Abstract:
An externally actuable, hermetically sealed switch is incorporated with an implantable medical device (IMD). A patient applies pressure against the tissue over the IMD and actuates the switch. The actuation of the switch causes the IMD to take predetermined actions, such as recording data, inhibiting therapy, initiating therapy, increasing therapy, requesting information, initiating a communications session, or performing a status check. Thus, the patient is able to interact with the IMD without requiring an external device such as a programmer, patient activator or magnet.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to implantable medical devices. More specifically, the present invention relates to implantable medical devices having features that are patient activated.  
         [0002]     DESCRIPTION OF THE RELATED ART  
         [0003]     Various implantable medical devices (IMDs) are commonly used to deliver therapies or to monitor physiological parameters. For example, pacemakers are commonly used to manage cardiac rhythms, defibrillators are used restore sinus rhythm to a heart in fibrillation, and implantable monitors, such as the Medtronic Reveal, are used to record data over time.  
         [0004]     Some IMDs include features that are actuated by the patient. For example, some cardiac monitors will constantly record data in predetermined, looping increments (e.g., 15 minutes), but will only commit that data to permanent memory if the patient indicates that a notable event has occurred (e.g., syncope). As another example, a patient having atrial fibrillation may choose to delay what may be an uncomfortable defibrillation therapy in hopes that the heart will autonomously restore sinus rhythm. That is, the implanted defibrillator may have a preprogrammed time delay before delivering the therapy, triggered by the detection of atrial fibrillation; however, the patient may signal the device to extend the delay. A patient or caregiver may also query the IMD to determine if it is functioning properly, if the IMD has delivered a suspected therapy, or to determine various other types of information.  
         [0005]     In any event, the patient provides an input to the various medical devices to initiate a given action. Typically, such patient communication includes placing a programming head over the IMD and utilizing a programmer to telemeter data to and from the device. Alternatively, the patient may have an RF device that transmits a signal that is received at the IMD to initiate the action. Such a communication device may take various forms, but requires the patient to utilize an external component to communicate with the device. As such, if the patient does not have the external component, communication with the IMD is precluded. Therefore, the patient may not be able to choose therapy options, signal the IMD to record data, request status or operability information from the IMD, or initiate other functionality.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention, in one embodiment, is an implantable medical device having a hermetically sealed switch disposed on an exterior portion of the housing. Thus, once implanted, the patient or a caregiver can actuate the switch by pressing against the tissue over the implant site.  
         [0007]     There are many actions that a patient may desire to actuate on the implantable medical device. Several have traditionally required an external device, such as a programmer, magnet, RF communications device, etc. With the present invention, the patient will always have the ability to toggle the desired function simply by actuating the switch. The switch can be used to initiate a therapy, inhibit a therapy, initiate a self diagnostic, confirm the delivery of a therapy, record data, enter a communications session with an external device, or perform any function the IMD is capable of performing.  
         [0008]     The switch is disposed on the casing of the housing, on a connector block, or on an edge portion of the housing. The force required to actuate the switch is set such that inadvertent pressure (e.g., lying down, wearing tight clothing) will not actuate the switch, yet the pressure required will not be so high that repeated actuation causes bruising or soreness to the surrounding tissue.  
         [0009]     In one embodiment, the present invention is an implantable medical device comprising a housing having an interior and an exterior. The device also includes a switch disposed on the exterior of the housing.  
         [0010]     In another embodiment, the present invention is an implantable medical device comprising means for physically communicating with the implantable medical device after implantation. In another embodiment, the present invention is an implantable medical device comprising a housing and processing means disposed within the housing. The device also includes switch means actuable external to the housing and in communication with the processing means  
         [0011]     In another embodiment, the present invention is an implantable medical device comprising a hermetically sealed housing, a processor disposed within the housing, and a lead coupleable to the housing for delivering therapy initiated by the processor. The device also includes a hermetically sealed switch disposed on an external portion of the hermetically sealed housing and in communication with the processor.  
         [0012]     The present invention also includes a method comprising applying pressure to tissue adjacent to an implanted medical device, wherein the application of pressure actuates a switch disposed on an exterior portion of the implanted medical device. The method further includes triggering an action within the implanted medical device based upon the actuation of the switch.  
         [0013]     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an illustration of a PCD type system according to the present invention.  
         [0015]      FIG. 2  is a block, functional diagram of a PCD type device adapted to carry out the features of the present invention.  
