Abstract:
An automated external defibrillator (AED) and methods for reducing the delay between termination of cardiopulmonary resuscitation (CPR) and administration of a defibrillating shock, among other disclosed apparatus and methods. In one embodiment, the AED includes an ECG sensor that obtains an ECG signal corresponding to patient heart activity and a prompting device that provides instructions regarding cardiopulmonary resuscitation. The AED also has a control system including a microprocessor programmed to run two rhythm analysis algorithms after instructions to terminate CPR. The two rhythm analysis algorithms analyze segments of the ECG signal for recognizing the presence of a shockable rhythm, with one algorithm having a delayed start relative to the other algorithm. The AED additionally includes a therapy generation circuit for treating the shockable rhythm with a defibrillation pulse in response to the control system determining the presence of a shockable rhythm.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to improved methods and apparatus involving the integrated use of Automated External Defibrillators (AEDs) and cardiopulmonary resuscitation (CPR). Specifically, this invention relates to AEDs and methods that quickly and reliably determine the presence of a shockable cardiac rhythm in a cardiac arrest victim during a resuscitation attempt such that minimal delay between CPR and delivery of a defibrillation shock is made possible. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cardiac arrest is widely-understood to be a substantial public health problem and a leading cause of death in most areas of the world. Each year in the U.S. and Canada, approximately 350,000 people suffer a cardiac arrest and receive attempted resuscitation. Accordingly, the medical community has long sought ways to more successfully treat cardiac arrest victims through CPR and application of defibrillation shocks to rapidly restore a normal heart rhythm to persons experiencing this type of event. AEDs were first developed decades ago to help treat incidents of cardiac arrest. Since their creation, AEDs have become prevalent in public locales such as offices, shopping centers, stadiums, and other areas of high pedestrian traffic. AEDs empower citizens to provide medical help during cardiac emergencies in public places where help was previously unavailable in the crucial early stages of a cardiac event. 
         [0003]    Fully automated external defibrillators capable of accurately detecting ventricular arrhythmia and non-shockable supraventricular arrhythmia, such as those described in U.S. Pat. No. 5,474,574 to Payne et al., have been developed to treat unattended patients. These devices treat victims suffering from ventricular arrhythmias and have high sensitivity and specificity in detecting shockable arrhythmias in real-time. Further, AEDs have been developed to serve as diagnostic monitoring devices that can automatically provide therapy in hospital settings, as exhibited in U.S. Pat. No. 6,658,290 to Lin et al. 
         [0004]    Despite advances in AED technology, many current AEDs are not fully functional in implementing the current medically suggested methods of integrated CPR and AED use. Most of the AEDs available today attempt to classify ventricular rhythms and distinguish between shockable ventricular rhythms and all other rhythms that are non-shockable. This detection and analysis of ventricular rhythms provides some real-time analysis of ECG waveforms. However, the functionality, accuracy and speed of a particular AED heavily depends on the algorithms and hardware utilized for analysis of ECG waveforms. In many implementations, the algorithms used in AEDs depend on heart rate calculations and a variety of morphology features derived from ECG waveforms, like ECG waveform factor and irregularity as disclosed in U.S. Pat. No. 5,474,574 to Payne et al. and U.S. Pat. No. 6,480,734 to Zhang et al. Further, in order to provide sufficient processing capability, current AEDs commonly embed the algorithms and control logic into microcontrollers. 
         [0005]    As advances have taken place in the field of AEDs, there have been significant medical advancements in the understanding of human physiology and how it relates to medical care as well. These advancements in medical research have lead to the development of new protocols and standard operating procedures in dealing with incidents of physical trauma. For example, in public access protocols for defibrillation, recent guidelines have emphasized the need for the use of both CPR and AEDs and suggested an inclusive approach involving defibrillation integrated with CPR. 
