Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/18—Applying electric currents by contact electrodes
  • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
  • A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
  • A61N1/39—Heart defibrillators
  • A61N1/3987—Heart defibrillators characterised by the timing or triggering of the shock

Definitions

• the present invention relates to devices used in electrical therapy and, in particular, to a defibrillator for rapidly delivering defibrillation pulses with minimal delay following intervals of cardio-pulmonary resuscitation (CPR) performed on a patient.
• CPR cardio-pulmonary resuscitation
• FIG. 1 depicts the conventional AED 6 being applied to a cardiac arrest victim 2 by a rescuer 4.
• AA anterior-anterior
• CPR cardio-pulmonary resuscitation
• the present invention provides an improved defibrillator that is easy to use and that enables a minimally trained user to easily, rapidly, and effectively deploy the defibrillator to treat the patient, while reducing the time interval between precordial compressions and delivery of a defibrillation shock.
• the present invention is directed to a method and system for quickly and accurately applying the defibrillating shock to a victim of sudden cardiac arrest, especially following delivery of CPR precordial compressions. According to one aspect of the invention, a delay between the administration of
• CPR and the delivery of defibrillation shock is minimized by quickly discriminating the end of a period of CPR and charging the defibrillator.
• a method of applying electrotherapy in an automatic external defibrillator (AED) of the type having a high voltage energy source, an ECG detector, and a CPR therapy module is provided.
• AED automatic external defibrillator
• an indication of CPR cessation is obtained in order to arm the AED for a subsequent electrotherapy shock.
• the charging of the AED may be initiated prior to the end of the
• the method further includes obtaining an ECG signal from the ECG detector prior the end of the CPR therapy interval, and determining whether the ECG signal is corrupted by CPR activity.
• a defibrillator having a CPR delivery system includes: a detector arranged to detect a signal indicating the cessation of CPR; an energy source for providing the defibrillation shock energy; a charging circuit for charging the energy source; and a controller for controlling the charging circuit responsive to the signal.
• the interval between the cessation of CPR to the defibrillator being charged for delivery of the defibrillation shock is less than about 10 seconds.
• the defibrillator further includes an ECG detector for detecting an ECG rhythm signal, so that processor may charge the defibrillator responsive to a detected shockable ECG rhythm.
• an apparatus for delivering a defibrillation shock to a patient includes at least one sensor adapted to contact the patient; a detector coupled to the sensor for detecting an input signal indicative of disturbances associated with the application of cardiopulmonary resuscitation; a processor for receiving the input signal from the detection system, for analyzing the detected input signal to produce a signal indicative of corruption of electrocardiographic (ECG) signals from the patient, and for determining if a defibrillation shock is needed; and a discharger for providing defibrillation shocks to a patient.
• ECG electrocardiographic
• the apparatus further includes an ECG front end coupled to the pair of electrodes to determine the patient impedance, an LCD display, and a speaker to notify an operator prior to discharging the defibrillation shock.
• Still another aspect of the invention provides a method for delivering a defibrillation shock to a patient using a defibrillator.
• the method includes charging the defibrillator prior to end of a cardio-pulmonary resuscitation (CPR) interval; analyzing an ECG signal prior to end of a cardio-pulmonary resuscitation (CPR) interval; and delivering a defibrillation shock after the cardio-pulmonary resuscitation (CPR) interval if there is no signal corruption associated with the administration of CPR.
• CPR cardio-pulmonary resuscitation
• a method for delivering a defibrillation shock to a patient from a defibrillator is provided.
• the method includes acquiring ECG data representative of an ECG signal for the patient and analyzing the ECG data to determine whether administration of a defibri Mating shock is appropriate.
• a CPR interval is initiated subsequent to the acquisition of ECG data.
• administration of a def ⁇ brillating shock is determined to be appropriate from the ECG data, arming the AED for delivery of the defibrillation shock to the patient.
