Abstract:
Determining the presence and type of a probe associated with an active implantatable medical device, in particular a cardiac pacemaker and devices having similar pacemaker functionality. This device includes circuits for producing monopolar or bipolar stimulation pulses, selectively with or without disconnection of a connection (S 1 , S 2 ) to a reference potential, and a circuit for sensing a pulse signal produced by the variation of potential induced on one and/or the other of terminals (RING, TIP) and/or on the metallic case (CASE) in response to an application of stimulation pulses. The device operates to analyze a characteristic of the shape ( 28 ), in particular the pulse width, and to deliver an indicator representative of the presence or the absence of a probe. The device also can selectively modify at least one operating parameter of the device according to the delivered indicator.

Description:
FIELD OF THE INVENTION 
   The present invention relates to “Active Implantable Medical Devices” as defined by the Jun. 20, 1990 Directive 90/385/CEE of the Council of the European Communities, more particularly to devices such as cardiac pacemakers, defibrillators, cardiovertors and/or “multisite” devices (for sensing and stimulation in multiple (3 or more) cardiac chambers) able to deliver to the heart pulses of low energy for the treatment of the disorders of the cardiac rhythm. 
   BACKGROUND OF THE INVENTION 
   Active implantable medical devices typically include a generator having a metallic case that contains the various electronic circuits and an energy source (battery). At the time of the implantation, the generator is connected electrically and mechanically to an external probe that is equipped with electrodes for intra-cardiac stimulation, making it possible to detect the potentials of depolarization of the myocardium, and to deliver to the myocardium the stimulation pulses produced by the generator. 
   Generally, it is possible to connect a given generator to one of two different types of probes, monopolar and bipolar. This is done at the choice of the surgeon and according to the type of pathology to be treated. In the case of a monopolar (also called “unipolar”) probe, the detection and stimulation are operated between the single electrode and the metallic case of the generator. In the case of a bipolar probe, the detection and stimulation can be carried out either in a differential mode between two electrodes of the probe, or in a common mode between the case of the generator and one or the other of the electrodes. Of course, a general set of internal operating parameters of the generator must be selected according to whether the probe used is monopolar or bipolar: the commutation (switching) of the terminals internal to the generator that are to be used, the collection (detection or sensing) of the depolarization signal, the adjustment of the stimulation parameters, the modification of the control algorithms operating the microprocessor, etc. 
   It will be understood that any error in the selection of the type of operation (monopolar or bipolar) can involve extremely serious consequences. For example, if the device is programmed for a bipolar stimulation but is equipped with a monopolar probe, this error will cause a loss of sensing and the application of an inappropriate stimulation, with a significant risk for the patient. In addition, after the manufacture of the generator, there can be a significant lapse of time between the shipping of the generator and its implantation in the body of the patient. This time can even reach one year to eighteen months. During this sometimes lengthy storage period preceding the implantation, it is essential that the apparatus, whose battery was connected right before shipping, presents an energy consumption that is as reduced as possible, so that the storage period does not have a notable incidence on the useful lifespan of the apparatus, i.e., the duration during which it will be functional after implantation. 
   With this objective, the device, and in particular its microprocessor, are placed in a sleeping mode having a very low energy consumption. Moreover, it is envisaged to have a mechanism interior to the device to detect the connection of a probe. In this way, the device can detect an implantation and awaken the circuit of the generator, to make it fully functional and to initialize a certain number of parameters, to memorize the starting data, etc. This function of activation can be fulfilled in various ways. For one example U.S. Pat. No. 5,350,401 envisages an activation pin having to be withdrawn by the surgeon from the pacemaker at the time of the implantation, to authorize a communication connection with an external programmer that will send a deactivation control signal to the pacemaker to deactivate the inhibition and allow normal operation. 