         [0006]    Along with its advantages, integrated use of CPR with defibrillation can, however, negatively impact the operation of an AED as chest compressions and relaxations are known to introduce significant motion artifacts in an ECG recording. During and after CPR, where a rescuer is instructed to apply chest compressions and relaxations at a prescribed rate of approximately 100 cycles per minute, the ability to obtain clean signal data from the patient can be challenging. 
         [0007]    In addition to the difficulty of obtaining a clean ECG signal, the importance of doing this quickly has recently been highlighted as the current AHA Guidelines emphasize the importance of minimizing interruptions between CPR and defibrillation. The guidelines state, “[d]efibrillation outcome is improved if interruptions (for rhythm assessment, defibrillation, or advanced care) in chest compressions are kept to a minimum”, and “[m]inimizing the interval between stopping chest compressions and delivering a shock (ie, minimizing the preshock pause) improves the chances of shock success and patient survival.” See Circulation 2010, 122: S678, S641. 
         [0008]    Some past AEDs implement an algorithm that requires an extended period of clean ECG signal data during a rescue to classify a sensed ventricular rhythm as shockable. Some prior art disclosures requiring a clean signal also discuss carrying out an initial assessment of ECG when CPR is ongoing, before relying on a temporary stoppage in CPR to acquire and perform an ECG analysis. Moreover, much of the recent scholarship in this area involves using tools which enable the entire analysis of ECG to take place while CPR is ongoing such that little or no stoppage of CPR is required. Accordingly, numerous techniques for identifying and filtering CPR artifacts for the purpose of ECG signal analysis have been proposed. However, many of these methods and analysis techniques have limitations or raise concerns related to providing appropriate care, especially in view of the newest AHA guidelines. 
         [0009]    Accordingly, improved methods and apparatus for quickly assessing shockable cardiac rhythms which minimize any time periods between CPR and delivery of a defibrillation shock by an AED are desired. 
       SUMMARY OF THE INVENTION 
       [0010]    Various embodiments of the present invention can overcome the problems of the prior art by providing a method and device to rapidly, but accurately, determine and verify the presence of a shockable cardiac rhythm to minimize delay between CPR and delivery of a defibrillation shock by a rescuer. 
         [0011]    In one embodiment, an automated external defibrillator (AED) is provided. This AED includes an ECG sensor that obtains an ECG signal corresponding to patient heart activity and a prompting device that provides cardiopulmonary resuscitation (CPR) instructions. Further, the AED also has a control system including a microprocessor programmed to run two rhythm analysis algorithms after instructions to terminate CPR have been provided. The two rhythm analysis algorithms analyze segments of the ECG signal for recognizing the presence of a shockable rhythm. One of the two rhythm analysis algorithms provides a delayed start shockable rhythm verification algorithm. The AED additionally includes a therapy generation circuit for treating the shockable rhythm with a defibrillation pulse in response to the control system determining the presence of a shockable rhythm. 
         [0012]    In another embodiment according to the present invention, an AED is disclosed. The AED includes an ECG sensor that obtains an ECG signal corresponding to patient heart activity. The AED also includes a prompting device for providing CPR instructions. The AED further includes a control system including a microprocessor in which the control system is adapted to determine the presence of a shockable a cardiac rhythm in a first segment of the ECG signal using a first algorithm. The control system is further adapted to determine the presence of a shockable cardiac rhythm in a second segment of the ECG signal using a second verification algorithm. The first algorithm and second verification algorithms run in parallel and analyze segments of the ECG signal. In this embodiment, the first segment begins when instructions to cease CPR are given. Thereafter, the second segment begins after a short number of seconds. The AED of this embodiment further includes a power generation circuit for providing power for a defibrillation pulse that may be used to treat shockable rhythms and a pulse delivery circuit. 
         [0013]    According to an embodiment of the present invention, an automated external defibrillator is provided for reducing the delay between termination of cardiopulmonary resuscitation and administration of a defibrillating shock. The AED includes an ECG sensor that obtains an ECG signal corresponding to patient heart activity and a processor. The processor runs multiple rhythm analysis algorithms that each independently determine the presence of a shockable rhythm based segments of the ECG signal with different start times following cardiopulmonary resuscitation in order to verify the presence of a shockable rhythm. 
