WO2011073932A1

WO2011073932A1 - Pacemaker device with fall -back monitoring

Info

Publication number: WO2011073932A1
Application number: PCT/IB2010/055859
Authority: WO
Inventors: Mike Nakagawa
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-12-17
Filing date: 2010-12-16
Publication date: 2011-06-23

Abstract

Disclosed is an external pacemaker device comprising an operativeness monitor adapted to monitor an operativeness of an ECG monitoring electrode, and an ECG source selector adapted to switch from the ECG monitoring electrode to a therapy electrode as the ECG source if a reduced operativeness of the ECG monitoring electrode is indicated and the pacemaker device is in a state requiring ECG monitoring..

Description

PACEMAKER DEVICE WITH FALL -BACK MONITORING

FIELD OF THE INVENTION

The field of the present invention relates to an operation method for an external pacemaker device. The field of the present invention also relates to an external pacemaker device. Furthermore, the field of the present invention relates to a computer program product comprising instructions that enable a processor to carry out a method of operation of an external pacemaker device.

BACKGROUND OF THE INVENTION

Patients with complete heart block or extreme bradycardia may be treated with external cardiac pacing, which is a feature available on several defibrillator/monitors. These conditions can be dangerous if the heart supplies insufficient cardiac output to sustain life. If the condition is transient and the patient is predominantly in a sufficient heart rhythm, the pacemaker may be set to demand-mode, i.e., the pacemaker therapy would only be applied if the instantaneous heart rate falls below a target threshold, so that the pacing is ready on demand.

For demand-mode pacing to work, the pacing device must be able to detect the cardiac activity, often by electrocardiogram (ECG) electrodes ("leads"), and deliver a stimulating electric current, generally by adhesive pad electrodes ("pads") identical or similar to those used for external defibrillation. The therapy pad electrodes are usually capable of monitoring an ECG signal when therapy is not being applied. However, the application of a pacing pulse creates a large electrical disturbance on the pad electrodes, rendering them unusable for ECG recording for a period of time lasting as much as several seconds. Separate ECG monitoring electrodes are less susceptible to the artifact from the pacing pulse because they are on an independent circuit.

However, if the signal from the ECG monitoring electrodes becomes compromised, such as if the adhesive electrode becomes dislodged from the patient, then the device will be unable to determine if the heart is continuing to function sufficiently. If the heart fails to function sufficiently while the monitoring electrodes fail to provide an adequate ECG signal, the condition of the patient may be severely compromised, and death may occur. One current approach to ensuring that the heart will beat sufficiently during this period is to immediately begin fixed-mode pacing, i.e., to start pacing at a fixed time interval at the minimum threshold rate, regardless of the intrinsic activity of the heart. This approach will often cause electrical therapy to be applied needlessly, often with pain and/or discomfort to the patient and/or clinician, with a theoretical possibility of inducing a potentially fatal cardiac arrhythmia. Additionally, if the device is operating on battery power, the charge of the battery will be needlessly reduced, possibly leaving the device unusable when needed most. A flow chart illustrating this approach is shown in Fig. 2.

Another approach, acknowledging that often these patients are being closely watched by clinicians and the loss of ECG connection may occur while the patient is being manipulated, is to sound a serious alarm indicating that demand-mode pacing is no longer possible by the device, and that the patient could experience a life-threatening dysrhythmia during this period of compromised monitoring and therapy. The application of pacing therapy is most effective if it starts immediately upon cessation of the intrinsic cardiac rhythm, and delays in responding to the alarm and correcting the situation may compromise the condition of the patient. A flow chart illustrating this approach is shown in Fig. 1.

United States patent application publication No. 2003/0004552 Al in the name of Plombon et al., entitled "Implantable Cardioverter/Defibrallator" suggests that, if a lead becomes inoperable, the implantable device can then reconfigure an electrical pathway such as a cardioversion and/or a defibrillation pathway by excluding the inoperable lead.

Measurements of electrical cardiac activity can result in a so-called "pseudo" ECG, where a "pseudo" ECG is measured internally rather than externally.

