referring now to fig1 , it illustrates an atrial defibrillation system embodying the present invention including an implantable atrial defibrillator shown in association with a schematically illustrated human heart in need of atrial fibrillation monitoring and potential cardioversion , an external programming device , and an external portable device , which further communicates with the remote service center . for illustration purposes , the schematic block diagram of the implantable atrial defibrillator is described to include the dual - chamber pacemaker functionality . in this device , a microprocessor and associated circuitry make up the controller , enabling it to output pacing pulses or cardioversion / defibrillation energy to the atrium and ventricle of the heart in response to sensed events and lapsed time intervals . the microprocessor communicates with a memory via a bi - directional data bus . the memory typically comprises a rom or ram for program storage and a ram for data storage . the device has atrial channels comprising atrial electrode , atrial lead , atrial sensing unit , atrial stimulation unit , and atrial cardioversion unit . the ventricular channels similarly comprise ventricular electrode , ventricular lead , ventricular sensing unit , ventricular stimulation unit , and a ventricular defibrillation unit . for each channel , the same lead and electrode are used for both sensing and pacing , while cardioversion / defibrillation may share the same electrode or use a different shock electrode . the sensing channels are used to control pacing and for measuring heart rate in order to detect cardiac arrhythmias . the device detects the occurrence and termination of an af , for example , by measuring the atrial rate as well as possibly performing other processing on the data received from the atrial sensing unit . the atrial cardioversion unit is interfaced to the microprocessor for delivering cardioverting energy to the atrium in need of cardioversion , in synchronous with a shockable r wave . as well known in the art , the microprocessor determines if an r wave is shockable by analyzing the ventricular rhythm based on the data received from the ventricular sensing unit to minimize the probability of ventricular arrhythmias induced by atrial cardioversion . preferably , the atrial sensing unit further checks the activity of the atrium to confirm the presence of af before discharging the cardioverting energy . a ventricular defibrillation unit is also provided to deliver shock therapy to the ventricle in case a ventricular tachyarrhythmia being detected by the ventricular sensing unit . the external programming device is arranged to communicate with a telemetry unit , which is coupled to the microprocessor over a bi - directional bus . the telemetry unit may be of the type well known in the art for conveying various information which it obtains from the microprocessor to the external programming device , or for receiving programming parameters from the external programming device and then conveys to the microprocessor for storage in the memory . in addition , the external portable device to be described hereinafter , can also communicate bi - directionally with the microprocessor through the telemetry unit comprising a first external bidirectional data transceiver . preferably , the parameters that may be received from or sent to the external portable device are vastly limited as compared to the parameters which may be received from or sent to the external programming device . to that end , the parameters which may be provided by the external portable device are preferably simple commands , such as initiate atrial cardioversion therapy , disable or enable automatic atrial cardioversion therapy , delay scheduled atrial cardioversion therapy by certain period of time , retrieve iegm and other diagnostic information from the implantable atrial defibrillator , and so on . these commands set the implantable atrial defibrillator into one of a number of modalities wherein each modality is determined and controlled by parameters that can only be selected by a physician operating the external programming device . the parameters which may be transmitted to the external portable device include simple acknowledgment to confirm receiving the commands from the external portable device , the signals warning the detection of af or indicating the termination of af , and some critical diagnostic information , such as the duration of the af since its onset , the mean cycle length of the af , the time interval to the scheduled automatic atrial cardioversion , the snapshot of the recorded iegm , and so on . in a preferred embodiment , the warning trigger signal is transmitted to the external portable device after a programmable delay after the automatic detection of af . this will prevent generating warning messages to the patient in case of short and self - terminating af episodes . preferably , the implantable atrial defibrillator can also be programmed to transmit the warning signal only after programmed number of anti - tachycardia pacing ( atp ) attempts failed to terminate the af , indicating atrial cardioversion will be the preferred choice to terminate af . after the warning trigger signal is transmitted to the external portable device , if af is terminated by the automatic or manual atrial cardioversion , or self - terminates before the atrial cardioversion , the implantable atrial defibrillator also sends an eoaf signal to the external portable device to clear the warning signal being generated . furthermore , the device includes a depletable power source , such as a lithium battery , which provides power to the electrical components of the device . referring now to fig2 , it illustrates the block diagram