Abstract:
An active implantable medical device including bidirectional communications between a generator and sensors or actuators located at the distal extremity of a lead. A lead ( 14 ) is connected at its proximal end to a generator ( 10 ) and has at the distal end electrodes ( 38, 42 ) able to come in contact with surrounding tissues. A two-wire connection ( 34, 36 ) connects these electrodes to the generator. The lead incorporates transducers ( 24, 26 ) of sensor or actuator type. The generator includes circuits for sending and receiving digital data ( 46,48,50,54,56 ) capable of producing instructions to one of the transducers and to receive and decode information from one of the transducers in response to a specific instruction produced by the generator. The transducer is able to receive, decode and carry out the aforementioned controls, as well as send data in response.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to “active medical devices” as defined by Directive 93/42/CEE of Jun. 14, 1993 of the Council of the European Communities, and more particularly to “active implantable medical devices” as defined by Directive 90/385/CEE of the Council of the European Communities. This definition includes with its scope devices that monitor cardiac activity and deliver impulses of stimulation, re-synchronization, defibrillation and/or cardioversion in the event of a cardiac rhythm disorder detected by the device, and also neurological devices, cochlear implants, etc., as well as devices for the measurement of pH or intra-corporeal impedance (such as devices that measure a trans-pulmonary impedance or an intra-cardiac impedance). 
       BACKGROUND OF THE INVENTION 
       [0002]    Implantable medical devices typically comprise a case that is generally referred to as a “generator,” electrically and mechanically connected to one or more “leads” that are in turn provided with electrodes intended to come in contact with the tissues to be stimulated by delivering an impulse (or pulse) and/or detected by sensing (or collecting) an electric signal: myocardium, nerve, muscle . . . etc. In the case of an implantable medical device for therapy, these electrodes can be intracardiac electrodes (placed in a cavity of the myocardium in contact with the intra-cardiac wall), pericardial (in particular, to define a reference potential, or to apply a shock), or intravascular (the lead, for example, is introduced into the coronary sinus until a site located in front of the wall of the left ventricle). 
         [0003]    A first aspect of the development of applications for these devices is the multiplication of the number of electrodes, in particular for the devices known as “multi-site” which make it possible to choose the sites of stimulation/detection in order to optimize the functioning of the device. Thus, in the particular case of the devices for the ventricular re-synchronization (such devices being known as Cardiac Resynchronization Therapy or “CRT” devices), once implanted into the patient a device provided with electrodes allowing to stimulate both ventricles. The stimulation of the right ventricle (and the right atrium) is operated by a traditional intracardiac lead, but for the left ventricle the access is more complex: the stimulation is generally operated by means of a lead introduced into the coronary sinus of the right ventricle and then pushed in a coronary vein on the pericardium, so that the extremity of the lead comes to be placed in front of the left ventricle. This procedure is rather delicate, because the diameter of the coronary vessel is reduced as the lead advances, so that it is not always easy to find the optimal position at the time of the implantation. Moreover, the proximity of the phrenic nerve can sometimes lead to inappropriate stimulations. It is to overcome these difficulties that the development was conducted on leads to obtain what is known as a “multi-electrode” lead, provided with, as an example, ten electrodes and of which it is possible to select after implantation the most effective stimulation electrode. 
         [0004]    To manage this multiplicity of electrodes, multiplexing systems were developed allowing the connection of the various electrodes with the two wires traversing the lead and connected at the output of the generator. The U.S. Patent Publication 2003/0149456 A1 (Rottenberg et al.) described a generator connected to a multi-electrode lead by two wires associated with a multiplexer/demultiplexer. These two wires, on the one hand, ensure the sensing of the depolarization signals and the delivery of the stimulation impulses, and, on the other hand, deliver to the multiplexer/demultiplexer the logical signals making it possible to control selection switches for one or more electrodes on the lead. These signals also ensure the supply to the multiplexing/demultiplexing circuit and to the switches the necessary energy for their functioning. The multiplexing/demultiplexing circuits and the switches are preferably located at the extremity of lead, therefore remotely from the generator. 
