Leadless cardiac pacemaker device configured to provide intra-cardiac pacing

Abstract

A leadless pacemaker device configured to provide for an intra-cardiac pacing, including: processing circuitry configured to generate ventricular pacing signals for stimulating ventricular activity, and a reception device for receiving a sensing signal indicative of an atrial activity, wherein the processing circuitry is configured to detect an atrial event derived from said sensing signal, wherein the atrial event is a valid atrial sense event, where a series of atrial events lie within a range for a normal atrial rate, and/or when the atrial rate variability is within a certain range indicating a regular atrial rhythm, wherein in case a valid atrial sense event is detected, the processing circuitry is further configured to: determine ventricular pacing events according to atrial events, calculate ventricular-atrial time delays, determine a correction value based a measured time delay and the calculated time delay, and adjust the ventricular pacing timing based on the correction value.

Claims

1. A leadless pacemaker device configured to provide for an intra-cardiac pacing, the leadless pacemaker device comprising: a processing circuitry configured to generate ventricular pacing signals for stimulating ventricular activity, and a reception device for receiving a sensing signal indicative of an atrial activity, wherein the processing circuitry is configured to detect an atrial event derived from said sensing signal, wherein the atrial event is a valid atrial sense event, where a series of atrial events lie within a range for a normal atrial rate, and/or when the atrial rate variability is within a certain range indicating a regular atrial rhythm, wherein in case a valid atrial sense event is detected, the processing circuitry is further configured to: determine a ventricular pacing event according to the atrial event based on a calculated atrial-ventricular (AV) delay, determine a calculated ventricular-atrial delay (VA.sub.calc) indicative of a time delay at which an atrial event (As) is predicted to occur following a prior ventricular event (Vs), measure a true occurrence of a time delay (VA.sub.true) at which an atrial event (As) occurs following a prior ventricular event (Vs) and determine a correction value (CV) based on a timing relation between VA.sub.true and the calculated ventricular-atrial delay (VA.sub.calc), and adjust said ventricular pacing timing based on the correction value (CV).

2. The leadless pacemaker device of claim 1, wherein in case no valid atrial sense event is detected, the processing circuitry is configured to determine a ventricular pacing event based on a calculated ventricular pacing event.

3. The leadless pacemaker device of claim 1, wherein the processing circuitry is configured to determine the calculated ventricular-atrial delay (VA.sub.calc) based on a calculated atrial-ventricular delay (AV) and a current ventricular interval (TV) indicative of a time interval between two successive ventricular pacing signals.

4. The leadless pacemaker device of claim 1, wherein the processing circuitry is configured to determine a multiplicity of time bins (B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2) and to evaluate into which time bin (B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2) VA.sub.true falls for determining the correction value (CV).

5. The leadless pacemaker device of claim 4, wherein each time bin (B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2) is defined by a lower tune limit and an upper limit.

6. The leadless pacemaker device of claim 4, wherein each time bin (B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2) is associated with a specific setting value, wherein the processing circuitry is configured to set the correction value (CV) using the setting value of the time bin (B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2) VA.sub.true falls in.

7. The leadless pacemaker device claim 4, wherein the processing circuitry is configured to increase a ventricular pacing rate, determined by a multitude of ventricular events, if VA.sub.true falls into a time bin (B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2) preceding the end of the calculated ventricular-atrial delay (VA.sub.calc), and to decrease the ventricular pacing rate if the true time of occurrence falls into a time bin (B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2) succeeding the end of the calculated ventricular-atrial delay (VA.sub.calc).

8. The leadless pacemaker device of claim 1, wherein the processing circuitry is configured to determine a VA delay feedback value, wherein the VA delay feedback value is proportional to the difference between the calculated ventricular-atrial delay (VA.sub.calc) and VA.sub.true, wherein the processing circuitry is configured to calculate the correction value (CV) based on the VA delay feedback value.

9. The leadless pacemaker device of claim 7, wherein the processing circuitry is configured to adjust said ventricular pacing rate to synchronize with an atrial sense rate, determined by a multitude of atrial events, according to a predefined first ramping function (R1) when the atrial sense rate is suited for pacing.

10. The leadless pacemaker device of claim 9, wherein the processing circuitry is configured to adjust said ventricular pacing rate to synchronize with a pacing rate defined by a rate responsive pacing algorithm according to a predefined second ramping function (R2) when the atrial sense rate is not suited for pacing.

11. The leadless pacemaker device of claim 1, wherein the processing circuitry is configured to generate a ventricular pacing signal if no intrinsic ventricular sense signal is detected within a predefined time window following a prior ventricular event (Vs).

12. The leadless pacemaker device of claim 1, wherein the reception device comprises at least two electrodes for receiving a sensing signal indicative of atrial activity.

13. The leadless pacemaker device of claim 12, comprising a housing having a tip and a far end, wherein one electrode is arranged in the vicinity of the tip and another electrode is arranged in the vicinity of the far end.

