Cardiac device

Abstract

A cardiac device comprising a transmitter (10) configured to emit at least one wave; a probe (12) configured to measure a shear wave caused by the wave from the transmitter (10); a detector (14) configured to detect a systole in an electrocardiogram signal; and an estimator (16) configured to determine a propagation rate of a plurality of shear waves caused by wave transmission in a plurality of directions toward a heart of a patient during at least one cardiac cycle, determine a shear wave having a maximum propagation rate during the systole using the detector (14) and derive a principal active cardiac stress response (160) therefrom.

Description

Technical Field

[0001] This invention relates to the field of cardiac measurement, and more specifically to the field of non-invasive cardiac measurement. Cardiac measurement includes the measurement of physical parameters, particularly mechanical parameters, of a patient's heart. Background Technology

[0002] Recent advances in imaging (particularly ultrasound or magnetic resonance imaging) have made it possible to obtain parameters that were previously only measurable through in situ methods. Such in situ methods involve surgical intervention or catheterization into the heart. Therefore, these methods are invasive and limiting. Furthermore, they can only be performed in suitable facilities with strict regulations.

[0003] Conversely, non-invasive measurements are easier to perform. However, these measurements do not allow for the measurement of all useful or readily available parameters. For example, known methods for obtaining radial artery blood pressure measurements use sensors placed close to the patient's skin, such as via a wristband, finger sensor, or smartwatch. However, the link between radial artery blood pressure and physical parameters within the heart, such as central blood pressure, is imprecise and indirect.

[0004] Another known method involves measurements via magnetic resonance or ultrasound cardiac elastography. This technique is non-invasive and is used to measure the apparent stiffness of cardiac tissue. Apparent stiffness is a parameter that varies during a heartbeat and depends on the measurement point. Theoretically, this apparent stiffness could be correlated with other useful cardiac parameters such as elastic modulus, cardiac pressure, and tissue stress. However, there is no direct link between this measurement and these cardiac parameters. Correlations between apparent stiffness and cardiac pressure have been observed, but they vary from person to person.

[0005] Therefore, there is no known method to obtain useful cardiac parameters non-invasively. Summary of the Invention

[0006] The present invention improves upon this situation. To this end, the present invention proposes a cardiac device comprising: a transmitter configured to emit at least one wave; a probe configured to measure shear waves induced by the wave from the transmitter; a detector configured to detect the systolic phase in an electrocardiogram signal; and an estimator configured to determine, during at least one cardiac cycle, the propagation rates of multiple shear waves induced by wave transmission in multiple directions toward the patient's heart, using the detector to determine the shear wave with the maximum propagation rate during the systolic phase and derive active cardiac stress therefrom.

[0007] This device is advantageous because it allows for direct acquisition of active stress within the heart tissue. Active stress is the force per unit area. This active stress allows for the direct and non-invasive acquisition of a large number of useful cardiac parameters. For example, intraventricular pressure can be derived from active stress. Cardiac symptoms can also be detected through active stress measurements; for example, the sequelae of infarction can be observed.

[0008] In various alternative embodiments, the device may have one or more of the following features:

[0009] - The cardiac device includes a calculator configured to determine ventricular pressure based on ventricular wall thickness, ventricular cavity radius, and active stress determined by an estimator.

[0010] The cardiac device includes an image analyzer configured to determine ventricular wall thickness and ventricular cavity radius based on at least one cardiac image.

[0011] - At least one heart image was obtained from shear wave imaging.

[0012] The cardiac device also includes an imager configured to provide shear wave imaging based on at least one shear wave measured by a probe.

[0013] -At least one wave from the transmitter is compressed ultrasound.

[0014] The transmitter and probe are implemented by a two-dimensional ultrasound echocardiography probe having a probe orientation defining the propagation direction, which can rotate about the propagation direction, and wherein the estimator is configured to determine the maximum propagation rate based on measurements performed by the probe in three coplanar and non-collinear directions.

[0015] - The transmitter and probe are implemented using a three-dimensional ultrasonic probe.

[0016] - A three-dimensional ultrasound probe is a three-dimensional ultrasound echocardiography probe. Attached Figure Description

[0017] Other features and advantages of the invention will be described in detail in the following description with reference to the accompanying drawings, wherein:

[0018] -

【 Figure 1 The diagram shows a schematic view of a cardiac device according to the present invention.