United States patent application publication No. 2007/0167849 Al in the name of Zhang et al, entitled "Implantable Medical Device Sensing Wireless ECG as Substitute for Intracardiac Electrogram" discloses a cardiac rhythm management (CRM) system with backup sensing in lead failure mode. US 2007/0167849 Al states that backup sensing is needed when a normal or primary sensing circuit no longer provides for reliable sensing of cardiac activities. A selection circuit produces a selection signal in response to an indication of a failure mode in which the primary sensing circuit fails to provide reliable sensing. As a remedy, a wireless ECG provides for backup sensing as part of a failure mode operation until the implantable medical device exits the failure mode, for example, when the lead problem is corrected.

United States patent No. 5,184,620 to Cudahy et al, entitled "Method of Using a Multiple Electrode Part Assembly" discloses a method of monitoring and providing therapeutic electrical impulses to a patient's heart. The method comprises inter alia, monitoring the ECG signals, determining whether pacing is required, and providing a pace signal to the appropriate electrodes if pacing is required and connecting a plurality of other electrodes to provide an optimal return path for the pace signal, determined from the ECG signals whether defibrillation is required. At least some of the same electrodes may be employed for ECG monitoring, pacing and defibrillation. During the execution of the method it may often be determined whether any of the electrodes are providing an invalid signal. If this is the case, any of the electrodes which are providing an invalid signal are uncoupled from the monitor and an electrode of a redundant plurality of electrodes is coupled to the monitor.

SUMMARY OF THE INVENTION

The teachings disclosed herein propose to switch ECG monitoring to the therapy pad electrodes, which are much larger, therefore have a larger adhesive surface, and are less likely to become dislodged or have a noisy signal because of insufficient contact area. While these pad electrodes would become unusable for monitoring if pacing therapy ensues, they can be used for monitoring until therapy is needed, if at all. During this period, the clinicians could be alerted to the loss of ECG monitoring electrode signal quality, and the signal may be restored before the pacing therapy is required. If the therapy electrodes detect a condition requiring pacing, then fixed-mode pacing could be initiated, since an ECG analysis was performed that verified the need, rather than automatically initiating pacing because of a failure of ECG monitoring. One implementation may automatically switch back to demand mode pacing if the ECG monitoring electrode signal becomes reestablished.

It would be desirable to provide an operation method for an external pacemaker device that responds to a loss of ECG monitoring functionality in a manner that is secure and comfortable for the patient. It would also be desirable, that the operation method for an external pacemaker device facilitates a power-efficient operation of the external pacemaker device, for example by avoiding an unnecessary administration of pacing pulses. At least one of these desires and/or possible other desires are addressed by an operation method for an external pacemaker device for stimulating a heart of a patient, wherein the method comprises:

a) determining if the external pacemaker device is in a pacing mode requiring a monitoring of an electrocardiogram signal from a patient to determine when pacing stimuli are needed; b) determining if at least one monitoring electrode used for the monitoring of the electrocardiogram signal is not or no longer operative;

c) if the monitoring of the electrocardiogram signal is required and if the at least one monitoring electrode is not or no longer operative, then monitoring the electrocardiogram using at least one therapy electrode of the external pacemaker device instead of the at least one monitoring electrode;

d) determining if the electrocardiogram signal being monitored by means of the at least one therapy electrode does not sufficiently clearly indicate an electrical activation of the heart;

e) if the electrocardiogram signal does not indicate the electrical activation of the heart, then performing fixed-mode external pacing on the patient.

As used herein, the term "external pacemaker device" encompasses dedicated, stand-alone, external pacemakers as well as a pacemaker functionality of another device, e.g. a defibrillator/monitor. The operation method according to the teachings disclosed herein acknowledges that in many situations the therapy electrode(s) may be used for the monitoring of the electrocardiogram signal for quite some time after an event of the at least one monitoring electrode becoming not or no longer operative. The external pacemaker device operating under the operation method becomes more graceful regarding the urgency with which a condition of the at least one monitoring electrode being inoperative needs to the resolved. The operation method is also secure for the patient because as a fail-safe operating mode the operation method causes the external pacemaker device to enter a fixed-mode external pacing mode when neither the at least one monitoring electrode nor the at least one therapy electrode provide a reliable electrocardiogram signal.

Demand-mode pacing is sometimes called synchronous pacing, and fixed- mode pacing is sometimes called asynchronous pacing. Demand-mode pacing includes an analysis of the ECG to determine if the intrinsic heart rate is below a threshold. A pacemaker pulse is delivered to ensure that the heart does not drop below a specified rate. Fixed-mode pacing delivers pacemaker pulses (or stimuli) at a constant (fixed) rate, regardless of the signals apparent on the ECG.