         [0014]    Another embodiment according to the present invention, includes a method for delivering a defibrillation shock with an automated external defibrillator (AED). The method includes charging an AED during cardiopulmonary resuscitation (CPR), prompting a break in CPR with a prompting device of the AED, and analyzing a first segment of patient ECG data immediately following CPR with a first algorithm to determine if the ECG data has an initial shockable classification. The method also includes monitoring the ECG data with the first algorithm after the initial shockable classification to verify that the shockable classification remains consistent. The method further includes analyzing a second segment of the ECG data with a delayed start time compared to the first segment of ECG data with a second verification algorithm while the first algorithm is concurrently analyzing and monitoring ECG data to obtain an independent rhythm classification. The method also includes the step of comparing using the rhythm classification of the second algorithm with the classification of the first algorithm to provide resuscitation advice. 
         [0015]    Yet another embodiment includes a method for reducing the delay between termination of cardiopulmonary resuscitation and administration of a defibrillating shock with an AED. This method includes the steps of initiating CPR, charging the AED, and prompting a break in CPR, analyzing a first set of ECG data immediately following CPR with a first algorithm to determine if the ECG data has a shockable rhythm classification. The method also includes the steps of analyzing a second set of ECG data obtained with a delayed start with respect to the first set of ECG data to determine if the ECG data has a shockable rhythm classification, and comparing the classification of the first set of ECG data and the second set of ECG data to determine whether a defibrillation shock should be delivered by the AED. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
           [0017]      FIG. 1  illustrates generally an example of a cardiac arrest victim being treated with CPR and an AED, according to an embodiment of the invention. 
           [0018]      FIG. 2  illustrates generally an example of a schematic drawing of the hardware of an AED, according to an embodiment of the invention. 
           [0019]      FIG. 3  illustrates generally a flowchart of the operation steps of the AED rhythm analysis according to an embodiment of the invention. 
           [0020]      FIG. 4  illustrates generally a chart setting forth an example timeline of rhythm assessment and AED operation with a successful match of rhythm assessment in algorithms generally run in parallel. 
           [0021]      FIG. 5  illustrates generally a chart setting forth an example timeline of rhythm assessment and AED operation which does not include a successful match of rhythm assessment in generally parallel algorithms. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The invention may be embodied in other specific forms without departing from the essential attributes thereof, therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive. 
         [0023]    In various embodiments of this invention an apparatus and method are disclosed for rapidly and reliably evaluating an ECG signal from a patient such that minimal delay between CPR and delivery of a defibrillation shock is made possible.  FIG. 1  depicts a cardiac arrest victim who is undergoing a resuscitation attempt and is being treated with an AED and CPR. The AED  100  is shown with electrode pads  104  and  106  coupled to the patient&#39;s chest and the rescuer  108  is shown in position for rapidly providing chest compressions to the patient  110 . 
         [0024]    The AHA currently recommends that all rescuers, regardless of training, should provide chest compressions to all cardiac arrest victims, and that chest compressions should be the initial CPR action for all victims regardless of age. CPR typically improves a victim&#39;s chance of survival by providing critical blood circulation in the heart and brain. 
         [0025]    Often, CPR alone will be insufficient to reverse cardiac arrest in a patient. In these cases, an AED  100  may be used to deliver an impulse of high amplitude current to a patient&#39;s heart to restore it to normal cardiac rhythm. However, there are many different types of heart rhythms, only some of which are considered shockable. The primary shockable rhythms are ventricular fibrillation (VF), ventricular tachycardia (VT), and ventricular flutter. Non-shockable rhythms may include bradycardias, electro-mechanical dissociation, idio-ventricular rhythms, and normal heart rhythms. 
