thedistal end portion 7 contacts the endocardium. In this case, in a state in which thedistal end portion 7 contacts the endocardium, thedistal end portion 7 may be deformed such that the extension direction of thedistal end portion 7 and the extension direction of theguide portion 8 are different from each other.

Thehandle 3 can be operated by the medical worker. The medical worker who operates a predetermined operating portion (not shown) provided in thehandle 3 can control theguide portion 8 of theshaft 2 to bend. Particularly, theguide portion 8 has a bendable portion (not shown) configured to bend in accordance with the operation of the medical worker. The connector 4 is configured to connect theelectrode catheter 1 to an input amplifier device (not shown). An electric signal indicating a variation of an electric potential inside the heart acquired by theelectrode catheter 1 is inputted to the input amplifier device through the connector 4.

Next, a specific configuration of thedistal end portion 7 of theshaft 2 will be described with reference to Fig. 2 and Figs. 3A to 3C. Fig. 2 is a perspective view showing thedistal end portion 7 and theguide portion 8. Fig. 3A is a side view showing a part of thedistal end portion 7 in an enlarged manner. Fig. 3B is a plan view of the part of thedistal end portion 7 in the enlarged manner. Fig. 3C is a sectional view of thedistal end portion 7 cut along a line A-A shown in Fig. 3A.

As shown in Fig. 2 and Figs. 3A to 3C, theelectrode catheter 1 is further provided with a plurality of ring electrodes 6 (specifically, ten ring electrodes 6), and a plurality of insulators 10 (specifically, ten insulators 10). The plurality ofring electrodes 6 are provided to surround an outercircumferential surface 7S of thedistal end portion 7, and disposed along the extension direction of thedistal end portion 7 so as to be separated from one another. Thering electrodes 6 are formed out of an electrically conductive material. For example, thering electrodes 6 may be formed out of platinum or an alloy of platinum and iridium. Each of theinsulators 10 is provided on the outercircumferential surface 7S of thedistal end portion 7 so as to cover a corresponding one of thering electrodes 6. In addition, theinsulator 10 exposes a portion of thecorresponding ring electrode 6. Particularly, the portions of the tenring electrodes 6 are exposed from theinsulators 10 respectively and correspondingly so that the portions of thering electrodes 6 exposed from theinsulators 10 can make contact with an endocardium of a heart simultaneously in a state in which thedistal end portion 7 is in contact with the endocardium. In other words, the portions of thering electrodes 6 exposed from theinsulators 10 respectively are positioned on the outercircumferential surface 7S of thedistal end portion 7 making contact with the endocardium. Incidentally, in the present embodiment, the number of thering electrodes 6 is not limited to ten but may be, for example, one. Likewise, the number of theinsulators 10 is not limited to ten but may be, for example, one in order to correspond the number of theinsulators 10 to the number of thering electrodes 6. In addition, each of thering electrodes 6 may be provided to continuously (entirely) surround the outercircumferential surface 7S, as shown in Fig. 3C, or may be provided to discontinuously surround the outercircumferential surface 7S. For example, as shown in Fig. 8, anotch portion 62 may be formed in thering electrode 6. In this case, thenotch portion 62 is filled with a correspondinginsulator 10. Further, although the thickness of theinsulator 10 is uniform in Fig. 3C, the thickness of theinsulator 10 may be not uniform. Moreover, the shape of theinsulator 10 is also not limited particularly.

In addition, as shown in Fig. 3C, theelectrode catheter 1 is further provided with a plurality of electric wires 12 (specifically, ten electric wires 12) provided in ahollow portion 13 of theshaft 2. Each of theelectric wires 12 extends along an extension direction of theshaft 2. Theelectric wire 12 is electrically connected to a corresponding one of thering electrodes 6 through aconnection conductor 16 provided inside thedistal end portion 7 of theshaft 2. An electric signal indicating a variation of an intracardiac electric potential over time is inputted from thering electrode 6 to the input amplifier device through theelectric wire 12 and the connector 4. For example, after amplifying a difference between an electric signal acquired by apredetermined ring electrode 6 and an electric signal acquired by aring electrode 6 different from thepredetermined ring electrode 6, the input amplifier device applies analog-to-digital conversion to the amplified difference between the electric signals. In this manner, the input amplifier device can generate data of an electrocardiogram waveform indicating a variation of a voltage between any tworing electrodes 6 in combination over time.

