Determination of cardiac compression location from dermal electrode signals

Abstract

A pad carrying an array of ECG and / or EIT electrodes can be used to measure ECG signal amplitudes and AMSA and / or EIT signals, a signal analyzer determines a cardiac position with respect to the pad, and an indication of cardiac position with respect to indicia can be provided on a top surface of the pad for output to the user to guide in performing chest compressions during CPR. The pad may integrate a defibrillator electrode. The apparatus may be an automated external defibrillator (AED).

Description

DETERMINATION OF CARDIAC COMPRESSION LOCATION FROM DERMAL ELECTRODE SIGNALS

[0001] This patent application is a continuation-in-part of US patent application 18 / 972,066 filed December 6, 2024, now pending, that claims priority to US provisional patent application 63 / 606,733 filed December 6, 2023 and titled “Autonomous Cardiopulmonary Resuscitation Device”, the contents of which are hereby incorporated by reference in their entirety.Technical Field

[0002] This patent application relates to tools used for cardiopulmonary resuscitation (CPR) and tools used to analyze dermal electrode signals such as electrocardiogram (ECG) signals or electrical impedance tomography (EIT) signals.Background

[0003] Despite recent technological advances, rates of survival of a patient suffering from cardiac arrest to hospital discharge are still under 10% in most regions of the world. Chest compressions, in cardiac arrest, are currently performed either manually or automatically by mechanical chest compression devices on the lower half of sternum at a specified rate and depth in accordance with American Heart Association (AHA) guidelines. However, patients may have different chest dimension, chest compliance, cardiac position, cardiac arrest etiology, and myocardial relaxation capacity. These characteristics are not currently accounted for during resuscitation. Recent literature has shown that optimal chest compression characteristics (site, rate, duty cycle, depth of compression and decompression) may be different from patient to patient. It is known that the position of chest compressions with respect to the patient’s cardiac position can play a significant role in the survival rate of the patient, namely survival is essentially zero if the position of cardiac compressions during CPR is merely a few centimetres away from the center of the left ventricle (Resuscitation, Volume 138, P8-14, May 2019, & Resuscitation, Volume 84, P1203-1207, September 2013).

[0004] CPR may be administered with measurement of a physiological parameter of the patient providing feedback as to whether chest compressions as currently administered arebeing effective. However, pre-CPR guidance specific to selecting a chest compression location corresponding to cardiac position for use during CPR is not available.Summary

[0005] In some embodiments, there is provided an apparatus comprising a pad carrying an array of ECG dermal electrodes configured to measure ECG signal amplitudes and AMSA, a calculator configured to calculate a cardiac position with respect to the pad, and an indicator configured to output the cardiac position relative to indicia provided on a top surface of the pad to guide the user in performing chest compressions during CPR. The pad may integrate a defibrillator electrode. The apparatus may be a stand-alone device, an automated external defibrillator (AED), a semi-automatic defibrillator or a monitor / defibrillator. One or more electrodes may be added as reference.

[0006] In some embodiments, there is provided an apparatus comprising one or more pads each carrying a plurality of surface electrodes configured to measure electrical impedance signal amplitudes, a calculator configured to calculate a cardiac position with respect to the pad, and an indicator configured to output the cardiac position relative to indicia provided on a top surface of the pad to guide the user in performing chest compressions during CPR. The pad may integrate a defibrillator electrode. The apparatus may be a stand-alone device, an automated external defibrillator (AED), a semi-automatic defibrillator or a monitor / defibrillator. One or more electrodes may be added as reference.

[0007] In this application, the calculation or the determination of the cardiac position or the location of the heart ventricles is understood to mean a position or a location that can serve as a guide for positioning effective cardiac compressions for CPR purposes. Optimal chest compressions may occur when the applied force is centered over the left ventricle, while avoiding pressure on the region where blood exits the heart, as such pressure may interfere with forward flow. Compressions applied to the right ventricle (which are likely to compress part of the left ventricle as well) may be less effective than compressions applied to the left ventricle, however, are more effective than compressions that miss the ventricles completely. In the case of locating using ECG signals, the locating is done using electrical impulses generated in the heart tissue that can then be related to the location where chest compressions are to take place. In the case of electricalimpedance signal detection, the ventricles as a whole may be detected and then the location where chest compressions are to take place, for example the left ventricle, may be related to the ventricles as a whole, or the detection may isolate specifically the left ventricle as the location for chest compressions.