• FIG. 1 is an illustration of a defibrillator being applied to a patient under cardiac arrest according to an embodiment of the present invention
• FIG. 2 depicts a representative hardware of the defibrillator illustrated in FIG. 1 according to an embodiment of the present invention
• FIG. 3 is a diagram of the hardware configured to deliver a defibrillation shock according to an embodiment of the present invention
• FIG. 4 is a flow chart illustrating the operation steps of the defibrillation system in accordance with an embodiment of the present invention
• FIG. 5 is a flow chart illustrating the operation steps of delivering a defibrillation shock according another embodiment of the present invention
• FIG. 6 is a flow chart illustrating the operation steps of delivering a defibrillation shock according another embodiment of the present invention.
• FIG. 7 is a flow chart illustrating the operation steps of delivering a defibrillation shock according another embodiment of the present invention.
• a conventional method of providing resuscitation of a victim will be described.
• a rescuer During the course of a resuscitation of a victim in sudden cardiac arrest, a rescuer often follows a protocol that calls for the application of defibrillation shocks from an Automated Electronic Defibrillator (AED) and delivering intervals of cardiopulmonary resuscitation (CPR) to promote the circulation of blood until normal circulation can be re ⁇ established.
• AED Automated Electronic Defibrillator
• CPR cardiopulmonary resuscitation
• the resuscitation protocol is directed to the rescuer via the AED using voice prompting.
• a victim of cardiac arrest due to ventricular fibrillation may receive several defibrillation shocks followed by a preprogrammed interval of CPR, during which the rescuer provides precordial compressions to the victim plus breathing assistance.
• precordial compressions during CPR are thought to provide artificial circulation, which improves chances of survival, by the victim.
• the operator is typically prompted to stop CPR so that the AED may analyze the victim's ECG rhythm to determine if more shocks are needed.
• the likelihood of survival rapidly falls as the time interval between cessation of compressions and the delivery of a defibrillation shock increases. It is therefore important to minimize this critical interval as much as possible, preferably to less than ten seconds. In conventional systems, four steps must occur following a CPR interval before an
• AED can deliver a shock: (1) The prescribed CPR time interval set by the rescue protocol must expire (one to three minutes, typically); (2) The patient's ECG rhythm must be analyzed to determine if the rhythm should be shocked; (3) The AED must fully charge its energy storage capacitor; and (4) The AED must arm to deliver the shock.
• AEDs typically issue voice prompts to the operator at the end of a CPR sequence in order to advise the operator not to touch the patient, which may interfere with and thus delay analysis of the patient's ECG rhythm.
• the operator is often again warned not to touch the patient and to deliver the shock by pressing a SHOCK button (if the device is semiautomatic) or to warn that a shock will be delivered (if the AED is fully automatic).
• prior art devices In most prior art devices, the four stages above proceed in serial sequence, which results in a period of typically 15 to 30 seconds or more between the end of precordial compressions and the possible delivery of a shock to a patient. In some cases, prior art devices partially charge the AED's energy storage capacitor to save some time prior to the completion of ECG analysis, but do not fully charge until analysis is completed. Some prior art AEDs employ artifact detection during attempts to analyze patient's ECG signals in order to determine if a shock should be delivered. Artifact detection acquires a disturbance signal, which can originate from patient motion or any other possible source of ECG disturbance (e.g. electromagnetic), and compares it to the patient's ECG, e.g.
• ECG disturbance e.g. electromagnetic
• prior art defibrillators have presented a shock hazard to the rescuer as the defibrillators are incapable of detecting whether the rescuer was in physical contact with the patient.
• One way to address this problem in the prior is to provide a "no touch" interval period prior to delivering the therapy shocks.
• this delay is undesirable as it delays the interval between the CPR precordial compressions, if occasion demands, and the delivery of defibrillation shock, thus preventing a quick response in administering a defibrillation shock which is vital in increasing the chance of surviving the cardiac arrest.