In addition, an operating wire (not shown) configured to bend theguide portion 8 of theshaft 2 may be provided in thehollow portion 13. When the operating wire bends in accordance with an operation performed on the handle 3 (see Fig. 1) by the medical worker, a part of theguide portion 8 bends. In addition, thehollow portion 13 may be filled with an insulating material so that theelectric wires 12 can be embedded therein.

Next, in anelectrode catheter 100 according to a background art, a variation between an impedance value measured between eachring electrode 6 and an impedance measuring electrode attached to a part (e.g. the back etc.) of a body of a subject when thering electrode 6 is not in contact with an endocardium and an impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is in contact with the endocardium will be described with reference to Fig. 4. (a) of Fig. 4 is a view showing a state in which thering electrode 6 is not in contact with the endocardium. (b) of Fig. 4 is a view showing a state in which thering electrode 6 is in contact with the endocardium. (c) of Fig. 4 is a graph showing the variation between the impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is not in contact with the endocardium and the impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is in contact with the endocardium. In (a) and (b) of Fig. 4, the section of thedistal end portion 7 perpendicular to the extension direction of thedistal end portion 7 is shown in order to illustrate the contact state between thering electrode 6 and the endocardium in an easy-to-understand manner. Theelectrode catheter 100 according to the background art differs from theelectrode catheter 1 according to the present embodiment at the point that theinsulators 10 are not formed on an outercircumferential surface 7S of thedistal end portion 7. In addition, the impedance measuring electrode may be attached to the body surface of the back etc. of the subject or may be placed inside the body of the subject. In this respect, one of thering electrodes 6 may function as the impedance measuring electrode. In addition, the impedance measuring electrode may be connected to the ground.

In the case where thering electrode 6 is not in contact with the endocardium, as shown in (a) of Fig. 4, the entire surface of thering electrode 6 makes contact with blood. Therefore, an impedance value between thering electrode 6 and the impedance measuring electrode is mainly determined based on electric conductivity α1 of the blood. On the other hand, in the case where thering electrode 6 is in contact with the endocardium, as shown in (b) of Fig. 4, the surface of thering electrode 6 makes contact with both the blood and the endocardium. Therefore, an impedance value between thering electrode 6 and the impedance measuring electrode is mainly determined based on the electric conductivity α1 of the blood and electric conductivity α2 of the endocardium. Here, each of the impedance values indicates the amplitude of impedance. The impedance value may be measured based on a value of an AC voltage of a predetermined frequency applied to thering electrode 6 and a current value outputted from thering electrode 6 or the impedance measuring electrode.

Since the electric conductivity α1 of the blood is larger than the electric conductivity α2 of the endocardium, the impedance value measured in the state in which thering electrode 6 is in contact with the endocardium is larger than the impedance value measured in the state in which thering electrode 6 is not in contact with the endocardium, as shown in (c) of Fig. 4. Thus, there is a variation between the impedance value measured when thering electrode 6 is not in contact with the endocardium and the impedance value measured when thering electrode 6 is in contact with the endocardium. On the other hand, in theelectrode catheter 100 according to the background art, the entire surface of thering electrode 6 is exposed to the outside. Accordingly, even in the state in which thering electrode 6 is in contact with the endocardium, the most part of the surface of thering electrode 6 still makes contact with the blood. Therefore, the impedance value is mainly determined by the electric conductivity α1 of the blood (i.e. the influence of the electric conductivity α2 of the endocardium on the impedance value is smaller than the influence of the electric conductivity α1 of the blood on the impedance value). As a result, the variation between the impedance value measured when thering electrode 6 is not in contact with the endocardium and the impedance value measured when thering electrode 6 is in contact with the endocardium is so small that it is difficult to accurately determine the contact between thering electrode 6 and the endocardium based on the variation between the impedance values. That is, when the variation between the impedance values is small, it is difficult to determine whether the variation between the impedance values is caused by noise or by the contact between thering electrode 6 and the endocardium.

Incidentally, determination about the contact between thering electrode 6 and the endocardium based on the variation between the impedance values may be automatically made by a computer (a processor such as a CPU) communicably connected to theelectrode catheter 1. In this case, the computer may automatically determine the contact between thering electrode 6 and the endocardium based on information indicating the variation between the impedance values acquired from theelectrode catheter 1 and a contact determination program. Alternatively, the contact determination may be subjectively made by the medical worker operating theelectrode catheter 1. In this case, the medical worker may visually recognize the variation between the impedance values acquired from theelectrode catheter 1 and displayed on a display device (not shown), to thereby subjectively determine the contact between thering electrode 6 and the endocardium.