A purpose of the monitoring of the electrocardiogram signal is to find out whether the electrocardiogram signal indicates an electrical activation (or activity) of the heart in order to generate a response if such activation cannot be clearly identified. In other words, it is determined whether the electrocardiogram signal does not contraindicate a necessity for delivering pacing therapy rather than the electrocardiogram signal indicating a necessity for delivering pacing therapy. If a heart beat or an electrical activation can be detected, than the administration of a pacing pulse is inhibited. If no heart beat or electrical activation can be detected, or if there is an uncertainty in the interpretation of a detected ECG signal, then a pacing stimulus may be delivered as a precaution. In this case, the operation method continues in fixed-mode pacing because one can no longer trust the

electrocardiogram signal detected via the at least one therapy pad after pacing has started. In summary, the operation method may not actually determine when pacing is needed, but will start if it is not sure pacing is not needed.

The operation method may further comprise, anytime while the at least one monitoring electrode is not or no longer operative:

determining if the at least one monitoring electrode is operative again;

determining if a demand-mode pacing is required;

if the at least one monitoring electrode is operative again, and if demand-mode pacing is required, then activating the demand-mode pacing of the external pacemaker device.

The action of activating the demand-mode pacing may require a deactivation of fixed-mode pacing if fixed-mode pacing had been activated previously. By determining if the at least one monitoring electrode is operative again, the operation method may respond to a re-establishment of a normal functionality of the ECG monitoring, for example by the intervention of a user. The operation method thus returns to a normal operating state.

Possibly the patient has not even remarked that the external pacemaker device has temporarily been in an operating state that requires ECG monitoring to be performed via the at least one therapy electrode, except for maybe the fact that the at least one monitoring electrode had become detached and that the external pacemaker device had output an alarm to inform the user and/or patient about the at least one monitoring electrode being not or no longer operative.

The operation method may further comprise, anytime while performing fixed- mode external pacing:

determining if the external pacing is terminated by a higher level command and if so terminating the fixed-mode external pacing;

waiting for the at least one therapy electrode to be operative again for monitoring the electrocardiogram signal;

monitoring the electrocardiogram signal by means of the at least one therapy electrode. The functionality of the operation method described in the previous paragraph allows a user to override the fixed-mode external pacing. A higher level control unit of or for the external pacemaker device could also issue the higher level command. For example, the external pacemaker device could be a part of a defibrillator having pacemaker functionality. If an analysis of the electrocardiogram signal indicates that the administration of a defibrillation pulse or a cardioversion pulse is advisable given a current shape of the electrocardiogram signal, the higher level command could instruct the pacemaker device to terminate the fixed-mode external pacing. Monitoring of the electrocardiogram signal by means of the at least one therapy electrode may be resumed once the electrical disturbances on the at least one therapy electrode have decayed.

The operation method may further comprise in action d) an evaluation of information from a data record of the patient to determine the necessity for delivering pacing therapy, taking into account if the electrocardiogram signal being monitored does not clearly indicate the electrical activation of the heart. The external pacemaker device may receive data about the patient such as the patient's age, weight, gender, relevant parts of the patient's medical history (i.e. occurrence of heart attacks in the past, other heart-related information), etc. The received data may be stored in the data record and influence a decision made by the operation method and/or the external pacemaker device as to when and under which circumstances a certain mode of pacing should be employed.

The operation method may further comprise during the execution of action d) while performing the fixed-mode external pacing:

periodically pausing in performing the fixed-mode external pacing, monitoring the electrocardiogram signal by means of the at least one therapy electrode and determining if an intrinsic rhythm of the patient has been restored.

The determination if an intrinsic rhythm of the patient has been restored may be achieved by monitoring the electrocardiogram signal via the at least one therapy pad. The pause or pauses in performing the fixed-mode external pacing could be brief, and may only determine that the allowable pause time is shorter than the recovery time of the electrode. The activation/deactivation of this pause feature could be left up to a physician's discretion.

The operation method may further comprise:

alerting a user about the at least one monitoring electrode not or no longer being operative;

determining if the user has responded to the alert;

if the user has not responded to the alert, going back to action d). Alerting the user gives the user an opportunity to correct failures that may have occurred during the execution of the operation method. For example, the user may reattach the at least one monitoring electrode to the patient, so that the at least one monitoring electrode becomes operative again.

