WO2007081248A1

WO2007081248A1 - An implantable heart stimulating device and method for evoked response detection

Info

Publication number: WO2007081248A1
Application number: PCT/SE2006/000063
Authority: WO
Inventors: Andreas Blomqvist; Anders Björling
Original assignee: St. Jude Medical Ab
Priority date: 2006-01-16
Filing date: 2006-01-16
Publication date: 2007-07-19

Abstract

The invention concerns an implantable heart stimulating device (10) including a con- trol circuit (14) comprising a first ventricular pacing circuit (37) adapted to enable pac ing of a ventricle (IV) and a first ventricular sensing circuit (35), adapted to communicate with one or more sensing electrodes or sensors (31, 32, 33). The control circuit (14) is arranged to be able to detect an evoked response to delivered pacing pulses by sensing within a first time window (ERl) that follows after a delivered pacing pulse. The control circuit (14) is arranged to be able to detect said evoked response with at least a first and a second evoked response detection method. The invention also concerns a method of operating an implantable heart stimulating device.

Description

AN IMPLANTABLE HEART STIMULATING DEVICE AND METHOD FOR EVOKED

RESPONSE DETECTION

BACKGROUND OF THE INVENTION 5

1. Field of the invention

The present invention relates to an implantable heart stimulating device with means for detecting an evoked response to delivered pacing pulses. 10

The invention also relates to a method of operating an implantable heart stimulating device.

2. Description of the prior art 15

Several different implantable devices for stimulating a heart are known. The devices are normally able to sense the electrical activity of the heart. Some implantable devices are able to deliver stimulation pulses to and/or sense the right atrium (in some case even the left atrium) and also to deliver stimulation pulses to and sense one or both of 20 the left and right ventricles.

Devices that are able to deliver stimulation pulses to both the left and right ventricle can be called bi-ventricular pacers. Such devices can be used to treat patients who suffer from different severe cardiac problems, e.g. patients suffering from congestive

25 heart failure (CHF). CHF is defined generally as the inability of the heart to deliver a sufficient amount of blood to the body. CHF can have different causes. It can for example be caused by a left bundle branch block (LBBB) or a right bundle branch block (RBBB). By using bi-ventricular pacing, the contraction of the ventricles can be controlled in order to improve the ability of the heart to pump blood. The stimulation

30 pulses to the two ventricles can be delivered simultaneously, but it is also known that the stimulation pulses to the two ventricles are delivered with a short time delay between them in order to optimise the pumping performance of the heart.

US-A-5 720 768 describes different possible electrode positions in order to stimulate 35 or sense the different chambers of the heart. US-A-6 070 100 describes that electrodes may be positioned in both the left and the right atrium as well as in the left and the right ventricle.

In connection with implantable pacers, it is known to detect the capture of the heart, i.e. to detect whether the heart actually reacts on a delivered stimulation pulse. This detection is also called evoked response (ER) detection. If the heart is not captured, it is possible to arrange the pacer to deliver a back-up pulse with a higher pulse energy than the first pulse. It is also possible to increase the pulse energy in future stimulation pulses if capture is not detected. In order to save battery it is important that the stimu- lation pulses are not delivered with an unnecessarily high energy. In order to determine a suitable pulse energy, it is known to perform an automatic threshold/capture search. By varying the energy of the stimulation pulses, and by detecting whether capture occurs, it is thus possible to find a threshold value for the stimulation pulse energy. Based on the threshold value, a suitable stimulation pulse energy can be determined.

US 6 192 275 Bl describes an implantable cardiac rhythm management device that is capable of automatically adjusting an evoked response detection threshold dependent upon a modulation of the amplitude of the evoked response. The document describes that respiration, activity level, and lead maturation, among others, effect the modula- tion of the evoked response and the amplitude of a signal associated with evoked response. The document describes that the device automatically adjusts the evoked response detection threshold to account for this modulation.

US 6 782 291 Bl describes an implantable cardiac stimulation device that senses evoked responses to applied pacing stimulation pulses. A pulse generator applies the stimulation pacing pulses to the heart in accordance with a pacing configuration. A sensor control selects an evoked response sensing electrode configuration from among a plurality of evoked response sensing electrode configurations in response to the pacing configuration. Signal-to-noise ratios obtained with the various electrode configura- tions are used to select a best electrode configuration for sensing evoked responses.

US 2003/0050671 Al describes an apparatus and a method for identifying fusion beats as part of an automatic capture routine in a cardiac stimulation device. The document describes different detection features that can be used in the capture detection function. By requiring each post-pulse electrical response to be closely correlated with an expected morphology for either a capture condition or a loss-of-capture condition before classification of the post-pulse electrical response as either capture or loss-of-capture respectively, it is possible to identify fusion beats. In various embodiments, this fusion identification is performed using both template matching and assessment of particular detection features. According to one embodiment, a moving average and a standard deviation are maintained for each detection feature, thereby creating an automatically adjusting evoked response detection threshold. In the document it is mentioned in paragraph 122 that a calibration process can be performed for multiple states, such as time of day, level of activity, etc., to obtain multiple capture templates and multiple loss of capture templates. The state-dependent templates are then used at the appropri- ate time based upon a currently assessed state.

