with reference to fig6 , the invention can be preferably implemented by suitable programming of the control software 52 of a known microprocessor 40 controlled pacemaker having suitable memory and data registers 50 , and signal conditioning input output circuits 30 , the pacemaker being coupled to a heart 10 by cardiac lead ( s ) 11 , 21 ( two conventional bipolar leads shown ). the control software also preferably integrates an automatic mode switching algorithm of the ddd - amc type , such as that described by the aforementioned ep - a - 0 488 904 and ep - a - 1 048 322 , and their respective corresponding u . s . pat . nos . 5 , 318 , 594 and 6 , 397 , 105 b1 , which u . s . patents are incorporated herein by reference in their entirety as if fully set forth herein . detection p : sensing of a spontaneous activity having its origin in the atrium a ( fig6 ); it will be considered that there is indeed a detection p if an atrial detection is not followed in a given delay , for example , 31 ms , by a ventricular detection ( otherwise , one would be in a situation of “ ventricularfar - field ” detection , i . e ., a sensing via the atrium of a remote depolarization coming from the ventricle ). detection r : sensing of a spontaneous activity having its origin in the ventricle v ( fig6 ). stimulation a : stimulation delivered in the atrium . stimulation v : stimulation delivered in the ventricle . atrial event : either detection p or stimulation a . ventricular event : either detection r or stimulation v . cardiac cycle : a delay separating two events of comparable nature in the same cavity , for example , separating two detections p , or two stimulations a . pp average : an average interval of the atrial rate / rhythm , calculated , for example , over eight cardiac cycles not including an extrasystole . escape interval ( ei ): the time interval , counted after a detection or a stimulation in a given cavity , following which a stimulation is delivered to the given cavity if no spontaneous event was detected in this given cavity . for the atrium , it is known as the atrial escape interval ( aei ). atrial extrasystole ( aes ): an atrial detection occurring inside the post - atrial atrial refractory period ( paarp ), the calculation of this paarp being that of the standard type ddd pacemaker . ventricular extrasystole ( ves ): a ventricular detection preceded by a ventricular detection or stimulation , with a coupling interval ( r - r interval or v - r interval ) less than or equal to a parametrable ( i . e ., a parameterized , programmable ) value of the pp average , for example a value less than or equal to 75 % of the pp average . for further details on the detection and the treatment of the extrasystoles , one will be able to refer to the ep - a - 0 550 342 and its corresponding u . s . pat . no . 5 , 312 , 451 commonly assigned herewith to ela medical , which describes an algorithm for the detection and treatment of the ves by an asynchronous stimulation of the atrium and a controlled stimulation of the ventricle , which description is incorporated herein by reference . in accordance with a preferred implementation of the invention employing an implanted device having a standard dual chamber cardiac pacing functionality , a certain number of functions , if they are present , are maintained just as they normally are . thus , the algorithms for cardiac stimulation , the algorithm for “ fallback ” of the cardiac rate , and for prevention of electronic tachycardias ( also referred to as pmt or pacemaker - mediated tachycardia ), and the algorithms that make it possible to calculate and apply paarp periods and for protection against a retrograde conduction in the event of suspicion of ves are used in their known and conventional manners . one now will discuss a way in which , in accordance with a preferred embodiment of the invention , the device includes the suspecting means manages the losses of atrial capture ( or the atrio - ventricular blocks ( avb )), and those for which it manages the losses of atrial detection . the management of the loss of capture is discussed with reference to the illustrated situations fig1 to 3 . the first case for management of loss of atrial capture corresponds to the situation illustrated on the chronogram of fig1 . this first case is that of having detected and analyzed the sequence of spontaneous and stimulated events and identified an absence of ventricular activity after an atrial stimulation ( this case being particular to a device that is equipped with automatic mode commutation ). as a result , the device suspects a loss of atrial capture , and takes the following actions : first , it applies an atrial counter - stimulation , provided that this function is activated by the physician ( the delay separating the counter - stimulation from the preceding atrial stimulation being a programmable interval ). next , the energy of the following atrial stimulation , or of the counter - stimulation , is increased . the value or level of energy applied is programmable and can be either the maximum energy permitted by the device , or an energy corresponding to a step ( i . e ., a programmable value ) above the current energy . for example , it may be desirable in certain circumstances to use the maximum energy level , e . g ., in the case of a counter - stimulation . two possibilities arise then : on the one hand , if the spontaneous ventricular activity ( detection r ) is restored ( the lower chronogram of fig1 ), then the device detects a normal behavior , without avd , but with a stimulation energy increased to compensate for the risk of loss of capture . on the other hand , ( the upper chronogram of fig1 ), if the authorized number of cycles n1 is reached without detecting ventricular activity , then any nonextrasystolic atrial event starts an avd , and this is maintained during n2 cycles , or until the occurrence of a nonextrasystolic detection r . preferably , n1 = 1 cycle , and n2 = 8 cycles . the maintenance of a detected condition over a number of cardiac cycles is known as persistence . the second case of management of atrial loss of capture corresponds to the situation illustrated on the chronogram of fig2 . this case concerns the lengthening of the atrio - ventricular conduction delay over a given number of cycles n3 , this number being programmable , for example , n3 = 3 cycles . if the atrial activity is systematically a stimulated activity ( stimulation a ), the device initially suspect a loss of atrial capture . in this case , the energy of the following stimulation is increased , with the parameterized value ( maximum energy or an energy corresponding to a step above the current energy ). then , if the normal atrio - ventricular conduction delay is restored ( the upper chronogram of fig2 ), the device returns to its initial operation mode aai , without avd , with an increased stimulation energy . in the contrary case the lower chronogram of fig2 , the initial atrial stimulation energy is restored , and a nonextrasystolic atrial event accordingly starts an avd , which occurs during n 2 successive cycles , or until the occurrence a nonextrasystolic detection r . in the case that a lengthening of the atrio - ventricular conduction delay also is observed after an atrial detection , the device then can suspect the beginning an avb and , at the end of n4 cycles , start an avd , which continues during n2 successive cycles or until the occurrence of a nonextrasystolic detection r . the third case of management of atrial loss of capture corresponds to the situation illustrated on the chronogram of fig3 . this third case is that of a sequence in which a stimulation a is followed by detection p of a p wave , which in turn is followed by the detection r of a spontaneous r wave , with this same sequence repeating itself over a programmable number of given cycles n4 , for example , n4 = 3 cycles . this p wave , shifted in time from the stimulation a , sensed by the device , is considered to be an aes . the device suspects then a loss of atrial capture and increases the energy for the following stimulation to the parameterized value ( maximum energy or energy corresponding to a step above current energy ). the device also has a functionality that enables it to restore the initial stimulation energy in the event of a temporary increase . in this regard , periodically , e . g ., every 24 hours , the stimulation energy is lowered by a step . the step is preferably a programmable value and may be the same as the step increment , or not . nevertheless , if an increase in energy occurs during 3 consecutive days , this “ reversibility ” is inhibited . one now will describe the manner in which the device in accordance with a preferred embodiment of the invention manages a loss of atrial detection with reference to the illustrated chronograms of fig4 and 5 . the first case of management of loss of atrial detection , illustrated in fig4 , is that of the detection of a ventricular event of a ves type , which one can assume is a loss of atrial detection if its coupling interval is higher than a programmed threshold value . in this first case , the atrial sensitivity is increased ( for example , the threshold applied to detect spontaneous activity ( i . e ., the detection threshold ) is decreased by a step ) until there is a return of a normal atrial detection , or a return to an atrial stimulation with a normal delay ( i . e ., in the absence of acceleration of the ventricular rate / rhythm between successive detections r ) between atrial stimulation and ventricular detection . the second case of management of atrial loss of detection corresponds to the situation illustrated on the chronogram of fig5 . if the delay between an atrial stimulation and a ventricular detection decreases by a quantity greater than one programmable duration , for example , 47 ms cycle to cycle , or compared to a delay defined as a normal delay , the device suspect a loss of atrial detection and increases the atrial sensitivity at the following cycle ( for example , by decreasing the sensitivity threshold by a step ) until the return of a normal delay between atrial stimulation and ventricular detection . a third case of management of loss of atrial detection is that of the passage of a detection p to a stimulation a if the a - r delay is less than the p - r delay by a programmable duration ( for example , 63 ms ); the device suspect then also a loss of detection , and increases the sensitivity at the following cycle . in the same manner as discussed for the stimulation energy , periodically , e . g ., every 24 hours , the device decreases the sensitivity ( by raising the detection threshold ) to allow a return to the initial value . nevertheless , if an increase in the sensitivity occurs during consecutive 3 days , this reversibility also is inhibited . suitable devices for which the present invention has application include , for example , the talent ™ and symphony ™, rhapsody ™ brand pacemakers and the alto ™ brand of defibrillators available from ela médical , montrouge france . with reference also to fig6 , these devices are microprocessor based systems 40 having circuits ( hardware and software ) that provides for receiving , conditioning and processing detected electrical signals 30 , and are capable of receiving software instructions 52 by telemetry ( not shown ), storing them in memory 50 , and then executing those instructions to perform the functions and control algorithm described above in implementing the present invention . the creation of suitable software instructions 52 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 . the detection circuits 22 used to detect the cardiac signals in the atrium and the ventricle , in the left and / or right chambers , as well as the circuits 24 used to stimulate those chambers are well known and any suitable design may be used . one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments , and the parameters provided with respect to numbers of cycles and time intervals are merely representative examples , which are presented for purposes of illustration and not of limitation .
an active implantable medical device , such as a double chamber pacemaker or defibrillator or cardiovertor , having an improved adjustment of atrial sensitivity and of atrial stimulation energy . this device includes control algorithms for suspecting a loss of atrial detection and / or atrial capture that operates by analysis of a sequence of detected stimulations and ventricular and atrial detections . the following conditions are detected : an absence of ventricular activity post - atrial stimulation ; and / or a lengthening , beyond a given limit , of the atrio - ventricular conduction delay over a predetermined number of successive cardiac cycles ; and / or an occurrence of an atrial detection consecutive to an atrial stimulation over a predetermined number of successive cardiac cycles ; and / or a ventricular extrasystole ; and / or reduction , below a given limit , of a delay between atrial stimulation and ventricular detection ; and / or the passage of an atrial detection to an atrial stimulation with concomitant reduction , below a given limit , of the delay between atrial event and ventricular detection . the atrial detection threshold and / or the atrial stimulation energy are adjusted , preferably stepwise , according to the detected conditions to provide improved patient care .