[0008] In some embodiments, the pad may be used in patients with sinus rhythm who are at high risk of cardiac arrest. In such cases, the pad may inform the clinician of the optimal chest compression site to use in the event of a cardiac arrest. A temporary or permanent mark may be left on the skin to identify this site.

[0009] In some embodiments, there is provided an automated CPR apparatus comprising a mechanical chest compression device, a pad carrying an array of electrodes configured to measure signal amplitudes, a calculator configured to calculate a cardiac position with respect to the pad, and at least one of: an indicator configured to output an indication of cardiac position with respect to indicia provided on a top surface of the pad to guide positioning of the mechanical chest compression device during CPR, and a positioning actuator configured to respond to the calculated cardiac position to position the mechanical chest compression device during CPR.Brief Description of the Drawings

[0010] The invention will be better understood by way of the following detailed description of embodiments of the invention with reference to the appended drawings, in which:

[0011] Figure 1 is an illustration of a human chest showing the ribcage and the position of the heart within the ribcage;

[0012] Figure 2 is an illustration of heat anatomy showing the location of the ventricles;

[0013] Figure 3 is an illustration of electrode placement in a five electrode ECG configuration;

[0014] Figure 4A is a graph showing a typical ECG pulse of a healthy heart;

[0015] Figure 4B is a graph showing an ECG of a fibrillating heart;

[0016] Figure 5 is an illustration of electrode placement in a five electrode ECG configuration including a multi-electrode pad;

[0017] Figure 6A is an oblique view of a multi-electrode pad with position indicators onthe top surface;

[0018] Figure 6B shows an exploded view of the multi-electrode pad with segmented electrodes on a lower layer;

[0019] Figure 7A is a block diagram of a ventricle location determination apparatus using ECG signals;

[0020] Figure 7B is a block diagram of a ventricle location determination apparatus using EIT signals;

[0021] Figure 8A is a flow diagram showing steps involved in ventricle location determination based on ECG signals;

[0022] Figure 8B is a flow diagram showing steps involved in ventricle location determination based on EIT signals;

[0023] Figure 9 is a schematic illustration of a chest compression apparatus;

[0024] Figure 10 is an oblique view of a stretcher board; and

[0025] Figure 11 is an oblique view of a patient on a stretcher board with a chest compression apparatus.Detailed Description

[0026] As shown in Figure 1 , the apex of the heart is positioned at the bottom left while the atria are located above and to the right. As illustrated in Figure 2, the apex portion of the heart comprises the right and left ventricles, the right ventricle pumping blood to the lungs, and the left ventricle pumping blood to the rest of the body.

[0027] During CPR, a patient’s heart is no longer pumping well enough, and the patient typically loses consciousness. A chest compression over the ventricles can be used to push blood out of ventricles into the pulmonary artery and aorta. Relaxation of the compression can allow blood to refill the ventricles from the atria. The rate of chest compressions may be roughly two per second, and roughly every twelve compressions air is pushed into the lungs. The goal is to maintain sufficient oxygenated blood flow to the brain until such time as the heart may restart.

[0028] As mentioned above, if the location of chest compressions is not directed to the region of the ventricles, but instead over the atria or to a side of the ventricles, the flow of blood due to the chest compressions may be insufficient. In addition, optimal chestcompressions occur when the applied force is centered over the left ventricle, while avoiding pressure on the region where blood exits the heart, as such pressure may interfere with forward flow. While Figure 1 shows a typical or average location of the heart within the chest cavity, there is sufficient variation of this location from person to person to frequently adversely affect CPR efficacy. While an invasive blood pressure measurement or the exhaled carbon dioxide level at the end of expiration can inform the person performing CPR whether CPR is working or failing, it can be a challenge to determine how to make adjustments to the location of chest compressions when performing CPR in the case that it is failing.

