Abstract:
An external cardiac device includes a detector used to detect an abnormal condition of a patient, a controller operating the defibrillator in response to a command and a therapy delivery circuit that delivers appropriate therapy, such antitachycardia, defibrillation or antibradicardia therapy. The defibrillator is attached to a patient by any attendant or bystander and a signal is sent to central station to alert a clinician that the device has been activated. Once the device has been attached, the defibrillator is adapted to monitor the patient and to transmit information to the remotely located operator. The operator then decides what kind of therapy is required and transmits an appropriate command to the device. In one embodiment, the device includes a base station communicating with the central station and a pulse generator which may be separable from the base station. In another embodiment a unitary pulse generator is used with means for communicating with the clinician directly. The device includes a speaker and a microphone to allow the operator and the attendant and/or patient to communicate with each other.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    A. Field of Invention  
           [0002]    This invention pertains to an external defibrillator system adapted to provide therapy selectively to patients suffering from sudden acute cardiac arrest. More particularly, the present invention pertains to an external defibrillator system including a pulse generator adapted to apply therapeutic pulses to a patient, a local controller which is normally interfaced with the pulse generator, except during the application of therapy, and a remote controller operated by a clinician which generates commands to control the operation of the pulse generator. The human operator receives instructions on how to position the pulse generator and other information from the clinician via a voice communication link.  
           [0003]    2. Description of the Prior Art  
           [0004]    The term Cardiac Emergency is used herein to denote situations leading to acute, potentially life threatening symptoms that may be caused by cardiac disease.  
           [0005]    The term Sudden Cardiac Arrest or SCA in a patient refers to a condition characterized by a loss of effective pumping action in the heart. More specifically, the patient&#39;s heart loses rhythm, starts to quiver and ceases to pump blood. The heart then usually goes into ventricular tachycardia (VT) and then typically generates to ventricular fibrillation (VF).  
           [0006]    During a heart attack (also called myocardial infarction) the blood vessels to the heart are clogged and the pumping capacity of the heart gets progressively reduced. If left untreated the heart muscles begin to die. The therapy for this condition typically consists of the administration of thrombolytic ( clot dissolving) drugs administered in an emergency health care facility.  
           [0007]    Thus, SCA results in an abrupt cessation of blood circulation to the vital organs, and once it occurs, unless the patient&#39;s heart is reverted rapidly to a sinus rhythm, death will occur. In fact SCA is considered to be the leading cause of death in the United States and throughout the world. The acute therapy for VT and VF consists of electrical shocks which are generally characterized as cardioversion pulses and ventricular defibrilliation shocks, respectively.  
           [0008]    Arrhythmias which cause SCA include ventricular tachycardia and ventricular fibrillation. Ventricular tachycardia is characterized by electrical disturbances which cause a dangerously high cardiac rate and may lead to ventricular fibrillation. Ventricular fibrillation refers to a state where cardiac electrical activity is completely disorganized and the heart is quivering. During ventricular fibrillation, the heart does not pump blood, and no beats can be detected.  
           [0009]    Other arrhythmias can lead to acute symptoms as well, including fainting, dizziness which, if left untreated, could become life threatening. These latter arrhythmias include bradycardia (which occurs when a person&#39;s heat beat slows down so much that not enough blood is being pumped through the body) and supra-ventricular arrhythmias (SVT).  
           [0010]    Arrhythmias may be detected from the patient&#39;s electrocardiogram (ECG), blood pressure, blood oxygenation level and other similar physiological parameters. Because the signals indicative of these parameters can be very complex, various algorithms are used to analyze these parameters to detect and classify an arrhythmia. Once detected, the arrhythmia can be eliminated by using antitachycardia therapy consisting of electrical stimulation. Two kinds of devices are presently available to provide antitachyarrhythmia therapy: internal or implanted cardioverter defibrillators (ICDs), and external defibrillators.  
