Impedance Measurement Using Burst Pulses to Prevent Noise in ECG

Abstract

The present invention is entitled "Impedance Measurement Using Burst Pulses to Prevent Noise in ECG". The present invention discloses a system and method for measuring the impedance of one or more of a plurality of lead wires in an electrocardiogram (ECG). The system and method may include applying a plurality of lead wires to a patient's body, applying a plurality of impedance pads to the patient's body, providing burst pulses from catheter electrodes of the ECG, measuring impedance signals across impedance pads in a plurality of impedance pads and lead wires in a plurality of lead wires, and determining the impedance of one or more lead wires based on the measured impedance signals. The plurality of impedance pads may define a first axis from the right side of the patient's chest to the left side of the patient's chest, a second axis from the upper chest region of the patient to the lower abdominal region of the patient, and a third axis from the center of the patient's back to the center of the patient's chest.

Description

Technical Field

[0001] The present invention relates to electrocardiograms, which are referred to herein as ECGs, and may also be referred to as EKGs. More particularly, the present invention relates to impedance measurement using burst pulses to prevent noise in the ECG. Background Art

[0002] Currently, electrocardiograms (referred to herein as ECGs, and may also be referred to as EKGs) are affected by the impedance of the patient's body, the impedance of the contacts that connect the probe to the patient's body, and the impedance from the connector itself. In order to understand and read the ECG, this impedance needs to be considered. When doctors use ECGs to study cardiac activity, impedance needs to be considered in order to effectively isolate electrical signals from the heart. Previous attempts to determine impedance were made using frequency multiplexing. In these frequency multiplexing attempts, other frequencies were used to measure impedance. These other frequencies are typically high frequencies and do not interfere with the measurement of electrical signals from the heart. However, the significantly different frequencies used can affect the accuracy of impedance measurement. That is, the response can vary based on the frequency of the signal, and since there are differences in frequency, frequency multiplexing tends to affect accuracy. Therefore, it is necessary to provide an improved method for measuring impedance so that the influence of such impedance can be removed from ECG studies, thereby being able to more clearly discern the electrical signals of the heart. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] A more detailed understanding may be obtained through the following detailed description provided by way of example in conjunction with the accompanying drawings, in which:

[0004] Figure 1 A block diagram of an ECG apparatus using burst pulses to perform impedance measurement to prevent noise is shown;

[0005] Figure 2 shows the use of impedance pads in conjunction with Figure 1 A diagram of an impedance configuration of a device for measuring impedance;

[0006] Figure 3 Shows the combination Figure 1 a diagram of the lead wire configuration of the device;

[0007] Figure 4 The method of the present invention is shown using burst pulses in a unipolar configuration to measure impedance; and

[0008] Figure 5 The method of the present invention is shown measuring impedance in a bipolar configuration. DETAILED DESCRIPTION

[0009] Electrocardiography, referred to herein as ECG and may also be referred to as EKG, is the process of recording the electrical activity of the heart over a period of time using electrodes placed on the skin or inside the heart (i.e., intracardiac ECG) using a special catheter. These electrodes detect small electrical changes caused by the electrophysiological pattern of depolarization of the heart muscle during each heartbeat. ECG is commonly or routinely performed for cardiology testing.

[0010] An intracardiac electrogram (ICEG) is an ECG with some added intracardiac leads (i.e., inside the heart). This type of electrogram can be used in conjunction with a conventional 12-lead ECG, or in place of a conventional 12-lead ECG. In a conventional 12-lead ECG, 10 electrodes are placed on the surface of the patient's limbs and chest. The overall magnitude of the heart's electrical potential is then measured from 12 different angles ("leads") and recorded for a period of time. The duration of the process can vary from tens of minutes to several hours. During each procedure, there are typically dozens of ablation periods, for example, each ablation period lasting from a few seconds to up to about 1 minute. By way of example, a conventional 12-lead ECG can be performed over a period of time (such as 10 seconds). In this way, the overall magnitude and direction of the electrical depolarization of the heart are captured at every moment throughout the cardiac cycle. The graph of voltage versus time produced by this medical procedure is called an electrocardiogram.