[0019] -

【 Figure 2 [This shows] Figure 1 A schematic view of the cardiac device in a construction for measuring ventricular pressure, and

[0020] -

Figure 3

[0021] The accompanying drawings essentially contain elements with defined properties. Therefore, they can be used not only to aid in understanding the invention, but also, where appropriate, to help in its interpretation.

[0022] Appendix A, containing mathematical formulas, is appended to the instruction manual. This appendix forms part of the instruction manual.

[0023] Now for reference Figure 1 .

[0024] The cardiac device 1 according to the present invention includes a memory 2, a transmitter 10 and a probe 12.

[0025] Memory 2 can be any type of data storage suitable for receiving digital data: hard disk drive, solid-state drive (SSD), any form of flash drive, random access memory, magnetic drive, cloud or local distributed storage, etc. Data stored in memory 2 can be erased after the cardiac device 1 has performed its tasks, or it can be saved. Data computed by the cardiac device can be stored in memory 2 or any similar type of storage.

[0026] Techniques have been developed for non-invasive observation of anisotropic (e.g., fibrous) media using ultrasound. For example, patent application PCT / FR2015 / 050058 relates to measuring the mechanical properties within anisotropic media by observing the propagation of ultrasound in the anisotropic medium.

[0027] In this configuration, transmitter 10 is a device capable of emitting ultrasonic waves. After the ultrasonic waves emitted by transmitter 10, directed towards the fibrous tissue 4 (e.g., the wall of the heart 6), enter the fibrous tissue, in response to this entry, the ultrasonic waves cause shear waves to propagate within the fibrous tissue along a plane orthogonal to the direction of ultrasonic wave propagation. As described in patent application PCT / FR2015 / 050058, this propagation is observed by probe 12 via compressed ultrasonic waves emitted at a higher rate.

[0028] The cardiac device 1 also includes a detector 14 and an estimator 16. The detector 14 determines multiple moments during which the observed heart is in systole (i.e., during cardiac contraction). The estimator 16 is connected to the transmitter 10, the probe 12, and the detector 14, so that the estimator 16 can receive data therefrom. The estimator 16 can derive one or more physical parameters from this data, specifically the active stress 160 of the cardiac tissue.

[0029] To perform propagation measurements, transmitter 10 and probe 12 are brought into contact with the patient's skin (where the heart 6 will be observed) and pointed towards the latter. Transmitter 10 and probe 12 work together to observe the propagation of shear waves within the cardiac tissue.

[0030] Transmitter 10 generates a focused ultrasound beam in a short time in a direction toward the heart 6. When the ultrasound beam reaches the heart, it causes displacement of the heart tissue 4 under the action of acoustic radiation pressure. This displacement takes the form of a shear wave, which propagates within the heart tissue 4 in a direction substantially orthogonal to the transmission direction.

[0031] Probe 12 observes the propagation of shear waves. For this purpose, probe 12 emits ultrasound waves in the form of compressed waves towards the heart 6 at a high rate. These ultrasound waves are reflected by the deformed heart tissue 4 under the action of the shear waves. The reflected waves are detected by probe 12, allowing observation of the displacement of the heart tissue 4. Probe 12 emits ultrasound waves at rates greater than 300 Hz or even 500 Hz. The propagation measurement of each individual shear wave can be completed within approximately a few milliseconds. Therefore, probe 12 can observe the propagation of shear waves within the heart tissue 4 with high accuracy and hundreds of times per second. Probe 12 further determines the propagation rate of the shear waves. Probe 12 can further correlate the determined propagation rate of the shear waves with their propagation direction.

[0032] For simultaneous operation, transmitter 10 and probe 12 can be controlled by a user and / or a controller. In the example described herein, transmitter 10 and probe 12 are interconnected for communication.

[0033] The applicant has observed that the propagation rate of shear waves is greatest within fibrous cardiac tissue when they propagate in a direction tangential to the direction of the tissue fibers. Therefore, by performing multiple propagation rate measurements in different propagation directions, the orientation of the fibers in the fibrous tissue and the propagation rate of the shear waves along these fibers can be determined.

[0034] More specifically, the problem of determining the propagation of shear waves along fibers can be summarized in the form of formula (1) in Appendix A, also known as the Christoffel formula. In this formula, the first term is also called the Christoffel matrix M, r is the density of the heart tissue, F is the polarization vector of the wave, and V is the propagation speed of the plane wave.