           [0011]    ICDs have been known since the early 1980s. These devices are implanted in the patient and include electrodes extending to the cardiac chambers to sense intrinsic cardiac activity and to provide stimulation signals. The intrinsic signals sensed in the cardiac chambers are used to classify the condition of the heart, and if a tachyarrhythmia is detected, then either cardioversion pacing pulses or defibrillation shocks are applied.  
           [0012]    In order for these kinds of devices to function properly, a clinician examines the patient and, after implantation, programs a plurality of parameters into the ICD which are used by a processor to classify the condition of the patient and determine the characteristics of the stimulation signals to be applied. Frequently these parameters are selected after the patient&#39;s heart rate is increased either naturally, with exercise, or with drugs. It is advisable to reprogram these parameters as the condition of the patient changes over time.  
           [0013]    External defibrillators capable of providing defibrillation shocks or other types of therapy are also well known. In case of a cardiac emergency, current external defibrillators must be operated manually by a trained professional such as an emergency medical technician, paramedic, firefighter, or police officer, etc. Existing external defibrillators do not monitor cardiac activity before a sudden cardiac arrest episode, and accordingly, the professional must examine the patient and determine his condition first, before any therapy is provided. Hence, inherently, the existing external defibrillators cannot be used by a layperson who has not received any training on how to operate the specific external defibrillator.  
           [0014]    An external defibrillator, described in commonly assigned U.S. Pat. No. 5,474,574 and incorporated herein by reference, includes an ECG sensor and requires several parameters to be programmed by a clinician before it can be used properly. Some of the programmable parameters pertain to the sensitivity of the ECG sensor required to detect ECGs reliably. Other parameters pertain to the size, number and duration of the shocks to be applied by the device. Since these parameters must be programmed separately for each patient, by the time this defibrillator is ready to be used, it is configured to a specific patient and cannot be used for a different patient without first reprogramming its parameters.  
           [0015]    In summary, existing external defibrillators are limited in that they must be operated by a professional, they do not have the capability to continuously monitor a patient and they require active intervention to initiate any therapy.  
           [0016]    There is a need for an external defibrillator which can be used successfully in case of a cardiac emergency by a layman, i.e., a person without any formal medical training under the supervision of a remotely located professional clinician.  
         OBJECTIVES AND ADVANTAGES OF THE INVENTION  
         [0017]    In view of the above, an objective of the present invention is to provide an external defibrillator system which can be distributed and placed at public places which can be used effectively by a person with no special medical training.  
           [0018]    A further objective is to provide an external defibrillator system able to allow remote monitoring of a patient and determine automatically if a patient is in need of therapy. A further objective is to provide an external defibrillator system through which a professional clinician from a remote location can provide instructions to an untrained person on how to secure the same to a patient, and then provide cardiac therapy.  
           [0019]    Other objectives and advantages of the invention will become apparent from the following description.  
           [0020]    Briefly, an external defibrillator system constructed in accordance with this invention includes a pulse generator and a base station adapted to hold the pulse generator when not in use and to provide continuous interfacing between the pulse generator and a trained medical professional. The pulse generator includes a sensing circuit used to sense physiological signals indicative of cardiac activity, a therapy delivery circuit that generates pacing or shock pulses, a controller that is used to operate the defibrillator in response to commands and a transceiver that provides communication directly or indirectly with the professional. Signals indicative of intrinsic cardiac activity, including R-waves and ventricular fibrillation, for example, are detected and transmitted to site of the professional. These signals are then classified as a cardiac condition either by the professional clinician or by an automated expert system. The clinician then generates a command designating a certain therapy to be applied to the patient. The command is sent to the pulse generator which then generates antiarrhythmia pulses appropriate to the patient&#39;s cardiac condition. Preferably the therapy is applied synchronously with the intrinsic cardiac activity of the patient.  
           [0021]    Preferably, the pulse generator also has a speaker and microphone through which an untrained person can communicate with the professional for the operation of the pulse generator. The pulse generator may also have a display on which some instructions can be provided.  