         [0016]      FIG. 3  is a perspective view of the external programming unit of  FIG. 1 .  
         [0017]      FIG. 4  is a planar view of an implantable medical device with a switch incorporated into the housing.  
         [0018]      FIG. 5  is a planar view of an implantable medical device with a switch incorporated into the connector block.  
         [0019]      FIG. 6  is a planar view of an implantable monitoring device with a switch incorporated into the housing.  
         [0020]      FIG. 7  is a schematic illustration of the IMD of  FIG. 4  implanted within a patient. 
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring now to  FIG. 1 , there are illustrated an IMD  10 , exemplary illustrated as a defibrillator, and leads  15  and  16 , making up a PCD (pacemaker cardioverter defibrillator) type system, representative of various implantable medical devices. The leads shown are illustrative, it being noted that other specific forms of leads are within the scope of this invention and that more or fewer leads may be employed depending upon the application. Ventricular lead  16  as illustrated has, located adjacent to the distal end, an extendable helix electrode  26  and a ring electrode  24 , the helix electrode being mounted retractably within an insulative head  27 . Electrodes  24  and  26  are used for bipolar ventricular pacing and for sensing ventricular depolarizations. While electrodes  24  and  26  may be used for bipolar pacing and sensing, electrode  26  may be used in conjunction with the surface of device casing  11 , which surface acts as a common or indifferent electrode in what is termed unipolar operation. Ventricular lead  16  also carries a coil electrode  20 , sometimes referred to as the RV (right ventricular) coil, for delivering defibrillation and/or cardioversion pulses. Coil electrode  20  is positioned on lead  16  so that when the distal tip is at the apex of the ventricle, coil  20  is positioned in the right ventricle. Lead  16  may also carry, optionally, an SCV coil  30 , positioned in the subclavian vein, which can be used, for example, for R wave sensing and/or applying cardioversion pulses. Lead  16  carries respective concentric coil conductors (not shown), separated from one another by appropriate means such as tubular insulative sheaths and running the length of the lead for making electrical connection between the PCD device  10  and respective ones of electrodes  20 ,  24 ,  26  and  30 .  
         [0022]     Atrial lead  15  as illustrated includes an extendable helix electrode  17  and a ring electrode, the helix electrode being mounted retractably within an insulative head  19 . Electrodes  17  and  21  are used for bipolar atrial pacing and for sensing atrial depolarizations. While electrodes  17  and  21  may be used for bipolar pacing and sensing, electrode  17  may be used in conjunction with the surface of device casing  10 , which surface acts as a common or indifferent electrode in what is termed unipolar operation. Note that, in this example, atrial lead  15  is not equipped with coils for use in the sensing and delivery of cardioversion of defibrillation pulses. This is not meant to preclude the inclusion of such applications that may be used advantageously with the present invention.  
         [0023]     PCD device  10 , is shown in combination with atrial and ventricular leads, with the lead connector assembly  13 ,  14 ,  18 , and  22  being inserted into the connector block  12  of the device  10 . As used herein, the term “PCD type” device refers to any device that can apply both pacing therapy and shock therapy for controlling arrhythmias. It should be appreciated that the present invention is applicable to various IMDs including, but not limited to pacemakers, cardioverters, defibrillators, monitors, drug pumps, neural stimulators, muscular stimulators, spinal stimulators, or any combination thereof. Furthermore, the present invention may be practiced with IMDs such as device  10  that include attachable leads or with various devices, such as an implantable subcutaneous monitor that have electrodes within the housing and do not utilize external leads.  
         [0024]      FIG. 2  is a functional schematic diagram of an implantable PCD in which the present invention may usefully be practiced. This diagram should be taken as exemplary of the type of device in which the invention may be embodied, and not as limiting, as it is believed that the invention may usefully be practiced in a wide variety of device implementations.  
         [0025]     The device is provided with a lead system including electrodes, which may be as illustrated in  FIG. 1 . Alternate lead systems may of course be substituted. If the electrode configuration of  FIG. 1  is employed, the correspondence to the illustrated electrodes is as follows. Electrode  311  corresponds to electrode  16 , and is the uninsulated portion of the housing of the implantable pacemaker/cardioverter/defibrillator. Electrode  320  corresponds to electrode  20  and is a defibrillation electrode located in the right ventricle. Electrode  318  corresponds to electrode  30  and is a defibrillation electrode located in the superior vena cava. Electrodes  324  and  326  correspond to electrodes  24  and  26 , and are used for sensing and pacing in the ventricle. Electrodes  317  and  321  correspond to electrodes  17  and  21  and are used for pacing and sensing in the atrium.  