[0029] In the following description, two ways to determine the optimal chest compression location over the left ventricle are described. The first way is to use ECG signals in which a pad carrying an array of surface electrodes to be placed over the heart area of the patient is used to determine the location of the left ventricle with respect to the pad. The second way is to use electrical impedance tomography (EIT) surface electrodes in a pad to be placed over the heart area of the patient to determine the location of the left ventricle with respect to the pad. EIT is a known technique for generating images of the lungs and heart, as for example is described in US patent application publication US2020 / 0138335 to Sender and for monitoring cardiopulmonary function as described in US patent application publication US2024 / 0008759 to Wi. Ventricles are chambers filled with blood and the impedance properties of blood are distinguishable from lung and other body organs or tissues. While EIT can be used for imaging, generating an image is not required for locating the left ventricle for the purposes of improving CPR. An advantage of EIT-based heart ventricle location over ECG-based heart ventricle location is that in certain electrical rhythms associated with cardiac arrest, the heart does not produce any ECG signals, whereas using EIT, the location of the ventricles is possible.

[0030] Figure 3 illustrates an example of placement of electrocardiogram (ECG) electrode placement on a patient in the case of five electrodes. ECG may be performed with more or fewer electrodes and their placement on the body varies in accordance with the chosen ECG technique.

[0031] Figure 4A illustrates an ECG signal from a single beat of a healthy heart, as is known in the art. For the purposes of determining the position of the left ventricle of apatient’s heart, Applicant proposes to use the signal strength or amplitude of the ECG signal as electrodes are at different locations on the body. For example, the V electrode may be at different positions over the heart region.

[0032] One of the most common cardiac rhythms during cardiac arrest is ventricular fibrillation. This rhythm is characterized by rapid, chaotic, and uncoordinated depolarization of myocardial cells in the ventricles. The rate is about 150 to 300 per minute and is illustrated in Figure 4B. Because of this, usual ECG waves (P-Q-R-S-T) as illustrated in Figure 4A cannot be identified. Since the electrical activity originates from the ventricles and the biggest myocardial mass is in the left ventricle, it is the applicants’ belief that the analysis of the electrical signals can help identify the left ventricle position non-invasively and allow optimal chest compression position early in cardiac arrest.

[0033] In sinus rhythm and pulseless electrical activity, the amplitude of the ECG signal (more precisely of the QRS waves) is associated with the electrodes position in relation to the heart. (Medical & Biological Engineering & Computing, Volume 52, P109- 119, 2014). This may be explained by the proximity to the heart ventricles and the ventricles’ mass (and thus the electrical potential).

[0034] To identify the optimal location, the applicants propose to use two different analyses. In the first analysis, the total amplitude (absolute maximum value + absolute minimum value) is calculated over multiple second window (e.g., 10 seconds). The electrode position with the highest amplitude is then identified as the optimal chest compression site.

[0035] In the second analysis, the amplitude spectrum area (the sum of products of frequencies and amplitude) of the ventricular fibrillation signal, over a multiple-second window (e.g. 10 seconds), is calculated for each electrode and the electrode with the highest amplitude spectrum area (AMSA) value is identified as the optimal chest compression site. To calculate the AMSA, an FFT is performed on the signal segments after a windowing function, such as a Hamming window, is applied to reduce spectral leakage. The frequency range of interest (for example 4-48 Hz) is then extracted based on the sampling frequency and FFT resolution. The amplitude spectrum is computed as the magnitude of the FFT output for each frequency bin within this range. Finally, the AMSA is obtained by summing the amplitude spectrum values, multiplied by thefrequency resolution. These analyses can be performed independently or simultaneously and repeatedly over time.

[0036] While using both of these two analyses is more reliable than using only one to determine the best location for performing chest compressions, for example over the left ventricle , it will be appreciated that a single analysis may suffice.

[0037] Another common cardiac rhythm during cardiac arrest is pulseless electrical activity (PEA). This rhythm is characterized by a sinusoidal electrical activity without mechanical activity. Because of this, usual ECG waves can be identified. Since the electrical activity originates from the ventricles and that the biggest myocardial mass is in the left ventricles, it is the applicants’ belief that the analysis of the electrical signals can help identify the left ventricle position non-invasively and allow optimal chest compression position early in cardiac arrest. These analyses can be performed simultaneously and repeatedly over time.