of the external portable device and its interfaces with the implantable atrial defibrillator and the remote service center . the overall functioning of the external portable device is controlled by its microprocessor , which reads and performs instructions stored in its associated memory . the instructions stored in memory preferably include instructions defining a communication protocol compatible with the implantable atrial defibrillator , and instructions defining a communication protocol compatible with the remote service center . the microprocessor of the external portal device communicates with the input unit to read from the keypad ( or press switches ) the patient inputted commands . one subset of the commands is designed to configure the external portable device , for example , to turn on or off certain outputs as described hereinafter , or select specific communication protocols . another subset of the commands is designed to establish communication between the external portable device and the remote service center through remote communication unit . for example , patient &# 39 ; s input can command the external portable device to transmit diagnostic information ( such as iegm data ) to the remote service center , and wait to receive acknowledgement . the third subset of the commands is designed to establish communication between the external portable device and the implantable atrial defibrillator through implant communication unit ( first external bidirectional data transceiver ). for example , patient &# 39 ; s input can command the external portable device to transmit corresponding commands to the implantable atrial defibrillator to initiate atrial cardioversion therapy , to disable or enable automatic atrial cardioversion therapy , to delay scheduled atrial cardioversion therapy by certain period of time ( or cancel therapy by delaying therapy indefinitely ), to retrieve iegm and other diagnostic information from the implantable atrial defibrillator , and so on . the implant communication unit ( first external bidirectional data transceiver ) also receives the acknowledgement and related diagnostic information sent from the implantable atrial defibrillator , and conveys these data to the microprocessor for storage in the memory . upon receiving the warning trigger signal of af detection from the implantable atrial defibrillator , the microprocessor of the external portable device communicates with the output unit to generate output that is perceptible by the patient . such output can be in the form of visible message , such as the light - up or blinking of a light emitting diode ( led ) or the text message displayed in a liquid crystal display ( lcd ), or in the form of audible message such as beep , ringing tone , or pre - recorded voice messages played by a speaker , or in the form of discernible vibration by a vibrator . according to the patient &# 39 ; s preference , one or multiple types of warning message can be respectively turned on or off via the keypad . for example , the visible warning message can be turned on while the audible warning message can be turned off during the night if the patient chooses not to be disturbed during sleep even if the implantable atrial defibrillator detects the af . besides generating warning messages , some diagnostic information that is received from the implantable atrial defibrillator and stored in memory ( such as the duration of the af since its onset , the mean cycle length of the af , and the time interval to the scheduled automatic atrial cardioversion ) can also be provided to the patient in the form of visual or audible messages . if the external portable device receives the eoaf signal from the implantable atrial defibrillator indicating af terminates , the previously generated warning message will be cleared . the external portable device , via its remote communication unit ( second external bidirectional data transceiver ), can further communicate with the remote service center . such long - range communication apparatus can be in the form of a mobile radio network , or a fixed - line telecommunication network , or the internet , as well known in the art . examples of such long - range communication apparatus have been taught in u . s . pat . no . 6 , 470 , 215 , u . s . pat . no . 6 , 574 , 509 , u . s . pat . no . 6 , 622 , 043 , all of which patents are assigned to the assignee of the present invention and incorporated herein by reference . besides generating warning messages to the patient , the external portable device can also transmit critical diagnostic information stored in memory to the remote service center , preferably including the duration of the af since its onset , the mean cycle length of the af , the number of failed atp attempts , and the iegm snapshot data . the remote service center receives the diagnostic information via compatible communication protocols , then sends acknowledgement back to the external portable device , which generates visible or audible output indicating receipt of the acknowledgement . the data received by the remote service center is stored in central database , and is promptly presented to the patient &# 39 ; s physician or responsible expert through proper means , such as fax or email as known in the art . by reviewing the received diagnostic information , the physician can evaluate the patient &# 39 ; s condition and provide expert advice to the patient who wishes to contact the physician before taking any action in response to the af warning generated by the external portable device . lastly , the external portable device includes a battery power source , which provides power to the electrical components of the device . the battery is chargeable by connecting to an external charger . fig3 illustrates