A method for monitoring myocardial mechanical properties during arrhythmia ablation

Abstract

To provide a method for monitoring cardiac muscle mechanical characteristics for determining an ablation condition so as to safely and reliably perform ablation when performing cardiac muscle catheter ablation.SOLUTION: A method which monitors cardiac muscle mechanical characteristics related to rigidity of the cardiac muscle for determining an ablation condition when catheter ablation for an irregular pulse treatment is performed, monitors the cardiac muscle mechanical characteristics by calculating the cardiac muscle mechanical characteristics according to two kinds of parameters of local impedance (LI) near a catheter end for inferring a distance between the catheter end measured by the sensor for local impedance measurement provided at the catheter end part and the cardiac muscle and contact force (CF) of the catheter end for assessing a contact state between the cardiac muscle and the catheter measured by a sensor for contact force measurement provided at the catheter end.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to radiofrequency catheter ablation and to a method for monitoring the mechanical properties of myocardial tissue to determine ablation conditions. [Background technology]

[0002] Arrhythmia refers to an abnormal heart rhythm and is classified as atrial or ventricular. Atrial fibrillation is a typical atrial arrhythmia, accounting for approximately half of all arrhythmia cases. There are approximately 730,000 patients in Japan (2008) and approximately 2.2 million patients in the United States (1991).

[0003] Atrial fibrillation is reported to be primarily caused by abnormal electrical excitation originating from the pulmonary veins, which is transmitted to the left atrium or forms a reentry circuit (circulation circuit) of electrical excitation within the myocardial tissue.

[0004] The first-line treatment for atrial fibrillation is defibrillation and rhythm control drugs to maintain sinus rhythm. However, drug therapy is only a symptomatic treatment and cannot cure the condition, and rhythm control drugs are often ineffective in cases of chronic atrial fibrillation. Over time, atrial fibrillation can progress from paroxysmal to chronic, becoming a major risk factor for heart failure and cerebral infarction.

[0005] Radiofrequency catheter ablation (RFCA) is a radical treatment alternative to drug therapy. Radiofrequency catheter ablation is a treatment method in which high-frequency electricity is passed through a catheter to the myocardial tissue, causing thermal coagulation and necrosis of the myocardial tissue by the Joule heat generated in the myocardial tissue, thereby blocking the abnormal electrical conduction described above.

[0006] Although radiofrequency catheter ablation has been proven to be superior to drug therapy, it can cause serious side effects, such as cardiac tamponade due to intratissue steam explosion, pulmonary vein stenosis or obstruction, phrenic nerve paralysis, esophageal disorders, and cerebral embolism due to thrombus formation.

[0007] In order to suppress such side effects, it has been necessary to strictly manage the conditions of radiofrequency catheter ablation. Conventionally, when performing myocardial catheter ablation, local impedance (LI) has been measured solely to estimate the positional relationship between the catheter and the myocardium. There have been reports on catheters used for this purpose (see Patent Document 1). It has also been known that the degree of contact between the catheter and myocardial tissue can be estimated by measuring contact force (CF) when performing catheter ablation.

[0008] The degree of proximity of the catheter to the myocardial tissue and the degree of contact between the catheter and the myocardial tissue have been used independently to determine the ablation conditions. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2017-529169 Summary of the Invention [Problem to be solved by the invention]

[0010] Conventionally, when performing myocardial catheter ablation, the local impedance (LI) was measured exclusively to estimate the positional relationship between the catheter and the myocardium. It was also known that the degree of contact between the catheter and the myocardial tissue could be estimated by measuring the contact force (CF) during catheter ablation. However, LI or CF alone cannot fully determine the mechanical properties of the myocardium, including its stiffness, and side effects such as perforation of the myocardium by radiofrequency ablation still occur.

[0011] An object of the present invention is to provide a method for monitoring myocardial mechanical properties in order to determine ablation conditions for performing ablation safely and reliably when performing myocardial catheter ablation. [Means for solving the problem]

[0012] The present inventors believed that the mechanical properties of myocardial tissue, such as hardness, affect the thermal denaturation of myocardial tissue caused by the application of radiofrequency current during radiofrequency catheter ablation, and conducted extensive research into methods for monitoring the mechanical properties of myocardial tissue.