[0038] In this case, to identify the optimal location, the applicants propose to use two different analyses. The total amplitude (absolute maximum value + absolute minimum value is calculated over multiple second window (e.g. 10 seconds). The electrode with the highest amplitude is then identified as the optimal chest compression site. In the second analysis R-wave amplitude is measured for every electrical cycle. A mean R- Wave value is calculated over a multiple second window (e.g. 10 seconds). These analyses can be performed independently or simultaneously and repeatedly over time. The R-Wave is selected because its value is maximal over the left ventricle, whereas the S-Wave is maximal over the right ventricle (Medical & Biological Engineering & Computing, Volume 52, P109-119, 2014).

[0039] While multiple physiological and anatomical factors influence the QRS amplitude, the proximity of the ECG electrode to the heart directly impacts the QRS amplitude (the closer the electrode to the heart, the bigger the QRS amplitude). On an individual patient, the lead with the highest amplitude should represent the closest to the left ventricle. By repeating this analysis in multiple axis and with both antero-posterior and sterno-apical pads this would allow us to identify the closest electrode to the ventricle. This site may be chosen to perform chest compression to optimize left and right ventricular compression fraction and to minimize chances of left ventricular outflow trackcompression since this structure is in the upper part of the heart near the atria. This electrode may be identified by a visual clue (e.g., LED) to advise the resuscitator on the optimal chest compression site. The optimal compression site may also be transferred to the mechanical chest compression device to automatically place the compression arm at the optimal location.

[0040] While the apparatus described herein are for determining the position of the left ventricle in a patient having cardiac arrest, it will be appreciated that in a patient at risk of cardiac arrest, it is possible to pre-emptively mark a patient or identify in the patient the location of the left ventricle for receiving cardiopulmonary resuscitation (CPR) in the future. The method can involve collecting ECG signals from the patient with at least one electrode placed over a heart region on a chest wall at a plurality of positions. In the case of a functioning heart, the amplitude of the ECG signals can be taken from the QRS amplitude. This can be done with a plurality of electrodes 20, as for example with the multi-electrode pad, or by using a single moveable electrode 20. Then one can determine from an amplitude of the ECG signals a location of the left ventricle of the patient. An indication of the location can then be provided to a person for performing CPR on the patient. This indication can be stored in a database or an electronically readable medical bracelet and retrieved by EMT personnel. It can provide an image of the patient’s chest showing the location, or measurements of the location with respect to an anatomical reference such as the ribs or sternum. Alternatively, marking a skin of the patient with the location, for example using an indelible dye marker or tattoo can be used.

[0041] While it is possible to move a single electrode 20 over the heart region to determine where on the patient’s chest the strongest ECG amplitude is found, this is not suitable for cardiac arrest since chest compressions needs to start as soon as possible. As illustrated in Figure 5, it is preferred to provide an arrangement of electrodes 20, such as a matrix, with the goal of obtaining ECG signals from a variety of positions on the body so that such signals can be obtained during the application of chest compressions.

[0042] Figure 6A provides an example of a multi-electrode pad 20 that is to be adhered to the chest with a suitable conductive adhesive. Suitable conductive adhesive is known in the art of ECG electrodes. However, the large surface area pad 20 on the skin side is broken up into 9 electrodes (any number greater than 3 may be practical) 20a through 20i.

[0043] An exploded view of a combined ECG monitoring and defibrillator pad is presented in Fig. 6B. In one proposed embodiment of the invention, the defibrillator pad may be composed of multiple layers: a stimulating conductive polymer layer 1 , a monitoring polymer layer 2, a conductive metal layer 3, an insulating foam cover layer 4 and a LED layer 5. Pad 20 may be connected to a defibrillator / monitor using a stimulating wire 6 and a monitoring wire 7. The pad 20 may also contain multiple LEDs 8.

[0044] While the pad 20 is illustrated as having a three by three matrix, it will be appreciated that it can be larger without limitation, for example three by four, four by four, four by five, five by five, or larger.

[0045] Figure 7A is a block diagram of a proposed apparatus for determining ventricular position based on ECG signals. An ECG signal processor 30 is connected to ECG electrodes, for example a multi-position electrode 20 and the remaining ECG electrodes 22. A monitor 32 may be provided to display the ECG, for example the best quality or strongest amplitude ECG. The ECG signal obtained using one multi-position electrode 20 and the remaining ECG electrodes 22 from processor 30 is then analyzed by the amplitude measurement unit 40 to extract the desired amplitude parameter.