         [0005]    Another aspect of the use of the implantable device is the integration of various sensors within the lead, more particularly of a blood acceleration sensor or a blood pressure sensor, in particular a sensor of the endocardiac acceleration (EA). The signals collected by these sensors allow the control of various functions of the device: in particular, the measurement of the peaks of endocardiac acceleration (PEA) gives representative information of the instantaneous hemodynamic state of the patient. 
         [0006]    Documents EP 0515319 A1 and its counterpart U.S. Pat. No. 5,304,208, EP 0582162 A1 its counterpart U.S. Pat. No. 5,454,838, and EP 0657260 A1 and its counterparts U.S. Pat. No. 5,693,075 and U.S. Pat. No. 5,496,351 (all three in the name of Sorin Biomedica Cardio SpA) describe endocardiac acceleration sensors provided at the distal end of an intracardiac lead, introduced into the myocardium and connected to the pacemaker or a defibrillator case. 
         [0007]    The presence of such sensors at the distal extremity of lead requires a specific connection for the transmission of the signals from the sensor to the generator connected at the opposed proximal extremity. This specific connection to the sensor comes in addition to the already existing connections between the generator and the electrodes located at the distal extremity of lead, connections themselves ensured by specific wires, with or without multiplexing. 
         [0008]    Lastly, a third aspect of the recent development of the implantable medical devices, in particular in the cardiac field, is the multiplication of the number of leads connected to the same generator. More recently developed devices typically include three different leads, respectively associated with the right ventricle, the left ventricle and the right atrium, each one of these leads itself being provided with several electrodes, and eventually with a sensor at the distal extremity of lead. 
         [0009]    The document WO 2006/029090 A2 (Proteus Biomedical, Inc.) proposes a system in which one two-wire bus conveys digital signals of selection/configuration of satellites integrated into the lead, as well as pulses of stimulation and analog sensed signals of the patient. Concern with this system arises with the fact that the coded selection/configuration signals also are delivered to the heart via the electrodes of the lead in the form of salvos of impulses. It is therefore necessary to very carefully calibrate these impulses in order not to start an inappropriate depolarization of cardiac tissue. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0010]    It is therefore an object of the present invention is to propose a system able to manage safely, completely, reliably and in an adaptable manner the operation of implantable medical devices implementing leads equipped with a multiplicity of electrodes and/or sensors, and including leads connected to the same generator. 
         [0011]    The invention broadly proposes a system that is able to manage globally all the configurations of leads and/or electrodes and/or sensors able to be associated to the same generator, without modification of the hardware components of the generator. The invention proposes an active implantable medical device of a known type, for example, according to the WO 2006/029090 A2 and its counterpart U.S. Pat. No. 7,214,189. 
         [0012]    One aspect of the invention is directed to an active implantable medical device, including a generator that has circuits for analyzing physiological signals and/or for producing stimulation impulses and is able to send and receive digital data with at least one lead, connected on its proximal side to the generator. The lead includes at its distal end at least one electrode to contact tissues to deliver stimulation impulses and/or to collect physiological signals; a two-wire connection able to connect the at least one electrode to the generator; at least one transducer of a sensor or an actuator type; and a connection for digital data communication, able to couple at least one transducer to the generator via the two-wire connection. The device further includes a communication circuit that sends and receives digital data inside the generator and produces a control in the direction of the transducer, said control being selected from among a plurality of controls. 
         [0013]    The transducer includes a circuit that is able to receive, decode, and carry out the delivered control and send information in response to the reception of a specific control requesting such information. The generator in turn includes a communication circuit that is able to receive and decode that information from the transducer. 
         [0014]    Further, the generator circuits are able to produce a control micro-impulse before the sending of said control in the direction of the transducer, said micro-impulse having at least one particular form characteristic, distinctive in comparison to and therefore distinguishable from said stimulation impulse. The lead includes on its distal end controlled switches, selectively interposed between said at least one electrode and said respective wires of the two-wire connection; and a control circuit coupled to the two-wire connection, able:
       i) to recognize the aforementioned particular form characteristic among the impulses detected on the two-wire connection, so as to discriminate between an impulse of stimulation and a control micro-impulse; and   ii) on detection of a control micro-impulse, to control the opening of the controlled switches so as to insulate the at least one electrode from the two-wire connection, this later being then connected only to the transducer.       