SUMMARY OF THE INVENTION

It is thus known from some of the above documents that it is possible to make some minor modification of the manner with which the evoked response is detected. Such minor modifications may thus involve sensitivity settings or detection threshold level or the used electrode configuration or the modification of a template used. However, the inventors of the present invention have realized that it would be advantageous to make a more substantial adjustment of the evoked response detection, depending on different circumstances.

One object of the present invention is to provide an implantable heart stimulating device with which the evoked response detection is better adapted to different circum- stances. Further objects and advantages of the invention will become clear from the following description and claims.

The above object is achieved by an implantable heart stimulating device including a control circuit comprising: a first ventricular pacing circuit, adapted to communicate with a first ventricular pacing electrode suited to be positioned in or at a first ventricle of a heart, wherein said first ventricular pacing circuit is adapted to enable pacing of such a ventricle; a first ventricular sensing circuit, adapted to communicate with one or more sensing electrodes or sensors suited to be positioned in or in relation to a first ventricle of a heart; said control circuit being arranged to be able to detect an evoked response to a pacing pulse delivered by said first ventricular pacing circuit by sensing, with said first ventricular sensing circuit, within a first time window that follows after a pacing pulse delivered by said first ventricular pacing circuit; said control circuit being arranged to be able to detect said evoked response with at least a first and a second evoked response detection method, which methods differ from each other concerning at least some detection criteria, wherein, in case the evoked response detection is based on sensing an electrical signal emitted by the cardiac tissue, said detection criteria, which differs between the first and the second evoked response detection methods, is not just sensitivity settings or detection threshold level or the used electrode configuration or a template criteria.

Since the device is arranged such that at least two different evoked response detection methods can be used, an evoked response detection method that is better adapted to the particular circumstance can be used. It is also possible to change from one evoked response detection method to another evoked response detection method, if the circum- stances change so that the other method becomes more suitable than the first mentioned method. A better adapted evoked response detection can thus be achieved with the present invention.

It should be noted that according to the invention, the detection of an evoked response it preferably done with the help of one or more evoked response detection signals. This signal can be based on different sensed entities. For example, the evoked response detection signal can be based on sensing an electrical signal emitted by the cardiac tissue (i.e. the evoked response detection signal is an IEGM; i.e. an intracardiac electrogram). However, the evoked response detection signal can also be a signal based on for ex- ample detected blood pressure or an impedance measured between different points.

According to an embodiment of the implantable heart stimulating device according to the invention, said control circuit is arranged to automatically switch between at least said first and second detection method. It is of course an advantage if the switching between the detection methods is performed automatically.

According to a further embodiment of the implantable heart stimulating device according to the invention, said control circuit is arranged to be able to carry out said automatic switching between at least said first and second detection method in dependence on one or more of the following: a) received information concerning the physical activity and/or the physiological state of a patient in whom the device is implanted, b) the energy of the delivered pacing pulses, c) the noise level in the evoked response detection signal.

The concept "physical activity" or the like refers to how physically active the patient in question is. For example, if the patient is walking, the patient will be more physically active than if the patient is resting or sleeping. The concept "physical activity" or the like herein also includes the heart rate and the breathing of the patient, since heart rate and breathing are often correlated to physical activity.

The concept "physiological state" includes the position of the body (e.g. if the patient is laying down or standing up), the mood of the patient (e.g. if the patient is upset or under stress or calm) and the pathological state (e.g. if the patient suffers from fever, high blood pressure, or congestive heart failure).

Different evoked response detection methods can be more or less suitable for use depending on the physical activity, the physiological state, the energy of the delivered pacing pulses or the noise level in the evoked response detection signal. Consequently, it is an advantage of the present invention that a suitable evoked response detection method is selected in dependence on these mentioned entities.

According to a further embodiment, the device is arranged to be able to provide said information concerning the physical activity and/or the physiological state by sensing or detecting one or more of the following entities: blood pressure, heart rate, temperature of the patient, acceleration of the body of the patient, position or posture of the body of the patient, the impedance between at least two points in the body of the patient, one or more chemical substances in the body of the patient, the morphology of the evoked response detection signal, the variation over several heart cycles of the evoked response detection signal. The detection or sensing of such entities provides information concerning the physical activity or the physiological state of the patient in question. Such information can thus be used when determining which evoked response detection method to use. According to a further embodiment, the control circuit is arranged to communicate with at least one sensor with the help of which said entity or entities are sensed or detected. Such a sensor can be used in order to determine some of the mentioned entities.