• one embodiment of the present invention provides a defibrillation system in which the delivery of electrical therapy shocks is triggered by a combination of the detection of a treatable arrhythmia via an ECG analysis and a detection of the cessation or absence of CPR precordial compressions.
• the defibrillation system reduces the time interval between precordial compressions and a subsequent delivery of the defibrillation shock.
• FIG. 2 is a simplified block diagram of a defibrillator 20 in accordance with this embodiment of the present invention.
• the defibrillator 20 may include a mechanical disturbance detector 10, an electrocardiogram (ECG) front end 32, a timer 34, a defibrillation activation/deactivation button 36, a high voltage (HV) switch 38, a processor 40, a voice circuit and speaker 41, a display 42, an energy storage capacitor network 44, a voltage charger 46, and a battery 48. While particular reference is made to the system block diagram of FIG. 1 , it is to be understood at the outset of the description which follows, that is contemplated that the apparatus and methods in accordance with embodiments of the present invention may be used with other hardware configurations of the planner board.
• ECG electrocardiogram
• HV high voltage
• the mechanical disturbance detector 10 is connected to a sensor 12 that is placed on the patient to detect the movement of the patient during the delivery of CPR precordial compressions. The movement of the patient that may potentially corrupt the accurate assessment of the signal of interest is detected and forwarded to the processor 40.
• the ECG front end 32 is connected to the electrodes 22 and 24 that are placed on the patient to amplify, filter, and digitize (using an analog to a digital converter) an electrical ECG signal generated by the patient's heart.
• the detected ECG samples are received by the processor 40, which runs a shock advisory algorithm for detecting VF or other shockable rhythm requiring treatment by the defibrillation shock.
• the ECG front end 32 is also capable of measuring the patient impedance across the electrodes 22 and 24 using a low-level test signal that is a non- therapeutic pulse to measure the voltage drop across the electrodes 22 and 24.
• the function of the mechanical disturbance detector 10 and the ECG front end 32 can be merged as one component, such that one of the electrodes connected to the ECG front end 32 may serve as a sensor for detecting the movement of the patient.
• the HV switch 38 is configured to sequentially deliver the defibrillation pulse across the pair of electrodes 22 and 24 to the patient in the desired polarity and duration. It should be noted that the HV switch 38 could be adapted to deliver a single polarity (monophasic), both negative and positive polarities (biphasic) or multiple negative and positive polarities (multiphasic) in the preferred embodiment.
• the timer 34 is connected to the processor 40 for providing a defibrillation pulse interval or duration when delivering the defibrillation pulse across the electrode pair 22 and 24.
• the activation/deactivation button 36 is connected to the processor 40 to enable the user to activate/deactivate the delivery of a defibrillation pulse across the electrodes 22 and 24 when the VF or other shockable rhythm is detected. Note that the activation/deactivation button 36 can function in both AED and manual modes in the preferred embodiment.
• the voice circuit/speaker 41 provides voice instructions to the user during the operation of the defibrillator 20. Alternatively, in other embodiments such as a fully automated AED the activation/deactivation button may be omitted.
• the display 42 connected to the processor 40, is preferably a liquid crystal display (LCD) and provides visible feedback to the user.
• the battery 48 provides power for the defibrillator 20 and in particular for the charger 46, which charges the capacitors in the energy-storage capacitor network 44.
• the energy-storage capacitor network 44 includes a plurality of capacitors and resistors that are arranged in series or parallel arrangement, or a combination of series and parallel arrangement to supply a plurality of voltage-level outputs across the electrodes 22 and 24. It will be apparent to those skilled in the art that a variety of RC arrangements can be implemented to generate different defibrillation pulse characteristics.
• the electrodes 22 and 24 connected to the ECG front end 32 are placed on a patient for obtaining the patient impedance.
• the defibrillation pulse delivered to the patient may be a fixed level, or a number of defibrillation pulses at different energy levels. This can be achieved by selecting the appropriate voltage level of the energy- storage capacitor network 44 from the set of configurations to deliver the desired impedance-compensated defibrillation pulse to the patient.
