Abstract:
A system for the detection of cardiac events occurring in a human patient is provided. At least two electrodes are included in the system for obtaining an electrical signal from a patient&#39;s heart. An electrical signal processor is electrically coupled to the electrodes for processing the electrical signal and a patient alarm means is further provided and electrically coupled to the electrical signal processor. The patient alarm means generates an escalating sensory alarm signal over a predetermined time period subsequent to the electrical signal processor if the processor detects a cardiac event. The patient alarm means may be further applied to a pacemaker or defibrillator system.

Description:
FIELD OF USE  
       [0001]     This invention is in the field of implantable medical device systems that monitor a patient&#39;s cardiovascular condition.  
       BACKGROUND OF THE INVENTION  
       [0002]     Heart disease is the leading cause of death in the United States. A heart attack (also known as an acute myocardial infarction (AMI)) typically results from a thrombus (i.e., a blood clot) that obstructs blood flow in one or more coronary arteries. AMI is a common and life-threatening complication of coronary artery disease. Coronary ischemia is caused by an insufficiency of oxygen to the heart muscle. Ischemia is typically provoked by physical activity or other causes of increased heart rate when one or more of the coronary arteries is narrowed by atherosclerosis. AMI, which is typically the result of a completely blocked coronary artery, is the most extreme form of ischemia. Patients will often (but not always) experience chest discomfort (angina) when the heart muscle is experiencing ischemia. Those with coronary atherosclerosis are at higher risk for AMI if the plaque becomes further obstructed by thrombus.  
         [0003]     The current treatment for a coronary artery narrowing (a stenosis) is the insertion of a drug-eluting stent such as the Cypher™ sirolimus-eluting stent from Cordis Corporation or the Taxus™ paclitaxel-eluting stent from the Boston Scientific Corporation. The insertion of a stent into a stenosed coronary artery is a reliable medical treatment to eliminate or reduce coronary ischernia and to prevent the complete blockage of a coronary artery, which blockage can result in an AMI.  
         [0004]     Acute myocardial infarction and ischemia may be detected from a patient&#39;s electrocardiogram (ECG) by noting an ST segment shift (i.e., voltage change). However, without knowing the patient&#39;s normal ECG pattern, detection from a standard  12  lead ECG can be unreliable.  
         [0005]     Fischell et al. in U.S. Pat. Nos. 6,112,116, 6,272,379 and 6,609,023 describe implantable systems and algorithms for detecting the onset of acute myocardial infarction and providing both patient alerting and treatment. The Fischell et al. patents describe how the electrical signal from inside the heart (which is called an “electrogram”) can be used to determine various states of myocardial ischemia.  
         [0006]     The Reveal™ subcutaneous loop Holter monitor sold by Medtronic, Inc., uses two case electrodes spaced about 3 inches apart to record electrocardiogram information. Recording can be triggered automatically when arrhythmias are detected or upon patient initiation using an external device. The Reveal is designed to record electrogram data only and does not include a patient alerting capability. The Reveal also does not have the capability to measure or alert the patient if there is an ST segment shift. In fact, the Reveal&#39;s high pass filtering and electrode&#39;spacing preclude accurate detection of changes in the low frequency aspects of the heart&#39;s electrical signal such as the ST segment of the electrogram.  
         [0007]     While pacemakers and Implantable Cardioverter Defibrillators (ICDs) monitor the patient&#39;s electrogram, they do not currently detect ST segment changes nor provide patient alerting.  
         [0008]     The term “medical practitioner” shall be used herein to mean any person who might be involved in the medical treatment of a patient. Such a medical practitioner would include, but is not limited to, a medical doctor (e.g., a general practice physician, an internist or a cardiologist), a medical technician, a paramedic, a nurse or an electrogram analyst. Although the masculine pronouns “he” and “his” are used herein, it should be understood that the patient, physician or medical practitioner could be a man or a woman. A “cardiac event” includes an acute myocardial infarction, ischemia caused by effort (such as exercise) and/or an elevated heart rate, bradycardia, tachycardia or an arrhythmia such as atrial fibrillation, atrial flutter, ventricular fibrillation, and premature ventricular or atrial contractions (PVCs or PACs respectively).  
         [0009]     It is generally understood that the term “electrocardiogram” is defined as the heart&#39;s electrical signals sensed by means of skin surface electrodes that are placed in a position to indicate the heart&#39;s electrical activity (depolarization and repolarization). An electrocardiogram segment refers to a portion of electrocardiogram signal that extends for either a specific length of time, such as 10 seconds, or a specific number of heart beats, such as 10 beats. A beat is defined as a sub-segment of an electrogram or electrocardiogram segment containing exactly one R wave. As used herein, the PQ segment of a patient&#39;s electrocardiogram or electrogram is the typically straight segment of a beat of an electrocardiogram or electrogram that occurs just before the R wave and the ST segment is a typically straight segment that occurs just after the R wave.  
         [0010]     Although often described as an electrocardiogram (ECG), the electrical signal from the heart as measured from electrodes within the body is properly termed an “electrogram”. As defined herein, the term “electrogram” is the heart&#39;s electrical signal voltage as sensed from one or more implanted electrode(s) that are placed in a position to indicate the heart&#39;s electrical activity (depolarization and repolarization). An electrogram segment refers to a portion of the electrogram signal for either a specific length of time, such as 10 seconds, or a specific number of heart beats, such as 10 beats. For the purposes of this specification, the terms “detection” and “identification” of a cardiac event have the same meaning.  