[0011] During each heartbeat, a healthy heart has an orderly progression of depolarization. This orderly depolarization pattern produces a characteristic ECG trace. For a well-trained clinician, the ECG conveys a wealth of information about the structure of the heart and the function of its electrical conduction system. Among other things, the ECG can be used to measure the rate and rhythm of the heartbeat, the size and position of the ventricles, the presence of any damage to the heart's muscle cells or conduction system, the effects of cardiac medications, and the function of implanted pacemakers. Interpretation of the ECG is fundamentally about understanding the heart's electrical conduction system. Normal conduction begins and propagates in a predictable pattern, and deviations from this pattern can be normal variations or pathological.

[0012] However, in order to determine the signals from the electrical conduction system of the heart, the measured signals need to be filtered to remove any unwanted and spurious signals or noise.

[0013] The present invention discloses a system and method for measuring the impedance of one or more of the multiple lead wires in an electrocardiogram (ECG). The system and method may include applying multiple lead wires to a patient's body, applying multiple impedance pads to the patient's body, providing burst pulses from a catheter electrode of the ECG, measuring impedance signals across impedance pads in multiple impedance pads and lead wires in multiple lead wires, and determining the impedance of one or more lead wires based on the measured impedance signals. Multiple impedance pads define a first axis from the right side of the patient's chest to the left side of the patient's chest. Multiple impedance pads define a second axis from the patient's upper chest area to the patient's lower abdominal area. Multiple impedance pads define a third axis from the center of the patient's back to the center of the patient's chest. Multiple lead wires include a standard 12-lead ECG, which includes three limb leads, three augmented limb leads arranged in a spoke manner on the coronal plane, and six precordial lead wires configured on a vertical transverse plane.

[0014] Alternatively, the system and method may include applying a plurality of lead wires to the patient's body and measuring impedance signals across pairs of lead wires of the plurality of lead wires during periods between ECG measurements. The plurality of lead wires includes a standard 12-lead ECG including three limb lead wires, three compression limb lead wires arranged in a spoke manner on a coronal plane, and six precordial lead wires configured on a perpendicular transverse plane. The plurality of lead wires are each paired with an adjacent lead wire in the plurality of lead wires.

[0015] A system for performing ECG and measuring impedance includes a plurality of lead wires for attaching to a subject to capture electrical signals, a signal processor for processing the captured electrical signals, and an output device for outputting the processed captured electrical signals, wherein the measured impedance is monitored and the signal processor removes the impedance from the processed captured electrical signals. The system may include a plurality of impedance pads configured to provide impedance information for measurement. The catheter electrodes may provide burst pulses to enable measurement of the impedance information. Alternatively, the system may measure impedance information of electrode pairs across a plurality of electrodes.

[0016] Figure 1 A block diagram of an apparatus 100 that can utilize impedance measurement using burst pulses is shown. The apparatus 100 can take the form of an ECG machine. The apparatus 100 includes a series of lead wires 110 tapered into a single multiplexed input 115. The series of lead wires 110 can be placed on a human test subject 105. Additional lead wires 107 can be intracardiac lead wires 107, which can be included with the series of lead wires 110, or separate from the lead wires (as shown).

[0017] The intracardiac leads 107 may be used for diagnostic or therapeutic treatments, such as for mapping electrical potentials in the heart 126 of the patient 105. Alternatively, the intracardiac leads 107 may be used, mutatis mutandis, for other therapeutic and / or diagnostic purposes in the heart or other body organs.

[0018] Intracardiac lead wire 107 may be inserted into the vascular system of patient 105 such that distal end 132 of lead wire 107 enters a chamber of patient's heart 126. Figure 1 A single lead wire 107 is shown with a single position sensor, but embodiments of the present invention may utilize probes with more than one position sensor.