         [0026]    In order to determine if a rhythm is shockable, AEDs analyze ECG data to classify the type of rhythm the patient is experiencing. Specifically, a pair of AED electrodes  104  and  106  are positioned on the patient&#39;s chest, as shown in  FIG. 1 , to obtain an ECG signal. Next, the ECG signal is analyzed by the AED and if the cardiac rhythm is deemed shockable, a defibrillation pulse is delivered to the patient. 
         [0027]    AEDs relying upon such an ECG analysis may be considered semi-automatic or fully-automatic. In general, semiautomatic defibrillators require a user to press a button to deliver the actual defibrillating shock, compared to fully-automatic defibrillators that can deliver therapy without such an input of the user. Various embodiments of the present invention can work with either automatic and/or semi-automatic AEDs. 
         [0028]    In  FIG. 1 , the AED  100  is shown coupled to a pair of electrodes  104  and  106  located on the patient&#39;s chest  110 . The AED  100  is equipped with a central compartment having a hinged lid  112  to house the electrode pads  104  and  106  when the defibrillator is not in use. The lid  112  is shown in an open configuration in  FIG. 1  and accordingly, is ready for use. In one embodiment, opening this lid  112  activates the AED  100  and begins sending prompts to the user. Prompts may include voice prompts from speaker  114  and visual prompts from the display  116 . 
         [0029]      FIG. 2  illustrates generally a block diagram of the hardware of an AED  200  implementing the improved shocking algorithms according to one embodiment of the invention. A digital microprocessor-based control system  202  is used for controlling the overall operation of AED  200 . The electrical control system  202  further includes an impedance measuring circuit for testing the interconnection and operability of electrodes  204  and  206 . Control system  202  includes a processor  208  interfaced to program memory  210 , data memory  212 , event memory  214  and real time clock  216 . The operating program executed by processor  208  is stored in program memory  210 . Electrical power is provided by the battery  218  and is connected to power generation circuit  220 . 
         [0030]    Power generation circuit  220  is also connected to power control unit  222 , lid switch  224 , watch dog timer  226 , real time clock  216  and processor  208 . A data communication port  228  is coupled to processor  208  for data transfer. In certain embodiments, the data transfer may be performed utilizing a serial port, usb port, firewire, wireless such as 802.11x or 3G, radio and the like. Rescue switch  230 , maintenance indicator  232 , diagnostic display panel  234 , the voice circuit  236  and audible alarm  238  are also connected to processor  208 . Voice circuit  236  is connected to speaker  240 . In various embodiments, rescue light switch  242  and a visual display  244  is connected to the processor  208  to provide additional operation information. 
         [0031]    In certain embodiments, the AED will have a processor  208  and a co-processor  246 . The co-processor  246  may be the rhythm analysis algorithm implemented in hardware and operably connected to the processor over a high-speed data bus. In various embodiments, the processor  218  and co-processor  246  are on the same silicon and may be implemented in a multi-core processor. Alternatively, the processor  208  and co-processor may be implemented as part of a multi-processor or even networked processor arrangement. In these embodiments, the processor  208  offloads some of the calculations to the co-processor thus optimizing the processing of the sensed signals from the electrodes  204  and  206 . In other embodiments, the processor  208  is optimized with specific instructions or optimizations to execute calculations. Thus, processor  210  may execute calculations in fewer clock cycles and while commanding fewer hardware resources. In other embodiments, the logic and algorithm of the control system  202  may be implemented in logic, either hardware in the form of an ASIC or a combination in the form of an FPGA, or the like. 
         [0032]    High voltage generation circuit  248  is also connected to and controlled by processor  208 . High voltage generation circuit  248  may contain semiconductor switches (not shown) and a plurality of capacitors (not shown). In various embodiments, connectors  250 ,  252  link the high voltage generation circuit  248  to electrodes  204  and  206 . Note that the high voltage circuit here is battery powered and is of high power. 