         [0011]     A heart signal parameter is defined to be a measured or calculated value created during the processing of one or more beats of the electrogram (or electrocardiogram). Heart signal parameters include the following: ST deviation (ST segment average value minus PQ segment average value), ST shift (ST deviation compared to a baseline average ST deviation), average signal strength, T wave peak height, T wave average value, T wave deviation, QRS complex width, number of PVCs per unit time, heart rate and R-R interval.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention system for the detection of coronary ischemia (including AMI) as described herein shall be called the “Guardian” system. The Guardian system detects cardiac events using an implanted sub-system called a “cardiosaver system” which is designed to detect cardiac events including arrhythmias and coronary ischemia. A “cardiac event” can be an acute myocardial infarction, ischemia caused by effort (such as exercise) and/or an elevated heart rate, bradycardia, tachycardia or an arrhythmia such as atrial fibrillation, atrial flutter, ventricular fibrillation, and premature ventricular or atrial contractions (PVCs or PACs respectively). The present invention cardiosaver system is designed to detect ischemia (including AMI) by identifying ST segment changes in a positive direction (ST elevation) or negative direction (ST depression).  
         [0013]     The cardiosaver system includes electrodes placed to advantageously sense electrical signals from the heart that is the electrogram. The electrodes can be placed within the heart and/or subcutaneously. The implanted portion of the Guardian system is the cardiosaver system as described by Fischell et al. in U.S. Pat. Nos. 6,112,116, 6,272,379 and 6,609,023, each of these patents being incorporated herein by reference. The Guardian system also includes external equipment that can include a physician&#39;s programmer and an external alarm device also described in the Fischell et al. patents.  
         [0014]     The present invention is a cardiosaver system that utilizes techniques for patient alerting designed to ensure the patient knows what is happening without startling the patient, which could cause an unwanted rise in heart rate at the time of a cardiac event when it is important to remain calm.  
         [0015]     In the Fischell et al. patents mentioned above, the concept of internal and external alarm signals is discussed, including the technique of using different patterns of sound, vibration or electrical tickle to assist the patient in differentiating between an emergency (major or critical) alarm where immediate medical attention is needed and a “see your doctor” alert where an appointment should be scheduled as soon as convenient.  
         [0016]     The present invention alerting system improves upon the Fischell et al. concepts by using alert escalation techniques that will communicate the emergency alarm, see doctor alert and/or other patient alert messages without startling or scaring the patient. One embodiment of the present invention uses an increasing amplitude of vibration over time from an internal alarm signal within the implanted cardiosaver. For example, the vibration amplitude might increase over a period of several minutes until it reaches a pre-set level. The escalating amplitude technique can also be applied if the internal alarm uses an electrical tickle or other means of alerting the patient. Also the present invention Guardian system may include an increasing amplitude for the external alarm signal generated by the external alarm system mentioned by Fischell et al. The external alarm signal can be a sound, vibration or visual display with sound being the preferred embodiment.  
         [0017]     It is also envisioned that not only can the amplitude of the internal and/or external alarm signals be increased over time, but the pattern and frequency of the signal might change. For example, the internal alarm might use sets of three successive vibrations with a short time between vibrations within a set and a longer time between sets where the time between sets of vibrations might decrease over time. The time between vibrations within a set might also decrease as the alert escalates. Another example might have the external alarm signal using a tone or tone sequence that increases in the pitch of the tones as the alert escalates. Finally, if a visual display using sets of light flashes is used as the external alarm signal, then the escalation might include the brightness of the flashes, an increase in the number of the flashes within a set, a decrease in the time between sets and a change in the color of the flashes.  
         [0018]     For the purposes of this invention, the term “alarm signal” refers to the complete signal internally or externally generated to alert the patient to the detection of a cardiac event. An alarm signal will continue until a timer turns it off after a pre-set time period (e.g., 5 minutes) or an alarm silence command is provided to the source generating the alarm. A typical alarm signal will be made up of a sequence of short (less than 10 seconds long) alerting signals. The alerting signals may be produced in sets with an inter-set time interval defined as the time interval between sets of alerting signals and the intra-set time interval defined as the time between alerting signals within a set of alerting signals.  
         [0019]     So in summary, the present invention is an implanted system for the detection of cardiac events having any combination of internal alarm signals and external alarm signals where, over the initial period of patient alerting, the alarm signals escalate by any or all of the following:  
         [0020]     a) An increase in amplitude of alerting signals over time;  
         [0021]     b) An increase in the number of alerting signals per set;  
         [0022]     c) A decrease in the time between alerting signals within a set;  
         [0023]     d) A decrease in the time between sets of alerting signals;  
         [0024]     e) A change in the frequency (vibrational frequency, sound pitch, color) of the alerting signals; and,  
         [0025]     f) An increase in the frequency, length and/or amplitude of each alerting signal within a set (including a set of one alerting signal).  
         [0026]     Another embodiment of the present invention is an implanted ischemia detection device with patient alerting that also includes pacemaker circuitry to pace the patient&#39;s heart as needed. Still another embodiment is an implanted ischemia detection device with patient alerting that includes Implantable Cardiac Defibrillator (ICD) circuitry to defibrillate the patient&#39;s heart as needed. Yet another embodiment is an implanted ischemia detection device with patient alerting that includes a combination of pacemaker and ICD circuitry.  
