Abstract:
An implantable medical device has an atrial fibrillation detector adapted to detect an atrial fibrillation. A telemetry unit is adapted to transmit an AF message to an external receiver. A control unit is connected to the atrial fibrillation detector and said telemetry unit and is adapted to only indicate an atrial fibrillation detected by the atrial fibrillation detector that lasts longer than a predetermined waiting time period of at least several hours. Additionally the implantable medical device has an atrial shock generator which is connected or connectable to an atrial defibrillation electrode and adapted to generate and deliver an atrial cardioversion pulse when triggered and the control unit is connected to the atrial shock generator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention refers to a medical device system for the management of the treatment of atrial fibrillation. The system includes an implant such as a cardiac pacemaker or an implantable cardioverter/defibrillator that can detect atrial fibrillation and can transmit, via a relay device, this information to a telematic application that can display this information to the physician. With this specific information from the pacemaker or the implantable cardioverter/defibrillator the physician can manage the appropriate therapy, e.g. anticoagulation or cardioversion. In addition the implantable cardioverter/defibrillator device can deliver an atrial cardioversion therapy or an atrial defibrillation shock to an atrium of a heart suffering from atrial fibrillation (AF). 
         [0003]    2. Description of the Related Art 
         [0004]    Fibrillation is a particular form of tachycardia that may occur as well in an atrium (atrial fibrillation) as in a ventricle (ventricular fibrillation) of a heart. Other forms of tachycardia are for example flutter. A tachycardia is characterized by a rapid heart rate. Typically, fibrillation is characterized by a very high rate of contraction of the heart chamber (atrium or ventricle) affected and of very low amplitude of the sensed electrical potential. Typically, during an episode of fibrillation, no coordinated contraction of the whole heart chamber occurs but only a circulating excitation of the myocardium wherein only one part of the heart chamber&#39;s muscle (the myocardium) is exited (depolarised) and thus contracted, whereas other parts of the myocardium already are repolarized and thus relaxed. Therefore, during episodes of fibrillation, the affected heart chamber is unable to efficiently pump blood. For this reason, a ventricular fibrillation (VF) usually is lethal if not treated within minutes or seconds. On the other hand, an atrial fibrillation usually is not life threatening, since the atrial contraction only contributes to a smaller part to the total pumping power of the heart that is typically expressed as an minute volume: pumped blood volume per minute. 
         [0005]    Even though atrial fibrillation or atrial flutter is not life threatening, there are several reasons for treating atrial fibrillation although such treatment is painful for the patient. 
         [0006]    Atrial fibrillation is the most common cardiac arrhythmia. The risk of developing atrial fibrillation increases with age—AF affects four percent of individuals in their 80s. An individual may spontaneously alternate between AF and a normal rhythm (paroxysmal atrial fibrillation) or may continue with AF as the dominant cardiac rhythm without reversion to the normal rhythm (chronic atrial fibrillation). Atrial fibrillation is often asymptomatic, but may result in symptoms of palpitations, fainting, chest pain, or even heart failure. These symptoms are especially common when atrial fibrillation results in a heart rate which is either too fast or too slow. In addition, the erratic motion of the atria leads to blood stagnation (stasis) which increases the risk of blood clots that may travel from the heart to the brain and other areas. Thus, AF is an important risk factor for stroke, the most feared complication of atrial fibrillation. 
         [0007]    Observational studies suggest that one in four to five strokes is due to atrial fibrillation. Depending on the risk profile of an individual patient, the yearly risk for a stroke is between 2% and 14%. 
         [0008]    Also, atrial fibrillation is compromising the heart&#39;s performance because of the loss of atrioventricular synchrony associate with an atrial fibrillation and can cause discomfort as for example fatigue. 
         [0009]    Atrial fibrillation occurs in many variants. Often it occurs just for an episode and spontaneously switches back to normal sinusrhythm after some hours without any additional therapy. This is called paroxysmal atrial fibrillation. On the other hand atrial fibrillation can persist and go over into a chronic status. This is called chronic atrial fibrillation. To restore normal sinusrhythm it is necessary to deliver adequate therapy to the patient. 
         [0010]    A typical treatment of a fibrillation is a cardioversion back to normal sinusrhythm or/and an anticoagulation therapy that reduces the risk of throboembolic complications. 
         [0011]    During a cardioversion procedure an ECG-triggered electrical current is delivered via a cardioverter/defibrillator device to the patient. This resets the heart back to normal rhythm. Normally an anticoagulation therapy must be performed for about 4 weeks before a cardioversion to avoid throboembolic complications. The only exception of the procedure can be made if in the first 48 h after the occurrence of atrial fibrillation a cardioversion can be performed. In this case, without providing this long-term anticoagulation, an acute cardioversion can be made. 