Next, in theelectrode catheter 1 according to the present embodiment, a variation between an impedance value measured between eachring electrode 6 and an impedance measuring electrode when thering electrode 6 is not in contact with an endocardium and an impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is in contact with the endocardium will be described with reference to Fig. 5. (a) of Fig. 5 is a view showing a state in which thering electrode 6 is not in contact with the endocardium. (b) of Fig. 5 is a view showing a state in which thering electrode 6 is in contact with the endocardium. (c) of Fig. 5 is a graph showing the variation between the impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is not in contact with the endocardium and the impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is in contact with the endocardium.

In the case where thering electrode 6 is not in contact with the endocardium, as shown in (a) of Fig. 5, the surface of thering electrode 6 exposed from a corresponding insulator 10 (hereinafter referred to exposed surface of the ring electrode 6) makes contact with blood. Therefore, an impedance value between thering electrode 6 and the impedance measuring electrode is mainly determined based on electric conductivity α1 of the blood. On the other hand, in the case where thering electrode 6 is in contact with the endocardium, as shown in (b) of Fig. 5, the most part of the exposed surface of thering electrode 6 makes contact with the endocardium although the exposed surface of thering electrode 6 makes contact with both the blood and the endocardium. Therefore, an impedance value between thering electrode 6 and the impedance measuring electrode is mainly determined based on electric conductivity α2 of the endocardium. That is, the impedance value in the state in which thering electrode 6 is not in contact with the endocardium is mainly determined by the electric conductivity α1 of the blood. On the other hand, the impedance value in the state in which thering electrode 6 is in contact with the endocardium is mainly determined by the electric conductivity α2 of the endocardium. Thus, there is a large variation between the impedance value measured when thering electrode 6 is not in contact with the endocardium and the impedance value measured when thering electrode 6 is in contact with the endocardium, as shown in (c) of Fig. 5.

According to the present embodiment, each of theinsulators 10 is provided on the outercircumferential surface 7S of thedistal end portion 7 of theshaft 2 so as to cover a corresponding one of thering electrodes 6 while exposing a portion of thecorresponding ring electrode 6. Thus, with the provision of theinsulators 10, surface areas of thering electrodes 6 exposed to the outside can be reduced. Particularly, in the state where thedistal end portion 7 is in contact with the endocardium, the surface areas of thering electrodes 6 making contact with the blood can be reduced. Therefore, the variation between the impedance value measured between each of thering electrodes 6 and the impedance measuring electrode when thering electrode 6 is not in contact with the endocardium and the impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is in contact with the endocardium is larger, in comparison with that in a situation that thering electrodes 6 are not covered with theinsulators 10 at all (see Fig. 4). Thus, based on the variation between the impedance values, it is possible to more accurately determine whether thering electrode 6 is in contact with the endocardium or not. Since it is possible to more accurately determine whether thering electrode 6 is in contact with the endocardium or not, it is consequently possible to accurately identify a variation of an electric potential inside the heart (e.g. inside a left atrium) of the subject. Thus, it is possible to provide theelectrode catheter 1 whose usability is improved.

In addition, in the present embodiment, the exposed surfaces of thering electrodes 6 exposed from theinsulators 10 respectively can make contact with the endocardium simultaneously. Accordingly, it is possible to simultaneously measure variations of intracardiac electric potentials corresponding to thering electrodes 6 respectively. Further, since the extension direction of thedistal end portion 7 of theshaft 2 and the extension direction of theguide portion 8 of theshaft 2 are different from each other, it is possible to increase a contact area between thedistal end portion 7 and the endocardium. Accordingly, it is possible to increase the number of thering electrodes 6 capable of making contact with the endocardium simultaneously. In addition, thering electrodes 6 are provided to surround the outercircumferential surface 7S of thefront end portion 7. Accordingly, work during production can be also simple.

(First Modification)
Next, anelectrode catheter 1A according to a first modification of the present embodiment will be described with reference to Figs. 6A to 6C. In the first modification, description about members having the same reference signs as those of members that have already been described in the description of the present embodiment will be omitted for convenience of explanation. Fig. 6A is a sectional view showing a part of adistal end portion 7 of ashaft 2 of theelectrode catheter 1A in an enlarged manner. Fig. 6B is a plan view showing the part of thedistal end portion 7 in the enlarged manner. Fig. 6C is a sectional view of thedistal end portion 7 cut along a line B-B shown in Fig. 6A.