         [0027]     It is also envisioned that there could be an escalating pattern where the number of alerting signals in each set increases while the length of each alerting signal decreases.  
         [0028]     It is also envisioned that the escalation of alerting might involve the sequencing of internal and external alarms. For example, the external alarm signal might begin first as people who are used to phones ringing are less likely to be startled by external alerting sounds. After a preset period of time, the internal alarm signal might begin. Neither, either or both the external and internal alarm signals in such a sequential activation might use one or more alarm signals that escalate by the means described above.  
         [0029]     Thus it is an object of this invention to have a Guardian system that can alert a patient to the detection of a cardiac event without causing a startle response.  
         [0030]     Another object of this invention is to have a Guardian system that can alert a patient to the detection of a cardiac event where the alarm signal escalates over time.  
         [0031]     Still another object of this invention is to have a Guardian system that can alert a patient to the detection of a cardiac event where the alarm signal escalates by increasing amplitude over time.  
         [0032]     Still another object of this invention is to have a Guardian system that can alert a patient to the detection of a cardiac event where the alarm signal escalates by increasing frequency over time.  
         [0033]     Yet another object of this invention is to have a Guardian system that can alert a patient to the detection of a cardiac event where the alarm signal escalates by decreasing the time between alerting signals within sets of the alarm signal.  
         [0034]     Yet another object of this invention is to have a Guardian system that can alert a patient to the detection of a cardiac event where the alarm signal escalates by decreasing the time between sets of alerting signals within the alarm signal.  
         [0035]     Yet another object of this invention is to have a Guardian system that can alert a patient to the detection of a cardiac event where the alarm signal escalates by increasing the number of alerting signals within sets of the alarm signal.  
         [0036]     Yet another object of this invention is to have a Guardian system that can alert a patient to the detection of a cardiac event where the alarm signal escalates by increasing the frequency, length and/or amplitude of each alerting signal with a set (including a set of one alerting signal).  
         [0037]     Yet another object of the present invention is to have a Guardian system with an implanted component having the capability to generate an internal alarm signal and an external alarm system capable of generating an external alarm signal where the patient alert initiates the external alarm signal before the internal alarm.  
         [0038]     Yet another object of the present invention is to have a Guardian system with an implanted component having the capability to generate an internal alarm signal and an external alarm system capable of generating an external alarm signal where the patient alert initiates the internal alarm signal before the external alarm.  
         [0039]     These and other objects and advantages of this invention will become obvious to a person of ordinary skill in this art upon reading of the detailed description of this invention including the associated drawings as presented herein.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]      FIG. 1  illustrates a Guardian system for the detection of a cardiac event such as an ST segment shift indicative of coronary ischemia and for warning the patient that a cardiac event is occurring;  
         [0041]      FIG. 2  is a block diagram of the implanted cardiosaver system;  
         [0042]      FIG. 3  illustrates an increase in amplitude of an alarm signal as the patient alert escalates;  
         [0043]      FIG. 4  illustrates a change in the number of alerting signals per set as the patient alert escalates;  
         [0044]      FIG. 5  illustrates a decrease in the time between alerting signals within a set of alerting signals as the patient alert escalates;  
         [0045]      FIG. 6  illustrates a decrease in the time between sets of alerting signals as the patient alert escalates;  
         [0046]      FIG. 7  illustrates a change in frequency of alerting signals as the patient alert escalates;  
         [0047]      FIG. 8  illustrates a change in the length of each alerting signal within a set of alerting signals as the patient alert escalates;  
         [0048]      FIG. 9  illustrates a progressive increase in the alerting signals within each set of alerting signals of an alarm signal; and,  
         [0049]      FIG. 10  illustrates an escalating patient alert with increasing intensity, increasing number of alerting signals per set, decreasing time between alerting signals within a set and decreasing time between sets of alerting signals.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]      FIG. 1  illustrates one embodiment of the Guardian system  10  consisting of an implanted cardiosaver system  5  and external equipment  7 . The cardiosaver system  5  includes a cardiosaver  11 , an antenna  6  and an electrode  4  that is part of a lead  2 . The cardiosaver  11  includes electronic circuitry that can detect a cardiac event such as an acute myocardial infarction or arrhythmia and can warn the patient when a cardiac event occurs. The cardiosaver  11  can store the patient&#39;s electrogram for later readout and can send and receive wireless signals  3  to and from the external equipment  7  via the implanted antenna  6  and the external antenna  25 . The functioning of the cardiosaver system  5  will be explained in greater detail with the assistance of  FIG. 2 .  
         [0051]     The cardiosaver system  5  has at least one lead  2  with at least one electrode  4 . In fact, the cardiosaver system  5  could utilize as few as one lead or as many as three and each lead could have as few as one electrode or as many as eight electrodes. The lead  2  in  FIG. 1  could advantageously be placed subcutaneously or through the patient&#39;s vascular system with the electrode  4  being placed into the apex of the right ventricle. For example, the lead  2  could be placed in the right ventricle or right atrium or the superior vena cava similar to the placement of leads for pacemakers and ICDs. The metal case of the cardiosaver  11  could serve as an indifferent electrode with the electrode  4  being the active electrode. Alternately, the lead  2  in  FIG. 1  could be placed through the patient&#39;s vascular system with the electrode  4  being placed into the apex of the left ventricle.  
