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 invention relates generally to electrotherapy circuits, and more particularly, to a defibrillator capable of delivering a synchronized defibrillation shock.
• Defibrillators deliver a high-amplitude current impulse to the heart in order to restore normal rhythm and contractile function in the patients who are experiencing arrhythmia, such as ventricular fibrillation ("VF") or ventricular tachycardia ("VT”) that is not accompanied by a palpable pulse.
• arrhythmia such as ventricular fibrillation ("VF") or ventricular tachycardia ("VT”) that is not accompanied by a palpable pulse.
• VF ventricular fibrillation
• VT ventricular tachycardia
• AEDs differ from manual defibrillators in that AEDs can automatically analyze the electrocardiogram ("ECG") rhythm to determine if defibrillation is necessary.
• ECG electrocardiogram
• the user is prompted to press a shock button to deliver the defibrillation shock to the patient when a shock is advised by the AED.
• FIG. 1 is an illustration of a defibrillator 10 being applied by a user 12 to resuscitate a patient 14 suffering from cardiac arrest.
• cardiac arrest otherwise known as sudden cardiac arrest, the patient is stricken with a life threatening interruption to their normal heart rhythm, typically in the form of VF or VT that is not accompanied by a palpable pulse (i.e., shockable VT).
• VF the normal rhythmic ventricular contractions are replaced by rapid, irregular twitching that results in ineffective and severely reduced pumping by the heart. If normal rhythm is not restored within a time frame commonly understood to be approximately 8 to 10 minutes, the patient 14 will die.
• the defibrillator 10 may be in the form of an AED capable of being used by a first responder.
• the defibrillator 10 may also be in the form of a manual defibrillator for use by paramedics or other highly trained medical personnel.
• a pair of electrodes 16 are applied across the chest of the patient 14 by the user 12 in order to acquire an ECG signal from the patient's heart.
• the defibrillator 10 analyzes the ECG signal for signs of arrhythmia. IfVF is detected, the defibrillator 10 signals the user 12 that a shock is advised. After detecting VF or other shockable rhythm, the user 12 then presses a shock button on the defibrillator 10 to deliver defibrillation pulse to resuscitate the patient 14.
• VF may also be treated with a synchronized shock, having the benefit of reduced dose requirement (Hsu et al., Circulation 1998;98:808-812; Kidwai et al., J Electrocardiol. 2002;35:235-44).
• shock synchronization has focused on the problem of synchronizing shocks to a broad variety of arrhythmias, both life threatening and non-life threatening. These arrhythmias may be either periodic (complexes repeat at precise time intervals) or non- periodic (interval between complexes is variable). Because of the necessity of accommodating non-periodic arrhythmias, the shocks must be triggered by a real-time morphological feature of the ECG waveform, occurring at some time after initiation of a shock sequence, either by button press or automatically.
• One aspect of the invention is a method and system for synchronizing delivery of shock therapy to a patient from a defibrillator.
• the period for a patient ECG waveform exhibiting a threshold periodicity is calculated and a time reference during the period of the ECG waveform is determined for delivery of shock therapy to the patient.
• the defibrillator is prepared for delivery of the shock therapy at the time reference during a subsequent period of the ECG waveform.
• Another aspect of the invention is a method and system for delivering a defibrillating shock to a patient.
• the periodicity of an ECG waveform of a patient is analyzed.
• a time reference at which to deliver the defibrillating shock during a period of the ECG waveform is determined and the defibrillating shock is delivered synchronized with the time reference for a subsequent period of the ECG waveform.
• an unsynchronized defibrillating shock is delivered to the patient.
• Another aspect of the invention is a defibrillator having electrodes configured to be electrically coupled to a patient, a high- voltage delivery circuit for generating a defibrillating pulse to be provided through the electrodes, and a defibrillator control circuit.
• the defibrillator control circuit is coupled to the electrodes and the high-voltage delivery circuit and is configured to analyze a patient ECG waveform and calculate a time during a period of the ECG waveform at which to deliver a defibrillating pulse if the ECG waveform exhibits a threshold periodicity.
• the defibrillator control circuit controls the high-voltage delivery circuit to deliver the defibrillating pulse to the patient synchronized with the calculated time during a later period of the ECG waveform.
• Figure 1 is an illustration of a defibrillator being applied to a patient suffering from cardiac arrest.
• Figure 2 is an illustration of a defibrillator and electrodes in which shock synchronization according to one embodiment of the present invention can be implemented.
• Figure 3 is a is a simplified block diagram of the defibrillator of Figure 2.