 
         [0017]    Preferably, the particular form characteristic of the control micro-impulse is a characteristic selected from among the group consisting of: a selected duration, a polarity, and an amplitude of the micro-impulse; and more preferably a combination of at least two of the forgoing characteristics. In addition, it is preferred that the control circuit obtains a supply voltage from the impulses detected on the two-wire connection. 
         [0018]    The aforementioned controls are preferably controls selected from among the group consisting of: a word (byte of data) of synchronization; a word of identification for the recipient transducer; a closing of the communication; a return to a default configuration of the transducer; a writing of data in a memory of the transducer; and a reading of data from the memory of the transducer. 
         [0019]    Further, the information is preferably an information field in a transmission containing information selected from among the group consisting of: a word of synchronization; a word of identification of the transmitting and/or receiving transducer; data contained in a memory of the transducer; an acknowledgment receipt following an action carried out on command of the generator; and a code of detection and correction of error. 
         [0020]    In an alternate preferred embodiment, the generator for an active implantable medical device has a receptacle to receive a lead able to be connected on its proximal side to the generator, said lead having at least one electrode, at least one distal transducer, and a two-wire connection able to connect to the generator the at least one electrode, and a connection for digital data communication, able to couple the at least one transducer to the generator via the two-wire connection:
       a circuit for analyzing physiological signals and/or producing stimulation impulses; and   a circuit for sending and receiving digital data, including:
           circuits for producing one or more controls signals to be delivered to the transducer; and   circuits for receiving and decoding the information received from the transducer in response to the reception of a specific control among the aforementioned controls;   circuits for producing the control micro-impulse before the sending of said controls signals to the transducer, said micro-impulse having at least a particular form characteristic, distinctive in comparison to the stimulation impulses.
 
In an alternate preferred embodiment, the lead has a proximal end and a distal end, and includes:
   
           at least one electrode at the distal end able to come in contact with surrounding tissues, to apply stimulation impulses and/or to collect physiological signals; and at least one transducer at the distal end of the sensor or actuator type;   an interface connector for connecting the lead to a generator at the proximal end with a two-wire connection able to connect the at least one electrode to the generator, and a connection for data communication able to couple the transducer to the generator via the two-wire connection,   circuits for receiving, decoding and carrying out a controls signals produced by the generator;   circuits for sending data in response to the reception of a specific controls signals;   controlled switches at the distal end having an open condition and a closed condition, interposed between the at least one electrode and the respective wires of the two-wire connection; and   a control circuit at the distal side coupled to the two-wire connection and able:
           i) to recognize a control micro-impulse having a particular form characteristic among the impulses detected on the two-wire connection, so as to discriminate between impulses of stimulation and control micro-impulses; and   ii) on detection of a control micro-impulse, to control the opening of the controlled switches so as to insulate the at least one electrode from the two-wire connection, this later being then connected only to the transducer.   
               
 
         [0034]    It is another object of the present invention, considered separately, to provide an improved generator as well as the lead for such a device and, as such, a control signal implemented within the device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    Further features, characteristics and advantages of the present invention will become apparent to a person of ordinary skill in the art in view of the following detailed description of preferred embodiments of the invention, made with reference to the annexed drawings, in which the same numerical references indicate, from one figure to another, identical or functionally similar elements, and in which: 
           [0036]      FIG. 1  represents, in a diagrammatic view, an implantable medical device including a generator and three leads intended to be implanted in three respective cavities of a patient&#39;s myocardium; 
           [0037]      FIG. 2  illustrates various wave forms of impulses traveling along the communication two-wire connection of one the leads; 
           [0038]      FIG. 3  illustrates, in the form of schematic blocks, the various circuits associated with the connection between the generator and the distal end of the lead, where the electrodes are situated, one actuator and one acceleration sensor; 
           [0039]      FIG. 4  illustrates a schematic circuit of selected components of the control circuit of the actuator of  FIG. 3 . 
           [0040]      FIG. 5  is a flow chart illustrating the various steps of the communication protocol, seen from the generator side; and 
           [0041]      FIG. 6  is a flow chart illustrating the various steps of the communication protocol, seen from the lead side. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0042]    With reference to  FIG. 1 , a preferred embodiment is shown in which reference  10  indicates the case of the generator which is a device that could be defibrillator, pacemaker or CRT device type. It will be noted that this embodiment of the present invention is not restrictive at all, and that the invention can apply to other types of implants such as devices of detection/stimulation of nerves, muscles, etc. 