According to still an embodiment, the control circuit is arranged to perform said automatic switching between at least said first and second detection method based on at least some other information than just the evoked response detection signal. Although the evoked response detection signal provides some information that can be used as a basis for determining whether switching between the methods should be carried out, it is advantageous if other information than that derived from the evoked response detection signal is used for determining whether switching between the methods should be carried out.

According to a further embodiment, the device and the control circuit are arranged to enable that said first detection method involves the use of one or more of the following detection calculations/measurements : a) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, b) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, c) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, d ) the morphology of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, e) the number of zero crossings in the evoked response detection signal;, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, f) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, g) the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, h) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, i) how steep the evoked response detection signal is, wherein the evoked response de- tection signal is based on sensing the impedance between different points of the body of the patient, j) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, k) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, 1 ) the morphology of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, m) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, n) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, o) the maximum or minimum of apeak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, p) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, q) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing blood pressure, r) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing blood pressure, s) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing blood pressure, t ) the morphology of the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, u) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, v) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, x) the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, y) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure.

The above points are suitable calculations/measurements that can be used in the detec- tion method. Although it is usually sufficient for a method to use only one of the points a) to y) above, it is within the scope of the invention that a combination of two or more of these points be used in a detection method.

According to a further embodiment, the device and the control circuit are arranged to enable that the second detection method involves the use of either at least one of the points a) to y) above that is not used in the first detection method or at least one further detection calculation/measurement that is not used in the first detection method. The second detection method thus differs substantially from the first detection method.

According to a further embodiment, the device and the control circuit are arranged to enable that the first detection method involves the use of the above-mentioned b) but not c), while the second detection method involves the use of c) but not b). In other words, according to this embodiment, the first detection method involves the use of an area calculation with a fixed baseline while the other detection method uses a baseline that is not fixed when calculating the area.

A further aspect of the invention relates to a method of operating an implantable heart stimulating device. This method comprises the following steps: deliver pacing pulses to a first ventricle of the heart of the patient in whom the device is implanted; detect an evoked response to a pacing pulse by sensing within a first time window that follows after a delivered pacing pulse, wherein the method of operating the implantable heart stimulating device includes at least a first and a second evoked response detection method, which methods differ from each other concerning at least some detection criteria, wherein, in case the evoked response detection is based on sensing an electrical signal emitted by the cardiac tissue, said detection criteria, which differs between the first and the second evoked response detection methods, is not just sensitivity settings or detection threshold level or the used electrode configuration or a template criteria.

Different manners of carrying out the method are clear from the description below and from the dependent method claims.

The method according to the invention has similar advantages to those described above in connection with the device according to the invention.

Further aspects and advantages of the present invention will become clear from the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 shows schematically an implantable heart stimulating device connected to leads with sensors and sensing and pacing electrodes positioned in a heart.

Fig 2 shows schematically a control circuit which may form part of the device.

Fig 3 shows schematically an evoked response detection signal.

Fig 4 illustrates schematically a method according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Fig 1 shows schematically an implantable heart stimulating device 10 according to the invention. The device 10 comprises a housing 12. The device 10 comprises a connec- tor portion 13. Via the connector portion 13, the device 10 can be connected to different leads. In Fig 1 the device 10 is connected to four leads 20, 30, 40 and 50.

The lead 20 includes a pacing and sensing electrode 21, 22.

Similarly to the lead 20, the lead 30 includes a pacing and sensing electrode 31, 32. According to this example, the lead 30 also includes a sensor 33, which can be a pressure sensor for sensing the blood pressure.

The lead 40 includes a pacing and sensing electrode 41 , 42.

In the shown example, the electrodes 21, 22, 31, 32, 41, 42 are bipolar electrodes with a tip portion 21, 31, 41 and a ring portion 22, 32, 42. However, it is within of the scope of the invention that instead unipolar electrodes can be used. This is known to a person skilled in the art.

On the lead 50, a further sensor 52 is positioned. This sensor 52 can for example be a sensor for sensing temperature or a sensor for sensing chemical substances. The sensor 52 does not necessarily have to be positioned in the heart, but can be positioned at an- other suitable position in the patient in whom the device 10 is implanted.

The device 10 comprises a control circuit 14, which will be described further below. According to the illustrated example, the device 10 also includes a sensor 54 which is connected to the control circuit 14. The sensor 54 can be an activity sensor or a posture sensor. An activity sensor senses how active the patient is. This sensor can for example comprise an acceleration sensor. A posture sensor senses the position of the patient, for example whether the patient is standing up or laying down.

According to the shown example, the sensor 54 is located in the device 10 itself, while the sensor 52 is located outside the device 10. It is however also possible that the sensor 54 is instead located outside the device 10. It is also possible that the sensor 52 is located in the device 10. The device 10 can also include, or be connected to, more or less sensors than just the two sensors 52, 54 shown in the figure. The device 10 together with the leads 20, 30, 40, 50 and the electrodes/sensors 21, 22, 31, 32, 33, 41, 42, 52 constitutes a heart stimulating system that can be implanted in a patient.