[0046] The ventricle location determination module 44 receives the amplitudes for the ECG measurements using the multi-position electrode 20 and calculates the ventricle position. The ventricle position or location determination process will be described below with reference to Figure 8A. For performing CPR, the ventricle position information is either provided to an interface unit for guiding a person performing CPR or to a positioning actuator unit 50. Knowledge of the position of the heart may alternatively be used for selecting defibrillator electrode locations, for example using unit 60 for defibrillator electrode position selection or guidance. Thus, a defibrillator device can direct a defibrillation charge to electrodes that are positioned on the patient so as to have the best result on the heart.

[0047] In some embodiments, unit 60 provides information for placing defibrillator electrodes, while in other embodiments, unit 60 is a defibrillator adapted to use the heart ventricle information from unit 44. When unit 60 is a defibrillator, it may use the pad 20 for the defibrillator electrodes, as illustrated by the dashed line in Figures 7A and 7B, and it will be understood that when the same electrodes are shared with the ECG 30 or the EIT 30’, thelatter devices may disconnect from the electrodes when a defibrillation pulse is delivered. Alternatively, the defibrillation electrodes may be separately provided on the pad 20 or 20’. The defibrillator 60 may use the location of the heart ventricles determined by unit 44 to decide on the selection of the electrodes to apply the impulse at a preferred location.

[0048] It will be appreciated that with a conventional AED used on an adult, the defibrillator pads are placed on the chest to allow for the defibrillator pulse to cause electrical current to flow through the whole region of the heart to cause the fibrillation of the heart muscles to stop. When the ventricles are located, the defibrillator pulse can be targeted to the heart muscles from the region of pad 20 or 20’ to back electrodes, such as electrodes 22 or 22’. Such a targeted pulse may be of lower power and may be less disturbing to the patient.

[0049] In the embodiment of Figures 7B and 8B, the surface electrodes are used to measure electrical conductivity, permittivity and / or impedance. EIT is a known technique that can be used for imaging.

[0050] As is explained in Wikipedia, electrical conductivity varies considerably among various types of biological tissues or due to the movement of fluids and gases within tissues. The majority of EIT systems apply small alternating currents at a single frequency, however, some EIT systems use multiple frequencies to better differentiate between normal and suspected abnormal tissue within the same organ. Typically, conducting surface electrodes are attached to the skin around the body part being examined. Small alternating currents are applied to some or all of the electrodes, the resulting equipotentials being recorded from the other electrodes. This process will then be repeated for numerous different electrode configurations and finally result in a two- or three-dimensional tomogram according to the image reconstruction algorithms used. Since free ion content determines tissue and fluid conductivity, muscle and blood will conduct the applied currents better than fat, bone or lung tissue. This property can be used to construct images. Compared to the conductivities of most other soft tissues within the human thorax, lung tissue conductivity is approximately five-fold lower, resulting in high absolute contrast.

[0051] In the present use of an EIT approach to locating ventricles (and, for example, more specifically the left ventricle) for CPR purposes, it will be appreciated that themeasurement technique may differ from typical E IT, for example instead of the source of the electrical current or potential need being small alternating currents applied between two surface electrodes while the remaining electrodes measure resulting equipotential responses, measurements may be limited to the powered electrodes. Also, the need to perform image reconstruction may be unnecessary when the electrode signals and their geometry may permit a direct determination of the location of the left ventricle.

[0052] In the example of Figure 7B, the apparatus can comprise a chest electrode pad 20’ that may be identical to the pad 20 of Figures 6A and 6B. However, in typical EIT imaging, the electrode array does not need a matrix or number of electrodes specifically over any region, and it will be appreciated that the left ventricle may be located using a different arrangement of the surface electrodes. A single or a number of opposed electrodes, for example located on a pad 22’ with electrodes disposed for example on opposite sides of the spinal column may be provided. Pad 22’ may have a shape or markings helping to guide the technician or user to place it with a middle line registered with the patient’s spinal column. The extent of the arrangement of electrodes on pad 22’ along the spinal column may be great enough to allow for locating the left ventricle even if the placement of pad 22’ is higher or lower than being perfectly centered at the level of the patient’s heart.