         [0026]     Electrodes  311 ,  318  and  320  are coupled to high voltage output circuit  234 . Electrodes  324  and  326  are located on or in the ventricle and are coupled to the R-wave amplifier  200 , which preferably takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured R-wave amplitude. A signal is generated on R-out line  202  whenever the signal sensed between electrodes  324  and  326  exceeds the present sensing threshold.  
         [0027]     Electrodes  317  and  321  are located on or in the atrium and are coupled to the P-wave amplifier  204 , which preferably also takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured P-wave amplitude. A signal is generated on P-out line  206  whenever the signal sensed between electrodes  317  and  321  exceeds the present sensing threshold.  
         [0028]     Switch matrix  208  is used to select which of the available electrodes are coupled to amplifier  210  for use in digital signal analysis. Selection of electrodes is controlled by the microprocessor  224  via data/address bus  218 , which selections may be varied as desired. Signals from the electrodes selected for coupling to bandpass amplifier  210  are provided to multiplexer  220 , and thereafter converted to multi-bit digital signals by A/D converter  222 , for storage in random access memory  226  under control of direct memory access circuit  228 . Microprocessor  224  may employ digital signal analysis techniques to characterize the digitized signals stored in random access memory  226  to recognize and classify the patient&#39;s heart rhythm employing any of the numerous signal-processing methodologies known to the art.  
         [0029]     The remainder of the circuitry is dedicated to the provision of cardiac pacing, cardioversion and defibrillation therapies, and, for purposes of the present invention may correspond to known circuitry. An exemplary apparatus is disclosed of accomplishing pacing, cardioversion and defibrillation functions follows. The pacer timing/control circuitry  212  includes programmable digital counters which control the basic time intervals associated with DDD, VVI, DVI, VDD, AAI, DDI and other modes of single and dual chamber pacing well known to the art. Circuitry  212  also controls escape intervals associated with anti-tachyarrhythmia pacing in both the atrium and the ventricle, employing any anti-tachyarrhythmia pacing therapies known to the art.  
         [0030]     Intervals defined by pacing circuitry  212  include atrial and ventricular pacing escape intervals, the refractory periods during which sensed P-waves and R-waves will not restart the escape pacing interval timing. The durations of these intervals are determined by microprocessor  224 , in response to stored data in memory  226  and are communicated to the pacing circuitry  212  via address/data bus  218 . Pacer circuitry  212  also determines the amplitudes and pulse widths of the cardiac pacing pulses under control of microprocessor  224 .  
         [0031]     During pacing, the escape interval timers within pacer timing/control circuitry  212  are reset upon sensing of R-waves and P-waves as indicated by signals on lines  202  and  206 , and in accordance with the selected mode of pacing on timeout trigger generation of pacing pulses by pacer output circuitry  214  and  216 , which are coupled to electrodes  317 ,  321 ,  324  and  326 . The escape interval timers are also reset on generation of pacing pulses, and thereby control the basic timing of cardiac pacing functions, including anti-tachyarrhythmia pacing. The durations of the intervals defined by the escape interval timers are determined by microprocessor  224 , via data/address bus  218 . The value of the count present in the escape interval timers when reset by sensed R-waves and P-waves may be used to measure the durations of R-R intervals, P-P intervals, P-R intervals, and R-P intervals, which measurements are stored in memory  226  and used in conjunction with the present invention to diagnose the occurrence of a variety of tachyarrhythmias, as discussed in more detail below.  
         [0032]     Microprocessor  224  operates as an interrupt driven device, and is responsive to interrupts from pacer timing/control circuitry  212  corresponding to the occurrences of sensed P-waves and R-waves and corresponding to the generation of cardiac pacing pulses. These interrupts are provided via data/address bus  218 . Any necessary mathematical calculations to be performed by microprocessor  224  and any updating of the values or intervals controlled by pacer timing/control circuitry  212  take place following such interrupts. A portion of the memory  226  may be configured as a plurality of recirculating buffers, capable of holding series of measured intervals, which may be analyzed in response to the occurrence of a pace or sense interrupt to determine whether the patient&#39;s heart is presently exhibiting atrial or ventricular tachyarrhythmia.  