It can be noted that figure 1 shows a bi-ventricular device 10, i.e. a device 10 which can sense and stimulate both the ventricles of the heart. However, it is within the scope of the invention that the device 10 can be mono-ventricular. In this case, the device 10 does not have to be connected to a lead like the lead 40 (although it could still be connected to such a lead 40, for example in order to use the electrodes 41, 42 for imped- ance measurement).

Fig 1 also schematically illustrates a heart with a right atrium RA, a left atrium LA, a right ventricle RV and a left ventricle LV.

The electrode 21, 22 constitutes a first atrial sensing and/or pacing electrode 21, 22 which is positioned in a first atrium IA of the heart, according to this embodiment the right atrium RA, in order to enable sensing and/or pacing of this atrium RA.

The electrode 31, 32 constitutes a first ventricular sensing and pacing electrode 31, 32, which is positioned in a first ventricle IV of the heart, in this embodiment the right ventricle RV. The first ventricular sensing and pacing electrode 31, 32 is adapted to enable sensing and pacing of this first ventricle IV.

The electrode 41, 42 constitutes a second ventricular sensing and pacing electrode 41, 42, which is positioned at a second ventricle 2V of the heart, in this embodiment the left ventricle LV. The second ventricular sensing and pacing electrode 41, 42 is adapted to enable sensing and pacing of this second ventricle 2V. The lead 40 may for example be introduced via the right atrium RA and the coronary sinus such that the electrode 41, 42 is positioned in for example the middle or great cardiac vein of the heart. How to introduce the lead 40 in this manner is known to a person skilled in the art.

It is also possible that the device 10 is connected to further leads and/or further electrodes or sensors, for example electrodes positioned in order to sense and/or pace the left atrium LA and electrodes designed to enable defibrillation. Fig 2 shows schematically the control circuit 14 in some more detail. The control circuit 14 includes a memoiy 15 connected to a control portion 18.

The control circuit 14 includes a first atrial sensing and/or pacing circuit 25, 27. In this embodiment, this circuit 25, 27 includes a sensing circuit 25 and a pacing circuit 27. The first atrial sensing and/or pacing circuit 25, 27 communicates with the first atrial sensing and/or pacing electrode 21, 22 via the lead 20. The first atrial sensing and/or pacing circuit 25, 27 is thus adapted to sense and/or pace an atrium IA, in this case the right atrium RA.

The control circuit 14 also includes a first ventricular sensing circuit 35 and a first ventricular pacing circuit 37. These circuits 35, 37 communicate with the first ventricular sensing and pacing electrode 31, 32 via the lead 30. The circuits 35, 37 are thus adapted to sense and pace a first ventricle IV, in this case the right ventricle RV.

The control circuit 14 also includes a second ventricular sensing circuit 45 and a second ventricular pacing circuit 47. These circuits 45, 47 communicate with the second ventricular sensing and pacing electrode 41, 42 via the lead 40. These circuits 45, 47 are adapted to sense and pace a second ventricle 2 V, in this case the left ventricle LV.

The control circuit 14 is arranged, or programmed, to include several operational features. The control circuit 14 is thus arranged to be able to detect an evoked response to a pacing pulse delivered by said first ventricular pacing circuit 37 by sensing within a first time window ERl that follows after a pacing pulse delivered by said first ven- tricular pacing circuit 37.

How to design a pacer to sense evoked response is known to a person skilled in the art. The first time window ERl may for example be set to begin 5ms to 30 ms, for example 15ms, after the delivery of a pacing pulse by the first ventricular pacing circuit 37. The length of the first time window ERl may for example be 30ms to 70ms, for example 50ms.

The sensing of the evoked response can be done with the help of said first ventricular sensing circuit 35. With the help of the sensing circuit 35 and the control portion 18 it is possible to sense an evoked response by detecting an electrical signal emitted by the cardiac tissue. In this context it can be noted that the control circuit 14 can also be arranged to sense the intrinsic R-waves (i.e. a depolarisation of the heart that is not caused by a pacing pulse delivered with the help of the device 10). As is known to a person skilled in the art, the control logic can be different for sensing an evoked response and for sensing an intrinsic R- wave. The control portion 18 can thus include different such detection logics.

An evoked response can also be detected by other means than by detecting signals emitted from the cardiac tissue. It is thus possible to detect an evoked response with the help of a blood pressure sensor, like the sensor 33. Since the blood pressure in a heart chamber increases when the heart chamber contracts, the blood pressure can be used to detect an evoked response.