The operation method may further comprise in action b):

informing a user about the at least one monitoring electrode being not or no longer operative, and using the at least one therapy electrode for electrocardiogram monitoring after a predetermined time if there was no response to the informing of the user.

The operation method may revert to monitoring the electrocardiogram signal via the at least one therapy electrode if the user has not responded within the predetermined time. During the predetermined time there are basically two possibilities: Either the patient has kept his intrinsic rhythm, so that there is no imminent danger to the patient, or the intrinsic rhythm of the patient has unfortunately ceased. In the latter case, fixed-mode external pacing may be employed if the electrocardiogram monitoring after the

predetermined time showed that there is no intrinsic rhythm of the patient.

The teaching disclosed herein may also be used in the context of a computer program product comprising instructions that enable a processor to carry out a method of operation of an external pacemaker device for stimulating a heart of a patient. The method comprises:

a) determining if the external pacemaker device is in a pacing mode requiring a monitoring of an electrocardiogram signal from a patient to determine when pacing stimuli are needed;

b) determining if at least one monitoring electrode used for the monitoring of the electrocardiogram signal is not or no longer operative;

c) if the monitoring of the electrocardiogram signal is required and if the at least one monitoring electrode is not or no longer operative, then using at least one therapy electrode of the external pacemaker device for electrocardiogram monitoring instead of the at least one monitoring electrode;

e) if the electrocardiogram signal does not indicate the electrical activation of the heart, then performing fixed-mode external pacing on the patient. The computer program-product may comprise further instructions that enable the processor to carry out a method comprising actions and features as described above in the context of the explanations to the operation method for an external pacemaker device.

The teaching disclosed herein may also apply to an external pacemaker device for stimulating a heart of a patient, the external pacemaker device comprising:

at least one electrocardiogram monitoring electrode for attachment to a patient; an electrocardiogram evaluator;

at least one therapy electrode for attachment to the patient and for delivering pacing pulses to the patient;

- an operativeness monitor adapted to monitor an operativeness of the least one electrocardiogram monitoring electrode;

an electrocardiogram source selector connected to the at least one electrocardiogram monitoring electrode, to the at least one therapy electrode and to the electrocardiogram evaluator, adapted for switching from the at least one electrocardiogram monitoring electrode as a source of electrocardiogram signal to be provided to the

electrocardiogram evaluator to the at least one therapy electrode as the source upon:

- reception of a signal from the operativeness monitor indicating a reduced operativeness of the at least one electrocardiogram monitoring electrode, and

- reception of an indication of the external pacemaker device being in a pacing mode requiring a monitoring of the electrocardiogram signal from the patient to determine when the electrocardiogram signal does not sufficiently clearly indicate an electrical activation of the heart.

The external pacemaker device may further comprise a user interface adapted to prompt the user about a reduced operativeness of the at least one electrocardiogram monitoring electrode, and adapted to receive an input from the user regarding a switching of the source from the at least one electrocardiogram monitoring electrode to the at least one therapy electrode.

The external pacemaker device may further comprise a pacing pulses generator adapted to provide pacing pulses of a demand-mode pacing scheme to the at least one therapy electrode, and also adapted to provide pacing pulses of a fixed mode pacing scheme to the at least one therapy electrode in case pacing pulses need to be administered to the patient while the operativeness monitor reports a reduced operativeness of the at least one electrocardiogram monitoring electrode. At least some of the features described above as optional features for the operation method for an external pacemaker device may used for the external pacemaker device itself as well. Such combinations are herewith disclosed.

As far as technically meaningful, the technical features disclosed herein may be combined in any manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a schematic flow chart of a part of an operation method for an external pacemaker device according to a first prior art solution.

Fig. 2 shows a schematic flow chart of a part of an operation method for an external pacemaker device according to a second prior art solution.

Fig. 3 shows a schematic flow chart of a part of an operation method for an external pacemaker device according to the teachings disclosed herein.

Figs. 4a and 4b show a schematic flow chart of another version of an operation method for an external pacemaker device according to the teachings disclosed herein.

Fig. 5 shows a schematic block diagram of an external pacemaker device according the teachings disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalence. It will also be understood that features of an aspect can be combined with a feature of a different aspect or aspects.