[0019] The signals on the series of lead wires 110 are input into the analog front end 125 via the input multiplexer 120. The analog front end 125 is provided to and controlled by the processor 130. As shown, the processor 130 may include a video controller 135, a digital signal processor 140, a microprocessor 145, and a microcontroller 150. The processor 130 is coupled to a data storage device 155. A data port and a printer 160 may be coupled to the processor 130. Other input / output devices 165 may be coupled to the processor 130. A display 170 may be used to provide an output of the ECG signal. A power / battery management system 175 may be included to provide power for the device 100 to operate.

[0020] A series of lead wires 110 include commonly used electrode forms, and may also include lead wires for ECG procedures. Each of the series of lead wires 110 may include a conductive pad in contact with the body 105, which forms a circuit with the electrocardiograph. On a standard 12-lead ECG, there are only 10 lead wires 110. A series of lead wires 110 may be grouped into three groups: limbs, pressurized limbs, and precordial areas. Generally speaking, a 12-lead ECG has a total of three limb leads and three pressurized limb leads arranged like wheel spokes on the coronal plane (vertical), and six precordial leads located on a vertical transverse plane (horizontal).

[0021] The analog front end 125 receives signals from the series of lead wires 110 and performs analog processing of the signals such as filtering.

[0022] Data storage device 155 is any device that records information. The data storage device may provide a storage medium for the signals included within device 100 and provide a location for computations of processor 130 to be stored.

[0023] The microprocessor 145 may be a computer processor that combines the functionality of a central processing unit (CPU) of a computer onto a single integrated circuit (IC) or onto several integrated circuits. The microprocessor 145 may be a multi-purpose, clock-driven, register-based programmable electronic device that accepts digital or binary data as input, processes the digital or binary data according to instructions stored in its memory or data storage device 155, and provides results as output. The microprocessor 145 includes both combinational logic and sequential digital logic.

[0024] Microcontroller 150 may be one or more small computers on a single integrated circuit. Microcontroller 150 may contain one or more CPUs as well as memory and programmable input / output peripherals. Program memory in the form of ferroelectric RAM, NOR flash, or OTP ROM and a small amount of RAM are also often included on the chip. Microcontrollers are designed for embedded applications, in contrast to microprocessors used in personal computers or other general-purpose applications that are composed of various discrete chips.

[0025] The digital signal processor 140 can perform digital signal processing to perform a variety of signal processing operations. Signals processed in this manner are digital sequences of samples representing continuous variables in domains such as time, space, or frequency. Digital signal processing can involve linear or nonlinear operations. Nonlinear signal processing is closely related to nonlinear system identification and can be implemented in the time, frequency, and space-time domains. Applying digital computing to signal processing allows for many advantages over analog processing in many applications, such as error detection and correction in transmission and data compression. DSP is applicable to both streaming data and static (stored) data.

[0026] Figure 2 shows the use of impedance pads to combine Figure 1 200 is an illustration of an impedance configuration 200 for measuring impedance with a device of the type shown in FIG. Configuration 200 includes a series of impedance pads configured to measure impedance in each of three axes relative to a patient 250. A first axis first impedance pad 205 may be placed on the right side of the chest of the patient 250. The pads 205 may form an axis (first axis) having a first axis located on the left side of the chest of the patient 250 and a second impedance pad 210 (on the left side of the chest of the patient 250). Figure 2 (shown in the middle horizontal).

[0027] The second impedance axis (second axis) (at Figure 2 The first impedance pad 215 and the second impedance pad 220 may be defined by a second axis first impedance pad 215 and a second axis second impedance pad 220. The second axis first impedance pad 215 may be placed on the upper chest or throat of the patient 250. The second axis second impedance pad 220 may be located on the abdomen of the patient 250.

[0028] The third impedance axis (third axis) (in and out Figure 2 The first impedance pad 225 and the second impedance pad 230 may be defined by a third axis first impedance pad 225 and a third axis second impedance pad 230. The third axis first impedance pad 225 may be placed at the center of the back of the patient 250. The third axis second impedance pad 230 may be placed at the center of the chest of the patient 250.