Another possibility is to detect an evoked response by sensing the impedance between different points of the body of the patient. The impedance can for example be sensed between the electrode surfaces 31 and 32, or between one of these electrode surfaces 31, 32 and a further electrode surface (for example located at the position shown for the sensor 33). The impedance measured is related to for example the amount of blood in a heart chamber, and since the amount of blood depends on whether the heart chamber in question has contracted or not, this impedance measurement can be used to detect an evoked response. How impedance measurements can be done is known from the prior art, see for example some of the above mentioned documents.

It can be noted that the beginning and the end of the evoked response detection window may differ depending on which detection method is used.

Similarly, the control circuit 14 is also arranged to be able to detect an evoked response to a pacing pulse delivered by said second ventricular pacing circuit 47. This can be done by sensing with said second ventricular sensing circuit 45, within a second time window ER2 that follows after a pacing pulse delivered by said second ventricular pacing circuit 47. The second time window ER2 can for example be set to begin 5ms to 30 ms, for example 15ms, after the delivery of a pacing pulse by the second ventricular pacing circuit 47. The length of the second time window ER2 may for ex- ample be 30ms to 70ms, for example 50ms. It should be noted that the first ERl and second ER2 time windows do not necessarily have to have the same length and they do not necessarily have to start or end the same the time period after the respective delivered pacing pulse.

Similarly to the above description in connection with the first ventricle IV, it is of course also for the second ventricle 2V possible to sense an evoked response by other means than be sensing the electrical activity of the heart tissue. It is thus possible to use blood pressure sensing or impedance sensing. Although not shown in Fig 1 , it is for example possible to arrange a pressure sensor on the lead 40.

As already indicated above, the first ventricular sensing circuit 35 and the second ventricular sensing circuit 45 can also be able to sense intrinsic events typical for an R- wave (QRS-complex) in the respective ventricle.

As is also normal in a heart stimulating device, the first atrial sensing and/or pacing circuit 25, 27 is also arranged to be able to detect events typical for a P-wave.

Fig 2 shows that the control portion 18 is also connected to the sensor 54, which, as mentioned above, for example can be an activity sensor or a posture sensor.

The control portion 18 is also, via the lead 50, connected to the sensor 52, which can be a temperature sensor or a sensor for sensing chemical substances, for example the amount of stress hormones in the blood of the patient.

The control circuit 14 is arranged to be able to operate with time cycles corresponding to normal heart cycles. Such an operation is normal for an implantable heart stimulating device. The time cycles are determined by preset timer intervals which also may depend on detected signals

The control circuit 14 is also arranged to be able to operate with normal PV and/or AV delays. It is also common that the delivery of pacing pulses can be inhibited if intrinsic events are sensed.

The control circuit 14 can also be arranged to, within a time cycle, be able to deliver pacing pules with both said first ventricular pacing circuit 37 and said second ventricu- lar pacing circuit 47 with a time gap VV between a pacing pulse delivered, or inhib- ited, by one of said pacing circuits 37 and 47 and the other one of said pacing circuits 37 and 47. A typical value of VV can be between Oms and 80ms.

Although not described in any detail here, the control circuit 14 can be arranged to include several other operational features that are known in connection with heart stimulation devices. Such features include, for example, blanking and refractory periods, the ability to deliver back-up pulses if a heart chamber is not captured when a pacing pulse has been delivered; the ability to perform capture threshold searches; the ability to carry out defibrillation; the ability to communicate with the help of so-called telemetry, etc.

Fig 3 shows schematically an evoked response detection signal. In this case the evoked response detection signal is a signal derived from the electrical activity of the cardiac tissue. However, similar detection signals can be derived by other means, such as by pressure sensing or impedance sensing as described above. Fig 3 also shows an example of an evoked response detection window ERl (or ER2).

There are several possible methods to determine whether the heart, or heart chamber in question, has been captured, i.e. whether the heart chamber is depolarised and con- tracted in response to a delivered pacing pulse. These methods involves analysing one or more features in the evoked response detection signal. If the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, these methods can, for example, involve the use of one or more of the following detection calculations/measurements .

a) How steep the evoked response detection signal is. This is normally done by determining one or more derivatives in the signal.

b) An area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated. This method usually involves the calculation of a negative

"integral". For example the following calculation can be used.

where N is the number of samples in the evoked response window, S₁ the value of the sample i and f_s is the sampling frequency. The baseline from which the area is calculated, is thus 0 according to this example.

c) An area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated. Also this method usually involves the calculation of a negative "integral". However, in this case the baseline from which the area is calculated is not fixed. For example the following calculation can be used.

s_ref = s, ,

where the symbols are as explained above. In this case, the baseline is thus not always 0. Instead, according to this example, the first sample ^₁ determines the baseline.

d ) The morphology of the evoked response detection signal. In this case, usually some form of template is used and the shape of the evoked response detection signal is compared with one or more such templates.

e) The number of zero crossings in the evoked response detection signal.

f) The time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal.

g) The maximum or minimum of a peak of the evoked response detection signal.

h) The time to the maximum or minimum of a peak of the evoked response detection signal.