   U.S. Pat. Nos. 5,522,856 and 5,370,666 detect the insertion of a probe by an impedance measurement that is carried out between the terminals of the connector head of the device. In the absence of a probe, the impedance is extremely high. As a probe is inserted, the impedance value decreases below a certain threshold. Crossing that threshold is detected to switch the pacemaker from the sleeping state mode to a mode where it becomes completely awake and functional. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   It is, therefore, an object of the present invention to propose a circuit that can, in an entirely automatic way, detect the connection of a probe in order to switch the device from a sleeping state mode at very low energy consumption to an awake mode where all the functionalities will be activated (with, correlatively, a higher level of energy consumption). 
   As it will be seen, the present invention makes it possible to achieve this goal without any intervention of the surgeon, therefore avoiding any handling or risk of omission (as in the case of a system requiring the insertion of a pin of activation), without continuously carrying out a direct impedance measurement between the terminals, and without recourse to an external programmer. 
   One aspect of the invention is directed to a device that can, in an entirely autonomous way, not only detect the connection of a probe, but also and especially determine the type of probe used—e.g., monopolar or bipolar—and consequently to commutate and parameterize the various circuits and algorithms of the device appropriately for the type of probe. This function, managed in an entirely automatic way by the device, makes it possible to minimize any risk of error resulting from a lack of conformity between the type of probe used and the programmed operating mode of the device. One thus avoids, for example, any risk of bipolar stimulation applied by error to a monopolar probe. 
   Another aspect of the invention concerns a device incorporating a safety function allowing for the detection of the particular configuration of the pacemaker, after having been equipped with a bipolar probe, yet before it is introduced into the implantation site (the incision or “pocket” in which the surgeon envisages to place the pulse generator), and when not connected to a reference potential electrode or plate. In this regard, the pacemaker is generally programmed by default in monopolar stimulation mode (e.g., factory set adjustment). In this case, it is important that the generator does not actually deliver monopolar stimulation pulses on the bipolar probe. This is because such pulses would be dangerous because of the absence of return to ground, the case of the generator being electrically in the air (floating potential) during this step. Thus, this safety must be maintained until the final and complete functional activation of the device. It will be seen that the device according to the present invention makes it possible to automatically detect this configuration, and thereby to inhibit the delivery of a bipolar stimulation. However, this inhibition will be maintained only as long as the situation (floating potential) persists, and automatically removed as soon as the connection with the reference potential is restored either by the insertion of the case of the generator in the pocket, or by a connection to a reference potential plate, thus making it possible to electrically close the circuit (to the ground). 
   The activation of the functionalities of the pacemaker will be thus completely automatic in the case of a bipolar probe. The surgeon will not have to use a reference plate or to force a mode of bipolar stimulation before the generator is installed in the pocket. It will be enough for the surgeon simply to insert the bipolar probe, and the safety will be automatically ensured for the length of time necessary to complete the implantation. 
   Another aspect of the invention is to propose a device making it possible to ensure a continuous monitoring, cycle to cycle, of the integrity of the probe during the course of operation. This is done in particular to detect a rupture or discontinuity of the wire to the proximal electrode in a bipolar probe, so as to immediately switch the operating mode of the device to a monopolar mode, a mode in which the probe can still remain functional given the rupture. 
   For this purpose, the invention broadly proposes an active implantable medical device including a metallic case containing a generator, the generator including a stimulation circuit able to produce stimulation pulses in monopolar mode and/or a bipolar mode, a connector head coupled to the metallic case that is equipped with at least two terminals that are able to be connected to electrodes of a probe for detection and stimulation, such that the terminals can be coupled to a monopolar probe or a bipolar probe. The generator includes means for detecting the presence of a probe connected to the connector head. 
   In a manner characteristic of the invention, the probe detecting means includes: means for producing monopolar or bipolar stimulation pulses, selectively and with or without a disconnection of a connection between the terminal(s) to a reference potential (hereinafter a “reference potential connection”); means for detecting at least one pulse signal produced by the variation of potential induced on one and/or the other of the terminals and/or on the metallic case by the application of the aforesaid stimulation pulses; discriminating means, able to analyze a characteristic of the shape of said at least one detected pulse signal and to deliver an indicator representative of the presence or absence of a probe; and control means, to selectively modify at least one operating parameter of the device according to the indicator delivered by the discriminating means. Preferably the shape characteristic is the width of the at least one detected pulse signal, and the width is compared to a predetermined threshold. 