[0013] The inventors discovered that by measuring the contact pressure (CF) between the catheter tip and myocardial tissue in addition to the local impedance (LI), which is the impedance near the catheter tip, and using an index that combines these two, it is possible to calculate the mechanical properties of the myocardium, including the stiffness of the myocardium, and determine appropriate conditions for high-frequency ablation that do not cause side effects based on these mechanical properties, thereby completing the present invention.

[0014] That is, the present invention is as follows. [1] A method for monitoring myocardial mechanical properties related to myocardial stiffness to determine ablation conditions when performing catheter ablation for treating arrhythmia, comprising: A method for monitoring myocardial mechanical properties by calculating them from two parameters: local impedance (LI) near the catheter tip, which is measured with a local impedance measurement sensor installed at the catheter tip to estimate the distance between the catheter tip and the myocardium, and contact pressure (CF) at the catheter tip, which is measured with a contact pressure measurement sensor installed at the catheter tip to evaluate the contact state between the myocardium and the catheter. [2] A method of monitoring myocardial mechanical properties as described in [1], in which LI and CF are measured at multiple points, a regression line is found between the LI and CF values, and the slope of the line is used as an index to calculate myocardial mechanical properties. [3] A catheter for use in the method of [1] or [2], which has multiple electrodes near the tip of the catheter for measuring LI and further has a sensor for measuring CF. [4] The catheter in [3] is an ablation catheter. [5] A device for monitoring myocardial mechanical properties related to myocardial stiffness to determine ablation conditions when performing catheter ablation for arrhythmia treatment, comprising: (i) a catheter having a plurality of electrodes near the tip of the catheter for measuring LI and further having means for measuring CF; (ii) a calculation means for calculating myocardial mechanical properties from the LI and CF measured by the catheter of (i); and (iii) a display unit for displaying the myocardial mechanical properties analyzed by the computing means; A device having: [6] The device of [5], wherein the catheter is an ablation catheter. [Effects of the Invention]

[0015] In the present invention, by measuring contact pressure (CF) in addition to local impedance (LI) and using an index that combines the two, it is possible to calculate myocardial mechanical properties, including myocardial stiffness. This makes it possible to optimize catheter ablation conditions such as current application position and current application time, thereby enabling ablation treatment that is more efficient and safer than conventional methods.

[0016] From the prior art, it was not possible to imagine how both the LI and CF values ​​could be used to determine the ablation conditions.

[0017] This invention is expected to dramatically reduce side effects by measuring the mechanical properties of the myocardial tissue that is the target of treatment, something that has not been possible with previous arrhythmia ablation monitoring, and is therefore expected to play an important medical role. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an overview of a catheter ablation system. [Figure 2] FIG. 1 shows a catheter with microelectrodes. [Figure 3] Figure 3 shows the measured size of radiofrequency lesions created by ablation, with Figure 3A showing the results at a catheter angle of 90°, Figure 3B showing the results at a catheter angle of 45°, and Figure 3C showing the results at a catheter angle of 30°. [Figure 4] In the mechanical property measurement, porcine myocardial tissue was fixed on a stage in a water pool and a catheter was pressed against it. Figure 4A shows the state where the position (strain) is 0, and Figure 4B shows the state where the catheter is pressed in (positive strain). [Figure 5] This figure shows the relationship between contact pressure and local impedance measured in the left and right ventricles. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below. The present invention relates to a method for monitoring myocardial mechanical properties, such as myocardial stiffness, to determine ablation conditions when performing catheter ablation for treating arrhythmia. The present invention also relates to a catheter used in the method and to a device including the catheter. Here, "catheter" refers to a thin tube that can be inserted into a blood vessel. The catheter of the present invention has a sensor for measuring local impedance (LI) near the catheter tip and a sensor for measuring contact force (CF) at the catheter tip to evaluate the contact state between the myocardium and the catheter.

[0020] The catheter of the present invention can be used to treat arrhythmias caused by abnormal electrical conduction, particularly tachyarrhythmias. Examples of such tachyarrhythmias include paroxysmal supraventricular tachycardia (PSVT) such as atrioventricular reciprocating tachycardia (AVRT: WPW syndrome) and atrioventricular nodal reentrant tachycardia (AVNRT), atrial flutter, atrial tachycardia, and atrial fibrillation (AF) (all of which are supraventricular tachyarrhythmias), and ventricular tachyarrhythmias such as ventricular tachycardia.

[0021] About catheter ablation The catheter of the present invention is a catheter that is inserted into the heart. Examples of such catheters include monitoring catheters for monitoring the mechanical properties of myocardium and ablation catheters that monitor the mechanical properties of myocardium and perform ablation on myocardial tissue. The catheter of the present invention is preferably a catheter for ablation therapy that can be used to ablate myocardial tissue. The ablation catheter has an ablation electrode, and ablation can be performed by passing electricity through the ablation electrode.

[0022] The catheter of the present invention may be one that is commonly used as a cardiac catheter. The tip of the catheter of the present invention may have a freely bendable structure. For example, a tension wire may be disposed in the catheter, and the tip can be bent by pulling the tension wire. Furthermore, the tip may be pre-bent to fit the shape of the treatment site. The device of the present invention may include a guide sheath or guide wire for inserting and advancing the catheter to the target site. The catheter size is preferably 6 to 8 Fr. The catheter may be inserted into the body via the femoral artery or brachial artery using standard methods. Alternatively, a catheter may be inserted via the femoral vein to reach the right atrium and then via the Brockenbrough technique to reach the left cardiac tissue via the atrial septum.

[0023] The device, which includes an ablation catheter, has a high-frequency current generator (high-frequency ablation device) and a current-carrying return electrode. By passing a high-frequency current between the electrode at the tip of the catheter in the heart and the return electrode, the temperature of the catheter tip is raised to about 60°C, causing tissue necrosis. The duration of each current application is approximately 30 to 60 seconds, and cauterization is performed several times. An overview of the catheter ablation system is shown in Figure 1.

[0024] Sensors for LI and CF measurements LI measurement sensor The mechanical properties of the myocardium related to the stiffness of the myocardium can be calculated using the local impedance (LI) near the catheter tip and the contact force (CF) at the catheter tip as parameters to evaluate the contact state between the myocardium and the catheter.

[0025] Here, the local impedance (LI) near the catheter tip refers to the resistance value generated by contact between the catheter tip and myocardial tissue. The local impedance changes depending on the distance between the catheter tip and the myocardial tissue, and the position of the catheter relative to the myocardial tissue can be estimated from the local impedance. The local impedance can be measured using a sensor provided near the catheter tip. Therefore, the catheter of the present invention has a sensor for measuring the local impedance near the tip.

[0026] A sensor for local impedance measurement is called an impedance measurement sensor, and includes a plurality of impedance detection electrodes including at least one pair of electrodes, and is capable of measuring impedance based on a change in the signal between the electrodes.

[0027] The electrode used for measuring local impedance is provided at the tip of the catheter of the present invention. The catheter of the present invention has at least two electrodes. The electrodes function as at least potential measurement electrodes. The catheter of the present invention may also have a current-passing electrode. The potential measurement electrode may also function as a current-passing electrode, or a current-passing electrode used only for current passage may be provided separately from a potential measurement electrode used only for potential measurement.

[0028] A current-carrying electrode is an electrode that can pass current to the area with which it is in contact, and the current-carrying electrode is connected to a lead wire disposed inside the catheter and is connected to a power supply unit via the lead wire.

[0029] The potential measuring electrodes can be used to measure the potential of the target site that the electrodes contact. There are at least two potential measuring electrodes, and they are positioned so that the potential difference can be measured.

[0030] As mentioned above, the presence of at least two means, for example, the presence of two, three, four, five or more, and preferably two to four.

[0031] For example, multiple electrodes may be provided on the exterior of the catheter tip. In this case, these electrodes may be, for example, ring-shaped electrodes that surround the catheter. When multiple ring electrodes are provided, the distance between the ring electrodes is within 10 mm, preferably within 5 mm. Furthermore, the shape of the electrodes is not limited to the above-described shapes, and they may be straight wires, or may be in the shape of a surface, ribbon, cylinder, dome, or other shapes. Surface shapes include both flat and curved shapes.

[0032] The size of the electrode is, for example, about 1 to 20 mm, preferably about 3 to 20 mm, more preferably about 3 to 17 mm, and even more preferably about 6 to 14 mm in length along the long axis of the catheter. 2 , preferably 10 to 80 mm 2 , more preferably 20 to 70 mm 2 That's about it.

[0033] The electrode material may be SUS, but it is preferable to use a material that does not have an adverse effect on the living body, such as gold, silver, platinum, tungsten, palladium, or alloys of these, Ni-Ti alloys, titanium alloys, etc.

[0034] The potential measurement electrodes are connected to a potential measuring device via lead wires, and a current is passed between the two electrodes, allowing the resulting voltage to be measured. The ratio of the potential difference between the electrodes to the applied current reflects the impedance of the location where the current is transmitted. In this case, when two electrodes are used, one electrode is used as the counter electrode, and the potential difference between the two electrodes is measured. In this case, for example, multiple electrodes may be provided with a gap between them. The catheter is placed so that the electrode portion is in contact with the myocardial tissue, and the potential is detected by the electrodes.

[0035] The above electrodes may further include a plurality of smaller electrodes. Such small electrodes are called microelectrodes or minielectrodes. The microelectrodes may be arranged, for example, circumferentially around the electrode at the tip of the catheter. For example, two, three, or four microelectrodes may be provided circumferentially on the electrode at the tip of the catheter. By providing microelectrodes in this manner, at least one of the multiple microelectrodes can come into contact with myocardial tissue regardless of the direction of the catheter, making it possible to measure local impedance between the microelectrode and an electrode provided proximal to the catheter tip. The area of ​​the microelectrode is, for example, 0.2 to 1 mm. 2 , preferably 0.3 to 0.8 mm 2 , and more preferably 0.4 to 0.7 mm 2 That's about it.

[0036] The electrode positions of such a catheter having microelectrodes are shown in Figure 2. Such a catheter is described in, for example, JP-A-2017-529169.

[0037] Because the local impedance value measurable by the catheter of the present invention and the distance between the catheter tip and the myocardial tissue are linear, the change in impedance can reveal the positional relationship, such as the distance between the catheter tip and the myocardial tissue. Note that the distance here is negative when the catheter tip and the myocardial tissue are separated and not in contact, and zero when they are in contact. Furthermore, when there is strong contact, the myocardial tissue is pressed and depressed by the catheter tip, and the catheter tip moves further into the myocardial tissue from its position at the time of contact, resulting in a positive distance. When the catheter and the myocardial tissue are separated from each other at the catheter tip, no strain occurs in the myocardial tissue. However, when the catheter and the myocardial tissue are in contact, the myocardial tissue is depressed and strain occurs. In other words, the strain in the myocardial tissue can be estimated from the distance between the catheter and the myocardial tissue, i.e., the positional relationship.

[0038] CF measurement sensor The contact force (CF) at the catheter tip refers to the pressure when the catheter tip is in contact with myocardial tissue. The contact pressure can be used to directly evaluate the state of contact between the myocardium and the catheter. Contact pressure can be measured using a contact pressure sensor attached to the catheter tip. Examples of contact pressure sensors that can be used include piezoelectric sensors using piezoelectric elements and strain gauge force sensors (load cells). When these sensors come into contact with myocardial tissue, a voltage corresponding to the applied pressure is generated, and this voltage can be measured. Alternatively, contact pressure can be measured by interference analysis using optical interferometry. In this case, a cylindrical sensor with three cavities arranged at equal intervals around the contact pressure sensor is used. When pressure is applied to the sensor, the width of the gap changes based on the pressure, so the gap can be measured. The gap can be measured using Fabry-Perot interferometry using optical fibers. Examples of sensors using optical interferometry include the sensor used in Abbott's TactiCath Quartz Ablation System N. The contact pressure sensor is preferably attached to the tip of the catheter. The contact pressure sensor is connected to a power source and an electric potential measuring device by lead wires arranged inside the catheter, and the signal from the contact pressure sensor can be detected by the electric potential measuring device.