Theelectrode catheter 1A according to the first modification differs in aninsulator 10A from theelectrode catheter 1 according to the present embodiment. In the first modification, oneinsulator 10A is formed on an outercircumferential surface 7S of thedistal end portion 7 so as to cover a plurality of ring electrodes 6 (specifically, ten ring electrodes 6). Theinsulator 10A has a plurality of opening portions 30 (specifically, ten opening portions), and each of the openingportions 30 exposes a portion of a corresponding one of thering electrodes 6. Particularly, the portions of the tenring electrodes 6 are exposed from the openingportions 30 respectively so that exposed surfaces of thering electrodes 6 exposed from the openingportions 30 can simultaneously make contact with the endocardium in a state in which thedistal end portion 7 is in contact with an endocardium of a heart. In other words, the exposed surfaces of thering electrodes 6 are positioned on the outercircumferential surface 7S of thedistal end portion 7 making contact with the endocardium.

Theelectrode catheter 1A according to the first modification also has effects and functions similar to or the same as theelectrode catheter 1 according to the present embodiment. That is, theinsulator 10A is provided on the outercircumferential surface 7S of thedistal end portion 7 of theshaft 2 so as to cover the plurality ofring electrodes 6, and each of the openingportions 30 of theinsulator 10A exposes the portion of a corresponding one of thering electrodes 6. Thus, with the provision of theinsulator 10A, it is possible to reduce surface areas of thering electrodes 6 exposed to the outside. Particularly, in the state in which thedistal end portion 7S is contact with the endocardium, it is possible to reduce the surface areas of thering electrodes 6 making contact with blood. Alternatively, in the state in which thedistal end portion 7 is in contact with the endocardium, the exposed surfaces of thering electrodes 6 may make contact with only the endocardium. Therefore, a variation between an impedance value measured between each of thering electrodes 6 and an impedance measuring electrode when thering electrode 6 is not in contact with the endocardium and an impedance value measured between thering electrode 6 and the impedance measuring electrode when thering electrode 6 is in contact with the endocardium is larger, in comparison with that in a situation that thering electrodes 6 are not covered with theinsulator 10A at all (see Fig. 4). Thus, based on the variation between the impedance values, it is possible to more accurately determine whether thering electrode 6 is in contact with the endocardium or not. Since it is possible to more accurately determine whether thering electrode 6 is in contact with the endocardium or not, it is consequently possible to accurately identify a variation of an electric potential inside the heart (e.g. inside a left atrium) of a subject. Thus, it is possible to provide theelectrode catheter 1A whose usability is improved.

(Second Modification)
Next, anelectrode catheter 1B according to a second modification of the present embodiment will be described with reference to Figs. 7A to 7C. In the second modification, description about members having the same reference signs as those of members that have already been described in the description of the present embodiment will be omitted for convenience of explanation. Fig. 7A is a sectional view showing a part of adistal end portion 7 of ashaft 2 of theelectrode catheter 1B in an enlarged manner. Fig. 7B is a plan view showing the part of thedistal end portion 7 in the enlarged manner. Fig. 7C is a sectional view of thedistal end portion 7 cut along a line C-C shown in Fig. 7A.

Theelectrode catheter 1B according to the second modification differs from theelectrode catheter 1 according to the present embodiment at the point that a plurality ofchip electrodes 6B (e.g. tenchip electrodes 6B) are provided in place of the plurality ofring electrodes 6. In addition, the insulator covering the ring electrodes is not provided in theelectrode catheter 1B. As shown in Figs. 7A to 7C, each of thechip electrodes 6B is provided on an outercircumferential surface 7S of thedistal end portion 7 of the shaft 2 (see Fig. 1), and configured to make contact with an endocardium. The number of thechip electrodes 6B provided on the outercircumferential surface 7S is, for example, ten. However, the number of thechip electrodes 6B is not limited particularly. The plurality ofchip electrodes 6B are disposed along an extension direction of thedistal end portion 7 so as to be separated from one another. Thechip electrodes 6B may be formed out of the same electrically conductive material as thering electrodes 6 according to the present embodiment. For example, thechip electrodes 6B may be formed out of platinum or an alloy of platinum and iridium. In addition, a dimension W of each of thechip electrodes 6B extending along an outer circumference direction D1 (see Fig. 7C) of thedistal end portion 7 is smaller than a circumferential length of thedistal end portion 7. Here, the circumferential length of thedistal end portion 7 is a value obtained by multiplying an outer diameter of thedistal end portion 7 by π. Particularly, it is preferable that the dimension W of thechip electrode 6B extending along the outer circumference direction D1 of thedistal end portion 7 is not larger than 50% of the circumferential length of thedistal end portion 7.

In addition, therespective chip electrodes 6B make contact with an endocardium of a heart simultaneously in the state in which thedistal end portion 7 is in contact with the endocardium. In other words, thechip electrodes 6B are positioned on the outercircumferential surface 7S of thedistal end portion 7 making contact with the endocardium. Each of thechip electrodes 6B is electrically connected to a corresponding one ofelectric wires 12 through aconnection conductor 16. Theelectric wires 12 are provided in ahollow portion 13 of theshaft 2.

According to the present modification, the dimension W of each of thechip electrodes 6B along the outer circumference direction D1 of thedistal end portion 7 is smaller than the circumferential length of thedistal end portion 7. Accordingly, a surface area of thechip electrode 6B exposed to the outside is smaller than the surface area of thering electrode 6 exposed to the outside (see Fig. 4). Therefore, in the state in which thedistal end portion 7 is in contact with the endocardium, the surface area of thechip electrode 6B making contact with blood is smaller than the surface area of thering electrode 6 making contact with blood. Alternatively, in the state in which thedistal end portion 7 is in contact with the endocardium, thechip electrode 6B may make contact with only the endocardium. As a result, a variation between an impedance value measured between thechip electrode 6B and an impedance measuring electrode attached to a subject when thechip electrode 6B is not in contact with the endocardium and an impedance value measured between thechip electrode 6B and the impedance measuring electrode when thechip electrode 6B is in contact with the endocardium is larger, in comparison with that in the case of thering electrode 6. Thus, based on the variation between the impedance values, it is possible to more accurately determine whether thechip electrode 6B is in contact with the endocardium or not. Since it is possible to more accurately determine whether thechip electrode 6B is in contact with the endocardium or not, it is consequently possible to accurately identify a variation of an electric potential inside the heart (e.g. inside a left atrium) of the subject. Thus, it is possible to provide theelectrode catheter 1B whose usability is improved.

Although the embodiment of the present invention has been described above, the technical scope of the present invention should not be interpreted limitedly based on the description of the present embodiment. The present embodiment is merely exemplified. It should be understood by those skilled in the art that various changes can be made on the embodiment within the scopes of the claimed inventions. The technical scopes of the claimed inventions should be defined based on the scope of the claims and its equivalent scope.

For example, in the present embodiment, thedistal end portion 7 of theshaft 2 is formed into a ring shape in order to configure the contact surface for making contact with the endocardium. However, the shape of thedistal end portion 7 is not limited thereto. For example, thedistal end portion 7 may be formed into a radial shape, a hexagonal shape or a spiral shape.

This application is based on Japanese Patent Application No. 2017-215639 filed on November 8, 2017, the entire contents of which are incorporated herein by reference.

Claims (6)

1. An electrode catheter for measuring an electric potential inside a heart of a subject, the electrode catheter comprising:
   a shaft that is inserted into the heart, wherein the shaft comprises a distal end portion that is configured to make contact with an endocardium of the subject, and a guide portion that is connected to the distal end portion;
   at least one ring electrode that is provided to surround an outer circumferential surface of the distal end portion; and
   at least one insulator that is provided on the outer circumferential surface so as to cover the ring electrode, wherein the insulator exposes a portion of the ring electrode.
2. The electrode catheter according to claim 1, wherein:
   the at least one ring electrode is a plurality of ring electrodes;
   the at least one insulator is a plurality of insulators;
   each of the insulators is provided on the outer circumferential surface so as to cover a corresponding one of the ring electrodes; and
   each of the insulators exposes a portion of the corresponding ring electrode.
3. The electrode catheter according to claim 1, wherein:
   the at least one ring electrode is a plurality of ring electrodes;
   the insulator is provided with a plurality of opening portions; and
   each of the opening portions exposes a portion of a corresponding one of the ring electrodes.
4. The electrode catheter according to any one of claims 1 to 3, wherein:
   the at least one ring electrode is a plurality of ring electrodes; and
   portions of the ring electrodes exposed from the insulator can make contact with the endocardium simultaneously.
5. The electrode catheter according to any one of claims 1 to 4, wherein an extension direction of the distal end portion and an extension direction of the guide portion are different from each other.
6. An electrode catheter for measuring an electric potential inside a heart of a subject, the electrode catheter comprising:
   a shaft that is inserted into the heart, wherein the shaft comprises a distal end portion that is configured to make contact with an endocardium of the subject, and a guide portion that is connected to the distal end portion; and
   at least one chip electrode that is provided on an outer circumferential surface of the distal end portion, and that is configured to make contact with the endocardium,
   wherein a dimension of the chip electrode extending along an outer circumference direction of the distal end portion is smaller than a circumferential length of the distal end portion.

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