• Figure 4 is a flow diagram of shock synchronization according to an embodiment of the present invention.
• FIG. 2 illustrates defibrillator 110 according to an embodiment of the present invention.
• the defibrillator 110 is configured as an AED, and is designed for small physical size, light weight, and relatively simple user interface capable of being operated by personnel without high training levels or who otherwise would use the defibrillator 110 only infrequently.
• a paramedic or clinical defibrillator tends to be larger, heavier, and have a more complex user interface capable of supporting a larger number of manual monitoring and analysis functions.
• a pair of electrodes 116 is connected to a connector 126 for insertion into a socket 128 on the defibrillator 110.
• an on-off switch 118 Located on a top surface of the defibrillator 110 is an on-off switch 118 that activates the defibrillator 110 and begins the process of the prompting the user 12 ( Figure 1) to connect the electrodes 116 to the patient 14.
• a battery condition indicator 120 provides a continual visual indication of the defibrillator status and the available battery charge.
• a display 122 preferably provides for display of text such as user prompts and graphics such as ECG waveforms.
• a shock button 124 provides for delivery of the shock to the patient 14 if ECG analysis indicates that a shockable rhythm is present. Administration of defibrillation shocks is done by prompting the user 12 to manually press the shock button 124.
• FIG. 3 is a simplified block diagram of the defibrillator 110 ( Figure 2) according to an embodiment of the present invention.
• An ECG front end 202 is connected to the pair of electrodes 116 that are connected across the chest of the patient 14.
• the ECG front end 202 operates to amplify, buffer, filter and digitize an electrical ECG signal generated by the patient's heart to produce a stream of digitized ECG samples.
• the digitized ECG samples are provided to a controller 206 that performs an analysis to detect VF, shockable VT or other shockable rhythm. If a shockable rhythm is detected, the controller 206 sends a signal to HV delivery 208 to charge-up in preparation for delivering a shock. Pressing the shock button 124 then delivers a defibrillation shock from the HV delivery 208 to the patient 14 through the electrodes 116.
• the controller 206 is coupled to further receive input from a microphone 212 to produce a voice strip.
• the analog audio signal from the microphone 212 is preferably digitized to produce a stream of digitized audio samples which may be stored as part of an event summary 130 in a memory 218.
• a user interface 214 may consist of the display 122, an audio speaker (not shown), and front panel buttons such as the on-off button 118 and shock button 124 for providing user control as well as visual and audible prompts.
• a clock 216 provides real-time clock data to the controller 206 for time-stamping information contained in the event summary 130.
• the memory 218, implemented either as on-board RAM, a removable memory card, or a combination of different memory technologies, operates to store the event summary 130 digitally as it is compiled over the treatment of the patient 14.
• the event summary 130 may include the streams of digitized ECG, audio samples, and other event data, as previously described.
• Figure 4 illustrates a process 400 for delivering a synchronized defibrillation shock if analysis of the ECG indicates a synchronized defibrillation shock should be administered.
• the controller 206 ( Figure 3) performs analysis to detect VF, shockable VT or other shockable rhythm.
• the controller 206 commands the HV delivery 208 to prepare for delivery of a defibrillation shock to the patient 14.
• the controller 206 performs further analysis of the ECG to determine if a synchronized defibrillation shock is to be delivered, and if so, calculate the timing for delivering a synchronized defibrillation shock to the patient 14 in response to the shock button 124 being pressed.
• the ECG is analyzed by the controller 206 at step 414 to determine whether the ECG exhibits a suitable level of periodicity.
• the threshold level of periodicity is set to identify ECG signals exhibiting a relatively high periodicity. That is, the threshold level of periodicity should provide sufficient confidence that delivering a synchronized defibrillation shock will be beneficial to the patient 14. Such a determination is well within the skill of those ordinarily skilled in the art.
• a process using an autocorrelation function can be applied by the controller 206 to determine whether the ECG is periodic.
• the periodicity of the ECG can be determined by applying alternative algorithms and processes which identify a recurrent characteristic of the ECG waveform. Suitable autocorrelation functions and alternative algorithms are known, and those ordinarily skilled in the art have sufficient knowledge to apply these functions and algorithms for determining periodicity of the ECG waveform. Consequently, a more detailed discussion regarding the determination of ECG periodicity has been omitted herein in the interest of brevity.
• the controller 206 determines that the ECG is not periodic, the defibrillation shock will be delivered to the patient 14 immediately in response to the shock button 124 being pressed at steps 418 and 422.