         [0052]     The lead  2  could advantageously be placed subcutaneously at any location where the electrode  4  would provide a good electrogram signal indicative of the electrical activity of the heart. Again for the lead  2 , the case of the cardiosaver  11  of the cardiosaver system  5  could be an indifferent electrode and the electrode  4  would be the active electrode. Although the Guardian system  10  described herein can readily&#39;operate with only two electrodes, or one electrode and the case of the cardiosaver being the other electrode, it is envisioned that multiple electrodes used in monopolar or bipolar configurations could be used.  
         [0053]      FIG. 1  also shows the external equipment  7  that consists of an external alarm transceiver  20 , a physician&#39;s programmer  18 , a pocket PC  12 , an emergency room diagnostic system  16  and the equipment  14  in a remote diagnostic center. The external equipment  7  provides the means to interact with the cardiosaver system  5 . These interactions include programming the cardiosaver  11 , retrieving data collected by the cardiosaver system  5 , and handling alarms generated by the cardiosaver  11 . It should be understood that the cardiosaver system  5  could operate with some but not all of the external equipment  7 .  
         [0054]     The external alarm transceiver  20  includes a battery  21 , an alarm disable/panic button  22 , a radio frequency transceiver  23 , a microphone  27 , an alarm-speaker  24 , an antenna  25 , a GPS satellite receiver  26 , and a standard interface  28  for providing wired or wireless communication with the pocket PC  12 , emergency room diagnostic system  16 , or physician&#39;s programmer  18 . A long distance voice/data communications interface  29  provides connectivity to the remote diagnostic center equipment  14  through voice and data telecommunications networks. For example, the microphone  27  and speaker  24  could be used for wired or wireless telephone calls to and from a medical practitioner at the remote diagnostic center. A built-in modem as part of the interface  29  would allow data to be transmitted to and from the remote diagnostic center equipment  14  over a voice connection. Alternately, a data communications capability of the interface  29  could allow data to be sent or received through a wired or wireless data network. The external alarm transceiver  20  may be a separate unit that can be carried by the patient and used by the patient&#39;s physician as the data interface to the cardiosaver system  5  or it may also be built into the pocket PC  12 , physician&#39;s programmer  18  or emergency room diagnostic system  16   
         [0055]     The pocket PC also described by Fischell et al. in U.S. Pat. No. 6,609,023 can provide the patient or physician the ability to check the status of the cardiosaver  11  and display a limited set of electrogram data uploaded from the cardiosaver  11 .  
         [0056]     The emergency room diagnostic system  16  is a more sophisticated system that can upload and display any of the data stored within the cardiosaver  11  and would, in its preferred embodiment, use a touch screen display to facilitate triage of patients arriving in an emergency room who have the cardiosaver system  5 . This should greatly reduce the time from arrival at the emergency room until treatment for cardiosaver system patients having a cardiac event.  
         [0057]     The purpose of the physician&#39;s programmer  18  shown in  FIG. 1  is to set and/or change the operating parameters of the implanted cardiosaver system  5  and to read out data stored in the memory of the cardiosaver  11  such as stored electrogram segments as described by Fischell et al. in U.S. Pat. No. 6,609,023.  
         [0058]     The external alarm transceiver  20  would typically be a pager-sized device that the patient would carry on his person or keep in close proximity. If a cardiac event is detected by the cardiosaver system  5 , an alarm message is sent by a wireless signal  3  to the alarm transceiver  20  via the antennas  6  and  25 . When the alarm is received by the alarm transceiver  20 , a patient alerting sound is played through the loudspeaker  24  to warn the patient that a cardiac event has occurred. Examples of such sounds include a periodic buzzing, a sequence of tones and/or a speech message that instructs the patient as to what actions should be taken. Furthermore, the alarm transceiver  20  can, depending upon the nature of the signal  3 , send an outgoing message to the remote diagnostic center equipment  14  to alert medical practitioners that a cardiosaver system alarm has occurred. The medical practitioners can then utilize the voice communications capabilities of the remote diagnostic center equipment  14  to call back the patient similar to the call that occurs to car drivers through the ONSTAR service when their car&#39;s air bags deploy in an accident. The optional GPS receiver  26  would allow the data sent to the remote diagnostic center equipment  14  to include patient location to facilitate the summoning of emergency medical services.  
         [0059]     The alarm disable/panic button  22  will turn off both the internal alarm of the implant  5  and the sound being emitted from the loudspeaker  24 . If no alarm is occurring, then pressing the alarm disable/panic button  22  will place a voice and/or data call to the remote diagnostic center similar to the call that is placed when the ONSTAR button is pressed in a car equipped to access the ONSTAR service. GPS information and a subset of patient electrogram data may be sent as well to the medical practitioners at the remote diagnostic center. The remotely located medical practitioner could then analyze the electrogram data and call the patient back to offer advice as to whether there is an emergency situation or the situation could be routinely handled by the patient&#39;s personal physician at some later time.  
         [0060]      FIG. 2  is a block diagram of the cardiosaver system  5 . The lead  2  includes the electrode  4  and the wire  12 . The wire  12  connects the electrode  4  to the amplifier circuit  36  that is also connected by the wire  15  to the cardiosaver case  8  acting as an indifferent electrode. The amplified electrogram signals  37  from the amplifier circuit  36  are converted to digital signals  38  by the analog-to-digital converter  41 . The digital electrogram signals  38  are then sent to the electrical signal processor  44 . The processor  44  in conjunction with the memory  47  can process the digital signals  38  according to the programming instructions stored in the program memory  45 . This programming (i.e. software) enables the cardiosaver system  5  to detect the occurrence of a cardiac event such as an ST segment elevation that is indicative of an acute myocardial infarction.  