           [0022]    Power for the therapy is provided by rechargeable batteries incorporated into the pulse generator. The battery is then trickle charged while the pulse generator is coupled to the base station.  
           [0023]    The base station is provided to hold the pulse generator while not in use, and acts as a repeater station to allow voice and data communication between the pulse generator and the remote location. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 shows a block diagram of an external defibrillator system constructed in accordance with this invention;  
         [0025]    [0025]FIG. 2 shows a block diagram of the pulse unit for the system of FIG. 1;  
         [0026]    [0026]FIG. 3 shows a block diagram of the base station for the system of FIG. 1;  
         [0027]    [0027]FIG. 4 shows a block diagram of the central station used to control the system of FIG. 1;  
         [0028]    [0028]FIG. 5 shows a more detailed diagram of the pulse unit of FIG. 2; and  
         [0029]    [0029]FIG. 6 shows a flow chart for the operation of the system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    Referring first to FIG. 1, an external defibrillator system  10  constructed in accordance with this invention includes a pulse generator  12  and a base station  14 . The pulse generator  12  includes a pulse unit  16  connected to a set of pulse electrodes  18  and a set of sense electrodes  20  by respective cables  22  and  24 . Other electrical coupler members may be used instead of the electrodes. Sensing may also be performed through other electrodes as well.  
         [0031]    The pulse unit  16  is also coupled to the base station by two channels. The first channel is an RF channel  26  and the second channel is either an inductive or wired channel  28 . The channel  28  is used to provide a charging current to rechargeable batteries within the unit  16  (discussed more fully below) and to exchange control signals when the pulse unit  16  is mounted in a cradle  30  of base station  14 . Channel  26  is used for exchanging control and voice-grade signals between the unit  16  and base station  14  when the unit  16  is removed from the cradle and used to apply therapy to a patient  32 .  
         [0032]    The base station  14  is connected by a standard communication channel  34  to a central station  36 . The central station  36  is manned by a professional  38  who selectively receives information through pulse generator  12 , base station  14  and sense electrodes  20  about patient  32  and who can also send commands to the pulse generator  12  to generate pulses defining a predetermined cardiac therapy. The pulses are applied to the patient  32  by pulse electrodes  18 .  
         [0033]    [0033]FIG. 2 shows a block diagram of the pulse generator  12 . As can be seen in this figure, pulse unit  16  includes a CPU  42 , an analog input/output (I/O) interface  44 , a transceiver  46  and a rechargeable battery  48 . The housing may also include a display  50  and an audio processor  52  associated with a speaker  54  and a microphone  56 . The housing  40  may also include an optional modem  57 (shown in FIG. 5). The cables  22 ,  24  are connected to I/O interface  44 . The transceiver  46  is coupled to an RF antenna  58 . The rechargeable battery  48  provides power to the other circuitry disposed in housing  40  and is coupled to a charging circuit  60 . The transceiver  46  and antenna  58  cooperate to maintain communication with the base station  14 .  
         [0034]    The base station  14 , shown in FIG. 3, has its own CPU  70 , a transceiver  72  to exchange messages with the pulse unit  16  via an antenna  74  and a modem  76  coupled to a standard telephone jack  78 . The base station  14  further includes a power supply  80  which is connected to a standard AC line (not shown) and provides power to an inductive interface  82 . The interface  82  provides energy for a trickle charge to the battery  48  via the battery charger circuit  60 .  
         [0035]    Finally, for the sake of completeness, details of the central station  36  are discussed. Station  36  includes a CPU  90  coupled to a display  92 , a memory  94 , a keyboard  96 , a speaker  98  and a microphone  100 . Communication with a plurality of base stations, such as station  14 , is established through a modem  102 . Obviously, other means of communicating between the central station  36  and base station  14  can be provided as well, such as cellular and other wired and wireless telephone connections, Internet connections and so on.  