         [0033]    Impedance measuring circuit  254  is connected to both connector  250  and real time clock  216 . Impedance measuring circuit  254  is interfaced to real time clock through analog-to-digital (A/D) converter  256 . Another impedance measuring circuit  258  may be connected to connector  250  and real time clock  216  and interfaced to processor  208  through analog-to-digital (A/D) converter  256 . A CPR device  260  may optionally be connected to the processor  208  and real time clock  216  through connector  252  and A/D converter  256 . The CPR device  260  may be a chest compression detection device or a manual, automatic, or semi-automatic mechanical chest compression device. Additional detailed discussions of some AED designs can be found in U.S. Pat. Pub. No. 2011/0105930 and U.S. Pat. Nos. 5,474,574, 5,645,571, 5,749,902, 5,792,190, 5,797,969, 5,919,212, 5,999,493, 6,083,246, 6,246,907, 6,263,238, 6,289,243, 6,658,290, 6,993,386, each of which is hereby incorporated by reference. 
         [0034]    The methods and systems utilized by embodiments of the present invention generally consist of employing two instances of rhythm analysis algorithms  300  and  301  that operate in parallel for assessment and verification in an AED or similar cardiac resuscitation device (like the one depicted in  FIG. 2 , for example) so as to improve the time to deliver therapy. The first rhythm analysis algorithm  300  operates immediately, with little or no initial hold-off period from the AED&#39;s instruction to cease CPR. The second algorithm is a verification algorithm and default therapy recommendation algorithm. The second rhythm analysis verification algorithm  301  operates after a delayed start as a verification algorithm. Specifically, the second rhythm analysis verification algorithm  301  starts operating after a hold-off period that is designed to reduce the impact of CPR artifacts on rhythm analysis. The defibrillator will advise shock if after an initial learning period, the first instance of rhythm analysis  300  indicates the presence of the same shockable rhythm throughout and the rhythm classification from the second rhythm analysis verification algorithm  301  coincides with that of the first classification from the first rhythm analysis algorithm  300 . If the rhythm classifications do not match, the second rhythm analysis verification algorithm  301  is allowed to complete a full analysis and monitoring period and the classification resulting from that second algorithm  301  is used to determine the classification as well as any subsequent protocol advice for rescue. 
         [0035]      FIG. 3  sets forth a more detailed flowchart describing the operational steps of an AED which utilizes a rhythm analysis coordinating two algorithms directed at segments with different start points for analysis of an ECG signal to quickly arrive at a cardiac rhythm classification and to verify assessments of shockable status. 
         [0036]    Specifically, operation of the AED  100  with one embodiment of the rhythm analysis algorithm first charges the AED capacitors with the internal battery during CPR, as set forth at numeral  302 . This charge may be triggered in a variety of ways. In some embodiments, charging may occur simply by activating the AED  100  by opening its cover, turning it on, or other similar method. In other preferred embodiments, charging only will occur if a previous analysis has found a shockable rhythm so that the operating life of the battery is not negatively impacted in a substantial way by such pre-charging. Next, at an appropriate point during CPR, the AED  100  provides a voice prompt indicating that the user  108  should stop CPR, as represented by numeral  304 . Immediately following the voice prompt either a momentary analysis holdoff period or no holdoff period at all is provided, as represented at  306 . This preliminary analysis holdoff period only lasts for around one second in various embodiments. Next, a first (or primary) rhythm analysis algorithm (RAA) engine (the first rhythm analysis algorithm  300  engine) is started at  308  and is analyzed at  310 . The analyze period for this algorithm may last for about four seconds in some embodiments. The first rhythm analysis algorithm  300  follows the analyze period with an operation at  312  in which a shockable decision is reached and monitored for a short length of time. In some embodiments, this shockable decision and monitoring phase lasts for around five seconds. A determination is then made at  314  if a consistent classification of a shockable rhythm has remained throughout the monitoring phase. While the first rhythm analysis algorithm  300  is being carried out, a second rhythm analysis verification algorithm  301  operates simultaneously in a parallel evaluation of ECG rhythm data. This second (or secondary) rhythm analysis verification algorithm  301  begins with an analysis holdoff period  316  which starts as the first rhythm analysis operation  310  begins. Next, the second rhythm analysis verification algorithm  301  starts when the holdoff period completes at  318 . By delaying the start of the second rhythm analysis verification algorithm  301 , data artifacts and disturbances that might impact signal integrity or the ability to obtain a clean signal are greatly reduced, but without reliance on any filtering of the ECG signal. The second rhythm analysis algorithm  301  then enters an analyze phase  320 . This analyze period  320  may last for five seconds, for example, in some embodiments. At the end of this period, a determination is made at  322  classifying the rhythm as shockable or non-shockable. 