[0035] The applicant discovered during his work that, during systole, the active tension term dominates the stress tensor of the fibrous cardiac media. This enabled him to reformulate the Christopher matrix M of Equation (1) into the general form of Equation (2) in Appendix A, where n1 is the cosine of the angle between the wave propagation direction and the fiber direction, and s1D This is active stress. In this formula, matrix M is represented in a reference frame, and its first vector is the fiber direction. By focusing on s... 1D *n1 2 The applicant derives formula (3) by substituting the fiber transverse polarization terms (the second and third terms on the diagonal of matrix M) into formula (1) in Appendix A. Then, the applicant establishes the relationship between the maximum propagation rate, cardiac tissue density, and active stress, expressed in the form of formula (4) in Appendix A, which corresponds to the case where n1 equals 1.

[0036] In this case, the density r is approximately equal to 1,060 kg / m³. 3 The density *r* shows little variation between individuals because of the high proportion of water within heart tissue. Therefore, the applicant's work can be used to measure active stress in humans.

[0037] To determine the active stress 160, the systolic phase must first be identified. For this purpose, the detector 14 determines the systolic phase based on the electrocardiogram (ECG) signal 140. In this case, the ECG signal 140 comes from an ECG machine 142 integrated into the cardiac device 1. Alternatively, the ECG signal 140 may originate from an external device to the cardiac device 1 and be stored in the memory 2. This alternative embodiment is not shown in the figures.

[0038] The contraction period lasts from 200 to 400 milliseconds. Given that the duration of measurements that the transmitter 10 and probe 12 can perform is on the order of milliseconds, a large number of propagation rate measurements can be performed in a single contraction period.

[0039] In this context, the estimator 16 is a program executed by the computer's processor. Alternatively, it can be implemented in a different manner using a dedicated processor. The term "processor" must be understood to mean any processor suitable for the data processing operations described herein. Such processors can be produced in any known manner and in the form of: personal computer microprocessors, field-programmable gate arrays (FPGAs) or system-on-chip (SoC) type dedicated chips, grid computing resources, microcontrollers, or any other form suitable for providing the computing power required to perform the operations described below. One or more of these elements can also be produced in the form of dedicated electronic circuits, such as application-specific integrated circuits (ASICs). Combinations of electronic circuits and processors can also be considered.

[0040] Estimator 16 receives a set of propagation rates determined by probe 12, each propagation rate being associated with the propagation direction of the shear wave therein. Estimator 16 receives information indicating the contraction period from detector 14. Based on this set of propagation rates, estimator 16 determines the maximum propagation rate of the shear wave during the contraction period.

[0041] To this end, a user or external controller controls the direction of wave emission from transmitter 10, thereby enabling multiple propagation rate measurements. Based on these measurements, estimator 16 determines the maximum propagation rate of the shear wave within the heart tissue 4, i.e., the direction of the fibers in the heart tissue 4.

[0042] To this end, estimator 16 can perform multiple propagation rate measurements in multiple propagation directions distributed in a plane tangent to the heart wall and take the maximum value among the measured propagation rates. For example, the multiple propagation directions can be selected such that their angular distribution is substantially uniform. Estimator 16 can further use formula (3) to interpolate the sine wave with at least three propagation rate measurements obtained from the coplanar and non-collinear propagation directions of the wave emitted from transmitter 10, and obtain the maximum propagation rate of the shear wave within the heart tissue 4.

[0043] After determining the maximum propagation rate, estimator 16 derives the active stress 160 from formula (4) in Appendix A.

[0044] In a first embodiment of the invention, the transmitter 10 and probe 12 are implemented in a two-dimensional ultrasound echocardiography probe. Ultrasound waves are emitted by the transmitter 10 and focused onto the heart tissue. The probe 12 emits unfocused waves at a very high rate to image the propagation of shear waves in a plane. By rotating the plane substantially about the axis of the main probe, the ultrasound waves scan a cone or a portion of a cone around the axis of the main probe. This allows the user to manually rotate the two-dimensional ultrasound echocardiography probe to obtain multiple propagation rate measurements in at least three propagation directions. The measurement of propagation directions can be manual, automatic, or guided. Thus, the maximum propagation rate of the shear waves can be determined within seconds and through simple processing operations, as described above. The ability to use the transmitter 10 and probe 12 in a two-dimensional ultrasound echocardiography probe is highly advantageous because these probes are inexpensive and available in most medical facilities. More generally, in this embodiment, the entire heart device 1 can be implemented in a conventional two-dimensional ultrasound echocardiography apparatus.