         [0043]    Generator  10  is associated with three distinct leads  12 ,  14  and  16  positioned in various sites of myocardium  18 . Lead  12  comprises at its distal end two sensors or actuators  20  and  22 , for example, an accelerometer  20  and one actuator  22  allowing the selection of an electrode of stimulation (it will be noted that the sensor and the actuator can be located in the same module or not, as deemed appropriate). 
         [0044]    The lead  14  comprises at its distal end a sensor  24 , for example, an accelerometer, and an actuator  26  allowing the selection of an electrode of stimulation (these elements will be described more in detail below with reference to  FIG. 3 ). Lastly, lead  16  integrates at its distal end three sensors or actuators  28 ,  30 ,  32 , for example, an accelerometer or a pressure sensor  28  and two actuators  30 ,  32  allowing the selection of two respective electrodes of stimulation. 
         [0045]    With reference to  FIG. 3 , the extremity of the lead  14  is described and illustrated in greater detail. It should be understood that the two other leads  12  and  16  are configured in a similar way. 
         [0046]    Lead  14  includes two wires of connection in the form of two micro-cables  34 ,  36  which extends along its length and are connected to generator  10 . These connection wires  34  and  36  will be indicated hereafter as “proximal micro-cable”  34  and “distal micro-cable”  36 , and the corresponding terminals of the generator will be indicated “distal” and “proximal,” by analogy with the positioning of the two electrodes of an intracardiac bipolar lead. 
         [0047]    Micro-cables  34  and  36  are connected to a sensor  24 , for example, an acceleration sensor, and to a control circuit  26  of the actuator. 
         [0048]    By convenience, for the simplicity of the example illustrated, element  24  is described in the form of a sensor, but the invention is not limited to this type of component: the element  24  can be a sensor (i.e., a signal transducer allowing to produce an electric signal resulting from the variations of a detected physical parameter), but also an active electronic circuit such as amplifier, filter, . . . associated or not to a sensor positioned near this circuit, or an Micro Electro Mechanical Systems (MEMS), or in a general way any technologically integrable active element positioned in the lead, typically at the extremity of a lead. 
         [0049]    The proximal micro-cable  34  can be connected to a proximal electrode  38  via a switch  40  controlled by circuit  26 , and the distal micro-cable  36  can be connected to a distal electrode  42  via a switch  44  controlled by circuit  26  (the internal structure of which will be described hereafter in more detail with reference to  FIG. 4 ). Switches  40  and  44  can, in a known manner, be produced in the form of a MOS transistors or of Micro Electro Mechanical Systems (MEMS), components technologically integrable on the substrate of a chip which can be incorporated in the body of lead. Such components, for example, are described in U.S. Patent Publication US2004/0220650 A1 to which one skilled in the art may refer. 
         [0050]    Generator  10  is provided, in addition to the traditional circuits of sensing/stimulation (not illustrated in as much as they form no part of the present invention), with circuit structures making it possible to read or write data coming from or going to sensor  24  or actuator  26 , or of any other sensor or actuator available on the lead. 
         [0051]    To generate a logical level “1” as illustrated on the  FIG. 2   c  (by convention, the logical level “1” corresponds to the high level), the generator controls the closing of switch  46  connecting micro-cable  34  to a source of constant voltage  48  (for example −2 V), as well as switch  50  connecting the micro-cable  36  to the reference (e.g., ground) potential via a capacitor  52 . Capacitor  52  is an insulating capacitor making it possible to avoid the passage of the continuous voltage; it is foreseen also to have a switching system, not represented, making it possible to discharge capacitor  52  at the proper time. At the same time, the generator  10  opens switch  54  connecting the micro-cable  34  to the reference potential. In an alternative embodiment, it is possible to send positive impulses on micro-cable  36  by switch  50  connected to a positive voltage, by connecting micro-cable  34  at the ground by switch  54 . Other variations will occur to a person of ordinary skill in the art. 
         [0052]    To generate a low logical level “0”, the generator closes switches  50  and  54 , and opens switch  46 . For the reading of a logical level “0” or “1” (low or high level, respectively) switches  46  and  54  are opened, and switch  50  closed: the reading of the logical level is done then via a reading (sensing) amplifier  56 . 