         [0012]    Another issue that has to be seen is the efficiency of a cardioversion, that is reduced the longer AF is present. 
         [0013]    The problem in daily clinical practice is to differ between the episodes of paroxysmal atrial fibrillation and the transition into chronic atrial fibrillation regarding the time window of 48 h. 
       BRIEF SUMMARY OF THE INVENTION 
       [0014]    It is an object of the invention to provide implantable medical device that provides an improved response to atrial fibrillation. 
         [0015]    According to the present invention the object of the invention is achieved by an implantable medical device featuring: 
         [0016]    an atrial fibrillation detector that is adapted to detect an atrial fibrillation 
         [0017]    a atrial cardioversion pulse generator that is connected or can be connect to an atrial defibrillation electrode and that is adapted to generate and deliver an atrial cardioversion pulse when triggered, 
         [0018]    a telemetry unit that is adapted to transmit an AF message to an external receiver, and 
         [0019]    a control unit, that is connected to said atrial fibrillation detector and said atrial shock generator and said telemetry unit. 
         [0020]    The control unit is adapted to only indicate an atrial fibrillation detected by the atrial fibrillation detector that lasts longer than a predetermined waiting time period of at least several hours. 
         [0021]    Preferably the predetermined waiting time period is a time period in the range from 10 to 14 hours. 
         [0022]    In one preferred embodiment of the invention, the control unit is adapted to automatically induce an atrial cardioversion therapy upon indication of an atrial fibrillation. 
         [0023]    In an alternative preferred embodiment of the invention, the control unit is adapted to send out an AF message via the telemetry unit upon indication of an atrial fibrillation. This allows a physician or any other person including a patient having the implantable medical device implanted to decide on there own whether or not an atrial cardioversion or an atrial defibrillation shall be induced. Then, cardioversion can be induced manually. 
         [0024]    Preferably, the control unit can be switched from an automatic atrial cardioversion mode according to the second last paragraph to a manual cardioversion mode according to the last paragraph and vice versa. 
         [0025]    In the automatic atrial cardioversion mode, the implantable medical device will allow for spontaneous natural cardioversion prior to initiating any (painful) atrial cardioversion therapy. 
         [0026]    In the manual atrial cardioversion mode, the implantable medical device will not unnecessarily send out an AF message potentially leading to premature action of a user or physician. Thus, a disadvantage of the prior art devices is avoided, where an AF message is immediately forwarded to a central service center and the central service center in turn sends AF event messages immediately or at the next routine message to the physician. If the AF event message would be sent out always when an AF episodes is detected this results in a high number of false positive alarms because of many spontaneous terminations of these types of episodes within the first few hours. 
         [0027]    On the other hand, if the delay is too long the risk of thromboembolic complications rises and the effort for a cardioversion is much higher. This is avoided by initiating an action—starting cardioversion therapy or sending out an AF message—after a well defined period of time of ongoing atrial fibrillation. 
         [0028]    Further preferred features include a control unit that is adapted to trigger an atrial cardioversion therapy in synchrony with a ventricular event. 
         [0029]    The object of the invention is further achieved by an automatic method for treating atrial fibrillation, comprising the steps of: 
         [0030]    detecting an atrial fibrillation, 
         [0031]    triggering a predetermined waiting time period of several hours of duration, and 
         [0032]    indicating an ongoing atrial fibrillation only if said predetermined waiting time period times out, wherein said predetermined waiting time period is reset prior to time out of said predetermined waiting time period if said detected atrial fibrillation ceases prior to time out of said predetermined waiting time period. 
         [0033]    It is to be appreciated that features of preferred embodiments of the invention may be combined in any useful manner thus arriving a further preferred embodiments of the invention not explicitly mentioned in this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
           [0035]      FIG. 1  shows a dual chamber pacemaker/atrial defibrillator/cardioverter connected to leads placed in a heart. 
           [0036]      FIG. 2  is a block diagram of the device of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
         [0038]    In  FIG. 1  a dual chamber pacemaker  10  as heart stimulator connected to pacing/sensing leads placed in a heart  12  is illustrated. The pacemaker  10  is electrically coupled to heart  12  by way of leads  14  and  16 . Lead  14  has a pair of right atrial electrodes  18  and  20  that are in contact with the right atria  26  of the heart  12 . Lead  16  has a pair of electrodes  22  and  24  that are in contact with the right ventricle  28  of heart  12  and an atrial cardioversion shock coil  50  placed in atrium  32  of heart  12 . Electrodes  18  and  22  are tip-electrodes at the very distal end of leads  14  and  16 , respectively. Electrode  18  is a right atrial tip electrode RA-Tip and electrode  22  is a right ventricular tip electrode  22 . Electrodes  20  and  24  are ring electrodes in close proximity but electrically isolated from the respective tip electrodes  18  and  22 . Electrode  20  forms a right atrial ring electrode RA-Ring and electrode  24  forms a right ventricular ring electrode RV-Ring. Atrial cardioversion shock coil  50  is coil electrode providing a relatively large geometric area when compared to the stimulation electrodes  18 ,  20 ,  22  and  24 . 