• the resulting chest movement tends to disturb the electrodes placed on the chest area. This is undesirable for detecting ECG signals as the movement of the electrodes on the chest skin area generates interfering electrical noise or artifacts, which may corrupt the ECG signal.
• the artifact in the ECG signal caused by mechanical disturbances of sensors, electromagnetic interference, other environmental conditions, or artifact caused by movement due to the cardio-pulmonary resuscitation (CPR) operation are nevertheless useful as indicators that CPR is being performed, when CPR is concluded, and when the patient is being handled.
• An accelerometer or other motion sensor may be included in some embodiments for such detection purposes.
• the defibrillator 20 is also provided with the display 42 for visually indicating the shock annunciation, or may be equipped with a voice circuit and speaker 41 for providing audible announcement just prior to delivering the defibrillation shocks.
• the defibrillation activation/deactivation 36 is provided for cancellation of the shock within the brief delay interval prior to therapy delivery.
• the motion of new mechanical disturbance and/or artifact can be detected automatically and cause the cancellation or delay of the defibrillation shock therapy.
• Figure 3 is a detailed description of the components that enable a rapid analysis during mechanical disturbances, so that arrhythmia determination can be made using artifact-free ECG, especially following the cessation of mechanical disturbance.
• detecting artifact can be performed in a variety of ways.
• signal processing and correlation of processed signals in accordance with the present invention may include various embodiments described in U.S. Patent Application No. 6,287,328, filed by the applicant and issued on September 11, 2001, entitled “Multi variable Artifact Assessment,” the teachings of which are incorporated herein by reference. Briefly, an input signal indicative of patient movement is received via the sensor 12 and provided to the measurement circuit 10.
• the signal is then sent to a signal processor 52 and forwarded to a correlator 60 for correlation with the patient's ECG signal, and the correlated signal is transmitted to the processor 40.
• an appropriate signal processing includes, for example, band-pass filters, Fourier transforms, wavelet transforms, time domain analysis, or joint time-frequency spectrograms.
• the method for correlating the data can be any correlation method known in the art.
• correlation methods include specific and general cross-correlation techniques, which include known mathematical functions as well as any process that effectively correlates the data.
• Specific implementations include, but are not limited to, finite sampled or continuous estimates of cross-covariance and cross-correlation, both biased and unbiased.
• correlation may perform similarity comparisons between any multiple signals.
• an input signal indicative of the patient voltages and impedance is received across the electrodes 22 and 24 and transmitted to a differential-mode amplifier 56 and a common-mode amplifier 62 which amplify the signal prior to transmitting the signal to the signals processors.
• the resulting signals are then transmitted to their respective signal processors 58 and 64 which process the signals to emphasize particular features.
• signal processor 58 supplies signal information for correlation with variables including common-mode signals, impedance signals, or motion signals from their respective processors.
• the resulting processed signals are then transmitted to a correlator 66, which correlates the signals.
• the input signal is transmitted to impedance detector 68, which provides a trans-electrode impedance signal to the signal processor 70.
• Signal processor 70 processes the signal from the impedance detector 68 to emphasize particular features of the signal.
• the resulting processed signal is then transmitted to a correlator 72, which correlates the signal processor 70 with the processed signal from the differential amplifier 58.
• the processor 40 receives the signals from the processor 40 and transmits the results of the correlators 66 and 72 to provide an indication of the degree of corruption of the ECG signal of interest.
• the processor 40 finally provides an output signal, which may be analyzed further as discussed with respect to FIG. 4 below.
• Figure 4 is a flow chart illustrating the operation steps of delivering an artifact- compensated defibrillation shock according to a preferred embodiment of the present invention.