         [0037]    Next, if the rhythm is deemed shockable by the second algorithm  301  and the first algorithm  300  gave a consistent classification indicating a shockable rhythm throughout the monitoring period, a shock is issued, at step  324 . In the case that either the first algorithm  300  was not consistently classified as shockable throughout the monitoring period or the second algorithm  301  classification was not shockable, the second algorithm classification is continued at  326 . The second algorithm is then classified as shockable or non-shockable throughout a continued period of monitoring and analysis at  328 . If the classification is shockable, a defibrillation shock is issued at  330 . If the rhythm is not classified as shockable, no shock is delivered and further CPR or rescue protocol prompts or recommendations are provided, at  332 . 
         [0038]    For purposes of this disclosure, the first rhythm analysis algorithm may also be understood as the primary rhythm analysis algorithm and the second rhythm analysis verification algorithm may also be understood as the secondary rhythm analysis algorithm or the second rhythm analysis algorithm in various embodiments. In certain embodiments, each of the rhythm analysis algorithms can be understood to be modified versions of the RHYTHMx® software algorithm of Cardiac Science Corporation. Note that this method may make use of existing rhythm analysis algorithms in current AEDs or be part of completely updated algorithms used to control AED operation in various embodiments. 
         [0039]    Use of two independent rhythm analysis algorithms for a shockable assessment and verification process is a useful and advantageous alternative over past prior art techniques. For example, alternative windowing techniques have been used throughout the prior art which restrict therapy decision-making to assessments of contiguous windows which are further subjected to a voting process to enhance consistency. This windowing technique has been modified somewhat in other disclosures to use overlapping windows of data for speeding up this assessment. One signal analysis technique that models overlapping windows and +has been know for decades for doing so is referred to as Welch&#39;s method although other similar techniques exist. Welch&#39;s method essentially teaches reduction in noise signals, like ECG signals, using spectral density estimation. The method is based on the concept of using periodogram spectrum estimates which are the result of converting a signal from the time domain to the frequency domain. Basically, a signal is split up into overlapping segments that are windowed and a Fourier transform operation is used to provide an array of power measurements vs. frequency bin. This overlapping in Welch&#39;s technique is deemed useful as it reduces problems at the boundaries between windows but provides a different computational methodology for approaching the problem of speeding up a rhythm assessment and specifically dealing with problematic post CPR signals. See U.S. Pat. No. 7,463,922. 
         [0040]    The current disclosure does not use such a windowing technique, and instead approaches the problem in a different way using a targeted assessment and verification process. It has been found that use of the currently disclosed, non-windowing process, that makes use of two entirely separate algorithms and verification process, allows one to better rapidly assess and verify the shock assessment. The methods discussed in the current application both make use of the period immediately following CPR and yet take into account the potential noise inaccuracies of this period, in a way that windowing data by past techniques does not contemplate. 
         [0041]      FIG. 4  depicts the rhythm analysis process in an alternate timeline format. Specifically,  FIG. 4  is a chart  400  setting forth an example timeline of rhythm assessment and AED operation with an initial match of rhythm assessment in the generally parallel rhythm analysis algorithm  300  and the rhythm analysis verification algorithm  301 . In this example, an ECG signal is analyzed and a defibrillation shock is delivered within ten seconds of CPR. 