   According to a first embodiment of the invention, the means for producing stimulation pulses operates to apply a stimulation pulse with a disconnection of the reference potential connection, and the discriminating means operates to compare the width of the pulse signal detected on the terminal of the proximal electrode and on the case to a given threshold. The discriminating means can then deliver an indicator, i.e., a parameter representative of:
         1. the absence of a probe or a non-implantation of the case after connection of a probe when the width of the detected pulse signal on the case is below the threshold;   2. the presence of a monopolar probe implanted when the width of the detected pulse signal on the case is greater than or equal to the threshold and the width of the detected pulse signal on the terminal of the proximal electrode is below the threshold; or   3. the presence of an implanted bipolar probe when the width of the detected pulse signal on the case and on the proximal terminal is greater than or equal to the threshold.
 
If, in another case, the means for producing stimulation pulses apply a bipolar stimulation pulse without a disconnection of the reference potential connection, the discriminating means can, by comparing the width of the detected pulse signal on the case with a low threshold and a high threshold, deliver an indicator representative of:
   1. the presence of a bipolar probe when the width of the detected pulse signal on the case is below the low threshold;   2. the absence of a probe when the width of the detected pulse signal on the case is included between the low threshold and the high threshold; or   3. the presence of a monopolar probe when the width of the detected pulse signal on the case is approximately equal to the high threshold.
 
If, in the following case, the means for producing stimulation pulses apply a monopolar stimulation pulse without disconnection of the reference potential, the discriminating means can deliver a representative indicator of:
   1. The absence of a probe when the width of the detected pulse signal on the case is included between the low threshold and the high threshold;   2. The presence of a bipolar probe when the width of the detected pulse signal on the terminal of the proximal electrode is below the low threshold; or   3. The presence of a monopolar probe when the width of the detected pulse signal on the terminal of the proximal electrode is equal or approximately equal to the high threshold.       

   According to an alternative embodiment of the invention, the means for producing stimulation pulses apply a bipolar stimulation pulse between the terminal of the proximal electrode and terminal of the distal electrode, without disconnection of the reference potential connection, and the discriminating means compares the width of the detected pulse signal on the case with a high threshold and a low threshold. The discriminating means can then deliver a representative indicator of:
         1. The absence of a probe or the non-implantation of the case after connection of a probe when the width of the detected pulse signal on the case is included between the two thresholds;   2. The presence of a bipolar probe when the width of the detected pulse signal on the case is below the low threshold; or   3. The presence of a monopolar probe when the width of the detected pulse signal on the case is equal to or approximately equal to the high threshold.       

   Advantageously, the control means, starting from an initial state of the device in which, before implantation, it operates temporarily in a sleep mode with reduced functionalities, on the delivery of an indicator representative of the presence of a probe, switches the device to a fully functional mode. The control means, on delivery of an indicator representative of the presence of a probe, also can carry out at least one action selected from among: activation of the analog detection circuits; activation of any physiological or activity sensor that may be present in, for example, a rate responsive cardiac pacing system; programming of the type of stimulation, monopolar or bipolar, according to the delivered indicator; initialization of the control algorithms for operation of the device; resetting and activation of the counter of diagnosis; and inscription in the memory of the date of implantation. 