[0053] The electrodes on pad 22’ may not include the area of the spinal column itself since the spinal column has a lower conductivity or permittivity than the muscle adjacent the spinal column. However, when the pad 22’ includes electrodes over the area of the spinal column, the position of the spinal column itself may be detected, and this may be used to determine the location of the left ventricle since the spinal column and sternum can be expected to be aligned. In this case, the quality of the alignment of the pad 22’ with respect to the spinal column may not matter.

[0054] The EIT signal generator 30’ illustrated schematically in Figure 7B comprises the hardware for generating currents, such as alternating currents, to selected electrodes and optionally for measuring not only conductivity but also voltages or electric fields.

[0055] The EIT signal data acquisition unit 40’ illustrated schematically in Figure 7B may comprises a combination of hardware and software for detecting and recording currents and voltages as required from selected electrodes from pad 20’ and pad 22’.While not shown, unit 40’ may act as a controller for unit 30’.

[0056] As described above, a patient requiring CPR may have a heart that has an abnormal heart rhythm, such as ventricular fibrillation or pulseless electrical activity, or have an arrested heart that has no electrical activity (asystole) . In such cases, relying on ECG signals to locate the heart may be difficult or impossible. Using EIT signal data from unit 40’, ventricle location determination unit 44’ may process the data to determine the location of the left ventricle relative to the electrodes of at least pad 20’. Unit 44’ may be implemented using a computer processor and program code. As described above, unit 44’ may generate an image of the heart or it may more simply determine a most likely location of the left ventricle.

[0057] In the case that an image is generated to determine the location of the left ventricle, in the case of adults, the EIT surface electrodes may be placed around the chest in a single transverse plane between the 4th and 6th intercostal spaces. In this case, the chest electrode pad 20’ may comprise one or more bands of electrodes on the chest and include locations over the lungs, while the back electrodes 22’ may comprise one or more bands of electrodes on the chest and include locations over the lungs as well. In such a case, the pads 20’ and 22’ may be integrated into a common thoracic belt to be placed on the patient so that the surface electrodes are in contact with the patient’s skin.

[0058] With reference to Figure 8B, the sequence for determining the location of the left ventricle in the embodiment of Figure 7A is described. Any clothing may be removed from the patient’s torso or ribcage area to expose the skin at the locations where the surface electrodes are to be applied. While EIT electrodes for imaging the lungs may comprise a strap placed around the ribcage, the use of pads carrying multiple electrodes may be easier and more suited for the measurements used for locating the left ventricle. In the case of women patients, pads may be placed under bra straps to place electrodes in locations normally covered by a bra. In the case of pads being used, step ST may comprise positioning a pad of surface electrodes 22’ on a back of the patient, and step S2’ may comprise positioning a pad of surface electrodes 20’ on a sternum of the patient.

[0059] At step S3’, the signal generator 30’ (or the data acquisition controller 40’) may select a connection to specific electrodes to obtain signals that measure from different regions. At step S4’, the generator 30’ provides the EIT signals and at step S5’ the EITsignal data is recorded. At step S6’, the check is made whether enough injection and detection locations have been used to have sufficient EIT signal data.

[0060] As described above, step S7’ may determine the left ventricle location without generating an image of the heart or heart ventricles.

[0061] As in the embodiment of Figure 7A, in the embodiment of Figure 7B the location of the left ventricle is related to a reference on the body of the patient so as to serve as guidance for positioning the location of cardiac massage for CPR purposes.

[0062] In the embodiment of Figure 7B, the operation of interface or actuator 50 and the operation of optional unit 60 need not be any different from the embodiment of Figure 7A.

[0063] It will be appreciated that both ECG and EIT measurements can be done using the same or separate electrodes. ECG data may provide useful information and / or feedback about the state of the heart even if location information is obtained using EIT. Also using both techniques can increase confidence in the location information obtained.

[0064] It will be appreciated that the integration of the left ventricle’s location determination functionality into a conventional AED, semi-automatic defibrillator or monitor / defibrillator can improve the outcome of patients receiving CPR and being treated by an this device. It will be appreciated that a defibrillator device only helps patients whose hearts are in a state of shockable rhythm. In such a state, the heart is failing to provide adequate blood circulation, and the patient will lose consciousness. When an AED device is connected to a patient in cardiac arrest, the AED device may alert that the patient in not in a state of shockable rhythm, and that CPR is required. When CPR is performed, the heartbeat may return either as non-shockable or as shockable. When the returned heartbeat is shockable, the AED device may warn the person performing CPR to stop so that a defibrillation pulse may be discharged to the patient. Defibrillation serves to “reset” a heartbeat that is non-perfusing to become a regular heartbeat and is not used to restart an asystolic heart.