         [0042]    The first timeline section  402  represents a ten second period of charging that occurs while CPR is performed. The end of the first timeline segment  402  corresponds to commencement of a voice prompt of the AED that occurs at  404 . This voice prompt at  404  instructs the rescuer to stop CPR and not to touch the victim. Specifically, the voice prompt states, “Do Not Touch Patient! Analyzing Heart Rhythm.” 
         [0043]    The prompt to cease CPR also coincides with the start of an analysis period  406  by the first rhythm analysis algorithm  300 . This period of analysis  406  could last for five seconds, as depicted in the chart, or for another suitable alternative time period. The first second of this analysis period  406  can include a brief hold-off period, such as a one second delay in some embodiments as well. During the analysis period  406 , ECG data is acquired and analyzed with respect to the shockability of the heart activity data presented. This is followed by an analysis and monitoring period  408 . This period begins with an assessment of the cardiac condition of ECG data indicating that either a shockable or non-shockable cardiac rhythm is present. This assessment is then continued to be analyzed and monitored over the period  408  to ensure that a consistent shockable or non-shockable assessment is made throughout this time period. 
         [0044]    Concurrently with the analysis period  406 , the second rhythm analysis verification algorithm  301  carries out an initial hold-off period  410 . This hold-off period  410  may last four to five seconds in some embodiments, for example. The hold-off period  410  is useful, in that, it avoids signals immediately following CPR and any potential impact of data artifacts and disturbances on signal integrity or on the ability to obtain a clean signal. The hold-off period  410  many culminate in a short learn period  412  in some embodiments in which ECG data is obtained. Once the hold-off period  410  is complete, acquired ECG data is evaluated by the second rhythm analysis verification algorithm  301  during an analyze period  414  to determine if a shockable or non-shockable rhythm exists. After a short time in the analyze period  414  (five seconds in some embodiments) a shockable rhythm determination is made which is compared to the determination made and monitored by the first rhythm analysis algorithm  300  during the concurrent period  408 . 
         [0045]      FIG. 4  illustrates an instance in which the classification during the analyze and monitor period  408  is “shockable” and the assessment after the first seconds of the analyze period  414  is also “shockable”. Because both of these classifications match, instructions to deliver a shock are immediately provided by the AED control circuit. Such a quick shock decision is accordingly made possible because this method increases confidence in early rhythm classifications that may be determined soon after CPR. 
         [0046]      FIG. 5  is a chart  500  setting forth an example timeline of rhythm assessment and AED operation which does not include an initial match of rhythm assessment in the parallel algorithms. Here, either the period  508  did not maintain a consistent “shockable” classification or the second rhythm analysis verification algorithm  301  revealed a non-shockable cardiac rhythm. In this situation, the rhythm analysis algorithm  301  completes the analysis period  514  and requests therapy based upon the classification determined by rhythm analysis algorithm  301  alone. 
         [0047]    A further set of voice prompts from the AED are depicted in  FIGS. 4 and 5 . These further voice prompts occur following the instructions given not to touch the patient at  404 . Specifically, the subsequent voice prompts  416  will announce “Preparing Shock. Move Away From The Patient!” 
         [0048]    With respect to battery charging, this charging is designed to continue during a period  418  partially common to the analyze and hold-off periods  406 ,  408 ,  410 ,  412  and  414 . However, the battery charge is short enough to be ready for defibrillation pulse delivery before an early shock decision can be made. Fast charging batteries are possible in some embodiments as well, which could complete charging is much less time than depicted in  FIGS. 4 and 5 . 
         [0049]    It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with an enabling disclosure for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof. 
         [0050]    The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 
         [0051]    Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention. 
         [0052]    For purposes of interpreting the claims for the present invention, it is expressly intended that the provisions of Section 112, sixth paragraph of 35 U.S.C. are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.