   It can also be envisaged to provide optionally a safety mechanism whereby, when the device operates in bipolar stimulation on a bipolar probe and in the event of delivery of an indicator that is not representative of the presence of a bipolar probe, it switches the device to a safety mode of operation with monopolar stimulation. In the same way, when the device receives from an external programmer an instruction parameter for setting the stimulation mode to bipolar, then the safety means authorizes the activation of the bipolar stimulation mode only if the discriminating means delivers an indicator representative of the presence of a bipolar probe. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further benefits, features and characteristics 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 in reference to the annexed drawings, in which: 
       FIG. 1  is a diagrammatic representation of the device according to the invention, with a generator equipped with a bipolar probe; 
       FIGS. 2 to 5  represent, for four different situations, on the one hand (on the left) the equivalent electric circuit seen from the terminals of the device and on the other hand (on the right) the shapes of the pulses likely to be detected on the various terminals of the device at the application of a stimulation pulse in the case where the reference potential connection is voluntarily disconnected; 
       FIGS. 6 to 8  are homologous with  FIGS. 2 to 5 , in the case where a reference potential connection is established; 
       FIG. 9  is a flow chart showing the various steps of an embodiment of an algorithm for detecting the presence of a probe and the type of probe, as well as actions taken consequently; 
       FIG. 10  is a flow chart showing an embodiment of a way in which it is possible to detect a loss of integrity of a bipolar probe; and 
       FIG. 11  is a flow chart showing the various steps of an embodiment of an algorithm making it possible, on the one hand, to increase the lifespan of the device by deactivation before the implantation (i.e., entering a sleep mode) and, on the other hand, the detection of the configuration where the case, after having been equipped with a bipolar probe, was not yet introduced by the surgeon into the pocket. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  represents, in a diagrammatic way, a cardiac pacemaker (or a device including the functions of cardiac detection and stimulation), primarily including a generator  10  and a stimulation probe  12 . Probe  12  is illustrated as a bipolar probe, thus including two electrodes: a distal electrode  14 , at the end of probe  12 , connected to terminal  16  of the generator, terminal  16  generally indicated “TIP”; and a proximal electrode  18 , typically of an annular shape, connected to another terminal  20  of generator, generally indicated “RING”. The shapes of the proximal and distal electrodes should be understood to be non limiting. 
   In addition, the metallic case of the generator  10  is connected internally on a terminal  22 , generally indicated “CASE”. Terminal  22  is used as reference potential compared to electrodes RING and TIP for the collection of the depolarization potentials and/or the application of stimulation pulses. 
   Generator  10  comprises a voltage source circuit (buttery)  24  ensuring the charge of a capacitor of large capacity C STO . Capacitor C STO , once charged, makes it possible to deliver the stimulation pulse on closing of switch  26 . Switch  26  is controlled by a control signal STIM delivered by the microcontroller (not shown) in a conventional manner. The closing of switch  26  causes a transfer of the energy accumulated in capacitor C STO  towards terminal TIP  16 , via a decoupling capacitor C OUT . 
   In the case of a bipolar probe (as illustrated on  FIG. 1 ), terminal RING  20  typically constitutes the electric reference, and thus is connected to the internal ground of the generator by closing of a switch S 1  controlled by a signal BIP produced by the microcontroller. When switch S 1  is open, a resistance R 1  is inserted between the ground G and electrode  20 . In addition, a capacitor C 1  between terminals  16  and  20  ensures a protection against the various electromagnetic interferences. 
   In a monopolar mode, terminal CASE  22  typically constitutes the electric reference, and is connected to the internal ground of the generator by closing of a switch S 2  controlled by a signal MONOP produced by the microcontroller. When switch S 2  is open, a resistance R 2  is inserted between the ground G and the electrode  22 . In addition, a capacitor C 2  between the terminals  16  and  22  ensures a protection against the various electromagnetic interferences. 
   Essentially, the mechanism of detecting a probe, and the type of probe, according to a preferred embodiment of the present invention, concerns applying bipolar or monopolar stimulation pulses, with or without a disconnection of the reference potential connection, and observing the signals produced on electrodes CASE and RING. These signals will be notably different according to whether the generator:
         1. is not implanted and is not equipped with a probe,   2. is equipped with a bipolar probe but not yet implanted,   3. is implanted and equipped with a bipolar probe, or   4. is implanted and equipped with a monopolar probe.
 
As one will describe herein, this discrimination can be carried out by an analysis of the detected pulse width and a comparison of that width with various thresholds.