         [0036]    [0036]FIG. 5 shows more details of the pulse unit  16 . As it can be seen in this figure, the analog interface  44  may have three sections: a defibrillator section  110 , a first ECG section  114  and a second ECG input section  116 . Associated with the analog interface  44  is a high voltage power supply  118 , a low voltage pacing power supply  120 , and a lead impedance measurement circuit  122 . The pulse unit  16  also includes an optional temperature sensor  124 , a diagnostic circuit  126 , an activation circuit  128 . The temperature sensor  124  is used to provide an indication of the patient&#39;s condition.  
         [0037]    Disposed in the housing of the pulse unit (not shown) there is provided the screen  50  and a couple of LEDs, a green LED  132  and a red LED  134  which are used to indicate the status of the defibrillator system, or at least the pulse unit  40 .  
         [0038]    The operation of the defibrillator system is now described in conjunction with the flow chart of FIG. 6 and the other FIGS.  1 - 5 . In step  200  the system runs a diagnostic test of itself using diagnostic circuit  126 . This circuit  126  may be adapted to check various functions including the microprocessors  42 ,  70 , the communication link between the pulse unit  16  and base station  14  and between the base station  14  and the central station  36 , the charge on batteries  48  and so on. This test is performed at regular intervals, for example, once a second. Alternatively some tests may be run every time while other tests may be run at rarer intervals, for example once a week or once a month. In step  202  at the end of the tests a decision is made as to whether the system  10  is operational or not. If it is not then in step  204  a message is sent to the central station providing an identification code identifying the system  10  and its physical location, and the problems associated with the system  10 , if known. Next, in step  204  the RED led  134  is activated and the system then goes into a stand-by mode in step  208  and the process is terminated. The red LED is activated to show that the system  10  is inoperative. A message to this effect may be displayed on screen  50 . The problem(s) of the system  10  may also be posed on the display  50 .  
         [0039]    If in step  202  no system failure is found then in step  210  the green LED is activated to indicate that the system is operational. Next, in step  212  a test is performed to determine if the system has been activated. Although it is preferable to provide the pulse unit  16  with as few manual controls as possible, some such controls may have to be provided. For example, a manual activating circuit  128  may have to be included. The circuit  128  may include a push-button (not shown) mounted on the housing. The purpose of this circuit  128  is to wake the system up and indicate that a cardiac incident is in progress and that the system is required to provide therapy. Of course the circuit  128  may include some automatic elements as well, such as a motion detector(not shown), a proximity detector, etc. In step  212  a check is performed to determine if activating circuit  128  has been triggered. If not, then the system continues in its diagnostic mode.  
         [0040]    While in the diagnostic mode, the pulse unit is resting on, or is otherwise coupled to the base station  12  . The power supply  80  in the base station  12  feeds power to the inductive interface  82 . The inductive interface  82  then generates an inductive field which is used to excite an inductive power input circuit within the battery charger  60  in the pulse unit  16 . The battery charger  60  which provides a trickle charge to battery  48 . Instead of an inductive coupling a hard wired connection may be established between interface  82  and battery charger  60  through a set of hard wired plugs (not shown).  
         [0041]    For the purposes of this discussion it is now assumed that patient  32  suffers a cardiac attack. An untrained attendant notices that the patient  32  needs help. Depending on the physical location of the system and the patient  32 , the attendant may be anyone in a hospital, a home or even a passerby. The attendant rushes to the pulse generator  12 , removes it from the base station  14  and returns to the patient  32 . When the pulse generator  12  is removed, or when the activation is otherwise activated, a signal is generated. In step  212  the activation is detected. In step  214  instructions are provided for the attendant for connecting the pulse generator to the patient  32 , including instructions for placing the pulse electrodes  18  (including defibrillation pads, pacing electrodes, etc.) and the sensing electrodes  20  (which may include a set of standard ECG electrodes) on the patient&#39;s body. The instructions may be provided on the display  50 , and/or orally through speaker  54  or may be printed on the housing  40 .  