One or more of the above detection calculations/measurements can then be used in a criteria for determining whether capture is the case. For a) the criteria can for example be that the value of the derivative is above a certain predetermined value. For b) and c) the criteria can for example be that the calculated area is above a certain predetermined value. For d) the criteria can be that a calculated difference between the evoked re- sponse detection signal and a template is below a predetermined value. Similar crite- . rias concerning times, maximum or minimum values, number of zero crossings etc. can be formulated for e) to h). A person skilled in the art knows how to formulate such suitable criterias.

Although a) to h) concern the case that the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, similar calculations/measurements can be performed if the evoked response detection signal is based on other facts, such as on sensing the impedance between different points of the body of the patient or on sensing blood pressure. Such examples are labelled i) to y) above and will therefore not be repeated here.

According to the invention, the control circuit 14 is arranged to be able to detect said evoked response with at least a first and a second evoked response detection method, which methods differ from each other concerning at least some detection criteria. In case the evoked response detection is based on sensing an electrical signal emitted by the cardiac tissue, said detection criteria, which differs between the first and the second evoked response detection methods, is not just sensitivity settings or detection threshold level or the used electrode configuration or a template criteria.

According to the preferred embodiment, the control circuit (14) is arranged to automatically switch between at least said first and second detection methods. This automatic switching can be made in dependence on one or more of the following: a) received information concerning the physical activity and/or the physiological state of a patient in whom the device (10) is implanted, b) the energy of the delivered pacing pulses, c) the noise level in the evoked response detection signal.

Information concerning the physical activity and/or the physiological state can be ob- tained by sensing or detecting one or more of the following entities: blood pressure, heart rate, temperature of the patient, acceleration of the body of the patient, position or posture of the body of the patient, the impedance between at least two points in the body of the patient, one or more chemical substances in the body of the patient, the morphology of the evoked response detection signal, the variation over several heart cycles of the evoked response detection signal. The control circuit 14 is arranged to communicate with at least one sensor 21, 22, 31, 32, 33, 41, 42, 52, 54 with the help of which said entity or entities are sensed or detected. Preferably, the control circuit 14 is arranged to perform said automatic switching between at least said first and second detection method based on at least some other information than just the evoked response detection signal, i.e. some further input is used in order to determine whether or not to switch to another detection method.

Preferably, the device 10 is arranged to enable that a first of the detection methods involves the use of at least one of the mentioned detection calculations/measurements a) to y), while a second detection method uses either at least one of the points a) to y) that is not used in the first detection method or at least one further detection calculation/measurement that is not used in the first detection method.

As a concrete example, the implantable heart stimulating device 10 can be set up to use two detection methods, where the first detection method involves the use of b) (integral with a fixed baseline) but not c) (integral with a non-fixed baseline), while the second detection method involves the use of c) but not b).

Similarly to the description below of a manner of carrying out a method according to the invention, for example the breathing of the patient may determine whether to use b) or c). The breathing of the patient may influence the evoked response detection signal. The level of this signal may thus vary depending on the breathing. The inventors of the present invention have found that if the breathing component of the evoked response detection signal is substantial, then c) will work better than b). If for example the patient is active such that the breathing component is substantial, then probably the use of c) is better than the use of b). However, if the breathing of the patient is not intense, then the breathing will not influence the evoked response detection signal substantially. In this case, it is better to use b) than c). The breathing of the patient may be detected directly or indirectly by different sensors or by analysing the evoked response detection signal over several heart cycles. On the bases of such detection/sensing the device 10 can thus automatically switch between b) and c).

Different methods of detecting evoked response may thus be used depending of different circumstances. Some examples are given below. When the patient is physically active, the risk for microdislodgements of the leads is greater than when the patient is resting. The movement of a lead may affect the morphology of the evoked response detection signal. Consequently, under such circumstances, a morphology based detection should be avoided. Under these circumstances it would be better to use a detection method that includes an area calculation or that is based on how steep the evoked response detection signal is. For example a), b) or c) should be used rather than d).

A high noise level in the evoked response detection signal may affect different pa- rameters, for example how steep the evoked response detection signal is or the positions and levels of the peaks in the signal. When the noise level is high, it may therefore be more beneficial to use for example a morphology based detection.

The posture of the patient may for example affect a measurement of the impedance between different points in the body of the patient. Consequently, whether an impedance measurement should be used in the evoked response detection may depend on the posture of the patient.

A high heart rate, which may occur during exercise for example, may affect the ability to detect an evoked response. If the heart rate is high, the paced ventricular events will be close to each other in time. This may lead to a residual charge in the sensing area, which may affect a number of the different evoked response detection methods. In such cases it may for example be suggested to switch from a method that uses the maximum of a negative peak in the evoked response detection signal to a detection method that is based on impedance measurement or on measurement of blood pressure.