       

   A first possibility, illustrated in  FIGS. 2 to 5 , concerns delivering a stimulation pulse with the two reference potential connections disconnected (i.e., switches S 1  and S 2  open), and observing the waveforms collected on electrodes RING and CASE. This possibility, although it requires the analysis of the signal on two electrodes and the delivery of a stimulation pulse that does not capture the heart (i.e., does not cause a depolarization of the myocardium), presents the advantage of authorizing the detection of a partially implanted device, with a bipolar probe connected to the generator but the case located out of the pocket. This faculty can be used in particular, as described below, “to awaken” the generator by making it leave the “sleep” mode at low energy consumption, and, by carrying out a certain number of initialization steps, as described below with reference in particular to the flow chart of  FIG. 11 . 
   Another possibility, illustrated by  FIGS. 6 to 8 , concerns delivering a stimulation pulse with the two reference potential connections intact (i.e., switches S 1  and S 2  closed). In the following description, one will consider in this case that the applied stimulation pulse is a bipolar pulse, i.e., one applied between terminals TIP and RING. But the invention could be implemented in a comparable manner by applying a monopolar stimulation pulse (thus between electrodes CASE and TIP) and by observing the shape of the detected pulse on electrode RING. This latter alternative, although less advantageous, should nevertheless be understood as within the framework of the present invention. 
   The detection of the presence of a probe, and of the type of probe, and of an effective implantation, is operated by a pulse width detecting circuit  28  that determines the width of the pulses collected on terminals CASE  22  and RING  20 . 
   One now will describe, in reference to  FIGS. 2 to 5 , a preferred embodiment of the invention making it possible to detect the connection of a probe and the generator implantation. In the initial state, at the time of shipping of the device, no probe is connected. The external configuration  30  ( FIG. 2 ) of electrodes CASE, RING and TIP as seen by the device thus corresponds to a very high impedance, theoretically infinite (an open circuit), between two of these three terminals. Under these conditions, a stimulation pulse applied by the device with the two reference potential connections disconnected (i.e., switches S 1  and S 2  open) has the shape illustrated in  FIG. 2 , namely a shape of rectangular crenel (squarewave) with height V STIM  and width W P . In this configuration, terminals CASE and RING are coupled on terminal TIP by means of the respective protective capacitors C 2  and C 1 . Detector circuit  28  thus will see on these terminals CASE and RING pulses such as illustrated on  FIG. 2 , with a abrupt step increment then a decaying return to the initial level according to a time-constant defined by R 1  and C 1  or R 2  and C 2 . The duration W O  at the middle height of the detected pulse is in this example about 200 μs. 
     FIG. 3  illustrates the case where the pacemaker is equipped with a bipolar probe, but where the case of the generator is neither implanted in the pocket nor connected to a reference potential electrode or a plate. It is about a particular configuration that must be detected to prevent a monopolar stimulation on a bipolar probe. In this case, the network of impedances  30 , seen internally by the pacemaker, comprises only one impedance RL 2  between the two electrodes RING and TIP, because electrode CASE is electrically in the air (floating). The stimulation pulse applied to terminal TIP always has the shape of a crenel and the detected pulse on terminal CASE takes the same shape as that previously described in  FIG. 2 , because of the only-internal coupling by the protective capacitor C 2 , with an abrupt step increase followed a progressive return to the initial level. On the other hand, the pulse collected on terminal RING presents the shape of a crenel similar to the stimulation pulse delivered on terminal TIP, because of the external coupling by impedance RL 2 . 
     FIG. 4  illustrates the case where the pacemaker is equipped with a bipolar probe, with the case of the generator implanted in the pocket or connected to a reference electrode. In this case, the network of impedances  30  corresponding to this probe, seen internally by the pacemaker, includes impedances RL 1 , RL 2  and RL 3  between three electrodes TIP, CASE and RING taken two by two. The pulses collected on terminals CASE and RING present then both the shape of a crenel similar to the stimulation pulse delivered on terminal TIP, because of the external coupling with terminal TIP by impedances RL 1 , RL 2  and RL 3 . 