         [0042]    While the attendant is positioning the electrodes on the patient, the pulse generator  12  sends a message through the base unit  14  to the central station  36  indicating that the pulse generator  12  has been activated (step  218 ). In step  220  the CPU  90  receives the message, identifies the system  10  and its location (either from the message, or from data stored in its memory  94 ) and generates an alarm message on display  92  for a clinician to indicate that the system  10  as been activated. An alarm may also be sounded through speaker  98 .  
         [0043]    In step  222  the clinician contacts the attendant and requests orally information about the patient, including the patient&#39;s age, sex, height, weight, any apparent medical conditions, etc. The clinician also checks with attendant whether the electrodes have been positioned. In step  224  the positioning of the electrodes is checked. More specifically, the measurement circuit  122  (FIG. 5) measures the impedance between the various sense and pace electrodes. Based on these measurements the system or the clinician may determine if the electrodes are positioned correctly (Step  226 ). If they are not, then in step  224  the clinician requests the attendant to reposition the electrodes until they are positioned properly. The attendant and the clinician speak to each other via the link established between the pulse generator  12  and station  36  through the speakers  54 ,  98  and microphones  56  and  100 . While this conversation is going on the pulse generator  12  also sends data to the central station  36 , including the impedance data collected by the measuring circuit  122 . Based on these measurements a set of these electrodes are selected for acquiring the ECG signal. If the impedance from the sense electrodes is not satisfactory, the ECG signal for the patient may be acquired using the pulse electrodes or a combination of the pulse and sense electrodes.  
         [0044]    Next in step  228 , the selected electrodes are used to acquire an ECG signal indicative of the cardiac activity of the patient. The ECG signal is transmitted to the clinician for analysis (step  230 ). Alternatively the CPU  42  may be provided with a program for analyzing the ECG and to detect the R-waves for the patient. Once the R-waves are detected the CPU  42  can detect the current heart rate (HR) of the patient. This heart rate can also be sent to the central station in step  230 .  
         [0045]    Next, in step  232 , the cardiac condition of the patient is classified. Preferably the criteria for this classification takes into consideration the current heart rate and other criteria such as the amplitude of the ECG or rate variability. Information from other optional sensors indicative of other parameters such as oxymetry (SpO2), patient impedance, motion sensing or blood pressure may also be used.  
         [0046]    Once the cardiac condition has been categorized, an appropriate therapy can be selected in step  234 . Steps  232  and  234  can be performed by the pulse generator  12  and/or the central station  36 .  
         [0047]    In step  236  the clinician informs the attendant that appropriate therapy is going to be administered to the patient. In step  238  the clinician initiates a command at his computer which is transmitted to the pulse generator  12 . In step  240  the pulse generator  240  provides a final warning to the attendant of the imminent therapy. This step is especially important in case of high energy level defibrillation shocks since these shocks may injure the attendant.  
         [0048]    Finally, in step  242  the pulse generator applies therapy to the patient in form of appropriate pulses, i.e., antibradicardia pacing pulses in case of bardycardia, antitachycardia pacing pulses in case of ventricular tachycardia, defibrillation shocks in case of ventricular fibrillation, and so on. Preferably, the therapy is delivered synchronously with the intrinsic heart beat of the patient as indicated by the detected R-waves.  
         [0049]    After the therapy has been applied in step  242 , the system returns to step  228  to acquire the new ECG for the patient, thereby determining if the therapy was effective or not.  
         [0050]    If communication is lost, or never established between the base station  14  and central station  36 , then a fallback mode may be provided in which the pulse generator generates pulses for the therapy on its own in an automatic mode and without instructions from the clinician. An external defibrillator of this type is described in commonly assigned co-pending application Ser. No. ______ incorporated herein by reference.  