         [0061]     A clock/timing sub-system  49  provides the means for timing specific activities of the cardiosaver system  5  including the absolute or relative time stamping of detected cardiac events. The clock/timing sub-system  49  can also facilitate power savings by causing components of the cardiosaver system  5  to go into a low power stand-by mode in between times for electrogram signal collection and processing. Such cycled power savings techniques are often used in implantable pacemakers and defibrillators. In an alternative embodiment, the clock/timing sub-system can be provided by a program subroutine run by the central processing unit  44 . It is also envisioned that the processor  44  may include an integral or external First-In-First-Out (FIFO) buffer memory to allow saving of data from before the detection of a cardiac event.  
         [0062]     Techniques for detecting cardiac events by the processor  44  are described by Fischell et al. in U.S. Pat. No. 6,609,023.  
         [0063]     An important aspect of the present invention is the filtering of the electrical signals sensed by the electrodes  4  and  8 . The preferred embodiment of the present invention cardiosaver  11  ( FIG. 1 ) will include high pass and/or low pass filtering of the electrical signals in the amplifier circuit  36 . An alternative embodiment would introduce filtering in any one, two or all of the following locations:  
         [0064]     1. a separate analog filter between the amplifier circuit  36  and analog-to-digital converter  41 ,  
         [0065]     2. a separate digital filter circuit placed between the analog-to-digital converter  41  and the processor  44 , and/or  
         [0066]     3. digital filtering performed by the processor  44  on the digital signals  38 .  
         [0067]     The memory  47  includes specific memory locations for patient data, electrogram segment data and any other relevant data.  
         [0068]     It is envisioned that the cardiosaver system  5  could also contain pacemaker circuitry  170  and/or defibrillator circuitry  180  similar to the cardiosaver system described by Fischell et al. in U.S. Pat. No. 6,240,049.  
         [0069]     The alarm sub-system  48  contains the circuitry and transducers to produce the internal alarm signals for the cardiosaver  11  ( FIG. 1 ). The internal alarm signal can be a mechanical vibration, a sound or a subcutaneous electrical tickle or shock.  
         [0070]     The telemetry sub-system  46  with antenna  6  provides the cardiosaver system  5  with the means for two-way wireless communication to and from the external equipment  7  of  FIG. 1 . It is also envisioned that short-range telemetry such as that typically used in pacemakers and defibrillators could also be applied to the cardiosaver system  5 . It is also envisioned that standard wireless protocols such as Bluetooth and 802.11 a  or 802.11 b  might be used to provide communication with a wider group of peripheral devices.  
         [0071]     A magnet sensor  190  may be incorporated into the cardiosaver system  5 . The primary purpose for a magnet sensor  190  is to keep the cardiosaver system  5  in an off condition until it is checked out just before it is implanted into a patient. This can prevent depletion of the battery life in the period between the time that the cardiosaver system  5  is packaged at the factory and the day it is implanted.  
         [0072]     The preferred embodiment of the present invention associated with a pacemaker/ICD or combined pacemaker/ICD would have the event detection and alerting function integrated within the pacemaker, ICD or combined pacemaker/ICD. It is also envisioned that the lead might connect both to a standard pacemaker, ICD or combined pacemaker/ICD and a cardiosaver having an electrical signal processor for cardiac event detection and the ability to generate an escalating patient alert.  
         [0073]      FIG. 3  is an example of use of increasing the amplitude of an alarm signal to provide an escalating patient alert.  FIG. 3  shows the progression over time of the three successive sets of alerting signals  31 ,  32  and  33  of the alarm signal  30 . The pattern displayed in  FIG. 3  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. The set  31  has alerting signals  31 A,  31 B and  31 C, each alerting signal within the set  31  having an amplitude  315 , a duration  316 , and a time interval between the alerting signals  31 A and  31 B and the alerting signals  31 B and  31 C of  311 . The set  32  has alerting signals  32 A,  32 B and  32 C, each alerting signal within the set  32  having an amplitude  325 , a duration  326  and a time interval between the alerting signals  32 A and  32 B and the alerting signals  32 B and  32 C of  321 . The set  33  has alerting signals  33 A,  33 B and  33 C, each alerting signal within the set  33  having an amplitude  335 , a duration  336  and a time interval between the alerting signals  33 A and  33 B and the alerting signals  33 B and  33 C of  331 . The time interval between the sets  31  and  32  is  312  and the time interval between the sets  32  and  33  is  323 . It can be seen that the alarm signal  30  provides an escalating patient alert by progressively increasing the amplitude over time as the amplitude  335  is greater than the amplitude  325  which is greater than the amplitude  315 . Ideally, such an escalating amplitude alert would start at level barely detectable by the patient and increase to a level that cannot be ignored. The physician&#39;s programmer  18  of  FIG. 1  would typically provide the capability to test different patterns and intensities of both internal and external alarm signals with the patient to set a patient alert that cannot be missed while also reducing the potential to startle the patient. It is also envisioned that the amplitude might also increase for successive alerting signals within a set. The present invention includes any increase in amplitude over time in any type of internal or external alarm signal. It is also envisioned that after a preset escalation period, the amplitude would reach a pre-set level and no longer increase. An important feature of the programmer  18  would be to set the initial alerting signal amplitude so that it is just barely perceptible and to set the highest alerting signal amplitude at a level that cannot be missed. Although  FIG. 3  shows a constant duration of the alerting signals ( 316 ,  326  and  336 ), a constant time between sets ( 312  and  323 ) and constant times between alerting signals within a set ( 311 ,  321  and  331 ) they need not be constant. The times between alerting signals  311 ,  321  and  322  are typically less than one second while the times between sets  312  and  323  are typically greater than one second.  
         [0074]      FIG. 4  is an example of use of increasing number of alerting signals within each set of alerting signals of an alarm signal to provide an escalating patient alert.  FIG. 4  shows the progression over time of the four successive sets of alerting signals  41 ,  42 ,  43  and  44  of the alarm signal  40 . The pattern displayed in  FIG. 4  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. The set  41  has one alerting signal  41 A, the alerting signal  41 A having an amplitude  45  and a duration  46 . The set  42  has two alerting signals  42 A and  42 B, each alerting signal within the set  42  having an amplitude  45 , a duration  46  and a time interval between the alerting signals  42 A and  42 B of  421 . The set  43  has three alerting signals  43 A,  43 B and  43 C, each alerting signal within the set  43  having an amplitude  45 , a duration  46  and a time interval between the alerting signals  43 A and  43 B and the alerting signals  43 B and  43 C of  431 . The set  44  has four alerting signals  44 A,  44 B,  44 C and  44 D, each alerting signal within the set  44  having an amplitude  45 , a duration  46 , and a time interval between the alerting signals  44 A and  44 B, the alerting signals  44 B and  44 C, and the alerting signals  44 C and  44 D of  44 . The time interval between the sets  41  and  42  is  412 , the time interval between the sets  42  and  43  is  423 , the time interval between the sets  43  and  44  is  434 . It can be seen that the alarm signal  40  provides an escalating patient alert by progressively increasing the number of alerting signals per set over time.  
         [0075]     Although the pattern shown in  FIG. 4  shows an increase by one of the number of alerting signals in successive sets, it is envisioned that an increase in the number of alerting signals per set could occur faster, e.g. an increase by two from one set to the next. It is also envisioned that the increase in the number of alerting signals per set could occur more slowly, e.g. an increase by one after every two sets. Ideally, such an escalating alert would start with a single alerting signal in a set such as the set  41  and increase to a preset number of alerting signals per set. The present invention includes any progressive increase in the number of alerting signals per set in an internal or external alarm signal. It is also envisioned that after a preset escalation period, the number of alerting signals per set would reach a pre-set level and no longer increase. Although  FIG. 4  shows a constant amplitude  45 , a constant duration of the alerting signals  46 , a constant time between sets ( 412 , 423  and  434 ) and constant times between alerting signals within a set ( 421 ,  431  and  441 ), they need not be constant. The times between alerting signals  421 ,  431  and  441  are typically less than one second while the times between sets  412 ,  423  and  434  are typically greater than one second. It is also envisioned that as the number of alerting signals within a set increases, the duration  46  of the alerting signals might decrease. This will subsequently reduce the total time for sets of alerting signals as the number of alerting signals increases.  
         [0076]      FIG. 5  is an example of use of decreasing time between alerting signals within a set of alerting signals of an alarm signal to provide an escalating patient alert.  FIG. 5  shows the progression over time of the three successive sets of alerting signals  51 ,  52  and  53  of the alarm signal  50 . The pattern displayed in  FIG. 5  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. The set  51  has alerting signals  51 A,  51 B and  51 C, each alerting signal within the set  51  having an amplitude  55 , a duration  516  and a time interval between the alerting signals  51 A and  51 B and the alerting signals  51 B and  51 C of  511 . The set  52  has alerting signals  52 A,  52 B and  52 C, each alerting signal within the set  52  having an amplitude  55 , a duration  526  and a time interval between the alerting signals  52 A and  52 B and the alerting signals  52 B and  52 C of  521 . The set  53  has alerting signals  53 A,  53 B and  53 C, each alerting signal within the set  53  having an amplitude  55 , a duration  536  and a time interval between the alerting signals  53 A and  53 B and the alerting signals  53 B and  53 C of  531 . The time interval between the sets  51  and  52  is  512  and the time interval between the sets  52  and  53  is  523 . It can be seen that the alarm signal  50  provides an escalating patient alert by progressively decreasing the time between alerting signals within successive sets over time as the time  511  is greater than the time  521  which is greater than the time  531 . It is also envisioned that the time between alerting signals might decrease for successive alerting signals within a set. The present invention includes any progressive decrease in the time between successive alerting signals in an internal or external alarm signal. It is also envisioned that after a preset escalation period, the time between alerting signals would reach a pre-set level and no longer decrease. Although  FIG. 5  shows a constant amplitude  55 , a constant duration of the alerting signals ( 516 ,  526  and  536 ) and a constant time between sets ( 512  and  523 ) they need not be constant. The times between alerting signals  511 ,  521  and  531  are typically less than the times between sets  512  and  523 .  
         [0077]      FIG. 6  is an example of use of decreasing time between sets of alerting signals of an alarm signal to provide an escalating patient alert.  FIG. 6  shows the progression over time of the four successive sets of alerting signals  61 ,  62 ,  63  and  64  of the alarm signal  60 . The pattern displayed in  FIG. 6  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. The set  61  has alerting signals  61 A and  61 B, each alerting signal within the set  61  having an amplitude  65 , a duration  616  and a time interval between the alerting signals  61 A and  61 B of  611 . The set  62  has alerting signals  62 A and  62 B, each alerting signal within the set  62  having an amplitude  65 , a duration  626  and a time interval between the alerting signals  62 A and  62 B of  621 . The set  63  has alerting signals  63 A and  63 B, each alerting signal within the set  63  having an amplitude  65 , a duration  636  and a time interval between the alerting signals  63 A and  63 B of  631 . The set  64  has alerting signals  64 A and  64 B, each alerting signal within the set  64  having an amplitude  65 , a duration  646  and a time interval between the alerting signals  64 A and  64 B of  641 . The time interval between the sets  61  and  62  is  612 , the time interval between the sets  62  and  63  is  623  and the time interval between the sets  63  and  64  is  634 . It can be seen that the alarm signal  60  provides an escalating patient alert by progressively decreasing the time between sets of alerting signals over time as the time  612  is greater than the time  623  which is greater than the time  634 . The present invention includes any progressive decrease in the time between successive sets of alerting signals in an internal or external alarm signal. It is also envisioned that after a preset escalation period, the time between sets of alerting signals would reach a pre-set level and no longer decrease. Although  FIG. 6  shows a constant amplitude  65 , a constant duration of the alerting signals ( 616 ,  626 ,  636  and  646 ) and a constant time between alerting signals within each set ( 611 ,  621 ,  631  and  641 ), they need not be constant. The times between alerting signals  611 ,  621 ,  631  and  641  are typically less than the times between sets  612 ,  623  and  634 .  
         [0078]      FIG. 7  is an example of use of increasing frequency (decrease in wavelength) for successive sets of alerting signals of an alarm signal to provide an escalating patient alert.  FIG. 7  shows the progression over time of the three successive sets of alerting signals  71 ,  72  and  73  of the alarm signal  70 . The pattern displayed in  FIG. 7  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. For a visual display a change in frequency would typically entail a change in color. The set  71  has alerting signals  71 A and  71 B, each alerting signal within the set  71  having a wavelength  717 , an amplitude  75 , a duration  716  and a time interval between the alerting signals  71 A and  71 B of  711 . The set  72  has alerting signals  72 A and  72 B, each alerting signal within the set  72  having a wavelength  727 , an amplitude  75 , a duration  726  and a time interval between the alerting signals  72 A and  72 B of  721 . The set  73  has alerting signals  73 A and  73 B, each alerting signal within the set  73  having a wavelength  737 , an amplitude  75 , a duration  736  and a time interval between the signals  73 A and  73 B of  731 . The time interval between the sets  71  and  72  is  712  and the time interval between the sets  72  and  73  is  723 . It can be seen that the alarm signal  70  provides an escalating patient alert by progressively decreasing the wavelength (increasing the frequency) of the alerting signals within successive sets over time as the wavelength  717  is greater than the wavelength  727  which is greater than the wavelength  737 . It is also envisioned that the wavelength of the alerting signals might progressively decrease for successive alerting signals within a set. The present invention includes any use of a progressive decrease in the wavelength (which is equivalent to an increase in frequency) of alerting signals in an internal or external alarm signal. It is also envisioned that after a preset escalation period, the frequency of the alerting signals would reach a pre-set level and no longer change. Although  FIG. 7  shows a constant amplitude  75 , a constant duration of the alerting signals ( 716 ,  726  and  736 ), a constant time between alerting signals within each set ( 711 ,  721 , and  731 ) and a constant time between sets ( 712  and  723 ), they need not be constant. The times between alerting signals  711 ,  721  and  731  are typically less than the times between sets  712  and  723 . Although the alerting signals  71 A,  71 B,  72 A,  72 B,  73 A and  73 B as well as all of the alerting signals for  FIGS. 2 through 6  are shown as square waves, it is envisioned that any wave structure including sine waves and triangular waves could be used by the cardiosaver system  5  of  FIG. 1 .  
         [0079]      FIG. 8  is an example of use of progressively increasing the duration of the alerting signals for successive sets of alerting signals of an alarm signal to provide an escalating patient alert.  FIG. 8  shows the progression over time of the three successive sets of alerting signals  81 ,  82  and  83  of the alarm signal  80 . The pattern displayed in  FIG. 8  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. The set  81  has alerting signals  81 A and  81 B, each alerting signal within the set  81  having an amplitude  85 , a duration  816  and a time interval between the alerting signals  81 A and  81 B of  811 . The set  82  has alerting signals  82 A and  82 B, each alerting signal within the set  82  having an amplitude  85 , a duration  826  and a time interval between the alerting signals  82 A and  82 B of  821 . The set  83  has alerting signals  83 A and  83 B each alerting signal within the set  83  having an amplitude  85 , a duration  836  and a time interval between the alerting signals  83 A and  83 B of  831 . The time interval between the sets  81  and  82  is  812  and the time interval between the sets  82  and  83  is  823 . It can be seen that the alarm signal  80  provides an escalating patient alert by progressively increasing the duration of the alerting signals for successive sets over time as the duration  836  is greater than the duration  826  which is greater than the duration  816 . It is also envisioned that the duration of alerting signals might increase for successive alerting signals within a set. The present invention includes any progressive increase in the duration of alerting signals in an internal or external alarm signal. It is also envisioned that after a preset escalation period, the duration of the alerting signals would reach a pre-set level and no longer increase. Although  FIG. 8  shows a constant amplitude  85 , a constant time between alerting signals within each set ( 811 ,  821  and  831 ) and a constant time between sets ( 812  and  823 ) they need not be constant. The times between alerting signals  811 ,  821  and  831  are typically less than the times between sets  812  and  823 .  
         [0080]      FIG. 9  is an alternative to the alarm signal  30  of  FIG. 3  as an example of use of increasing amplitude of an alarm signal to provide an escalating patient alert.  FIG. 9 . shows the progression over time of the three successive sets of alerting signals  91 ,  92  and  93  of the alarm signal  90 . The pattern displayed in  FIG. 9  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. The set  91  has alerting signals  91 A,  91 B and  91 C with amplitudes  915 A,  915 B and  915 C respectively. Each alerting signal within the set  91  has a duration  916  and a time interval between the alerting signals  91 A and  91 B and the alerting signals  91 B and  91 C of  911 . The set  92  has alerting signals  92 A,  92 B and  92 C with amplitudes  925 A,  925 B and  925 C respectively. Each alerting signal within the set  92  has a duration  926  and a time interval between the alerting signals  92 A and  92 B and the alerting signals  92 B and  92 C of  921 . The set  93  has alerting signals  93 A,  93 B and  93 C with amplitudes  935 A,  935 B and  935 C respectively. Each alerting signal within the set  93  has a duration  936  and a time interval between the alerting signals  93 A and  93 B and the alerting signals  93 B and  93 C of  931 . The time interval between the sets  91  and  92  is  912  and the time interval between the sets  92  and  93  is  923 . It can be seen that the alarm signal  90  provides an escalating patient alert by progressively increasing the amplitude over time as the amplitude increases with each successive alerting signal within each set, e.g.  915 C is greater than the amplitude  915 B which is greater than the amplitude  915 A. There is also shown a progressive increase in amplitude between sets  91 ,  92  and  93 . Ideally, such an escalating amplitude alert would start at level barely detectable by the patient and increase to a level that cannot be ignored. The physician&#39;s programmer  18  of  FIG. 1  would typically provide the capability to test different patterns and intensities of both internal and external alarm signals with the patient to set a patient alert that cannot be missed while also reducing the potential to startle the patient. It is also envisioned that after a pre-set escalation period, the amplitude would reach a pre-set level and no longer increase. Although  FIG. 9  shows a constant duration of the alerting signals ( 916 ,  926  and  936 ), a constant time between sets ( 912  and  923 ) and constant times between alerting signals within a set ( 911 ,  921  and  931 ) they need not be constant. The times between alerting signals  911 ,  921  and  931  are typically less than one second while the times between sets  912  and  923  are typically greater than one second.  
         [0081]      FIG. 10  is an example of use of a combination of progressive escalating features of an alarm signal to provide an escalating patient alert.  FIG. 10  shows the progression over time of the three successive sets of alerting signals  101 ,  102  and  103  of the alarm signal  100 . The pattern displayed in  FIG. 10  can be applied to internal and/or external alarm signals using vibration, sound, electrical stimulation (tickle) or a visual display. The set  101  has two alerting signals  101 A and  101 B, each alerting signal within the set  101  having an amplitude  1015 , a duration  1016  and a time interval between the alerting signals  101 A and  101 B of  1011 . The set  102  has three alerting signals  102 A,  102 B and  102 C, each alerting signal within the set  102  having an amplitude  1025 , a duration  1026  and a time interval between the alerting signals  102 A and  102 B and the alerting signals  102 B and  102 C of  1021 . The set  103  has four alerting signals  103 A,  103 B,  103 C and  103 D, each alerting signal within the set  103  having an amplitude  1035 , a duration  1036  and a time interval between the alerting signals  103 A and  103 B, the alerting signals  103 B and  103 C and the alerting signals  103 C and  103 D of  1031 . The time interval between the sets  101  and  102  is  1012  and the time interval between the sets  102  and  103  is  1023 . It can be seen that the alarm signal  100  provides an escalating patient alert by combining several of the escalating features seen in FIGS.  3  though  7  including: 
    a) progressively increasing the amplitude of the alerting signals over time as the amplitude  1035  is greater than the amplitude  1025  which is greater than the amplitude  1015 ;     b) progressively increasing the number of alerting signals in each set as the set  101  contains two alerting signals, the set  102  contains  3  alerting signals and the set  103  contains  4  alerting signals;     c) progressively decreasing the time interval between alerting signals within each set as the time interval  1011  is greater than the time interval  1021  which is greater than the time interval  1031 ; and,     d) progressively decreasing the time interval between sets of alerting signals as the time interval  1012  is greater than the time interval  1023 ,      
         [0086]     Although the alarm signal  100  shows a combination of four different escalation features of the alarm signals  30 ,  40 ,  50  and  60 , it is envisioned that an escalating signal could include any combination of two, three or more of the escalation techniques shown in the examples of  FIGS. 3 through 10 . It is also envisioned that the present invention would also include any escalating alerting pattern that would over time become more and more perceptible to a patient.  
         [0087]     Although the techniques for escalating patient alerting has been discussed with respect to an implanted system for the detection of cardiac events, it is also envisioned that these techniques are equally applicable to systems for the detection of cardiac events that are entirely external to the patient. For clarity, the time interval between alerting signals within a set is hereby termed as the intra-set time interval and the time interval between sets of alerting signals is hereby termed the inter-set time interval.  
         [0088]     Various other modifications, adaptations, and alternative designs are of course possible in light of the above teachings. Therefore, it should be understood at this time that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically described herein.