   The case illustrated in  FIG. 5  is the one where the pacemaker is equipped with a monopolar probe, with the case of the generator implanted in the pocket or connected to a reference electrode. One will note that with a monopolar probe, if the case is neither implanted nor connected to a reference electrode, the situation is identical to that depicted in  FIG. 2 . The pacemaker being by default in a monopolar stimulation mode (as a normal factory adjustment), this situation does not present a risk and no particular safety measure needs to be taken before the complete functional activation of the device. The configuration of impedance  30  is that illustrated in  FIG. 5 , namely a single impedance RL 1  between CASE and TIP, and with a very high impedance, theoretically infinite, between on the one hand RING and CASE, and on the other hand RING and TIP. The detected pulse on terminal CASE presents the shape of a crenel similar to the stimulation pulse delivered on terminal TIP, because of the external coupling by impedance RL 1 . On the other hand, the pulse collected on terminal RING presents an abrupt step followed by a progressive return to the initial level, because of the internal coupling by the protective capacitor C 1 . 
   Thus, a simple analysis of the detected pulses on terminals CASE  22  and RING  20  by the detecting circuit  28  make it possible to discriminate between a generator that is not implanted ( FIG. 2 ) and a partially implanted generator ( FIGS. 3 to 5 ). In the case of a generator that is not implanted, the width of the signal that is also detected on terminals CASE or RING is W O . As soon as a probe is connected, the detected pulse width on terminals CASE and/or RING becomes W p . This discrimination makes it possible to detect immediately, i.e., in the interval of a cardiac beat, the connection, even partial, of a bipolar or monopolar probe, and whether the generator is or is not placed in the pocket. This detection is in particular used “to awaken” the generator immediately. This is so that the generator leaves a low energy consumption mode and commutates to a mode where it will be fully functional, with, in particular preference, a safety stimulation ensuring the capture by the stimulation pulse throughout the implantation procedure. The implementation of these functions will be described more in detail below with reference to the flow chart of  FIG. 11 . 
   One now will describe, with reference to  FIGS. 6 to 8 , the way in which the invention makes it possible to detect whether the device was correctly implanted and the implantation phase is completed. With this intention, one applies a bipolar pulse (for example) with the two reference potential connections established (i.e., switches S 1  and S 2  closed) and one analyzes the shape of the detected signal on terminals TIP and CASE. 
     FIG. 6  shows the shape of the pulse collected on terminal CASE for a bipolar pulse applied between terminals TIP and RING, when the generator is not implanted. The pulse observed on terminal CASE presents a step increment followed by a relatively slow exponential decay, defined by the time-constant of the internal components R 1  and C 1 , the W o  duration of the pulse at one-half the maximum excursion (“half height”) being approximately 200 μs. 
     FIG. 7  shows the shape of the pulse collected on terminal CASE when the bipolar pulse is applied with the generator correctly implanted and equipped with a bipolar probe. In this case, the circuit of the generator sees three impedances RL 1 , RL 2  and RL 3  between three respective terminals TIP, CASE and RING for the probe. The shape of the pulse observed on terminal CASE when a stimulation pulse is applied between terminals TIP and RING falls with V STIM  and goes up quickly, with a time-constant RL 1 /(RL 2 +RL 3 )*C 1 . For a maximum impedance of 2 kilohms, the maximum duration of the pulse is less than 20 μs, a value defining a low threshold W MIN . 
     FIG. 8  shows the shape of the pulse collected on terminal CASE when the bipolar pulse is applied between terminals TIP and CASE with the generator correctly implanted and equipped with a monopolar probe. In this case, the impedance between TIP and CASE are only that of tissues, while the impedance between TIP and RING, or between RING and CASE, is very high, theoretically infinite. The shape of the signal observed on terminal CASE is this practically the same one as that of the pulse detected on terminal TIP, because of low impedance RL 1  coupling terminals CASE and TIP. 