• the controller 206 determines that the ECG is periodic at step 414, the controller 206 performs further processes to synchronize delivery of the defibrillation shock when the shock button 124 is pressed.
• the period T of the ECG is calculated by the controller 206 at step 426.
• the period T can also be determined using the same function, as is known.
• Alternative algorithms or processes can also be used to determine the period T of the ECG as well.
• the controller further analyzes the periodic ECG to identify a time reference to during a period T of the ECG.
• the time reference to represents a time during a period T of the ECG at which delivery of a defibrillating shock is synchronized.
• the time reference t 0 can be based on a morphological feature or an ECG waveform characteristic, such as an amplitude maximum, a first derivative maximum, or a second derivative maximum.
• the time reference t 0 is selected based on zero crossings of the ECG waveform.
• the time reference t 0 is selected based on characteristics other than, or in addition to, a morphological feature of the ECG.
• the time reference t 0 is identified by analyzing data representing the most recent period T of the ECG.
• the data for one or more previous periods T of the ECG can be analyzed by the controller 206 to select a time reference to.
• the time reference to is used to calculate a time at which to deliver a defibrillation shock during a later period T of the ECG in the event the shock button 124 is pressed.
• occurrence of the time reference to during a following period T of the ECG can be predicted.
• the predicted time at which to deliver the defibrillation shock is (t o +nT), where n is an integer value greater than zero.
• identifying a time reference t 0 in a current period T of the ECG (step 430) corresponding to the time at which a synchronized defibrillation shock should be delivered to the patient 14 can be used for actually delivering a synchronized defibrillation shock at a predicted time during a subsequent period T of the ECG.
• delivery of the defibrillation shock can be synchronized with the morphological event represented by the time reference t 0 .
• a time offset can also be added to the predicted time to provide the HV delivery 208 with enough time to be activated and triggered to actually deliver the defibrillation shock at the predicted time.
• the controller 206 continues to analyze data for the most recent period T of the ECG to identify a time reference t 0 and calculate a predicted time to deliver the defibrillation shock in the event the shock button 124 is pressed.
• delivery of the defibrillation shock to the patient 14 will be synchronized with the predicted occurrence of the morphological feature represented by the time reference to in a following period T of the ECG waveform.
• a shock may be delivered, but at the end of a time-out period, or the defibrillation shock may be simply aborted.
• the ECG exhibits sufficient periodicity a synchronized shock will be delivered at the predicted time following the pressing of the shock button.
• the system determines that the ECG is not periodic, and delivers the shock immediately.
• a shock is delivered sooner than for a conventional system performing real-time analysis and struggling with the borderline ECG to detect a triggering event, which delivers a shock only after the time-out period expires.
• Embodiments of the present invention address the problem of synchronization failure by focusing on treatment of life-threatening arrhythmias possessing a high degree of periodicity. There are additional benefits resulting from the fact that many VF, especially those associated with short arrest durations, also exhibit high periodicity. Synchronized shocks delivered to these VF rhythms may reduce defibrillation thresholds and therefore dose requirements.
• the predictive method previously described can be used in both automatic defibrillators as well as manual mode defibrillators.
• manual mode systems where a shock will be delivered if the shock button is pressed, the predictive method will be able to determine the appropriate time following the pressing of the shock button to deliver the shock for synchronized delivery.
• embodiments of the present invention include a system that monitors a patient's ECG and determines a degree of periodicity, as well as the corresponding rhythm period (interval of ECG complex repetition).
• a morphological feature of the ECG is identified in a periodic waveform for time reference. If a shock is deemed beneficial (via separate arrhythmia detection system), and a shock sequence is initiated either automatically or by button press, the shock delivery time is based on the periodicity of the ECG. That is, for rhythms with low periodicity, an unsynchronized shock is delivered immediately and for rhythms with high periodicity, the shock is delivered at a time equal to the morphological time reference, plus an integer multiple of the rhythm period, both previously determined.
• ECG periodicity (step 414) may be performed before the shock advised step 410.
• the process would determine whether a shock is advised.
• the subsequent shock advised step may use a particular algorithm. For instance, when high ECG waveform periodicity is determined the shock advised analysis may consider an identified morphological feature of the ECG. Accordingly, the invention is not limited except as by the appended claims.

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• 2006
  • 2006-11-09 EP EP06821386A patent/EP1954345A2/de not_active Withdrawn
  • 2006-11-09 JP JP2008539595A patent/JP2009515587A/ja not_active Withdrawn
  • 2006-11-09 WO PCT/IB2006/054181 patent/WO2007054906A2/en active Application Filing

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