[0065] Therefore, by modifying at least one of the defibrillator electrodes of an AED to be a multi-electrode for ECG monitoring purposes, the AED device may not only alert that CPR is required, but also be adapted to determine the left ventricle position with respect to the multi-electrode pad. By giving the instruction to apply chest compressions at a location referenced on the pad as determined from the ECG signals, the effectiveness ofthe CPR is more likely.

[0066] The steps involved in ventricle position or location determination are illustrated according to one embodiment in Figure 8. At step SO, the process begins. At step S1 , the body electrodes 22 are attached to the skin of the patient in accordance with the chosen ECG methodology. In the case of a multi-electrode array 20, for example, one placed on the lower sternum area, step S2 involves placing the pad 20 on the patient. The processor 30 then collects the signals from electrodes 20 and 22 in step S3. Unit 40 then analyzes the ECG signals to identify the absolute maximum and minimum value of the ECG signal within a given time window, typically of at least a second and more typically around 10 seconds, at step S4. Step S5 the AMSA is calculated on the ECG signal in a time window that may the same or different from the time window in S4. While it is preferable to measure and record the ECG signals from all positions of the multi-electrode 20 simultaneously, it is also possible to do so sequentially, for example over different pulses and with averaging. In this case, at step S6, one redirects the method to step S2 until all electrode positions of electrode 20 are measured and with sufficient averaging.

[0067] In step S7, the electrical potential source location in the heart is determined. This may be done by taking the greatest value from steps S4 and S5 and the corresponding electrode 20 position. Alternatively, an interpolation may be done if the electrode 20 spacing is great enough.

[0068] In step S8, the position of the cardiac ventricles is output to the user. This may take the form of selectively illuminating a small LED 50a through 50i on a top surface of pad 20. This may also take the form of a spoken word audio output to provide the location with reference to indicia provided on pad 20. AED devices are known to use spoken word audio output to provide instructions and information to the user of the device.

[0069] In step S8’, the position of the cardiac ventricles is output to an actuator to position the mechanical chest compression device accordingly. As shown in Figure 9, a panel 60 may be placed under the back of the patient, and a frame 62 can be attached to the panel 60 to support the positioning actuator 50 and the chest compression motor drive 52. In this case, the frame 62 may have a guide, such as a laser guide, for ensuring that the technician places the pad 20 at a known location with respect to the actuator 50.

[0070] Such a laser guide may also be associated with the motor drive 52 or the palm56 to allow a manual adjustment to the position of the motor drive 52 with respect to frame 62 using a position adjustment mechanism 50 so that the laser can be aligned with indicia or an indicator associated with pad 20 or 20’ so that the pad 56 can be located over the determined location of the heart ventricles.

[0071] In Figure 9, a negative pressure flexible cover 58 is connected via a conduit 54 to a vacuum or suction source in the motor drive 52 so that lifting of the shaft 54 and the chest compression palm 56 helps to pull on the chest to expand the ribcage using the cover 58. In this way, the mechanical chest compression device 52 can perform ventricle compression and ribcage expansion for better circulation of oxygenated blood.

[0072] If the determined position of the cardiac ventricles based on the ECG signals were to change after the onset of chest compressions, the vacuum source can be interrupted briefly to allow the palm 56 and cover 58 to be lifted from the chest so that the actuator 50 can reposition the palm 56 to be more accurately over the expected location of the ventricles. Then the vacuum source can resume along with the regular chest compressions and ventilation.

[0073] Figure 10 illustrates a patient stretcher board that includes panel 60. Figure 11 shows schematically a patient positioned on the stretcher board with the automated chest compression device mounted to the panel 60. It will be appreciated that the panel 60 may comprise back electrodes 22 in a suitable array or layout for EIT-based detection of the heart location, e.g. to locate the left ventricle. EIT electrodes may be used in conductive contact with the skin of the patient or they may be only capacitively coupled.