         [0033]     The arrhythmia detection method of the PCD may include prior art tachyarrhythmia detection algorithms. As described below, the entire ventricular arrhythmia detection methodology of presently available Medtronic pacemaker/cardioverter/defibrillators is employed as part of the arrhythmia detection and classification method according to the disclosed preferred embodiment of the invention. However, any of the various arrhythmia detection methodologies known to the art, as discussed in the Background of the Invention section above might also be usefully employed in alternative embodiments of the implantable PCD.  
         [0034]     In the event that an atrial or ventricular tachyarrhythmia is detected, and an anti-tachyarrhythmia pacing regimen is desired, appropriate timing intervals for controlling generation of anti-tachyarrhythmia pacing therapies are loaded from microprocessor  224  into the pacer timing and control circuitry  212 , to control the operation of the escape interval timers therein and to define refractory periods during which detection of R-waves and P-waves is ineffective to restart the escape interval timers.  
         [0035]     In the event that generation of a cardioversion or defibrillation pulse is required, microprocessor  224  employs the escape interval timer to control timing of such cardioversion and defibrillation pulses, as well as associated refractory periods. In response to the detection of atrial or ventricular fibrillation or tachyarrhythmia requiring a cardioversion pulse, microprocessor  224  activates control circuitry  230 , which initiates charging of the high voltage capacitors  246 ,  248  via charging circuit  236 , under control of high voltage charging control line  240   242 . The voltage on the high voltage capacitors is monitored via VCAP line  244 , which is passed through multiplexer  220  and in response to reaching a predetermined value set by microprocessor  224 , results in generation of a logic signal on Cap Full (CF) line  254 , terminating charging. Thereafter, timing of the delivery of the defibrillation or cardioversion pulse is controlled by pacer timing/control circuitry  212 . Following delivery of the fibrillation or tachycardia therapy the microprocessor then returns the device to cardiac pacing and awaits the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization.  
         [0036]     In the illustrated device, delivery of the cardioversion or defibrillation pulses is accomplished by output circuit  234 , under control of control circuitry  230  via control bus  238 . Output circuit  234  determines whether a monophasic or biphasic pulse is delivered, whether the housing  311  serves as cathode or anode and which electrodes are involved in delivery of the pulse.  
         [0037]     In modern implantable cardioverter/defibrillators, the physician, from a menu of therapies that are typically provided, programs the specific therapies into the device. For example, on initial detection of an atrial or ventricular tachycardia, an anti-tachycardia pacing therapy may be selected and delivered to the chamber in which the tachycardia is diagnosed or to both chambers. On redetection of tachycardia, a more aggressive anti-tachycardia pacing therapy may be scheduled. If repeated attempts at anti-tachycardia pacing therapies fail, a higher energy cardioversion pulse may be selected for subsequent delivery. Therapies for tachycardia termination may also vary with the rate of the detected tachycardia, with the therapies increasing in aggressiveness as the rate of the detected tachycardia increases. For example, fewer attempts at anti-tachycardia pacing may be undertaken prior to delivery of cardioversion pulses if the rate of the detected tachycardia is below a preset threshold.  
         [0038]     In the event that fibrillation is identified, the typical therapy will be the delivery of a high amplitude defibrillation pulse, typically in excess of 5 joules. Lower energy levels may be employed for cardioversion. As in the case of currently available implantable pacemakers/cardioverter/defibrillators, it is envisioned that the amplitude of the defibrillation pulse may be incremented in response to failure of an initial pulse or pulses to terminate fibrillation.  
         [0039]      FIG. 3  is a perspective view of programming unit program  20 . Internally, programmer  20  includes a processing unit (not shown in the Figure) that is a personal computer type motherboard, e.g., a computer motherboard including an Intel Pentium 3 microprocessor and related circuitry such as digital memory. The details of design and operation of the programmer&#39;s computer system will not be set forth in detail in the present disclosure, as it is believed that such details are well-known to those of ordinary skill in the art.  
         [0040]     Referring to  FIG. 3 , programmer  20  comprises an outer housing  60 , which is preferably made of thermal plastic or another suitably rugged yet relatively lightweight material. A carrying handle, designated generally as  62  in  FIG. 2 , is integrally formed into the front of housing  60 . With handle  62 , programmer  20  can be carried like a briefcase.  