the operation of the atrial defibrillation system including the implantable atrial defibrillator ( implant ) and the external portable device ( external device ) in the automatic activation mode . as already pointed out , the implant will automatically detect an atrial fibrillation by continuously monitoring the atrial rate . upon detection of an atrial fibrillation the implant actively generates an atrial fibrillation warning trigger signal which then is transmitted to the external device . upon reception of the warning trigger signal , the external device will put out a warning message and activate an af delay button which enables a patient to delay or delete a scheduled atrial fibrillation therapy . as an option , the implant is adapted to start anti - tachycardia pacing upon detection of an atrial fibrillation . preferably , several anti - tachycardia pacing attempts are started . should an anti - tachycardia pacing be successful and lead to an end of atrial fibrillation , the implant will generate an - end - of - atrial - fibrillation signal ( eoaf signal ) and transmit such signal to the external device . upon receipt of the end of atrial fibrillation signal ( eoaf signal ) the external device will clear a warning signal and deactivate the atrial fibrillation delay button . simultaneously , the external device will put out an “ af terminated ” message . as an option not further illustrated in fig3 , after the implant device detects an af , it generates the warning signal only after a programmable delay , preferably also after a programmed number of atp attempts fail to terminate the af . as another option not further illustrated in fig3 , the implant and the external device may also be adapted to retrieve and display information regarding a current atrial tachycardia or atrial fibrillation episode . in a preferred embodiment , the external device provides for the possibility of entering a data request command by the patient . such data request command is transmitted from the external device to the implantable atrial defibrillator and causes the implantable atrial defibrillator to transmit diagnostic information to the external device the diagnostic information then is displayed by the external device to the patient . if no end of atrial fibrillation has occurred within a scheduled period of time after detection of atrial fibrillation , the implant will trigger an atrial fibrillation therapy . this atrial fibrillation therapy may be delayed by a delay timer which is said upon receipt of an af therapy delay command by the implant . such af therapy delay command would be transmitted from the external device to the implant if the patient has triggered an af therapy delay button . alternatively , patient may opt to cancel the schedule atrial therapy by setting an extremely long therapy delay . af therapy is started at the timeout of the therapy delay . if af therapy is started , the implant generates an af therapy acknowledgement signal and transmits such signal to the external device . upon receipt of the af therapy acknowledgement signal the external device will clear the af warning message and deactivate the af therapy delay button . simultaneously , the external device will put out an “ af therapy acknowledge ” message . if af therapy is successful and the implant detects an end of atrial fibrillation , the implant will generate an end of atrial fibrillation signal ( eoaf signal ) and send the signal to the external device . upon receipt of said eoaf signal , the external device will display an “ af terminated ” message . in an improved embodiment not illustrated in fig3 , the external device may be adapted to display diagnostic and therapy information to the patient after successful termination of an atrial fibrillation episode . such information may be displayed automatically . alternatively , the information can be retrieved by the patient by pressing a data request command button . turning out to fig4 illustrating the operation of the atrial defibrillation system if the patient activation mode is selected . since the patient activation mode in many respect is similar to the automatic activation mode , only the differences will be discussed . in the patient activation mode , the implant detects an atrial fibrillation the same way it would detect an atrial fibrillation in the automatic activation mode . the af detection triggers the implant device to generate a warning signal to the patient . alternatively , the warning signal is generated after a programmable delay , or preferably after a programmed number of atp attempts fail to terminate the af . upon receiving of a warning trigger signal , the external device displays the warning message and activates an af trigger button ( instead of an af therapy delay button ). by pressing the af trigger button , the patient can manually initiate an af therapy . once an af therapy is started , the operation of the atrial defibrillation system in the patient activation mode is similar to the operation in the automatic activation mode . detection of an end of atrial fibrillation prior to initiating the atrial fibrillation therapy causes the external device to clear the warning signal and to deactivate the af trigger button . in addition , the external device may put out an “ af terminated ” message . regarding retrieval and display of diagnostic and therapy operation , the atrial defibrillation system may operate in the patient activation mode the same way as in the automatic activation mode . although the invention has been described above with reference to a preferred embodiment , it should be noted that such an embodiment is merely illustrative of the application of the principles of the invention . in summary , the present invention has the following claims .