[0029] The system coordinates impedance measurements with ECG studies and utilizes the impedance measurements from the catheter electrodes ( Figure 2 Impedance is measured by an electrical signal transmitted to six pads 205, 210, 215, 220, 225, 230 on the patient 250 (not shown in the figure). Those familiar with ECG procedures will understand that the catheter electrode can be directly positioned in the patient's heart. For example, the catheter can be inserted into the patient's heart internally. The catheter electrode can be, for example, accommodated at the tip of the catheter shaft. The catheter electrode emits a burst of low-frequency electrical signals from less than 1 milliampere to 100 microamperes, which are absorbed by the six pads 205, 210, 215, 220, 225, 230 on the patient 250 body. Generally speaking, the use of pads 205, 210, 215, 220, 225, 230 and catheter electrodes is a unipolar measurement. The burst can have the same or approximately the same frequency as the signal measured during the ECG so as to eliminate any frequency errors in the impedance measurement and impedance removal.

[0030] By way of example only, each channel in an ECG test may be sampled 20,000 times per second, for a measurement time of 1 / 640 second. This yields a time of approximately slightly less than 1 / 20000 second between measurements, during which time multiplexing may be employed to measure impedance. More specifically, in this example, the time between measurements may be 1 / 19200 second.

[0031] When the ECG is not sampling the electrical signal from the heart, a burst pulse from the catheter can be provided. This time multiplexing avoids interference with the ECG reading. Because the system uses time multiplexing (rather than frequency multiplexing), any frequency can be used for the burst pulse. This allows the impedance to be measured using signals of the same or approximately the same frequency. The electrical signal from the heart is not sampled continuously, only in a multiplexed form. Therefore, the catheter electrode can be used when the electrical signal from the heart is not being sampled. Typical values ​​are about 100 ohms to 200 ohms.

[0032] Figure 3 Shows the combination Figure 1 300. The lead wire configuration 300 includes a series of lead wires configured to measure electrical signals relative to a patient 350. Generally, there are ten lead wires connected to a specific part of the body. The lead wires are divided into two groups: six chest lead wires 325 and four peripheral lead wires 335.

[0033] Six chest leads 325 are generally positioned relative to the chest of patient 350. A first of the chest leads 3251 is positioned near the center of the chest of patient 350. A lateral lead 3256 is positioned on the side of the body of patient 350. The other chest leads 3252, 3253, 3254, 3255 are located between the first chest lead 3251 and the lateral chest lead 3256. By way of illustration, chest lead 3252 is positioned at the intersection of the 4th intercostal space and the sternum of patient 350. Chest lead 3254 is positioned at the 5th intercostal space, in line with the middle of the clavicle. Chest lead 3253 can be positioned centrally between chest lead 3252 and chest lead 3254. Chest lead 3255 can be positioned at the 5th intercostal space in the axillary region.

[0034] Four peripheral leads 335 may be positioned to capture signals at the left and right wrists and the left and right legs. These leads may be positioned at the shoulders and abdomen (as shown) or directly on the limbs when referencing signals from the arms and legs. For example, lead 335 RA Positionable on the right shoulder of the patient 350, lead wire 335 LA Positionable on the left shoulder of the patient 350, lead wire 335 RL can be positioned in the right lower abdomen of the patient 350, and 335 RL It can be positioned in the left lower abdomen of the patient 350. Individually, the lead wires can be used in a monopolar configuration as described, where each lead wire is operated individually. For example, such lead wires can be brought together and tied to the ground or pad.

[0035] Alternatively, the lead wires may be used in a bipolar configuration. That is, the lead wires may be used in pairs, and the pair has a signal collected between the lead wires. For example, lead wires may be used that pass through an imaginary Einstein triangle.

[0036] Impedance can be measured by transmitting from one lead wire to another lead wire. Such impedance measurement can utilize lead wires 350 that are already included on the patient 325 body, so reference may not be required. Figure 2 The pad shown and described. The impedance measurement between two lead wires is called a bipolar measurement of impedance.