         [0041]     An articulating display screen  64  is disposed on the upper surface of housing  60 . Display screen  64  folds down into a closed position (not shown) when programmer  20  is not in use, thereby reducing the size of programmer  20  and protecting the display surface of display  64  during transportation and storage thereof.  
         [0042]     A floppy disk drive is disposed within housing  60  and is accessible via a disk insertion slot (not shown). A hard disk drive is also disposed within housing  60 , and it is contemplated that a hard disk drive activity indicator, (e.g., an LED, not shown) could be provided to give a visible indication of hard disk activation.  
         [0043]     As would be appreciated by those of ordinary skill in the art, it is often desirable to provide a means for determining the status of the patient&#39;s conduction system. Normally, programmer  20  is equipped with external ECG leads  24 .  
         [0044]     In accordance with the present invention, programmer  20  is equipped with an internal printer (not shown) so that a hard copy of a patient&#39;s ECG or of graphics displayed on the programmer&#39;s display screen  64  can be generated. Several types of printers, such as the AR-100 printer available from General Scanning Co., are known and commercially available.  
         [0045]     In the perspective view of  FIG. 3 , programmer  20  is shown with articulating display screen  64  having been lifted up into one of a plurality of possible open positions such that the display area thereof is visible to a user situated in front of programmer  20 . Articulating display screen is preferably of the LCD or electro-luminescent type, characterized by being relatively thin as compared, for example, a cathode ray tube (CRT) or the like.  
         [0046]     As would be appreciated by those of ordinary skill in the art, display screen  64  is operatively coupled to the computer circuitry disposed within housing  60  and is adapted to provide a visual display of graphics and/or data under control of the internal computer.  
         [0047]      FIG. 4  is a planar view of IMD  10 . As previously described, IMD  10  includes a housing having the hermetically sealed casing  11  and connector block  12 . A hermitically sealed switch  100  is located within the casing  11 . In one embodiment, switch  100  is a momentary switch that makes contact (or breaks contact) when pushed. Other types of switches such as a toggle on/off type switch could be used. Once implanted, the switch  100  is actuated by applying pressure to the tissue over the implant site. With sufficient pressure the switch  100  is actuated and a predetermined action is initiated. The switch  100  may have an identifying physical feature such as a raised profile, bump, or depression or cavity, to facilitate location of the switch by the patient with palpitation prior to forcefully activating the switch by pressing on it.  
         [0048]     In this manner, the patient can initiate certain actions within IMD  10  without requiring the use of an external device, such as a programmer, magnet, RF transceiver or the like. Thus, the action can be taken at any time and provides an additional level of freedom of operation to the patient.  
         [0049]     The actions taken by actuating switch  100  include most capabilities of the IMD  10 . The action of the switch  100  may depend on the duration of time that the switch is depressed. By way of example, such actions include inhibiting the delivery of a therapy. As previously described, the IMD  10  may determine that a particular therapy is appropriate, e.g., defibrillation for atrial fibrillation; however, the patient may prefer to wait an extended period of time to allow the rhythm to stabilize on its own. Thus, in this example, actuating the switch  100  causes the IMD  10  to inhibit the delivery of a therapy. The inhibited therapy could be any therapy that the patient can safely choose to forego based on personal comfort. Conversely, actuation of the switch  100  initiates a therapy or increases a level of therapy, again based on the patient&#39;s personal comfort level.  
         [0050]     Actuation of the switch  100 , in another embodiment, queries the IMD  10  for a status or to perform a self-diagnostic. Thus, the patient can actuate the switch  100  and then receive a confirmation that the IMD  10  is operable. Such a confirmation could be delivered by tactile stimulation (e.g., vibration), the generation of certain sounds, tones or alarms, by sending a signal to an external device (e.g., a programmer), or through any other communication platform. Likewise, the patient could query the device to determine whether a particular therapy had been delivered. For example, the patient may wish to determine if a perceived shock was really delivered or if it was a phantom shock.  
         [0051]     In yet another embodiment, actuation of the switch  100  causes the IMD  10  to record data. Such data includes, for example, a date and time stamp indicative of when the patient felt symptoms. Alternatively, actuation of the switch  100  causes the IMD  10  to record physiological data from a predetermined time frame. That is, the IMD  10  continuously monitors such data, but only records that data when the patient indicates, through actuation of switch  100 , that symptoms have been detected. This is advantageous in that the patient can cause the IMD  10  to record data at any time, without requiring the use of an external actuator that can be lost, forgotten, or inconveniently located. For retrieval of data, actuation of the switch  100  could be programmed, in one embodiment, to initiate a telemetry session with a remote device and facilitate data transfer.  