   Thus, the simple analysis by the detecting circuit  28  of the width of the pulse on terminals CASE  22  and RING  20  (width taken, for example, at half-height) makes it possible to determine the configuration of impedances and thus the three cases just described. This in turn allows the device to determine the presence of a probe, the type of probe and the integrity of the return circuit to ground resulting from an effective implantation in the pocket. Circuit  28  is a circuit in which the thresholds of detection are programmed, i.e., under microprocessor control, in a suitable manner way to discriminate in a non ambiguous way the three cases of possible waveforms as just described. For example, a high threshold is 500 μs, a low threshold is 100 μs. 
   One now will describe the operation of an embodiment the device of the invention, with reference to the flow charts of  FIGS. 9 to 11 . In the description relating to the flow charts of  FIGS. 9 and 10 , for the clearness of discussion one will disregard the specific protection corresponding to the particular case where the pacemaker was equipped with a bipolar probe, but where the case of the generator is neither implanted in the pocket, nor connected to a reference potential electrode or plate, as this particular situation will be treated with reference to the flow chart of  FIG. 11 . 
     FIG. 9  is a flow chart showing the various steps of the algorithm making it possible to detect the implantation of the device and to parameterize it consequently. After installation of the battery (not shown in  FIG. 9 , but see voltage source  24 ,  FIG. 1 ), at the time of shipping (t=0) and after initialization of a counter N (step  32 ), the generator operates in a stimulation mode known as a “safety mode” with simultaneous delivery of bipolar and monopolar stimulation pulses (step  34 ), at a relatively low frequency, about 70 bpm. In this way, when a probe is connected to the generator terminals by the surgeon immediately before the implantation itself, the pulses will be already delivered on the electrode (or the electrodes) of the probe, whether the latter is monopolar or bipolar. After a predetermined period of time T (step  36 ), the generator detects the width W of the pulse on terminal CASE (W CASE ) of the generator operating in a bipolar stimulation mode (step  38 ). If the width W is greater than a predetermined threshold value W MIN  and less than the pulse width W P  of the stimulation pulse (step  40 ), then the device is not yet implanted, and it remains in the safety stimulation mode returning to step  34 . 
   In the contrary case (step  42 ), counter N is decremented by one and, if it is not null (zero) (step  44 ), the counting of the period T is re-initialized (step  46 ) and the device returns at step  34  to the safety stimulation mode. The opposite case means that the test of step  40  detected three times consecutively on terminal CASE a pulse having a width W that is lower than W MIN  or equal to W P , i.e., it detected the presence of a probe. Therefore, it determines that the device was definitively implanted. By precaution, the period T is preferably selected so that 3×T corresponds to a duration greater than the average duration of an implantation, i.e., 3×T&gt;20 minutes approximately. 
   Once the presence of a probe is detected, the pacemaker determines, according to the pulse width W CASE  on terminal CASE, whether it is a bipolar or a monopolar probe (steps  48 ,  50  and  52 ). If the pulse width W CASE  is less than W MIN , the implanted probe is a bipolar probe, whereas otherwise it is a monopolar probe. The safety stimulation mode is then stopped (step  54 ) and stimulation in the determined programmed mode is activated (step  56 ). 
   After step  56 , a verification algorithm is also activated, according to the invention, providing a continual checking of the integrity of the probe (step  58 ) (described more in detail with reference to  FIG. 10 ). Lastly, the appropriate physiological algorithms are initialized (step  60 ), the counters of diagnosis are reset to zero and activated (step  62 ) and, if the device is equipped with a real time clock, the date of implantation is registered in memory (step  64 ). 