[0045] In the second embodiment, the transmitter 10 and probe 12 are implemented in a three-dimensional ultrasound echocardiography probe. In this configuration, the transmitter 10 emits ultrasound waves in multiple propagation directions, scanning a non-zero solid angle, such as a cone around the axis of the main probe. In this case, the maximum propagation rate can be measured without moving or rotating the three-dimensional ultrasound echocardiography probe. This makes the determination of active stress more reliable, rapid, and accurate. Furthermore, the cardiac device 1 in this configuration has the advantage of being able to be implemented in a conventional three-dimensional ultrasound echocardiography device.

[0046] In the third embodiment, the cardiac device 1 is implemented in a stand-alone device of the type described in patent application PCT / FR2015 / 050058, which differs from an echocardiography device. This dedicated device provides propagation measurements nearly equivalent to those provided by a three-dimensional echocardiography probe, while being simpler in design and less expensive. The transmitter 10 and probe 12 are configured to perform maximum propagation rate measurements without moving or rotating the stand-alone device. The portion of the stand-alone device containing the transmitter 10 and probe 12 can be smaller than the intercostal distance. This smaller size increases the accuracy of the measurements performed by the probe 12. Implementing the cardiac device 1 in this type of stand-alone device simplifies its manufacture. Furthermore, in this configuration, the cardiac device 1 can interface with a separate conventional medical device to which it can transmit data, specifically the determined active stress 160.

[0047] Now for reference Figure 2 .

[0048] The applicant has discovered a method for determining ventricular pressure from active cardiac stress. To this end, the applicant has modeled the mechanical properties of a roughly spherical ventricular cavity of thickness d and radius R under static equilibrium. Under pressure p, where e = d / R, the applicant derived formula (5) in Appendix A. This formula (5) relates the active stress 160, thickness d, and radius R to the internal pressure 220, where a cor This is a correction factor. Thickness d and radius R are the geometric data of the ventricular cavity.

[0049] In the embodiments described herein, the cardiac device 1 includes a calculator 22. The calculator 22 receives active stress 160 and geometric data 202 from an estimator 16. The calculator 22 determines the ventricular pressure based on the active stress 160 and geometric data 202 using formula (5) in Appendix A.

[0050] The cardiac device 1 may optionally include an image analyzer 20 for generating geometric data 202.

[0051] Image analyzer 20 retrieves image data 200 from the ventricular cavity of the observed heart. Image analyzer 20 derives geometric data 202 of the ventricular cavity from it. Image analyzer 20 determines at least the ventricular wall thickness d and the ventricular cavity radius R.

[0052] Image data 200 can be generated using cardiac imaging methods such as ultrasound (echocardiography), magnetic resonance imaging (MRI), computed tomography (CT), radiography (nuclear medicine), or any other non-invasive cardiac imaging method. The image data can be stored in memory 2. In the example described herein, image data 200 originates from a third-party device.

[0053] Geometric data 202 and, where appropriate, image data 200 are stored in memory 2.

[0054] In the first embodiment (and correspondingly the second embodiment), the image analyzer 20 is connected to a two-dimensional echocardiography probe (and correspondingly a three-dimensional echocardiography probe), and the latter provides the necessary image data to the image analyzer 20. In the third embodiment, the cardiac device 1 also provides the necessary image data to the image analyzer 20. The image analyzer 20 may utilize machine learning methods or algorithms to analyze the image data. For example, the image analyzer 20 may include a neural network (especially a convolutional neural network) to identify shapes within the image data from which geometric data can be derived.

[0055] By defining the contours of the heart's inner wall (endocardium) and outer wall (epidermis), echocardiographic images of the heart can be used to measure the ventricular wall thickness (d) and ventricular cavity radius (R). This segmentation can be done manually or automatically.

[0056] Alternatively, images from a time-motion (TM) echocardiography probe can be obtained, representing the echocardiographic line as a function of time. This image provides a visualization of the heart wall, which can then be segmented manually or automatically to calculate the ventricular wall thickness d and the ventricular cavity radius R.