• the defibrillator 20 is deployed by attaching the sensor 12 and the electrodes 22, 24 to the cardiac victim to analyze a patient input signal. Note that it is common to perform CPR including precordial compressions on the victim in conjunction with the use of the defibrillator during rescue attempts, so possibly ongoing CPR is detected by the input signal from the sensor 12.
• step 100 the system 20 begins to charge the capacitor 44 to an intermediate level at a predetermined interval prior to the end of the CPR precordial compression.
• step 102 the system 20 sends a message to the rescuer to stop the CPR, during which the capacitor is still being charged. A short interval, for example 3 seconds or less, is allowed in step 104.
• the electrodes 22 and 24 connected to the ECG front end 32 detect an input signal, i.e., ventricular fibrillation (VF) and the patient impedance, measured by measuring a low-level test signal or delivering a non-therapeutic signal in step 106.
• Motion information is acquired by motion disturbance detector 10 or motion sensor.
• step 108 the ECG signal is tested against the other measurements in order to determine if the ECG signal is being corrupted.
• the signal processing is implemented in order to emphasize a particular feature of the data in the input signal.
• various implementations of processing including known techniques such as filters, Fourier transforms, wavelet transforms, or joint time-frequency spectrograms, are employed.
• the lower spectral portion of a Fourier transform of an ECG signal might be correlated with a similarly processed impedance signal in order to enhance the detection of an artifact resulting from a defibrillator operator performing CPR on a patient being monitored.
• the analyzing step 108 performs the function of measuring similarities between the processed cardiac signal and the processed corrupted signals. The resulting comparisons are then analyzed to determine an indication of the amount of artifacts present within the potentially corrupted cardiac signal. If artifact and/or motion are detected in step 108, the process returns to step 106.
• step 108 determines that acquired ECG data is not corrupted the ECG data is analyzed by processor 40 to determine if a shock is required in step 109. If a shock is not required, the AED may provide alternate care instructions to the rescuer. If the ECG rhythm should be shocked, however, the AED completes its capacitor charge in step 1 10. Further, absence of either ECG corruption or motion disturbance signals in step 108 indicates that the rescuer has discontinued CPR, and it is therefore appropriate to immediately arm the defibrillator to deliver a shock. Processor 40 then sends a signal to the HV switch 38 to actuate the switches to discharge the desired defibrillation shock to the patient.
• the processor 40 may notify the operator via the display 42 to press the shock button 36 to actuate manually the delivery of the defibrillation shock to the patient. Accordingly, the defibrillation shock is discharged to the patient in step 110, then the patient's heart is monitored to determine whether a subsequent defibrillation shock is necessary. If so, the above steps may be repeated to deliver the subsequent defibrillation shock.
• FIG. 5 is a flow chart illustrating the operation steps of delivering an artifact- compensated defibrillation shock according to another embodiment of the present invention.
• an instruction to stop the CPR operation is given to the rescuer in step 200, then the charging of the capacitor 44 to a full level is initiated.
• a short interval is allowed after the discontinuation of the CPR compression in step 202, then the electrodes 22 and 24 connected to the ECG front end 32 detect an input signal, i.e., ventricular fibrillation (VF) and the patient impedance, as well as the input signal due to potentially corrupted signal and/or the movement of the patient during a CPR operation in step 204.
• VF ventricular fibrillation
• the ECG and disturbance signals are analyzed, and if artifact/and or motion disturbance is detected in step 206, the process returns to step 204. If the ECG data is not corrupted, the ECG data is analyzed by processor 40 to determine if a shock is required in step 209. If a shock is not required, the AED may provide alternate care instructions to the rescuer in step 210. Note that absence of either ECG corruption or motion disturbance signals in step 108 indicates that the rescuer has discontinued CPR, and it is therefore appropriate to immediately arm the defibrillator to deliver a shock. If the ECG rhythm should be shocked, the AED completes its capacitor charge in step 208.
• FIG. 6 is a flow chart illustrating the operation steps of delivering a defibrillation shock according to yet another embodiment of the present invention.