Figs. 1 and 2 have already been described in the introductory portion of the application.

Fig. 3 shows a schematic flow chart of a part of the operation method for an external pacemaker device according to the teachings disclosed herein. After the start of the operation method a demand-mode external pacing is initiated at 301. An electrocardiogram signal is monitored via monitoring electrodes at 303. A (demand-mode) pacing therapy is initiated if/when an analysis of the monitored electrocardiogram signal indicates a necessity for a pacing therapy. More particularly as long as an electrocardiogram signal is monitored that does not indicate acute problems of the patient's heart, no pacing therapy is scheduled. At some point in time during the monitoring of the electrocardiogram signal one or more of the monitoring electrode may be come unavailable. This may be due to a movement of the patient or due to the patient being manipulated by a caregiver, for example. At a decision point 305 the operation method periodically checks whether all potential monitoring electrodes have become unavailable. The question at decision point 305 is directed to all potential monitoring electrodes because sometimes a certain redundancy exists within the set of monitoring electrodes so that an unavailable electrode may be replaced by another available electrode. If it has been determined at decision point 305 that not all potential monitoring electrodes have become unavailable (i.e. there are still some monitoring electrodes assuring the monitoring function of the external pacemaker device), the operation method proceeds to a decision point 319. At the decision point 319 it is checked, if a command to stop pacing has been received. The command could be issued by a user or by higher level control logic. If no such command has been received, the operation method goes back to the action 303 to continue monitoring the ECG and to initiate therapy if/when needed.

The external pacing is terminated at 321 if at the decision point 319 it had been determined that a command to stop pacing had been received.

Going back to the decision point 305, if it had been determined that no meaningful ECG monitoring is possible anymore because the potential monitoring electrodes had become unavailable, the operation method continues at action 307. In order to provide continued ECG monitoring capability to the external pacemaker device, the ECG monitoring is switched to the therapy electrodes. In addition a clinician is alerted.

While in the therapy electrode monitoring state the operation method performs a couple of tests and checks on a periodical basis. A first test is performed at 309 and determines if a pacemaker activation is needed given an analysis of the electrocardiogram signal monitor via the therapy electrode(s). If this is the case, fixed mode-pacing is initiated at 311. If no pacemaker activation is needed the operation method goes on to decision point 313 where it is determined if the electrode off-condition has been corrected. If so, the operation method goes back to the action 301 in order to initiate "no external pacing". In this case the operation method is back in a normal mode of an operation. If at 313 it could not be determined if the electrodes-off condition has been corrected, the operation method continues at decision point 315. At decision point 315 it is determined whether the clinician has responded to the alarm. If so, the operation method continues at the already mentioned decision point 319 to check whether a command to stop pacing has been received. If not, the operation method goes on to decision point 317 in order to determine whether fixed-mode pacing has been activated. If fixed-mode pacing has been activated the method loops back to the decision point 313. In the other case, i.e., fixed-mode-pacing has not been activated, the method goes to decision point 309 in order to determine whether a pacemaker activation is needed.

Fig. 4A shows an aspect of another version of the operation method for an external pacemaker device. After the start it is determined at decision point 401 if a pacing mode has been selected that requires ECG monitoring. The method periodically loops back around decision point 401 if this is not the case.

In the alternative the ECG may indicate a problem, either with the patient's heart rhythm and/or electrical heart activity or with an operativeness of the monitoring electrode. At a decision point 403 it is determined if the monitoring electrode(s) are not or no longer operative. The method goes to sub-procedure 405 if the monitoring electrode(s) are still operative because in this case it is the patient's ECG that indicates that the patient may require pacing.

The sub-procedure 405 carries out the necessary actions and may then return to decision point 401.

In case the monitoring electrode(s) are not or no longer operative the method continues at 407 to perform ECG monitoring via the at least one therapy electrode. If at a decision point 409 an electrical activity of the patient's heart is detectable, then the method branches back to action 407 for continued ECG monitoring via the therapy electrode(s). If no electrical activity of the heart is detectable at 409, the method continues at 411 with initiating fixed-mode external pacing of the patient. At 413 an optional action of periodically pausing in fixed mode external pacing to monitor the ECG is performed.

Subsequent to the action 413 the flow chart is continued in Fig. 4B at the indicated connection point A.

In Fig. 4B the flow chart that started in Fig. 4 A is continued at connection point A.