The energy of the pacing pulses may also influence the evoked response detection. A high energy means that the polarisation increases. Under such circumstances it may be important to change for example a baseline used in a calculation in different evoked response detection methods. Furthermore, some detection methods should preferably then be avoided, for example a detection method based on the maximum negative peak may not be suitable when the energy of the pacing pulses is high (at least not without changing a threshold value). Different criterias of how to change between different evoked response detection methods can thus be formulated for different cases. Consequently, an automatic switching can be preformed depending of factors like those described above.

A manner of carrying out a method according to the invention is illustrated schematically in Fig. 4.

An initial first evoked response detection method is used. The method can for example use the calculation b) mentioned above.

Pacing pulses are delivered to at least a first ventricle of the heart of the patient in whom the device is implanted and evoked responses are detected, with said first method, within a first time window that follows after each pacing pulse.

Information concerning the physical activity and/or the physiological state is provided. This can be done by sensing or detecting of one or more of the following entities: blood pressure, heart rate, temperature of the patient, acceleration of the body of the patient, position or posture of the body of the patient, the impedance between at least two points in the body of the patient, one or more chemical substances in the body of the patient, the morphology of the evoked response detection signal, the variation over several heart cycles of the evoked response detection signal. The sensing can be carried out with the help of one or more sensors or by other means.

For example, the "physical activity" of which information is provided can be the breathing of the patient. This information can for example be provided by monitoring the variation over several heart cycles of the evoked response detection signal, since the signal level may vary with breathing. Another manner of providing information about breathing is to measure an impedance between different points in the body of the patient, between which points at least a part of the lungs of the patient is located.

In addition (or alternatively) to the information concerning the physical activity and/or the physiological state of a patient in whom the device is implanted, information of the energy of the delivered pacing pulses and/or of the noise level in the evoked response detection signal can be considered. In dependence on such information it is decided whether or not to use another (a second) evoked response detection method than the mentioned first evoked response detection method.

The switching between the first and the second detection methods can be performed automatically by the device 10.

The methods differ from each other concerning at least some detection criteria, wherein, in case the evoked response detection is based on sensing an electrical signal emitted by the cardiac tissue, said detection criteria, which differs between the first and the second evoked response detection methods, is not just sensitivity settings or detection threshold level or the used electrode configuration or a template criteria.

If the first detection method involves the use of b), as according to this example, then the second detection method can involve the use of at least another one of the points a) to y) (but not of b) or some further detection calculation/measurement that is not used in the first detection method. For example, the second detection method can involve the use of c).

The automatic change between b) and c) can be done in dependence of the detected breathing of the patient.

The invention is not limited to the described embodiments but may be varied and modified within the scope of the following claims.

Claims

1. An implantable heart stimulating device (10) including a control circuit (14) comprising: a first ventricular pacing circuit (37), adapted to communicate with a first ventricular pacing electrode (31, 32) suited to be positioned in or at a first ventricle (IV) of a heart, wherein said first ventricular pacing circuit (37) is adapted to enable pacing of such a ventricle (IV); a first ventricular sensing circuit (35), adapted to communicate with one or more sens- ing electrodes or sensors (31, 32, 33) suited to be positioned in or in relation to a first ventricle (IV) of a heart; said control circuit (14) being arranged to be able to detect an evoked response to a pacing pulse delivered by said first ventricular pacing circuit (37) by sensing, with said first ventricular sensing circuit (35), within a first time window (ERl) that follows after a pacing pulse delivered by said first ventricular pacing circuit (37); said control circuit (14) being arranged to be able to detect said evoked response with at least a first and a second evoked response detection method, which methods differ from each other concerning at least some detection criteria, wherein, in case the evoked response detection is based on sensing an electrical signal emitted by the car- diac tissue, said detection criteria, which differs between the first and the second evoked response detection methods, is not just sensitivity settings or detection threshold level or the used electrode configuration or a template criteria.

2. An implantable heart stimulating device (10) according to claim 1 , wherein said control circuit (14) is arranged to automatically switch between at least said first and second detection method.

3. An implantable heart stimulating device (10) according to claim 2, wherein said control circuit (14) is arranged to be able to carry out said automatic switching between at least said first and second detection method in dependence on one or more of the following: a) received information concerning the physical activity and/or the physiological state of a patient in whom the device (10) is implanted, b) the energy of the delivered pacing pulses, c) the noise level in the evoked response detection signal.

4. An implantable heart stimulating device (10) according to claim 3, wherein the device (10) is arranged to be able to provide said information concerning the physical activity and/or the physiological state by sensing or detecting one or more of the following entities: blood pressure, heart rate, temperature of the patient, accel- eration of the body of the patient, position or posture of the body of the patient, the impedance between at least two points in the body of the patient, one or more chemical substances in the body of the patient, the morphology of the evoked response detection signal, the variation over several heart cycles of the evoked response detection signal.