[0074] It is explicitly stated that all features disclosed in the description and / or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure as well as for the purpose of restricting the claimed invention independent of the composition of the features in the embodiments and / or the claims. It is explicitly stated that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure as well as for the purpose of restricting the claimed invention, in particular as limits of value ranges.

Claims

What is claimed is:

1. An apparatus for determining a location of a heart on a patient, the apparatus comprising: a pad carrying an array of first electrodes to be placed over an area of the heart on a patient’s chest; a plurality of second electrodes; a device for measuring electric potentials using said first electrodes and said second electrodes, the device connectable to said pad and said plurality of second electrodes for generating a measurement signal for each electrode of said array of first electrodes; and a signal analyzer connectable to said device for determining from said measurement signal for each electrode of said array of first electrodes a location referenced with respect to said array of first electrodes corresponding to a location of heart ventricles.

2. The apparatus of claim 1 , wherein the device comprises an electrocardiogram (ECG) device, said measurement signal is an ECG signal, and said plurality of second electrodes comprise a plurality of body electrodes.

3. The apparatus of claim 2, wherein the signal analyzer is configured to measure a maximum and a minimum of an amplitude of said ECG signal for each electrode of said array of ECG electrodes over a given time window.

4. The apparatus of claim 2 or 3, wherein the signal analyzer is configured to measure an amplitude spectrum area (AMSA) an amplitude of said ECG signal for each electrode of said array of ECG electrodes over a given time window.

5. The apparatus of any one of claims 1 to 4, wherein the device comprises an electrical impedance tomography (EIT) device, said measurement signal is an EIT signal, and said plurality of second electrodes comprise a plurality of back electrodes.

6. The apparatus of claim 5, wherein said plurality of back electrodes are arranged on a pad.

7. The apparatus of claim 5 or 6, wherein the EIT device and signal analyzer are configured to determine said location of heart ventricles without generating an image of the heart ventricles.

8. The apparatus of claim 5 or 6, wherein the EIT device and signal analyzer are configured to generate an image of the heart ventricles.

9. The apparatus of any one of claims 1 to 8, further comprising an indicator connected to the signal analyzer for providing an indication of said location of heart ventricles.

10. The apparatus of claim 9, wherein said indication of said location of heart ventricles is provided with respect to a reference marking on said pad carrying an array of first electrodes.11 . The apparatus of claim 9, wherein said indicator comprises LEDs located on said pad.

12. The apparatus of any one of claims 9 to 11 , wherein said indicator further comprises a CPR guidance interface.

13. The apparatus of claim 12, wherein said interface comprises an audio speaker.

14. The apparatus of any one of claims 1 to 13, wherein the location of heart ventricles is a location of a left heart ventricle.

15. An automated cardiopulmonary resuscitation (CPR) system comprising: an apparatus for determining a location of a heart on a patient as defined in any one of claims 1 to 14; a chest compression motor drive having a chest compression pad; and a positioning mechanism for positioning said chest compression motor drive, wherein the location of the heart ventricles can be used to position said chest compression pad.

16. The system of claim 15, wherein said positioning mechanism comprises a positioning actuator, said positioning actuator connected to said signal analyzer for positioning said chest compression pad in accordance with said location of heart ventricles provided by said signal analyzer.

17. A method of pre-emptively marking a patient at risk of a heart attack to receive cardiopulmonary resuscitation (CPR), the method comprising: using the apparatus for determining a location of a heart on a patient as defined in any one of claims 1 to 14 to determine said location of heart ventricles; and providing an indication of said location of heart ventricles to a person for performing CPR on the patient.

18. The method of claim 15, wherein said providing comprises marking a skin of thepatient with said location.

19. An automated external defibrillator (AED) system comprising: an apparatus for determining a location of a heart on a patient as defined in any one of claims 1 to 14; two defibrillation electrodes; an interface connected to said signal analyzer for providing an indication of said location of heart ventricles and at least warning of defibrillation; and a defibrillator connected to said apparatus, said interface and to said two defibrillation electrodes for determining when a defibrillation charge should be automatically administered, providing through said interface said warning of defibrillation and delivering said defibrillation charge.

20. The AED system as defined in claim 19, wherein said two defibrillation electrodes comprise said pad carrying an array of first electrodes to be placed over an area of the heart on a patient’s chest, wherein said defibrillator is configured to select electrodes from said array based on said location of heart ventricles.

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