         [0039]    Referring to  FIG. 2  a simplified block diagram of a dual chamber pacemaker  10  is illustrated. During operation of the pacemaker leads  14  and  16  are connected to respective output/input terminals of pacemaker  10  as indicated in  FIG. 1  and carry stimulating pulses to the tip electrodes  18  and  22  from an atrial stimulation pulse generator A-STIM  32  and a ventricular pulse generator V-STIM  34 , respectively. Further, electrical signals from the atrium are carried from the electrode pair  18  and  20 , through the lead  14 , to the input terminal of an atrial channel sensing stage A-SENS  36 ; and electrical signals from the ventricles are carried from the electrode pair  22  and  24 , through the lead  16 , to the input terminal of a ventricular sensing stage V-SENS  38 . 
         [0040]    Controlling the dual chamber pacer  10  is a control unit CTRL  40  that is connected to sensing stages A-SENS  36  and V-SENS  38  and to stimulation pulse generators A-STIM  32  and V-STIM  34 . Control unit CTRL  40  receives the output signals from the atrial sensing stage A-SENS  36  and from the ventricular sensing stage V-SENS  38 . The output signals of sensing stages A-SENS  36  and V-SENS  38  are generated each time that a P-wave representing an intrinsic atrial event or an R-wave representing an intrinsic ventricular event, respectively, is sensed within the heart  12 . An As-signal is generated, when the atrial sensing stage A-SENS  36  detects a P-wave and a Vs-signal is generated, when the ventricular sensing stage V-SENS  38  detects an R-wave. 
         [0041]    Control unit CTRL  40  also generates trigger signals that are sent to the atrial stimulation pulse generator A-STIM  32  and the ventricular stimulation pulse generator V-STIM  34 , respectively. These trigger signals are generated each time that a stimulation pulse is to be generated by the respective pulse generator A-STIM  32  or V-STIM  34 . The atrial trigger signal is referred to simply as the “A-pulse”, and the ventricular trigger signal is referred to as the “V-pulse”. During the time that either an atrial stimulation pulse or ventricular stimulation pulse is being delivered to the heart, the corresponding sensing stage, A-SENS  36  and/or V-SENS  38 , is typically disabled by way of a blanking signal presented to these amplifiers from the control unit CTRL  40 , respectively. This blanking action prevents the sensing stages A-SENS  36  and V-SENS  38  from becoming saturated from the relatively large stimulation pulses that are present at their input terminals during this time. This blanking action also helps prevent residual electrical signals present in the muscle tissue as a result of the pacer stimulation from being interpreted as P-waves or R-waves. 
         [0042]    Furthermore, atrial sense events As recorded shortly after delivery of a ventricular stimulation pulses during a preset time interval called post ventricular atrial refractory period (PVARP) are generally recorded as atrial refractory sense event A rs  but ignored. 
         [0043]    Control unit CTRL  40  comprises circuitry for timing ventricular and/or atrial stimulation pulses according to an adequate stimulation rate that can be adapted to a patient&#39;s hemodynamic need as pointed out below. 
         [0044]    Still referring to  FIG. 2 , the pacer  10  includes a memory circuit MEM  42  that is coupled to the control unit CTRL  40  over a suitable data/address bus ADR  44 . This memory circuit MEM  42  allows certain control parameters, used by the control unit CTRL 
         [0045]    in controlling the operation of the pacemaker  10 , to be programmable stored and modified, as required, in order to customize the pacemaker&#39;s operation to suit the needs of a particular patient. Such data includes the basic timing intervals used during operation of the pacemaker  10  and AV delay values and hysteresis AV delay values in particular. 
         [0046]    Further, data sensed during the operation of the pacemaker may be stored in the memory MEM  42  for later retrieval and analysis. This includes atrioventricular interval data that are acquired by the control unit CTRL  40 . Control unit CTRL  40  is adapted to determine the atrioventricular interval data as required for automatic atrioventricular interval analysis by determining the time interval between an atrial event, either sensed (As) or stimulated (Ap) and an immediately following ventricular sensed event Vs as indicated by the ventricular sensing stage V-SENS  38 . 
         [0047]    A telemetry circuit TEL  46  is further included in the pacemaker  10 . This telemetry circuit TEL  46  is connected to the control unit CTRL  40  by way of a suitable command/data bus. Telemetry circuit TEL  46  allows for wireless data exchange between the pacemaker  10  and some remote programming or analyzing device, which can be part of a centralized service center serving multiple pacemakers. 