[0037] Using leads in bipolar measurements can provide the added benefit that the lead furthest from the most recent measurement can be used to measure impedance. For example, if the electrical signals of the heart are measured on leads 1 and 2, impedance can be measured on leads 16 and 17. A lead can be defined as the connection between two electrodes. For example, lead 1 can be defined as, for example, lead 335 LA With 335 RA The lead wire 2 may include a lead wire 335 RA With 335LL The lead wire 3 may include a lead wire 335 LA With 335 LL A connection piece between. One pattern that can be used is, for example, by connecting an electrode to an adjacent electrode to form a pair. Other lead wires formed by electrode combinations can also be used based on the disclosure contained herein, and this will be obvious to a person of ordinary skill in the relevant art.

[0038] During bipolar operation, the window of opportunity for bipolar impedance measurement at a sampling frequency of at least 20 kHz provides 50 μs for each electrode. To enable the measurement, the multiplexer can provide a 3 μs connection for measuring the impedance between two electrodes. A sampling frequency of up to 200 kHz can be used. During a given window of opportunity, only a single lead wire is connected, and the N-1 lead wires are not connected.

[0039] Figure 4 A method 400 is shown that can be performed in a unipolar configuration. The method 400 includes applying a plurality of lead wires at step 410. At step 420, the method 400 includes applying a plurality of impedance pads. At step 430, a unipolar impedance measurement can be performed by applying a burst pulse from a catheter electrode. At step 440, a plurality of measurements can be made across impedance pads in the plurality of impedance pads and lead wires in the plurality of lead wires. At step 450, an impedance of one or more lead wires can be determined through the plurality of measurements.

[0040] Figure 5 A method 500 is shown that may be performed in a bipolar configuration. The method 500 includes applying a plurality of lead wires at step 510. At step 520, bipolar impedance measurements may be performed across the lead wires in the lead wire pairs between ECG measurements.

[0041] The provided methods may be implemented in a general purpose computer, a processor, or a processor core. By way of example, suitable processors include a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), and / or a state machine. Such processors may be manufactured by configuring a manufacturing process using the result of processed hardware description language (HDL) instructions and other intermediate data including a network table (such instructions can be stored on a computer readable medium). The result of such processing may be a mask work that is subsequently used in a semiconductor manufacturing process to manufacture a processor that implements the features of the present disclosure.

[0042] The methods or flow charts provided herein may be implemented in a computer program, software or firmware incorporated into a non-transitory computer-readable storage medium for execution by a general-purpose computer or processor. Examples of non-transitory computer-readable storage media include read-only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media (e.g., internal hard disks and removable disks), magneto-optical media, and optical media (e.g., CD-ROM disks and digital versatile disks (DVDs)).

Claims

1. A system for performing an electrocardiogram (ECG) and measuring impedance, the system comprising: a plurality of impedance pads configured to provide impedance information for said measuring; a plurality of lead wires for attachment to a subject to capture electrical signals including an impedance across at least one of the plurality of lead wires; a signal processor electrically coupled to the plurality of lead wires for processing the captured electrical signals at least by removing the impedance of the at least one lead wire from the captured electrical signals; and an output device, the output device being used to output the processed captured electrical signal; The system is configured to measure an impedance signal across an impedance pad among the plurality of impedance pads and a lead wire among the plurality of lead wires, and to determine the impedance of the at least one lead wire based on the measured impedance signal.

2. The system of claim 1, wherein a catheter electrode provides burst pulses to enable said measuring of said impedance information.

3. The system of claim 1, wherein the plurality of lead wires comprises a standard 12-lead ECG.

4. The system of claim 1, wherein the plurality of lead wires comprises three limb lead wires.

5. The system of claim 1, wherein the plurality of lead wires comprises three compression limb lead wires arranged in a spoke fashion in a coronal plane.

6. The system of claim 1, wherein the plurality of lead wires comprises six precordial lead wires arranged in a perpendicular transverse plane.

Images