         [0053]    The internal structure of control circuit  26  of the actuator is represented more in detail in  FIG. 4 . Circuit  26  ensures not only the controlling of switches  40  and  44 , via controls  58 ,  60  produced by a logical circuit  62 , but also the generation of logical levels “0” or “1” to the generator  10 , so as to allow a bidirectional communication of data not only in the direction generator to actuator, but also in return in the direction actuator to generator. To generate a logical level “0”, circuit  26  closes a switch  64  putting in direct connection the two micro-cables  34  and  36 ; the switch  66 , which role will be described below, is then in an open state (in the alternative embodiment mentioned above, switch  50  would be closed, and switches  54  and  46  open). To generate a logical level “1”, circuit  26  opens switch  64  and closes switch  66  making it possible to apply to micro-cable  34  a continuous fixed voltage generated by a circuit  68 . Switches  64  and  66  are controlled by logic circuit  62 . 
         [0054]    To put the lead in a configuration authorizing the exchange of data, the generator  10  produces a micro-impulse applied between micro-cables  34  and  36 . This micro-impulse, represented on the  FIG. 2   b , presents a duration, a polarity and/or a specific amplitude, discriminating in relation to the other signals likely to be present on micro-cables  34  and  36 , for example, signals of stimulation (such as those illustrated  FIG. 2   a ) or injection of current for a bio-impedance measurement. This micro-impulse lasts for example 5 μs with an amplitude of 150 mV. A comparator  70 , whose two inputs are connected respectively to micro-cables  34  and  36 , detects this particular form and informs logic circuit  62  by signal  72 . The logic circuit  62  then generates the signals  58  and  60  which control the opening of switches  40  and  44 . 
         [0055]    It will be noted that comparator  70  plays a double role: in addition to the detection of a specific impulse for the controlling of switches  40  and  44 , it also ensures the detection of the logical levels “0” or “1” sent by generator  10  in direction of logic circuit  62 . 
         [0056]    To function, circuit  26  requires a power supply. Power is brought by the logical signals traveling on micro-cables  34  and  36 , such as those of the  FIG. 2   c  described above. To ensure the continuity of this power supply, a diode  74  charges a capacitor  76  when the voltage on micro-cable  36  is higher than the voltage on micro-cable  34 . Capacitor  76  stores the load and feeds circuit  68 , which includes a voltage multiplier making it possible to generate voltages  78  and  80  being used to supply comparator  58  and the logic circuit  62 . The charging of capacitor  76  takes place when, on the generator side, switches  46  and  50  are closed and switch  54  is open, and on the actuator side, switches  64  and  66  are open. The discharge of capacitor  52  takes place when, on the generator side, switches  50  and  54  are closed and switch  40  is open, and, on the actuator side, switch  64  is closed and switch  66  open. The power supply of any other sensor or actuator present on the lead can be carried out on the same manner. 
         [0057]    Now we will describe, with reference to  FIGS. 5 and 6 , the communication protocol between the generator and the various sensors and actuators (or other similar active elements) integrated into the various leads connected to this generator.  FIG. 5  illustrates this protocol seen from the generator side, while  FIG. 6  illustrates this same protocol seen from the lead side. 
         [0058]    The initial state is that corresponding to block  100  ( FIG. 5 ), with generator  10  of  FIG. 1  connected to a plurality of leads  12 ,  14 ,  16  . . . carrying themselves a plurality of sensors and/or actuators  20 ,  22  . . .  30 ,  32  . . . . Each sensor or actuator contains a register with digital data, intended to be programmed, read and/or written remotely from generator  10 . 
         [0059]    In the communication protocol, generator  10  is the Master. It can decide to program, read or write simultaneously the registers of one or several leads  12 ,  14  or  16 . 
         [0060]    The selection of a lead is done by the sending of a micro-impulse (blocks  110 ,  110 ′ or  110 ″), as it was described previously and illustrated in reference to the  FIG. 2   b . The detection of such a micro-impulse by the sensors and actuators of the lead provokes the control switches to disconnect the electrodes from the associated to the micro-cables within the lead. In the example of  FIGS. 3 and 4 , this micro-impulse is detected by the circuit  70  which, via the logic circuit  62 , controls the opening of switches  40  and  44 , which in turn causes to isolate the distal electrode  42  and proximal electrode  38  from the respective micro-cables  36  and  34 , which in turn are only connected to the sensor  24  and actuator  26 . 