• processor 40 monitors a CPR interval of a predetermined time.
• processor 40 commands the charger 46 to fully charge capacitor 44 in a manner that full charge will be reached prior to the timeout of the CPR interval.
• ECG data plus the various signals indicative of disturbance are acquired in step 302.
• step 304 the ECG data is examined for corruption. If the ECG data is corrupted due to CPR, more data is acquired. However, if the data is not corrupted, a determination is made if the patient's ECG rhythm should receive a defibrillation shock in step 306. In step 308, processor 40 continues to update the rhythm's shock determination until timeout of the CPR interval.
• processor 40 Upon timeout of the CPR interval, in step 310 processor 40 causes voice circuit and speaker 41 to prompt the rescuer not to touch the patient.
• processor 40 examines the recently determined shock decision. If a defibrillation shock is not appropriate, the device directs the rescuer to alternative patient care such as, for example, additional CPR. If a shock is appropriate, step 316 examines disturbance data to assure that detectable handling of the patient has ceased. If handling is detected, a prompt is issued to the rescuer to stop touching the patient per step 318. If no handling is detected, processor 40 arms the defibrillator to shock in step 320, and the AED immediately issues a prompt to the rescuer to deliver the shock.
• the advantage of this embodiment is that if the performance of CPR does not corrupt the patient's ECG signal, it is possible to make all of the needed decisions for the next shock while CPR is still ongoing. In this manner, the AED can be ready to deliver a shock immediately upon timeout of the CPR interval. Thus, the delay between cessation of CPR and the shock can approach zero seconds.
• Figure 7 is a flow chart illustrating the operation steps of delivering a defibrillation shock according to another embodiment of the present invention.
• the electrodes 22 and 24 connected to the ECG front end 32 detect an input signal, for example, ventricular fibrillation (VF) and the patient impedance, measured by measuring a low-level test signal or delivering a non-therapeutic signal in step 702. Additionally, an input signal due to potentially corrupted signal and/or the movement of the patient is acquired.
• the motion information is obtained by motion disturbance detector 10 or motion sensor.
• a determination is made whether the ECG data is corrupted. If the ECG data is determined to be corrupted, more data is acquired until the processor 40 can make a determination whether a shock is appropriate.
• the ECG data acquired at 702 is analyzed by the processor 40 to determine if a shock is required.
• a shock may be appropriate under certain conditions where a shockable rhythm is detected, for example, where the ECG data indicates the presence of VF or ventricular tachycardia (VT), as well known in the art.
• the processor 40 can utilize analyses previously described, or known in the art, to make the determination of whether a shock is appropriate.
• the processor 40 initiates a CPR interval and sends signals to the voice circuit and speaker 41 or to the display 42, or to both, at step 706 to provide a visual and/or audio cue to the rescuer to begin CPR compressions.
• the steps 706 and 708 are reversed so that the CPR interval and administration of CPR are initiated prior to the determination if a shock is appropriate.
• the administration of CPR and the determination if a shock is appropriate can also overlap.
• the voltage charger 46 begins to charge the energy storage capacitor network 44 at a time such that a full charge will be reached prior to the completion of the CPR interval.
• the processor 40 sends a signal to the voice circuit and speaker 41 or to the display 42, or to both, directing the rescuer to cease administration of CPR and to stand clear of the patient.
• the processor 40 arms the defibrillator 20 to deliver a defibrillating shock to the patient at step 720.
• a process such as that described with respect to Figure 7 allows for delivery of a defibrillation shock almost immediately following the completion of the CPR interval where a shockable rhythm is detected from the ECG signal acquired prior to the initiation of the CPR interval. In this manner, the time between the cessation of CPR compressions and delivery of the defibrillating shock can be reduced.
• the previously described process can be utilized with a variety of different resuscitation protocols.

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• 2005
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  • 2005-07-19 EP EP05780818A patent/EP1778349A2/de not_active Withdrawn
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