[0057] Given that the ventricular cavity is approximately spherical, formula (5) includes a correction factor a. cor The correction factor can be predetermined, for example, through digital simulation or by measurement on a group of patients. Alternatively, the correction factor can be determined during processing by a component of the cardiac device 1 capable of geometric or image analysis. For example, this analysis can be performed by the image analyzer 20 based on image data 200. In the example described herein, the correction factor can vary between 0.6 and 1, preferably between 0.75 and 0.95, and even more preferably, it can be set to 0.9. The applicant estimates the variability of the correction factor between individuals to be approximately 10%. This variability is far less than that of known noninvasive pressure measurements. The use of the calculator 22 and the image analyzer 20 thus enables a noninvasive measurement of ventricular pressure 220 with significantly higher accuracy than conventional methods.

[0058] The non-invasive measurement of ventricular pressure p by cardiac device 1 makes it possible to diagnose a variety of conditions using inexpensive equipment and simple medical procedures. For example, heart failure can be detected by measuring ventricular pressure using cardiac device 1 implemented in a two-dimensional echocardiogram probe. This non-invasive pressure measurement can also be used for cardiac resynchronization therapy.

[0059] The image analyzer 20 and the calculator 22 are programs executed by one or more processors of the computer. Alternatively, they can be implemented in different ways using a dedicated processor or on a separate machine.

[0060] Now for reference Figure 3 .

[0061] In this embodiment, the cardiac device 1 includes an imager 24 for generating image data. When the cardiac device 1 is implemented in an echocardiography apparatus, the imager 24 includes a portion of the echocardiography apparatus that performs one or more echocardiograms.

[0062] The use of active stress to measure ventricular pressure has already been described. The sequelae of infarction can also be observed from contractile force (i.e., the maximum value of active stress). This contractile force measurement can be performed throughout the entire systolic cycle. Therefore, a contractile force below normal indicates that the area has been affected by infarction.

[0063] Appendix A

[0064] (1) MF-rV 2 F = 0

[0065] (2) [Math.1]

[0066]

[0067] (3) V=n1.(s 1D / r) 1 / 2

[0068] (4) s 1D =rV 2

[0069] (5) p = a cor .es 1D

Claims

1. A cardiac device, the cardiac device comprising: A transmitter (10) configured to transmit multiple waves; A probe (12) configured to measure shear waves caused by waves from the transmitter (10); a detector (14) configured to detect the systolic phase in an electrocardiogram signal; And an estimator (16) configured to determine, during at least one cardiac cycle, the propagation rates of a plurality of shear waves caused by the transmission of the plurality of waves in a plurality of directions toward the patient’s heart, the estimator being further configured to use the detector (14) to determine the shear wave among the plurality of shear waves that has the maximum propagation rate during the systolic phase and to derive active cardiac stress (160) from the maximum propagation rate.

2. The cardiac device according to claim 1, the cardiac device comprising a calculator (22) configured to determine ventricular pressure (220) based on ventricular wall thickness, ventricular cavity radius and active stress (160) determined by the estimator (16).

3. The cardiac device according to claim 2, the cardiac device comprising an image analyzer (20) configured to determine the ventricular wall thickness and the ventricular cavity radius based on at least one cardiac image.

4. The cardiac device according to claim 3, wherein, The image analyzer (20) is configured to determine the ventricular wall thickness and the ventricular cavity radius based on at least one cardiac image derived from shear wave imaging.

5. The cardiac device according to claim 4, further comprising an imager (24) configured to provide shear wave imaging based on at least one shear wave measured by the probe (12).

6. The cardiac device according to any one of claims 1 to 5, wherein, The at least one wave from the transmitter (10) is a compressed ultrasonic wave.

7. The cardiac device according to any one of claims 1 to 5, wherein, The transmitter (10) and the probe (12) are implemented by a two-dimensional echocardiography probe having a probe orientation that defines the propagation direction and can rotate about the propagation direction, and wherein the estimator (16) is configured to determine the maximum propagation rate based on measurements performed by the probe (12) in three coplanar and non-collinear directions.

8. The cardiac device according to any one of claims 1 to 5, wherein, The transmitter (10) and the probe (12) are implemented by a three-dimensional ultrasonic probe.

9. The cardiac device according to claim 8, wherein, The three-dimensional ultrasound probe is a three-dimensional ultrasound echocardiography probe.

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