         [0048]    The pacemaker  10  in  FIG. 1  is referred to as a dual chamber pacemaker because it interfaces with both the right atrium  26  and the right ventricle  28  of the heart  12 . Those portions of the pacemaker  10  that interface with the right atrium, e.g., the lead  14 , the P-wave sensing stage A-SENS  36 , the atrial stimulation pulse generator A-STIM  32  and corresponding portions of the control unit CTRL  40 , are commonly referred to as the atrial channel. Similarly, those portions of the pacemaker  10  that interface with the right ventricle  28 , e.g., the lead  16 , the R-wave sensing stage V-SENS  38 , the ventricular stimulation pulse generator V-STIM  34 , and corresponding portions of the control unit CTRL  40 , are commonly referred to as the ventricular channel. 
         [0049]    In order to allow rate adaptive pacing in a DDDR or a DDIR mode, the pacemaker  10  further includes a physiological sensor ACT  48  that is connected to the control unit CTRL  40  of the pacemaker  10 . While this sensor ACT  48  is illustrated in  FIG. 2  as being included within the pacemaker  10 , it is to be understood that the sensor may also be external to the pacemaker  10 , yet still be implanted within or carried by the patient. A common type of sensor is an activity sensor, such as a piezoelectric crystal, mounted to the case of the pacemaker. Other types of physiologic sensors are also known, such as sensors that sense the oxygen content of blood, respiration rate, pH of blood, body motion, and the like. The type of sensor used is not critical to the present invention. Any sensor capable of sensing some physiological parameter relatable to the rate at which the heart should be beating can be used. Such sensors are commonly used with “rate-responsive” pacemakers in order to adjust the rate of the pacemaker in a manner that tracks the physiological needs of the patient. 
         [0050]    With respect to atrial fibrillation detection and therapy, the pacemaker  10  comprises an atrial fibrillation detector  52  that is part of control unit CTRL  40  and that is connected to atrial sensing stage A-SENS  36 . Further an atrial cardioversion shock generator  54  is provided that is connected via a terminal A-COIL to the atrial coil electrode  50  on ventricular electrode lead  16 . The atrial cardioversion shock generator  54  is also connected to the control unit CTRL  40  and can be triggered by control unit CTRL  40  to generate an atrial cardioversion pulse or an atrial defibrillation shock when needed. Such atrial cardioversion pulse or shock for treatment of an atrial fibrillation is applied to the atrium the atrial coil electrode  50 . 
         [0051]    A defibrillation shock usually has a much higher intensity than for example a stimulation or pacing pulse. The intensity of a defibrillation shock shall be sufficient to render the whole myocardium of the fibrillating heart chamber refractory in order to interrupt a circulating excitation of the myocardium and thus to synchronize the contraction of the myocardium of the heart chamber in all it&#39;s parts. 
         [0052]    When an atrial defibrillation shock is delivered at the wrong point of time during a heart cycle the atrial defibrillation itself can cause a ventricular fibrillation. Therefore, delivery of the atrial defibrillation shock during the so-called vulnerable phase of the ventricle is to be avoided. For this reason, control unit  40  is adapted to trigger an atrial defibrillation shock synchronously with a ventricular event. Such ventricular event may be the sensed event sensed by the ventricular sensing stage  38  or a stimulated ventricular event caused by a ventricular stimulation pulse delivered by ventricular stimulation pulse generator  34 . 
         [0053]    The control unit CTRL  40  is adapted to respond to a detection of an atrial fibrillation by means of the atrial fibrillation detector  52  by starting a timer  56  that is reset, if the atrial fibrillation should naturally cease. When not reset, the timer 56 times out after 12 hours. Then, control unit CTRL  40  either triggers the atrial cardioversion shock generator  54  or it triggers the telemetry circuit TEL  46  to send out an AF message that eventually is received by a central service center and then is forwarded to a physician or to a patient pacemaker  10  is implanted to. 
         [0054]    Whether or not control unit CTRL  40  automatically triggers the atrial cardioversion shock generator  54  to generate and deliver an atrial cardioversion pulse or only triggers sending of an AF message depends on whether pacemaker  10  is in its automatic or in its manual AF mode. The pacemaker  10  can be switched from an automatic atrial cardioversion mode according to the second last paragraph to a manual cardioversion mode according to the last paragraph and vice versa. 
         [0055]    Although an exemplary embodiment of the present invention has been shown and described, it should be apparent to those of ordinary skill that a number of changes and modifications to the invention may be made without departing from the spirit and scope of the invention. In particular, it is possible to implement the features of the claimed atrial fibrillation treatment system into state of the art implantable medical devices such as implantable pacemakers or implantable cardioverter/defibrillator. This invention can readily be adapted to such devices by following the present teachings. All such changes, modifications and alterations should therefore be recognized as falling within the scope of the present invention.