         [0051]    The system described in FIGS.  1 - 5  can be used in a home or an office. For home use, the system is advisable for survivors of SCA or a heart attack, for patients diagnosed with congestive heart failure, patients being monitored at home after cardiac surgery such as a cardiac bypass or valve replacement and patients associated with several risk factors which indicate possible heart attacks, the symptoms including high blood pressure, family history of cardiac problems or obesity.  
         [0052]    Since large number of cardiac emergencies occur in office buildings, the system may also be installed there as well. However, since such buildings are relatively large as compared to private residences, a more robust system is envisioned for this implementation including stronger RF transceivers between the base station and the pulse generator.  
         [0053]    In an alternate embodiment of the invention, the base station  14  is eliminated and the pulse generator is equipped with a transceiver or other means of accessing the central station, including a cellular telephone or other wireless means which are becoming quite popular. For this purpose the pulse generator  12  may be equipped with modem  57  which can facilitate communication directly with the central station  36 .  
         [0054]    In summary, a cardiac system is disclosed in which a relatively simple defibrillation device is provided which is operated/controlled from a remote location through a communication link. The defibrillation device may be provided as a stationary or a portable unit. Stationary units may include home-type version to be used by patients at home, or in a more robust office-type version for a clinician. In either case, the stationary device may include a base station which is mounted on a wall or other solid mounting position and a detachable member that can be dismounted from the base station and carried to the patient.  
         [0055]    The portable unit preferably has a unitary construction including the defibrillation, control and communication circuitry. Communication from the portable unit may be achieved through a standard telephone, a cell telephone, satellite communication etc.  
         [0056]    A large number of therapies may be applied through the device, including:  
         [0057]    defibrillation, delivered by the device in response (preferably) to a command from a remote operator, with a bystander having the capability of overriding the remotely initiated shocks;  
         [0058]    pacing controlled either locally or remotely;  
         [0059]    drug delivery initiated either locally or remotely, including antiarrhythmic drugs or thrombolic drugs (for this purpose, the device may include a storage compartment and, if necessary, a syringe or other means of administering the same);  
         [0060]    The system may also include one or more of the following options:  
         [0061]    voice and/or video communication means between the remote operator and the bystander and/or patient;  
         [0062]    event recorders (located locally or remotely) to document the symptoms and therapy applied to the patient and the efficacy of the system.  
         [0063]    The defibrillation device described here has the following advantages:  
         [0064]    it is simple and easy to use, especially by an untrained attendant;  
         [0065]    it can be provided without any external controls thereby insuring that it is not mishandled;  
         [0066]    it includes a base station which can be mounted on a wall and located in a visible and accessible site, and a pulse generator mounted at the base station;  
         [0067]    the pulse generator has a speaker and microphone used for audio communication with a clinician at a central station;  
         [0068]    the communication link is established by RF between the pulse generator and the base station and by standard telephone lines between the base station and the central station;  
         [0069]    the device has self adhesive ECG monitoring and defibrillation electrodes attached to the patient by an attendant;  
         [0070]    a set of 12 ECG sense electrodes are used to capture the ECG signals, these signals being used by the central station, or the pulse generator to diagnose the patient;  
         [0071]    the pulse generator is capable of delivering antiarrhythmia therapy ranging from antibradycardia pacing pulses to high energy defibrillation shocks, the therapy being initiated by the central station;  
         [0072]    it has an integral self-diagnosing circuitry which activates itself automatically or is randomly activated in demand from a remote location, i.e. the central substation; if a malfunction is detected the central station is automatically notified;  
         [0073]    the results of the diagnosis are monitored by the central station;  
         [0074]    data from a plurality of cardiac systems is stored in a central station;  
         [0075]    the system has an alphanumeric display that can be used provide instructions to the attendant;  
         [0076]    the system has rechargeable batteries that can be charged while the device us on standby to save power;  
         [0077]    the system generally is operated from the remote central station which so that the attendant need not have special qualifications to operate the required devices.  
         [0078]    Obviously numerous modifications may be made to this invention without departing from its scope as defined in the appended claims.