At a subsequent decision point 415 it is determined if a higher level command to terminate fixed-mode pacing has been received. If this is not the case, the method proceeds to decision point 417 to determine whether the monitoring electrode(s) is/are operative again. The method loops back to the decision point 415 if the monitoring electrode(s) is/are not operative again, and the method continues at decision point 419 otherwise. At the decision point 419 it is checked if a demand-mode pacing is required. Demand-mode pacing may be available again, because the monitoring electrodes(s) are operative again as determined at the decision point 417. If the answer is no, then the method loops back to decision point 415, again. In the contrary case, the method continues at action 421 and switches from fixed-mode pacing to demand-mode pacing. The method then continues at the sub-procedure 405 shown in Fig. 4A.

Going back to the decision point 415, an alternative path is to an action 423, namely if a higher level command was received to terminate fixed-mode pacing. The operation method then terminates the fixed-mode pacing at the action 423. At a subsequent action 425 the operation method waits for the therapy electrode(s) to be operative again. As mentioned before, the administration of a pacing pulse via the therapy electrode causes electrical disturbances in the therapy electrodes. A certain waiting period allows the electrical disturbances to decay so that the therapy electrodes may be used for ECG monitoring again.

After the waiting period of action 425 has passed the method proceeds to a decision point 427 to determine if a higher level command has been received to terminate any pacing activity completely. The higher level command analyzed at the decision point 427 could be the same as the higher level command analyzed at the decision point 415, or it could be a separate higher level command. The operation method, or at least the part of the operation method that is relevant for the teachings disclosed herein, ends if such a higher level command to completely terminate the pacing has been received. In the other case the operation method branches back to the action 407 in Fig. 4 A via connection point B.

Fig. 5 shows a schematic block diagram of an external pacemaker device according to the teachings disclosed herein.

The external pacemaker device comprises a pacing circuitry 102 arranged to deliver pacing pulses to a patient. The pacing circuitry 102 is connected to therapy electrodes (or pads) 106, 108 by means of two lead wires 105, 107. The therapy electrodes 106, 108 may be adhesive pads that are attached to the patient prior to the beginning of

monitoring/pacing.

The external pacemaker device also comprises, or maybe connected to, a set of monitoring electrodes 214, 216, 218. Note that the illustrated number of three monitoring electrodes is only an example and that there could be any number monitoring electrodes, for example four, five, ten electrodes (for continuous 12-lead ECG), or more. The monitoring electrode 214, 216, 218 are intended to be connected with an electrocardiogram evaluator 204. Moreover, the monitoring electrodes 214, 216, 218 are connected to an operativness monitor 205. The connection between the monitoring electrodes 214, 216, 218 and the electrocardiogram evaluator is accomplished via a switch matrix 206. The switch matrix 206 comprises three switches 207, 208, 209 in the version depicted in Fig. 5. The switches 207, 208, and 209 are three-contact-switches. The first switch 207 has a contact that is connected to the monitoring electrode 214 via the monitoring lead 213. The two other contacts of the switch 207 are connected to the therapy electrodes 106, 108 via the respective leads 105, 107. The second switch is connected to the monitoring electrode 216 via one of its contacts and monitoring lead 215. As was the case with the first switch 207, the second switch 208 is also connected to the therapy electrodes 106, 108 via the other two contacts and the lead 105 and 107. The third switch 209 is connected to the monitoring electrode 218 via monitoring lead 217 and also to the therapy electrodes 106, 108 in a similar manner as the switches 207 and 208.

The switches 207, 208, 209 are controlled by the operativeness monitor 205 via control lines or commands 227, 228 and 229. Usually, the operativeness monitor 205 well give the monitor electrode 214, 216, 218 precedence if the operativeness monitor 205 has ascertained that the monitoring electrode 214, 216, 218 are available and operative. If one of the monitoring electrodes 214, 216, 218 is not or no longer operative then the operativeness monitor 205 may choose to substitute one of the therapy electrodes 106, 108 for the non- operative one of the monitoring electrodes 214, 216, 218. For example, the switch 207 could be controlled by the operativeness monitor 205 to temporarily connect the therapy electrode 106 with the electrocardiogram evaluator 204 if/when the monitoring electro 214 is not operative.