5. An implantable heart stimulating device (10) according to claim 4, wherein the control circuit (14) is arranged to communicate with at least one sensor (21, 22, 31, 32, 33, 4I₅ 42, 52, 54) with the help of which said entity or entities are sensed or detected.

6. An implantable heart stimulating device (10) according to any one of the claims 2-5, wherein the control circuit (14) is arranged to perform said automatic switching between at least said first and second detection method based on at least some other information than just the evoked response detection signal.

7. An implantable heart stimulating device (10) according to any one of the preceding claims, wherein the device (10) and the control circuit (14) are arranged to enable that said first detection method involves the use of one or more of the following detection calculations/measurements : a) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, b) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, c) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, d ) the morphology of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, e) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, f) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, g) the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, h) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, i) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, j) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, k) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, 1 ) the morphology of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, m) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, n) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, o) the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, p) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, q) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing blood pressure, r) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing blood pressure, s) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing blood pressure, t ) the morphology of the evoked response detection signal, wherein the evoked re- sponse detection signal is based on sensing blood pressure, u) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, v) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, x) the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, y) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pres- sure.

8. An implantable heart stimulating device (10) according to claim 7, wherein the device (10) and the control circuit (14) are arranged to enable that the second detection method involves the use of either at least one of the points a) to y) of claim 7 that is not used in the first detection method or at least one further detection calculation/measurement that is not used in the first detection method.

9. An implantable heart stimulating device (10) according to claim 8, wherein the device (10) and the control circuit (14) are arranged to enable that the first detection method involves the use of b) of claim 7 but not c) of claim 7, while the second detection method involves the use of c) of claim 7 but not b) of claim 7.

10. A method of operating an implantable heart stimulating device comprising the following steps: deliver pacing pulses to a first ventricle of the heart of the patient in whom the device is implanted; detect an evoked response to a pacing pulse by sensing within a first time window that follows after a delivered pacing pulse, wherein the method of operating the implantable heart stimulating device includes at least a first and a second evoked response detection method, which methods differ from each other concerning at least some detection criteria, wherein, in case the evoked response detection is based on sensing an electrical signal emitted by the cardiac tissue, said detection criteria, which differs between the first and the second evoked response detection methods, is not just sensitivity settings or detection threshold level or the used electrode configuration or a template criteria.

11. The method of claim 10, wherein the switching between at least said first and second detection method is performed automatically.

12. The method of claim 11 , wherein the automatic switching between at least said first and second detection method is done in dependence on one or more of the following: a) received information concerning the physical activity and/or the physiological state of a patient in whom the device is implanted, b) the energy of the delivered pacing pulses, c) the noise level in the evoked response detection signal.

13. The method of claim 12, wherein said information concerning the physical activity and/or the physiological state is provided by sensing or detecting one or more of the following entities: blood pressure, heart rate, temperature of the patient, acceleration of the body of the patient, position or posture of the body of the patient, the impedance between at least two points in the body of the patient, one or more chemical substances in the body of the patient, the morphology of the evoked response detection signal, the variation over several heart cycles of the evoked response detection signal.

14. The method of claim 13, wherein said entity or entities are sensed or detected with the help of at least one sensor.

15. The method of any one of the claims 11-14, wherein the automatic switching between at least said first and second detection method is based on at least some other information than just the evoked response detection signal.

16. The method of any one of the claims 10-15, wherein said first detection method involves the use of one or more of the following detection calculations/measurements : a) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, b) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, c) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, d ) the morphology of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, e) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, f) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, g) the maximum or minimum of apeak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, h) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing an electrical signal emitted by the cardiac tissue, i) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, j) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, k) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, 1 ) the morphology of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, m) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, n) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, o) the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the impedance between different points of the body of the patient, p) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing the imped- ance between different points of the body of the patient, q) how steep the evoked response detection signal is, wherein the evoked response detection signal is based on sensing blood pressure, r) an area defined by the evoked response detection signal, with a fixed baseline from which the area is calculated, wherein the evoked response detection signal is based on sensing blood pressure, s) an area defined by the evoked response detection signal, with a baseline that is not fixed from which the area is calculated, wherein the evoked response detection signal is based on sensing blood pressure, t ) the morphology of the evoked response detection signal, wherein the evoked re- sponse detection signal is based on sensing blood pressure, u) the number of zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, v) the time to one or more zero crossings and/or the time between zero crossings in the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, x) the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pressure, y) the time to the maximum or minimum of a peak of the evoked response detection signal, wherein the evoked response detection signal is based on sensing blood pres- sure.

17. The method of claim 16, wherein the second detection method involves the use of either at least one of the points a) to y) of claim 16 that is not used in the first detection method or at least one further detection calculation/measurement that is not used in the first detection method.

18. The method of claim 17, wherein the first detection method involves the use of b) of claim 16 but not c) of claim 16, while the second detection method involves the use of c) of claim 16 but not b) of claim 16.