     FIG. 10  illustrates the way in which the process of the invention, in accordance with a preferred embodiment, allows the uninterrupted monitoring of the integrity of a bipolar probe after implantation. This process in particular makes it possible to detect a rupture of the wire of the proximal electrode  18 , that would have as a consequence a loss of capture likely to involve significant risks for the patient. This rupture causes a modification of the impedance of the equivalent circuit  30  so that the pulse received on terminal CASE will present the illustrated shape, with a width W P . Consequently, if bipolar stimulation is programmed (step  66 ), and if the pulse width W CASE  collected on terminal CASE is less than threshold W MIN  (step  68 ), this means that the probe is functional (see below). Bipolar stimulation is then continued (return at step  66 , and counter N is set to a predetermined value, for example, N=3). 
   In the contrary case, the bipolar probe behaves like a monopolar probe, which is revealed by a shortening of the pulse collected on terminal CASE to a width appreciably equal to W P  (i.e., not significantly less that W p . On this event, which presumes that W p  was previously less than W MIN , the device switches to a monopolar stimulation mode (step  72 ) for safety. This condition is temporary, until its confirmed by three successive concordant tests during a given interval of time T (steps  72  to  82 ). If the defect is thus confirmed, then the pacemaker switches definitively to monopolar stimulation (step  84 ). 
   It will be noted that this process can be also used to prevent a physician mistakenly reprogramming a bipolar stimulation on a device that had been implanted with a monopolar probe, a situation which would have the same consequences as the rupture of the wire of proximal electrode of a bipolar probe. 
   Thus, after the physician has programmed a bipolar stimulation mode, the device produces the first bipolar stimulation and detects on terminal CASE a pulse of a certain width W CASE . If this width W CASE  is less than W MIN , the configuration is in conformity and the modification of programming is accepted. In the contrary case, then the implanted probe is a monopolar probe, incompatible with a bipolar stimulation, and the change of programming mode is refused by the device. 
   Referring now to  FIG. 11 , it illustrates the way in which the process of the invention, in a preferred embodiment, can be used to improve the lifespan of the device, and to take into account the particular case where the pacemaker was equipped with a bipolar probe, but where the case of the generator is neither implanted in the pocket, nor connected to a reference potential electrode or plate. 
   It is known that many functions of the device involve a high current consumption, but are not necessary prior to an implantation. The lifespan of the battery, and thus the expiration date (i.e., the “use before” date) of the device before implantation, can be improved if these functions are deactivated at the shipping of the device, and automatically activated when the connection to a probe is detected. As illustrated on  FIG. 11 , with the delivery, the generator is in a sleep mode, consuming a low current. In particular, the analog circuits (detection amplifiers, circuits of polarization of the sensors and analog circuits for the treatment of the signals) are de-activated and the functions of the microcontroller are reduced to the minimum, with a simple stimulation at slow intervals, for example, 70 bpm on the atrium and the ventricle, a stimulation rate sufficient for the detection of a probe (steps  86  to  90 ). 
   As soon as the presence of a probe, atrial or ventricular, is detected, and the effective implantation is confirmed or the case is connected to a reference electrode (step  90 ), where one then tests whether the width W CASE  of the pulse on terminal CASE is appreciably equal to (i.e., not significantly less than width W P  of the pulse of stimulation), the device switches operating mode, leaving the sleep state mode having an initial set of operating parameters involving low energy consumption (step  92 ), by activating the programmed stimulation mode, monopolar or bipolar (step  93 ), by starting the activation of the detection amplifiers and other analog circuits (step  94 ), by activating any physiological or activity sensors present (step  96 ), and by restoring a general set of programmed operating parameters with full activation for the programmed mode (step  98 ). 
   Suitable devices for which the present invention has application include, for example, the NewAge™ pacemaker from Sorin CRM (Saluggia, Italy). These devices are microprocessor based systems with memory, data registers and the like (microcontrollers) having circuits for receiving, conditioning and processing detected electrical signals, providing stimulation pulses and detecting myocardial activity including the pulse width detection. Of course any such circuits as are available and known to those skilled in the art, including the aforementioned switches may be used as well as circuits able to perform these functions not yet commercialized. The creation of suitable software instructions for controlling an implant to perform the aforementioned functions of the present invention are believed to be within the abilities of a person of ordinary skill in the art. 
   One 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.