[0039] Mechanical properties of myocardial tissue As described above, the catheter of the present invention includes a sensor for measuring LI and a sensor for measuring CF, and can measure both simultaneously.

[0040] LI and CF can be used to evaluate the mechanical properties of myocardial tissue, which refer to comprehensive properties based on the mechanical structure of the myocardium, including the stiffness, deformability, and thickness of the myocardial tissue.

[0041] Hooke's law is a law that governs the elasticity of elastic bodies. In Hooke's law, which is expressed as E=σ / ε, E represents the strength of the elastic body (elastic modulus), σ represents strain, and ε represents stress.

[0042] Materials for which Hooke's law applies are called linear elastic materials (Hooke's elastic materials). Cardiac muscle tissue is also considered to be a linear elastic material for which Hooke's law applies as an approximation when strain and stress are below a certain level, i.e., in the elastic range.

[0043] The LI measured by the LI measurement sensor included in the catheter of the present invention reflects the strain of the myocardial tissue corresponding to the distance between the catheter tip and the myocardial tissue, and the CF measured by the CF sensor reflects the stress generated in the myocardial tissue due to being pressed by the catheter.

[0044] Therefore, according to Hooke's law, the value obtained by dividing CF by LI (CF / LI) represents the mechanical property, i.e., elasticity, of myocardial tissue. CF / LI represents the slope of a graph when measurement results are plotted with LI on the horizontal axis and CF on the vertical axis.

[0045] In the present invention, the mechanical properties of myocardial tissue can be monitored by calculating CF / LI from the measured CF (g) and LI (Ω). Since LI reflects the distance between the catheter tip and the myocardial tissue, it can also be expressed as distance (mm) by formulating the relationship between impedance and distance. For example, LI and CF can be measured at multiple points, a regression line can be found between the LI and CF values, and the slope of the line can be used as an index to calculate the myocardial mechanical properties.

[0046] Using CF / LI as an index, it is possible to evaluate whether the myocardial tissue whose mechanical properties have been monitored is hard or soft, and the results of this evaluation can determine the conditions for myocardial ablation, including the magnitude of the input when high-frequency current is applied, the duration of current application, contact pressure, angle, number of times, and temperature measurements of other organs.

[0047] However, the ablation conditions cannot be determined univocally from the CF / LI value, and a doctor must make an appropriate decision based on the patient's condition, etc. Therefore, the monitoring method using the catheter of the present invention is also a method for obtaining auxiliary data for determining the ablation conditions.

[0048] If the catheter including the LI measurement sensor and CF measurement sensor of the present invention is an ablation catheter with components for ablation, ablation can be performed under the determined conditions. If the catheter including the LI measurement sensor and CF measurement sensor of the present invention is a monitoring catheter without components for ablation, ablation can be performed using a separate ablation catheter. For example, the mechanical properties of myocardial tissue can be monitored to determine the ablation conditions, and then, after a certain period of time, ablation can be performed using the ablation catheter.

[0049] In this way, by monitoring the mechanical properties of myocardial tissue and determining the ablation conditions before performing ablation, it is possible to reduce side effects such as cardiac tamponade induced by intratissue steam explosion, pulmonary vein stenosis or obstruction, phrenic nerve paralysis, esophageal disorders, and cerebral embolism due to thrombus formation.

[0050] Devices including catheters The catheter-containing device of the present invention includes a catheter including an LI measurement sensor and a CF measurement sensor, and may further include a high-frequency generator, high-frequency transmission means, a potential measuring device connected to a potential measurement electrode via a lead wire, and a power source connected to a current-carrying electrode via a lead wire. It may also include a device that receives and stores the LI measured by the LI measurement sensor and the CF measured by the CF measurement sensor included in the catheter, and a device that calculates the mechanical properties of myocardial tissue from the LI and CF. The calculation device is also a data processing unit that processes the LI and CF data. It may also include a display device that displays data related to the calculated mechanical properties.

[0051] The LI and CF measured by the LI and CF measuring sensors in the catheter are converted into electrical signals and sent to a data processing unit, which is a calculation device (calculation unit). The data processing unit processes the received data and sends the processed data to a display unit, which displays the data. The data processing unit can be a personal computer or the like, and may include a memory for recording the LI and CF, a central processing unit (CPU) for processing the data, and a storage device such as a hard disk or flash memory for storing the conditions and parameters required for calculation processing in the central processing unit and for storing the calculation results. The display unit also includes a monitor or printer for displaying the data.

[0052] A physician performing catheter ablation can determine the ablation conditions using the obtained information on the mechanical properties as auxiliary information. [Example]

[0053] The present invention will be specifically explained by the following examples, but the present invention is not limited to these examples.

[0054] Ablation catheter and local impedance (LI) measurement A 4 mm open-irrigated ablation catheter (IntellaNav MiFiOI®) with three microelectrodes integrated into the distal tip electrode was used for the experiments. This catheter has a dome electrode and three microelectrodes integrated into the distal tip electrode, with three equally spaced 0.8 mm diameter microelectrodes located 2 mm from the catheter tip. Local impedance was measured from the ablation catheter's microelectrodes (IntellaNav MiFi OI) by driving a non-excitatory alternating current (5.0 A, 14.5 kHz) between the microelectrodes and the distal tip electrode to generate a local potential field. As a result, three LIs were measured, and only the maximum LI was used for analysis. The ablation catheter (IntellaNav MiFiOI®) cannot measure contact force (CF). Therefore, CF was measured using a pressure-current transducer (load cell) as described in the next section.

[0055] In vitro experimental setup For all experiments, porcine myocardial tissue was extracted within 48 hours of dissection. The tissue was fixed on a stage in a water pool (Figure 4). A saline solution was prepared in the water pool using 20 g of salt per 10 L of water to achieve an initial LI of 90 Ω. The saline solution in the water pool was maintained at 37 °C using a thermostat system (Thermo-Mate BF-400, Yamato Scientific Co., Ltd., Tokyo, Japan). The saline solution was circulated across the surface of the myocardial tissue at a flow rate of 5 L / min to simulate blood flow. The tip of the catheter was fixed to a support post 10 mm distal to the fourth electrode, and the support post was connected to a load cell (DPU-2N, Imada Co., Ltd., Toyohashi, Japan) to measure the contact force (CF) on the catheter tip over time. The voltage waveform from the load cell was recorded using a 16-bit digital encoder (DP850, Yokogawa Electric Corporation, Tokyo, Japan). A scale was used to calibrate the contact force (CF) at the catheter tip and the load cell voltage values ​​ranging from 0 to 30 g. A video camera with a frame rate of 24 fps was used to record the position of the catheter tip.

[0056] Ablation Protocol A radiofrequency (RF) system (Rhythmia Mapping system, Boston Scientific) was used. Porcine myocardial left ventricular tissue was fixed on a stage in a water pool. Radiofrequency lesions were created on the epicardium of the left ventricle (LV). Radiofrequency ablation was performed at 30 watts of power and for 30 seconds. CF (0g, 5g, 10g, 20g, and 30g) and catheter angle (30°, 45°, and 90°) were varied in each set (120 lesions in total, n = 8 each). The catheter angles of 90°, 45°, and 30° relative to the porcine myocardial tissue surface were assessed with a protractor. All lesions were evaluated using the initial LI (LI increase) and LI decrease as ablation parameters.