         [0052]     Upon actuation, the switch, in one embodiment, provides an indication of actuation. For example, the switch  100  provides tactile feedback when fully depressed, such as a “clicking” sensation. Alternatively, a sound, vibration, or other perceivable alert could be generated to indicate that the switch  100  has been actuated.  
         [0053]     While many actions actuable by switch  100  are implemented by a single deployment of the switch  100 , the present invention is not so limited. That is, more complex commands can be delivered to the IMD  10  through a series of switch actuations. For example, depressing switch  100  a multiple number of times during a predetermined time period causes a different action that simply actuating the switch  100  once. As can be imagined, various combinations of timing and the number of actuations can be utilized to communicate a wide variety of information to the IMD  10 . Also, the duration of switch (e.g., push and hold for some predetermined period, e.g., one to three seconds) contact may encode information and become a different command. By way of example, an initial deployment of the switch  100  inhibits the delivery of a therapy. Subsequent deployment of the switch  100  indicates a time interval. For example, the second actuation causes inhibition for five minutes, the third another five minutes (a total of ten minutes), and so on.  
         [0054]     Switch  100  can take various forms so long as a hermetic seal is maintained. For example, switch  100  is a membrane switch disposed within the housing  11  or “can” of the IMD  10 .  FIG. 5  illustrates the switch  100  disposed within the connector block  12  of the IMD  10 . When IMD  10  is implanted subcutaneously, the switch  100  is positioned on the housing  11 . For submuscular or submammary implants, the switch  100  may be mounted on the connector block  12  or along the edge of the housing  11 , to facilitate actuation.  
         [0055]     The amount of force required to actuate the switch  100  should be chosen to facilitate patient actuation while minimizing accidental actuation. For example, the force required should be sufficiently high so that a patient lying on their chest or wearing tight clothing will not inadvertently cause the switch  100  to actuate. Conversely, the force required should not be so high that deployment of the switch  100  causes pain, discomfort, or bruising.  
         [0056]     While the switch  100  has been described in the context of a pacemaker/defibrillator/cardioverter, the switch  100  can be utilized in a wide variety implantable medical devices such as, muscle stimulators, neural stimulators, drug pumps and the like.  FIG. 6  is a planar view of an IMD  10  in the form of an implantable cardiac monitor  120 , with an externally actuable switch  130  incorporated thereon. Monitor  120  includes a hermetically sealed housing  115  having multiple electrodes  125  for sensing cardiac signals. Once implanted, external actuation of the switch  139  causes predetermined results. For example, actuation of the switch  130  could toggle the device on and off. Alternatively, actuation could query the device as to its status and a signal could be generated if the monitor  120  is functioning properly. In another example, actuation of the switch  130  could cause certain information to be recorded such as the date and time or the cardiac data sensed for a predetermined time period could be stored in memory. As another example, actuation of the switch  130  could cause the monitor  120  to begin a telemetry session and to uplink to an external device.  
         [0057]      FIG. 7  is a schematic illustration of IMD  10  implanted within a patient  135 . The patient  135  is aware of the relative position of the IMD  10  beneath the skin and/or muscle. Thus, when appropriate, the patient  135  presses one or more fingers against the tissue, which in turn contacts the housing  11  of the IMD  10 . With sufficient force, this action will actuate the switch  100 . Preferably, the patient  135  is alerted when the switch  100  is successfully actuated. For example, the switch  100  may provided a clicking sensation when deployed. Alternatively, a sound or other perceivable alert may be generated by the IMD simply as an alert that the switch  100  has been actuated.  
         [0058]     Depending upon the programmed action of the switch  100 , various safety protocols may be implemented. For example, if inadvertent actuation of the switch  100  could cause a serious consequence, IMD can be programmed so that a single actuation is insufficient to trigger the action. With the generation of a sound or other perceivable alert, the patient  135  is notified that the switch  100  is being inadvertently actuated and corrective action can be taken. With such a protocol, the patient  135  may be required to actuate switch  100  in a predetermined sequence or a specific number of times within a predetermined time frame to initiate the desired action.  
         [0059]     Although the present invention has been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.