         [0061]    Advantageously, the generator can function according to an optional mode called “salvo mode.” This means that, for example, every 8 ms the sensor  24  sends to the generator the recorded data accumulated during the last 8 ms. In such a case, the generator awaits a response from the sensor of the lead (block  111 ), this response corresponding to the sequence of blocks  201 ,  209 ,  216  and  217  ( FIG. 6 ) with successively: sending a synchronization word (byte) (block  201 ); sending an identification word (byte) of the register in which the data to be transmitted by the sensor (block  202 ) are contained; sending a code indicating that the response is a response of the type of data packet, specific in the mode salvo (block  209 ); sending the data themselves and sending a checking and correction of error code (code CRC) allowing to secure the transmission (block  216 ); end of the communication (block  217 ). 
         [0062]    It will be noted that, here and in the following detailed description, the controls can exist without comprising a synchronization word, for example, if one uses a width modulation of impulses of which the duration is sufficiently large to tolerate desynchronized clocks, and whose width determines the logical level. The synchronization word can in addition include a coded preamble which makes it possible to test the synchronization of the clocks. In addition, the words can use the known “Manchester” encoding. 
         [0063]    Lastly, the identification word makes it possible to identify not only the register, but also the transducer and the lead: the identification of the lead is indeed necessary to avoid, by cross talk, the programming of another lead provided with actuators. 
         [0064]    If the generator is not in salvo mode (tested at block  109 ), it checks by a impedance measurement ( FIG. 5  element “HiZ” at block  140 ) that the sensors and actuator are well disconnected from the electrodes. This measurement is operated, in a traditional way, by injection of a current and measurement of the resulting voltage between the two micro-cables. If, by detecting a high impedance value, this measurement confirms the effective disconnection of the electrodes, then the generator sends on the two-wire connection a synchronization byte (block  112 ) in order to allow the synchronization of the generator clocks with the actuator and the sensors of the selected lead. 
         [0065]    The generator sends then a byte of identification (block  113 ), followed by one of the three following instructions:
       end of the communication and closing of the connection switches to the electrodes, with the sending of a CRC code to secure the transmission (block  114 );   return of all the actuator and sensors to a default configuration, with a CRC code to secure the transmission (block  116 );   another control to come (block  115 ).       
 
         [0069]    The following controls might follow:
       writing a packet of bytes starting from a given address on one of the actuators or sensors of a lead (block  117 );   reading a packet of bytes starting from an address given on one of the actuators or sensors of a lead (block  118 );   reading a register at a given address on one of the actuator or sensors of a lead (block  119 );   writing a register at a given address on one of the actuator or sensors of a lead (block  120 );   reading a register at a given address on all the actuator and sensors of the same lead (block  121 );   writing a register at a given address on all the actuator and sensors of the same lead (block  122 ).
 
All these controls are followed with a CRC code in order to secure the transmission. The generator then waits for the response of the lead (blocks  123  to  128 , following respectively blocks  117  to  122 ). The response, on the leads side, to the controls  117  to  122  is schematized by blocks  203  to  207  on  FIG. 6 . According to the cases, the response of the lead can take several forms (blocks  210  to  215 , respectively):
   ACK: code indicating a correct reception of the control emitted by the generator;   NAK: code indicating that this reception is erroneous;   DATA+CRC: sending of the requested data, followed with a check code CRC;   ACK/NAK  1  . . . N: each actuator or sensor of the lead answers sequentially by a ACK/NAK, in a given order;   DATA+CRC  1  . . . N: each actuator or sensor of the lead responses sequentially by providing the requested data DATA, followed by an associated check code CRC, in a given order.       
 
         [0081]    The communication then ends (block  217 ). In any event, if a micro-impulse, produced by the generator to open the switches of the actuator, is not followed in a given time period (for example, 100 μs) by another signal received on the generator, the switches are again closed to allow a return to the configuration by default, so as to be able to ensure with certainty the sensing of signals of the cardiac depolarization and/or the application of signals of stimulation or defibrillation. 
         [0082]    A person skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation.