Abstract:
In one embodiment, a wearable defibrillation system may sense whether its wearer meets an unconscious bradyarrhythmia condition that can be associated with becoming unconscious. Even though such a condition might not be helped with a defibrillation pulse, the wearable defibrillation system may still administer pacing pulses to prevent the bradycardia from becoming worse, such as a sudden cardiac arrest. In some embodiments, the pacing pulses are administered at a frequency too slow for the patient to regain consciousness. An advantage is that, because the patient remains unconscious, he does not experience the sometimes severe discomfort due to the pacing pulses.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application claims priority from U.S. Provisional Patent Application Ser. No. 61/704,390, filed on Sep. 21, 2012, titled: “Titrated Transthoracic Pacing System to Temporarily Sustain Life”, the disclosure of which is hereby incorporated by reference for all purposes. 
    
    
     BACKGROUND 
     When people suffer from some types of heart arrhythmia, the result may be that blood flow to various parts of the body is reduced. Some arrhythmias may even result in a Sudden Cardiac Arrest (SCA). SCA can lead to death very quickly, e.g. within 10 minutes, unless treated in the interim. 
     Some people have an increased risk of SCA. Population at a higher risk includes individuals who have had a heart attack, or a prior SCA episode. People with an increased risk of SCA are recommended to receive an Implantable Cardioverter Defibrillator (“ICD”). An ICD continuously monitors the person&#39;s electrocardiogram (“ECG”). If certain types of heart arrhythmia are detected, then the ICD delivers an electric shock through the heart. 
     Before receiving an ICD, people with an increased risk of an SCA are sometimes given a wearable external defibrillator system. A wearable defibrillator system typically includes a harness, vest, or other garment for wearing by the patient. The system includes a defibrillator and external electrodes, which are attached on the inside of the harness, vest, or other garment. When the patient wears the system, the external electrodes may then make good electrical contact, with the person&#39;s skin, and therefore can help monitor the patient&#39;s ECG. If a shockable heart arrhythmia is detected, then the defibrillator delivers the appropriate electric shock through the body, and thus through the heart. 
     BRIEF SUMMARY 
     The present description gives instances of devices, systems, software, and methods, the use of which may help overcome problems and limitations of the prior art. 
     In one embodiment, a wearable defibrillation system may sense whether its wearer meets an unconscious bradyarrhythmia condition that can be associated with becoming unconscious. Even though such a condition might not be helped with a defibrillation pulse, the wearable defibrillation system may administer pacing pulses to prevent the bradycardia from becoming worse, such as a sudden cardiac arrest. In some embodiments, the pacing pulses are administered at a frequency too slow for the patient to regain consciousness. An advantage is that, because the patient remains unconscious, he does not experience the sometimes severe discomfort due to the pacing pulses. 
     These and other features and advantages of this description will become more readily apparent from the following Detailed Description, which proceeds with reference to the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of components of a wearable defibrillator system, made according to embodiments. 
         FIG. 2  is a diagram showing components of an external defibrillator, such as the one belonging in the system of  FIG. 1 , and which is made according to embodiments. 
         FIG. 3A  is a timing diagram of pacing pulses delivered according to embodiments. 
         FIG. 3B  is a timing diagram of pacing pulses delivered according to embodiments, in which a perfusion pulse occurring naturally in the patient has been detected. 
         FIG. 3C  is a timing diagram of pacing pulses delivered according to embodiments, in which the pacing interval has been elongated from that of  FIG. 3A  so as to ensure the patient will not regain consciousness at this time. 
         FIG. 4  is a flowchart for illustrating methods according to embodiments. 
         FIG. 5  is a flowchart for illustrating methods according to embodiments. 
         FIG. 6  is a diagram showing how an optimum pacing frequency may be found heuristically according to embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     As has been mentioned, the present description is about wearable defibrillation systems, software, and methods. Embodiments are now described in more detail. 
     A wearable defibrillator system made according to embodiments has a number of components. One of these components is a support structure, which is configured to be worn by the patient. The support structure can be any structure suitable for wearing, such as a harness, a vest, one or more belts, another garment, and so on. The support structure can be implemented in a single component, or multiple components. For example, a support structure may have a top component resting on the shoulders, for ensuring that the defibrillation electrodes will be in the right place for defibrillating, and a bottom component resting on the hips, for carrying the bulk of the weight of the defibrillator. A single component embodiment could be with a belt around at least the torso. Other embodiments could use an adhesive structure or another way for attaching to the person, without encircling any part of the body. There can be other examples. 
       FIG. 1  depicts components of a wearable defibrillator system made according to embodiments, as it might be worn by a patient  82 . Patient  82  may also be referred to as person  82 , and/or wearer  82  since he or she wears components of the wearable defibrillator system. 
     In  FIG. 1 , a generic support structure  170  is shown relative to the body of person  82 , and thus also relative to his or her heart  85 . Structure  170  could be a harness, a vest, one or more belts, a garment, as per the above; it could be implemented in a single component, or multiple components, and so on. Structure  170  is wearable by person  82 , but the manner of wearing it is not depicted, as structure  170  is depicted only generally in  FIG. 1 . 
     A wearable defibrillator system is configured to defibrillate the patient, by delivering electrical charge to the patient&#39;s body in the form of an electric shock or one or more pulses.  FIG. 1  shows a sample external defibrillator  100 , and sample defibrillation electrodes  104 ,  108 , which are coupled to external defibrillator  100  via electrode leads  105 . Defibrillator  100  and defibrillation electrodes  104 ,  108  are coupled to support structure  170 . As such, all components of defibrillator  100  can be therefore coupled to support structure  170 . When defibrillation electrodes  104 ,  108  make good electrical contact with the body of person  82 , defibrillator  100  can administer, via electrodes  104 ,  108 , a brief, strong electric pulse  111  through the body. Pulse  111 , also known as a defibrillation shock or therapy shock, is intended to go through and restart heart  85 , in an effort to save the life of person  82 . Pulse  111  can also be one or more pacing pulses, and so on. 
     A prior art defibrillator typically decides whether to defibrillate or not based on an electrocardiogram (“ECG”) of the patient. However, defibrillator  100  can defibrillate, or not defibrillate, also based on other inputs. 
     The wearable defibrillator system may optionally include an outside monitoring device  180 . Device  180  is called an “outside” device because it is provided as a standalone, for example not within the housing of defibrillator  100 . Device  180  is configured to monitor at least one local parameter. A local parameter can be a parameter of patient  82 , or a parameter of the wearable defibrillation system, or a parameter of the environment, as will be described later in this document. 
     Optionally, device  180  is physically coupled to support structure  170 . In addition, device  180  can be communicatively coupled with other components, which are coupled to support structure  170 . Such a component can be a communication module, as will be deemed applicable by a person skilled in the art in view of this disclosure. 
       FIG. 2  is a diagram showing components of an external defibrillator  200 , made according to embodiments. These components can be, for example, included in external defibrillator  100  of  FIG. 1 . The components shown in  FIG. 2  can be provided in a housing  201 , which is also known as casing  201 . 
     External defibrillator  200  is intended for a patient who would be wearing it, such as person  82  of  FIG. 1 . Defibrillator  200  may further include a user interface  270  for a user  282 . User  282  can be patient  82 , also known as wearer  82 , if conscious. Or user  282  can be a local rescuer at the scene, such as a bystander who might offer assistance, or a trained person. Or, user  282  might be a remotely located trained caregiver in communication with the wearable defibrillator system. 
     Defibrillator  200  may include an internal monitoring device  281 . Device  281  is called an “internal” device because it is incorporated within housing  201 . Monitoring device  281  can monitor patient parameters, system parameters and/or environmental parameters, all of which can be called patient data. In other words, internal monitoring device  281  can be complementary or an alternative to outside monitoring device  180  of  FIG. 1 . Allocating which of the system parameters are to be monitored by which monitoring device can be done according to design considerations. 
     Patient physiological parameters include, for example, those physiological parameters that can be of any help in detecting by the wearable defibrillation system whether the patient is in need of a shock, plus optionally their history. Examples of such parameters include the patient&#39;s ECG, blood oxygen level, blood flow, blood pressure, blood perfusion, pulsatile change in light transmission or reflection properties of perfused tissue, heart sounds, heart wall motion, breathing sounds and pulse. Accordingly, the monitoring device could include a perfusion sensor, a pulse oximeter, a Doppler device for detecting blood flow, a cuff for detecting blood pressure, an optical sensor, illumination detectors and maybe sources for detecting color change in tissue, a motion sensor, a device that can detect heart wall movement, a sound sensor, a device with a microphone, an SpO2 sensor, and so on. Pulse detection is taught at least in Physio-Control&#39;s U.S. Pat. No. 8,135,462, which is hereby incorporated by reference in its entirety. In addition, a person skilled in the art may implement other ways of performing pulse detection. 
     In some embodiments, the local parameter is a trend that can be detected in a monitored physiological parameter of patient  82 . A trend can be detected by comparing values of parameters at different times. Parameters whose detected trends can particularly help a cardiac rehabilitation program include: a) cardiac function (e.g. ejection fraction, stroke volume, cardiac output, etc.); b) heart rate variability at rest or during exercise; c) heart rate profile during exercise and measurement of activity vigor, such as from the profile of an accelerometer signal and informed from adaptive rate pacemaker technology; d) heart rate trending; e) perfusion, such as from SpO2 or CO2; f) respiratory function, respiratory rate, etc.; g) motion, level of activity; and so on. Once a trend is detected, it can be stored and/or reported via a communication link, along perhaps with a warning. From the report, a physician monitoring the progress of patient  82  will know about a condition that is either not improving or deteriorating. 
     Patient state parameters include recorded aspects of patient  82 , such as motion, posture, whether they have spoken recently plus maybe also what they said, and so on, plus optionally the history of these parameters. Monitoring device  180  or monitoring device  281  may include a motion detector, which can be made in many ways as is known in the art. Or, one of these monitoring devices could include a location sensor such as a Global Positioning System (GPS), which informs of the location, and the rate of change of location over time. Many motion detectors output a motion signal that is indicative of the motion of the detector, and thus of the patient&#39;s body. Patient state parameters can be very helpful in narrowing down the determination of whether SCA is indeed taking place. 
     System parameters of a wearable defibrillation system can include system identification, battery status, system date and time, reports of self-testing, records of data entered, records of episodes and intervention, and so on. 
     Environmental parameters can include ambient temperature and pressure. A humidity sensor may provide information as to whether it is raining. Presumed patient location could also be considered an environmental parameter. The patient location could be presumed if monitoring device  180  or  281  includes a GPS sensor. 
     Defibrillator  200  typically includes a defibrillation port  210 , such as a socket in housing  201 . Defibrillation port  210  includes nodes  214 ,  218 . Defibrillation electrodes  204 ,  208 , for example similar to electrodes  104 ,  108  of  FIG. 1 , can be plugged into defibrillation port  210 . Plugging can be from their leads, such as leads  105  of  FIG. 1 , so as to make electrical contact with nodes  214 ,  218 , respectively. It is also possible that defibrillation electrodes  204 ,  208  are connected continuously to defibrillation port  210 , instead. Either way, defibrillation port  210  can be used for guiding, via electrodes, to the wearer the electrical charge that has been stored in energy storage module  250 . The electric charge delivered to the wearer will be the shock for defibrillation, pacing, and so on. 
     Defibrillator  200  may optionally also have an ECG port  219  in housing  201 , for plugging in ECG electrodes  209 , which are also known as ECG leads. It is also possible that ECG electrodes  209  can be connected continuously to ECG port  219 , instead. EGG electrodes  209  can help sense an ECG signal, e.g. a 12-lead signal, or a signal from a different number of leads, especially if they make good electrical contact with the body of the patient. ECG electrodes  209  can be attached to the inside of support structure  170  for making good electrical contact with the patient, similarly as defibrillation electrodes  204 ,  208 . 
     Defibrillator  200  also includes a measurement circuit  220 . Measurement circuit  220  receives physiological signals from EGG port  219 , if provided. Even if defibrillator  200  lacks ECG port  219 , measurement circuit  220  can obtain physiological signals through nodes  214 ,  218  instead, when defibrillation electrodes  204 ,  208  are attached to the patient. In these cases, the patient&#39;s ECG signal can be sensed as a voltage difference between electrodes  204 ,  208 . Plus, impedance between electrodes  204 ,  208  and/or the connections of ECG port  219  can be sensed. Sensing the impedance can be useful for detecting, among other things, whether these electrodes  204 ,  208  and/or ECG electrodes  209  are not making good electrical contact with the patient&#39;s body. These physiological signals can be sensed, and information about them can be rendered by circuit  220  as data, other signals, etc. 
     Defibrillator  200  also includes a processor  230 . Processor  230  may be implemented in any number of ways. Such ways include, by way of example and not of limitation, digital and/or analog processors such as microprocessors and digital-signal processors (DSPs); controllers such as microcontrollers; software running in a machine; programmable circuits such as Field Programmable Gate Arrays (FPGAs), Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices (PLDs), Application Specific Integrated Circuits (ASICs), any combination of one or more of these, and so on. 
     Processor  230  can be considered to have a number of modules. One such module can be a detection module  232 . Detection module  232  can include a ventricular fibrillation (“VF”) detector. The patient&#39;s sensed ECG from measurement circuit  220  can be used by the VF detector to determine whether the patient is experiencing VF. Detecting VF is useful, because VF results in SCA. 
     Another such module in processor  230  can be an advice module  234 , which generates advice for what to do. The advice can be based on outputs of detection module  232 . There can be many types of advice according to embodiments. As one example, a Shock Advisory Algorithm can render the advice to shock the patient by delivering a charge, as opposed to not shock the patient. Shocking can be for defibrillation, pacing, and so on. 
     Processor  230  can include additional modules, such as other module  236 , for other functions. In addition, if monitoring device  281  is indeed provided, it may be operated in part by processor  230 , etc. 
     In some embodiments, processor  230  is configured to determine whether the patient who is wearing the wearable defibrillation system meets an unconscious bradyarrhythmia condition. The unconscious bradyarrhythmia condition can be defined in a number of ways according to embodiments. One such way is if the patient&#39;s heart rate is less than a threshold, such as 45 beats per minute (bpm), 40 bpm, 35 bpm or even less. At such low heart rates, people are known to become unconscious. As such, the unconscious bradyarrhythmia condition is a proxy for interring when the patient is unconscious. The determination about the unconscious bradyarrhythmia condition being met can further be confirmed, as will be seen later in this document. 
     The unconscious bradyarrhythmia condition is detected because, while most sudden cardiac arrests are caused by a ventricular tachyarrhythmia, it is possible for a cardiac arrest to be caused by extreme bradyarrhythmia (asystole or extreme bradycardia). While a high-energy shock can be effective for treating a ventricular tachyarrhythmia. It can be useless for treating an extreme bradyarrhythmia. When a patient has such bradyarrhythmia, he could also faint, i.e. become unconscious. 
     There are a number of ways for determining whether the unconscious bradyarrhythmia condition is met. In some embodiments, the determination is made from the physiological parameter, either in part or exclusively. In other embodiments, the determination is made from the patient&#39;s ECG, such as by counting QRS complexes. 
     Defibrillator  200  optionally further includes a memory  238 , which can work together with processor  230 . Memory  238  may be implemented in any number of ways. Such ways include, by way of example and not of limitation, volatile memories, nonvolatile memories (NVM), read-only memories (ROM), random access memories (RAM), magnetic disk storage media, optical storage media, smart cards, flash memory-devices, any combination of these, and so on. Memory  238  is thus a non-transitory storage medium. Memory  238 , if provided, can include programs for processor  230 , and so on. The programs can include sets of instructions. The programs can be operational for the inherent needs of processor  230 , and can also include protocols and ways that decisions can be made by advice module  234 . In addition, memory  238  can store prompts for user  282 , if they are a local rescuer. Moreover, memory  238  can store data. The data can include patient data, system data and environmental data, for example as learned by monitoring device  281  and monitoring device  180 . The data can be stored memory  235  before it is transmitted out of defibrillator  200 , or stored there after it is received by it. 
     Defibrillator  200  may also include a power source  240 . To enable portability of defibrillator  200 , power source  240  typically includes a battery. Such a battery is typically implemented as a battery pack, which can be rechargeable or not. Sometimes, a combination is used, of rechargeable and non-rechargeable battery packs. Other embodiments of power source  240  can include an AC power override, for where AC power will be available, an energy storage capacitor, and so on. In some embodiments, power source  240  is controlled by processor  230 . 
     Defibrillator  200  additionally includes an energy storage module  250 , which can thus be coupled to the support, structure of the wearable system. Module  250  is where some electrical energy is stored, when preparing it for sudden discharge to administer a shock. Module  250  can be charged from power source  240  to the right amount of energy, as controlled by processor  230 . In typical implementations, module  250  includes a capacitor  252 , which can be a single capacitor or a system of capacitors, and so on. As described above, capacitor  252  can store the energy in the form of electrical charge, for delivering to the patient. 
     Defibrillator  200  moreover includes a discharge circuit  255 . Circuit  255  can be controlled to permit the energy stored in module  250  to be discharged to nodes  214 ,  218 , and thus also to defibrillation electrodes  204 ,  208 . Circuit  255  can include one or more switches  257 . Those can be made in a number of ways, such as by an H-bridge, and so on. 
     In embodiments, if it is determined that the patient meets the unconscious bradyarrhythmia condition, portions of the stored electrical charge are delivered to the patient as pacing pulses or shocks. Such pulses are seen in  FIG. 1  as pulse  111 , except that pacing pulses do not have the high energy of defibrillation pulses. 
     User interface  270  can be made in any number of ways. User interface  270  may include output devices, which can be visual, audible or tactile, for communicating to a user. User interface  270  may also include input devices for receiving inputs from users. For example, interface  270  may include a screen, to display what is detected and measured, provide visual feedback to rescuer  282  for their resuscitation attempts, and so on. Interface  270  may also include a speaker, to issue voice prompts, etc. Sounds, images, vibrations, and anything that can be perceived by user  282  can also be called human perceptible indications. Interface  270  may additionally include various controls, such as pushbuttons, keyboards, touchscreens, a microphone, and so on. In addition, discharge circuit  255  can be controlled by processor  230 , or directly by user  282  via user interface  270 , and so on. 
     In some embodiments, an output device of user interface  270  is configured to issue a query to the patient, after the unconscious bradyarrhythmia condition is determined to be met, as a warning. The query can be spoken, or tactile, and intended for the patient to reply so as to confirm that he is fine. An input device of user interface  270  can be configured to receive an input from the patient in response to the query, for example within a preset available-reply time. In such embodiments, the unconscious bradyarrhythmia condition can be confirmed to be met if the input device does not receive the input, such as within the specific reply time. 
     In addition, an output device of user interface  270  can be configured to transmit a warning to bystanders, if the patient is determined to meet the unconscious bradyarrhythmia condition. The warning could include an appraisal of the situation, and possibly include a request to call for help. 
     Defibrillator  200  can optionally include a communication module  290 , for establishing one or more wired or wireless communication links with other devices of other entities, such as a remote assistance center, Emergency Medical Services (EMS), and so on. Module  290  may also include an antenna, portions of a processor, and other sub-components as may be deemed necessary by a person skilled in the art. This way, data and commands can be communicated, such as patient data, episode information, therapy attempted, CPR performance, system data, environmental data, and so on. 
     In some embodiments, communication module  290  is configured to transmit an alert message to a remotely located third party, if the patient is determined to meet the unconscious bradyarrhythmia condition. This way, the third party can send for help. 
     Defibrillator  200  can optionally include other components. 
     Some patients with extreme bradyarrhythmia respond to transthoracic pacing, in which a pacing stimulus triggers ventricular depolarization, in which the left ventricle contracts and ejects a bolus of blood into the aorta. For example, transthoracic pacing is commonly used when a patient develops third degree atrioventricular block, which can happen during an acute myocardial infarction. In such cases, the pacing is continued until either the atrioventricular block goes away, or help arrives for the patient, such as the patient being admitted at an electrophysiology laboratory to have a long-term pacemaker implanted. Particular patterns of pacing are now described. 
       FIG. 3A  is a timing diagram of pacing pulses delivered according to embodiments. Pacing pulses  321 ,  322 ,  323 ,  324  are shown as monophasic, but they equivalently could be biphasic. Pacing pulses  321 ,  322 ,  323 ,  324  are delivered at a uniform pacing interval PI_A, the inverse of which defines a pacing frequency or rate. 
     Optionally, the pacing frequency is purposely slower than a person&#39;s normal heartbeat frequency, so that the patient will not regain consciousness. For example, the pacing frequency can be less than 50 beats per minute (bpm) or 45 bpm, or even a lesser frequency. As such, the patient can be paced for a long time without the discomfort of experiencing the pacing pulses while conscious. It will be appreciated that such a pacing frequency is often still faster than the patient&#39;s original bradyarrhythmia pulse, and thus the intervention of pacing is much more likely to preserve the patient&#39;s blood flow, and prevent damage to the patient&#39;s organs. 
     In some embodiments, pacing-on-demand is implemented. For example, processor  230  can be configured to detect perfusion pulses occurring naturally in the patient. Detection can be performed in many ways, such as for example using the same instrumentality that was used to determine that the unconscious bradyarrhythmia condition was met, or one of the monitoring devices. In such embodiments, after the last detected naturally occurring perfusion pulse, a subsequent pacing pulse is then delivered. The subsequent pacing pulse can be delivered at least after a pacing interval has elapsed, which corresponds to a frequency of 50 bpm, 45 bpm, 40 bpm, 35 bpm or less. An example is now described. 
       FIG. 3B  is a timing diagram of pacing pulses delivered according to embodiments. Pacing pulses  331 ,  332 ,  333 ,  334  were initially intended to be delivered at pacing interval PI_A, similar to that of  FIG. 3A . However, a patient&#39;s perfusion pulse  340  is detected. Accordingly, after pulse  340  subsequent pulse  333  is delivered later, e.g. after pacing interval PI_A. 
     A system according to embodiments may face a tradeoff in competing desires. One desire is for the pacing frequency to be high, so as to pump as much blood as possible to the organs. The competing desire is for the pacing frequency to not be so high as to help the patient regain consciousness, for the time being. An optimum pacing frequency can thus be defined for the patient. The challenge is that each patient may have a different such optimum frequency. The sample values mentioned above are drawn from the experience that generally people at these heart rates do not stay conscious. 
     According to embodiments, the pacing frequency can thus be changed. The sample values mentioned above can be used as a first frequency, in which the pacing pulses can initially be delivered. However, if it is later determined that the patient no longer meets the unconscious bradyarrhythmia condition, the pacing pulses are then delivered at a second frequency that is smaller than the first frequency. An example is now described. 
       FIG. 3C  is a timing diagram of pacing pulses delivered according to embodiments. Pacing pulses  351 ,  352 ,  353 ,  354  are delivered at a pacing interval PI_B, which is elongated from PI_A of  FIG. 3A , so as to ensure the patient will not regain consciousness at this time. Given the inverse relationship, the longer pacing interval PI_B corresponds to a lesser pacing frequency than the pacing frequency of  FIG. 3A . 
     Even if the initial pacing frequency does not help the patient to regain consciousness, a system might not know if the patient can be paced at a higher frequency still without regaining consciousness. So, in some embodiments, while the pacing pulses are initially delivered at a first frequency, the pacing pulses can then be delivered at a second frequency that is larger than the first frequency. However, if it is later determined that the patient no longer meets the unconscious bradyarrhythmia condition, the pacing pulses can then be delivered at a third frequency that is smaller than the second frequency. In some embodiments, the third frequency is the same as the first frequency. 
     The above-mentioned devices and/or systems perform functions, processes and/or methods, as described in this document. The functions, processes and/or methods may be implemented by one or more devices that include logic circuitry. The logic circuitry may include a processor that may be programmable for a general purpose, or dedicated, such as processor  230 . 
     The logic circuitry may also include one or more storage media, such as memory  238  or another memory. Such a storage medium can be a non-transitory computer-readable medium. These storage media, individually or in combination with others, can have stored thereon programs that the processor may be able to read, and execute. More particularly, the programs can include instructions in the form of code, which the processor may be able to execute upon reading. Executing is performed by physical manipulations of physical quantities, and may result in the functions, processes and/or methods to be performed. In addition, these storage media may store data. 
     Moreover, methods and algorithms are described below. These methods and algorithms are not necessarily inherently associated with any particular logic device or other apparatus. Rather, they are advantageously implemented by programs for use by a computing machine, such as a general-purpose computer, a special purpose computer, a microprocessor, etc. 
     Often, for the sake of convenience only, it is preferred to implement and describe a program as various interconnected distinct software modules or features, individually and collectively also known as software. This is not necessary, however, and there may be cases where modules are equivalents aggregated into a single program, even with unclear boundaries. In some instances, software is combined with hardware, in a mix called firmware. 
     This detailed description includes flowcharts, display images, algorithms, and symbolic representations of program operations within at least one computer readable medium. An economy is achieved in that a single set of flowcharts is used to describe both programs, and also methods. So, while flowcharts described methods in terms of boxes, they also concurrently describe programs. 
     Methods are now described. 
       FIG. 4  shows a flowchart  400  for describing methods according to embodiments. The methods of flowchart  400  may also be practiced by embodiments described above. 
     According to an operation  410 , a patient parameter is sensed. The parameter can be the patient&#39;s ECG, or a physiological parameter other than the ECG, such as from one of the monitoring devices. 
     According to another operation  420 , it is determined whether the patient meets an unconscious bradyarrhythmia condition. Operation  420  can be done and confirmed as described above. 
     According to another, optional operation  430 , if the patient is not determined to meet the unconscious bradyarrhythmia condition, execution can return to operation  410 . Else, according to another optional operation  433 , a query can be issued to the patient as a warning. Then according to another operation  436 , if a response to the query is received; execution can return to operation  430 . Else, according to another operation  440 , pacing pulses are delivered to the patient. The pulses can be at pacing frequencies as described elsewhere in this document. 
     According to a further, optional operation  450 , messages can be transmitted. A message can be a warning to bystanders and/or an alert message to a remotely located third party, as per the above. 
       FIG. 5  shows a flowchart  500  for describing methods according to embodiments, for particularly managing the timing and frequency of pacing pulses. The methods of flowchart  500  may also be practiced by embodiments described above. 
     According to an operation  541 , it is inquired whether a perfusion pulse is detected. If not, then according to another, optional operation  542 , it is inquired whether a pacing interval has passed. If not, the execution returns to operation  541 . If, however, at operation  541  a perfusion pulse is detected, such as pulse  340  in  FIG. 3B , then according to another, optional operation  543 , a clock is restarted for the pacing interval. Execution then returns to operation  542 . The restarting can accommodate on-demand pacing, such as for pulse  333  waiting for a full pacing interval after pulse  340  in  FIG. 3B . 
     At operation  542 , when the pacing interval has indeed passed, according to another operation  540 , a pacing pulse is delivered. Then according to another operation  546 , the clock for the pacing pulse is restarted, similarly with operation  543 . 
     Then, according to another, optional operation  530 , it is inquired whether the patient is regaining consciousness. Operation  530  can be implemented in any number of ways, such as by exploiting a patient parameter, the output of a motion detector, and so on. If yes, then according to another, optional operation  548 , the pacing interval is incremented, so as to reduce the pacing frequency. If not, then according to another, optional operation  549 , the pacing interval may be decremented, so as to increase the pacing frequency. Operations  548  and  549  will impact operation  542 , which is a relationship indicated with dot-dash arrows. 
     Optional operations  530 ,  548  and  549  are intended for searching and finding the optimum pacing frequency of the patient for the criteria described above. Once that frequency is found, then operations  530 ,  548  and  549  may be skipped from flowchart  500 . A method is now described in more detail. 
     The optimum pacing frequency may be found heuristically, according to embodiments where the pacing frequency is changed until the optimum is found. An example is now described. 
       FIG. 6  is a diagram showing how an optimum pacing frequency may be found heuristically according to embodiments. The procedure of  FIG. 6  may be performed by the wearable defibrillator system during an actual episode, or in a doctor&#39;s office when a patient is first fitted with the wearable defibrillator system. 
     In  FIG. 6 , the horizontal axis is for time, and the vertical axis is for a number of occurrences per minute. Line  610  defines the heart rate consciousness threshold of the patient, in bpm. If the patient&#39;s heart is beating faster, he would be conscious, while if slower, unconscious. Line  610  could be a zone, and so on. By the time it is determined that the patient meets the unconscious bradyarrhythmia condition, his heart rate can be below line  610 , and the patient is unconscious. Importantly, that threshold is not known for every patient, which is why line  610  intercepts the vertical axis at a value shown with a question mark. 
     Broken line  620  indicates the actual frequency of pacing, in pulses per minute (“PPM”). A time T 1 , line  620  starts at a certain value. Then, thanks to operation  549  of  FIG. 5 , line  620  is incremented at times T 2 , T 3 , T 4 , T 5 , in search of line  610 . Incrementing can be dynamic, automatically, or by the doctor. Incrementing should have hysteresis, to avoid going back and forth with small changes in pacing rate. The hysteresis may be implemented by not switching up very quickly. At time T 5 , according to comment  630 , it is detected that the patient is regaining consciousness. At that time, line  610  has been identified as some value that was crossed at time T 5 . Then the final pacing frequency can be determined at a level close to, but less than line  610 , and applied, such as after time T 7 . Optionally, before T 7 , at time T 6  the pacing frequency is dropped sharply for a little time, to ensure the patient becomes unconscious again, and then at T 7  it is raised again at the level closer to, but less than line  610 . 
     The invention can also be applied to external defibrillators, based on the present description. External defibrillators used by hospitals end EMS teams can detect bradyarrhythmia, and provide pacing pulses. When it comes to dealing with discomfort, they typically have the means of sedating the patient while keeping him conscious. 
     In the methods described above, each operation can be performed as an affirmative step of doing, or causing to happen, what is written that can take place. Such doing or causing to happen can be by the whole system or device, or just one or more components of it. In addition, the order of operations is not constrained to what is shown, and different orders may be possible according to different embodiments. Moreover, in certain embodiments, new operations may be added, or individual operations may be modified or deleted. The added operations can be, for example, from what is mentioned while primarily describing a different system, device or method. 
     This description includes one or more examples, but that does not limit how the invention may be practiced, indeed, examples or embodiments of the invention may be practiced according to what is described, or yet differently, and also in conjunction with other present or future technologies. 
     A person skilled in the art will be able to practice the present invention in view of this description, which is to be taken as a whole. Details have been included to provide a thorough understanding. In other instances, well-known aspects have not been described, in order to not obscure unnecessarily the present invention. 
     Other embodiments include combinations and sub-combinations of features described herein, including for example, embodiments that are equivalent to: providing or applying a feature in a different order than in a described embodiment; extracting an individual feature from one embodiment and inserting such feature into another embodiment; removing one or more features from an embodiment; or both removing a feature from an embodiment and adding a feature extracted from another embodiment, white providing the advantages of the features incorporated in such combinations and sub-combinations. 
     The following claims define certain combinations and subcombinations of elements, features and steps or operations, which are regarded as novel and non-obvious. Additional claims for other such combinations and subcombinations may be presented in this or a related document.