[0057] RF lesion creation and measurement After creating a radiofrequency lesion on the LV epicardium, a cross section was cut at the center of the surface lesion, and macroscopic images were taken. Using image analysis software (Image J, free software), the size of all lesions for each catheter angle was evaluated as maximum lesion width (MW), maximum superficial width (SW), and maximum lesion depth (MD) (Figures 3A, 3B, and 3C). To ensure objectivity, the average of the lesion measurements from two individuals was used. Representative lesions were fixed in formaldehyde for approximately 1 week within 1 hour after the ablation procedure.

[0058] statistical analysis All statistical analyses were performed using JMP 14 software (SAS Institute Inc, Cary, NC, USA). Data are presented as mean ± standard error (SE) for continuous variables. The significance of the relationship between lesion size (maximum lesion width, maximum surface width, and maximum lesion depth) and different contact angles, CF, initial LI, and LI decline was assessed by analysis of variance. Differences between the three catheter angle groups (30°, 45°, and 90°) were analyzed using Tukey's HSD test. The statistical significance level was set at p<0.05.

[0059] Results and Discussion As shown in Figure 4, the catheter was pressed against the porcine myocardial tissue, and the catheter displacement (strain), contact pressure, and local impedance were continuously measured.

[0060] Generally, stress and strain behavior changes depending on the mechanical properties of an object, and a method is used to calculate the elastic modulus of the object from a stress-strain diagram. Local impedance has previously been reported to correlate with the positional relationship between the catheter and myocardial tissue, suggesting that strain can be inferred from local impedance. Figure 5 shows the relationship between contact pressure and local impedance measured in the left ventricle (LVepi1-3) and right ventricle (Rvepi1-3). Continuous changes are plotted as the catheter is pressed downward in Figure 4. The left ventricle, which pumps blood throughout the body, is the thickest and stiffest tissue in the heart. In contrast, the right atrium and left atrial walls are thin. Our results revealed that differences in the mechanical properties of these myocardial tissues can be interpreted as differences in the coefficients of the approximation equations for contact pressure and local impedance. Using this approach, we believe that simultaneous measurement of contact pressure and local impedance will enable intraoperative diagnosis of the myocardial wall. [Industrial Applicability]

[0061] The catheter of the present invention can be used for ablation of myocardial tissue. [Explanation of symbols]

[0062] 1 Ablation catheter 2. Myocardial tissue 3. Current-carrying return electrode 4. High-frequency cauterization device 5 Catheter 6 electrodes 7. Microelectrodes

Claims

1. 1. A method for monitoring myocardial mechanical properties related to myocardial stiffness to determine ablation conditions when performing catheter ablation for treating arrhythmia, comprising: A method for monitoring myocardial mechanical properties by calculating them from two parameters: local impedance (LI) near the catheter tip, which is measured with a local impedance measurement sensor installed at the catheter tip to estimate the distance between the catheter tip and the myocardium, and contact pressure (CF) at the catheter tip, which is measured with a contact pressure measurement sensor installed at the catheter tip to evaluate the contact state between the myocardium and the catheter.

2. 2. A method for monitoring myocardial mechanical properties according to claim 1, wherein LI and CF are measured at multiple points, a regression line is determined for the LI and CF values, and the slope of the line is used as an index to calculate myocardial mechanical properties.

3. 3. A catheter for use in the method of claim 1 or 2, having a plurality of electrodes near the tip of the catheter for measuring LI, and further having a sensor for measuring CF.

4. The catheter of claim 3, which is an ablation catheter.

5. 1. An apparatus for monitoring myocardial mechanical properties related to myocardial stiffness in order to determine ablation conditions when performing catheter ablation for treating arrhythmia, comprising: (i) a catheter having a plurality of electrodes near the tip of the catheter for measuring LI and further having means for measuring CF; (ii) a calculation means for calculating myocardial mechanical properties from the LI and CF measured by the catheter of (i); and (iii) a display unit for displaying the myocardial mechanical properties analyzed by the computing means; A device having:

6. The device of claim 5 , wherein the catheter is an ablation catheter.

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