As a variant to the switch matrix 206 illustrated in Fig. 5 a complete switch matrix could be provided which would make it possible to freely connect the monitoring electrodes 214, 216, 218 with any of the three illustrated inputs of the electrocardiogram evaluator 204. This could be used to substitute one of the monitoring electrodes 214, 216, 218 for another of the monitoring electrodes.

Another option would be to connect all attached electrodes to a digital circuit comprising analogue-to-digital converters. The signals from the attached electrodes may then be converted to digital values. The choice of a particular pacing electrode may then be decided and executed in software.

The external pacemaker device shown in Fig. 5 further comprises a control unit 220 and a user interface unit 230. The control unit 220 communicates with the pacing circuitry 102, the electrocardiogram evaluator 204, the operativeness monitor 205, and the user interface unit 230 via a data bus. Other techniques of linking a number sub-units together may also be employed, such as point-to-point connections, direct wiring, or a device-internal network.

The user interface unit 230 is connected to user interface devices such as a display 231, a loudspeaker 232, and a keyboard 233. The user interface devices 231, 232, 233 are only examples and could be completed or replaced by other types of user interface devices.

Other variations to the disclosed embodiment(s) can be understood and effected by those skilled in the art in practicing the claimed invention from study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single unit may perform functions of several items recited in the claims and vice versa. The mere fact that certain measures are recited in mutually different dependent claims does not mean that combinations of these measures cannot be used to advantage. Any reference signs found in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An operation method for an external pacemaker device for stimulating a heart of a patient, the method comprising:

2. The operation method according to claim 1, further comprising, anytime while the at least one monitoring electrode is not or no longer operative:

- determining if the at least one monitoring electrode is operative again;

determining if a demand-mode pacing is required;

3. The operation method according to claim 1, further comprising, anytime while performing fixed-mode external pacing:

determining if the external pacing is terminated by a higher level command and if so terminating the fixed-mode external pacing; waiting for the at least one therapy electrode to be operative again for monitoring the electrocardiogram signal;

monitoring the electrocardiogram signal by means of the at least one therapy electrode.

4. The operation method according to claim 1, further comprising during the execution of action e) while performing the fixed-mode external pacing:

periodically pausing in performing the fixed-mode external pacing, monitoring the electrocardiogram signal by means of the at least one therapy electrode, and determining if an intrinsic rhythm of the patient has been restored.

5. The operation method according to claim 1, further comprising:

determining if the user has responded to the alert;

if the user has not responded to the alert, going back to action d).

6. The operation method according to claim 1, further comprising in action b):

7. Computer-program product comprising instructions that enable a processor to carry out a method of operation of an external pacemaker device for stimulating a heart of a patient, the method comprising:

c) if the monitoring of the electrocardiogram signal is required and if the at least one monitoring electrode is not or no longer operative, then using at least one therapy electrode of the external pacemaker device for electrocardiogram monitoring instead of the at least one monitoring electrode; d) determining if the electrocardiogram signal being monitored by means of the at least one therapy electrode does not sufficiently clearly indicate an electrical activation of the heart;

8. An external pacemaker device for stimulating a heart of a patient, the external pacemaker device comprising:

at least one electrocardiogram monitoring electrode for attachment to a patient; - an electrocardiogram evaluator;

an operativeness monitor adapted to monitor an operativeness of the at least one electrocardiogram monitoring electrode;

- an electrocardiogram source selector connected to the at least one

electrocardiogram monitoring electrode, to the at least one therapy electrode, and to the electrocardiogram evaluator, adapted to switch from the at least one electrocardiogram monitoring electrode as a source of an electrocardiogram signal to be provided to the electrocardiogram evaluator to the at least one therapy electrode as the source upon:

9. The external pacemaker device according to claim 8, further comprising a user interface adapted to prompt the user about a reduced operativeness of the at least one electrocardiogram monitoring electrode, and adapted to receive an input from the user regarding a switching of the source from the at least one electrocardiogram monitoring electrode to the at least one therapy electrode.

10. The external pacemaker device according to claim 8, further comprising a pacing pulse generator adapted to provide pacing pulses of a demand-mode pacing scheme to the at least one therapy electrode, and also adapted to provide pacing pulses of a fixed-mode pacing scheme to the at least one therapy electrode in case pacing pulses need to be administered to the patient while the operativeness monitor reports a reduced operativeness of the at least one electrocardiogram monitoring electrode.