14. A method for operating a leadless pacemaker device configured to provide for an intra-cardiac pacing, comprising: generating, using a processing circuitry, at least one ventricular pacing signals for stimulating ventricular activity, receiving, using a reception device, a sensing signal indicative of an atrial activity, detecting an atrial event (As) derived from said sensing signal, wherein the atrial event is a valid atrial sense event, where a series of atrial sense events lie within a range for a normal atrial rate, and/or when the atrial rate variability is within a certain range indicating a regular atrial rhythm, in case a valid atrial sense event is detected, determine a ventricular pacing event according to the atrial event based on a calculated atrial-ventricular (AV) delay, determine a calculated ventricular-atrial delay (VA.sub.calc) indicative of a time delay at which an atrial event (As) is predicted to occur following a prior ventricular event (Vs), measure a true occurrence of a time delay (VA.sub.true) at which an atrial event (As) occurs following a prior ventricular event (Vs) and determine a correction value (CV) based on a timing relation between true occurrence of a time delay at which an atrial event (As) occurs following a prior ventricular event (Vs) (VA.sub.true) and the calculated ventricular-atrial delay (VA.sub.calc), adjust said ventricular pacing timing based on the correction value (CV).

Description

DESCRIPTION OF THE DRAWINGS

(1) The various features and advantages of the present invention may be more readily understood with reference to the following detailed description and the embodiments shown in the drawings. Herein,

(2) FIG. 1 shows a schematic view of the human heart:

(3) FIG. 2 shows a schematic view of a leadless pacemaker device;

(4) FIG. 3 shows a schematic view of a leadless pacemaker device, indicating signal vectors between different electrodes of the leadless pacemaker device;

(5) FIG. 4A shows a graphical representation of an intra-cardiac electrogram (IEGM);

(6) FIG. 4B shows sequential diagram of atrial senses and ventricular paces;

(7) FIG. 5 shows a portion of the intra-cardiac electrogram, illustrating the adjustment of a ventricular rate according to an atrial sense rate;

(8) FIG. 6 illustrates a schematic of an adjustment mechanism for adjusting the ventricular pacing rate;

(9) FIG. 7 illustrates an adjustment of the ventricular rate when switching between different pacing modes;

(10) FIG. 8A shows an intra-cardiac electrogram, prior to processing;

(11) FIG. 8B shows a processed signal stream derived from the intra-cardiac electrogram to derive atrial events;

(12) FIG. 9 shows a portion of the processed signal to determine characteristic values from that signal for the determination of an atrial event;

(13) FIG. 10 shows the establishment of windows around a calculated ventricular-atrial delay for determining whether a ventricular rate is in synchrony with an atrial sense rate;

(14) FIG. 11 shows a flow diagram for switching between different modes of a pacemaker device;

(15) FIG. 12 shows a flow diagram for switching from a synchronous mode to an asynchronous mode; and

(16) FIG. 13 shows a flow diagram for switching from an asynchronous mode to a synchronous mode.

DETAILED DESCRIPTION

(17) Subsequently, embodiments of the present invention shall be described in detail with reference to the drawings. In the drawings, like reference numerals designate like structural elements.

(18) It is to be noted that the embodiments are not limiting for the present invention, but merely represent illustrative examples.

(19) In the instant invention it is proposed to provide a leadless pacemaker device providing for an intra-cardiac pacing, in particular a ventricular pacing.

(20) FIG. 1 shows, in a schematic drawing, the human heart comprising the right atrium RA, the right ventricle RV, the left atrium LA and the left ventricle LV, the so-called sinoatrial node SAN being located in the wall of the right atrium RA, the sinoatrial node SAN being formed by a group of cells having the ability to spontaneously produce an electrical impulse that travels through the heart's electrical conduction system, thus causing the heart to contract in order to pump blood through the heart. The atrioventricular node AVN serves to coordinate electrical conduction in between the atria and the ventricles and is located at the lower back section of the intra-atrial septum near the opening of the coronary sinus. From the atrioventricular node AVN the so-called HIS bundle H is extending, the HIS bundle H being comprised of heart muscle cells specialized for electrical conduction and thrilling part of the electrical conduction system for transmitting electrical impulses from the atrioventricular node AVN via the so-called right bundle branch RBB around the right ventricle RV and via the left bundle branch LBB around the left ventricle LV.

(21) In case of a block at the atrioventricular node AVN, the intrinsic electrical conduction system of the heart H may be disrupted, causing a potentially insufficient intrinsic stimulation of ventricular activity, i.e., insufficient or irregular contractions of the right and/or left ventricle RV, LV. In such a case, a pacing of ventricular activity by means of a pacemaker device may be indicated, such pacemaker device stimulating ventricular activity by injecting stimulation energy into intra-cardiac tissue, specifically myocardium M.

(22) Within the instant text, it is proposed to use a leadless cardiac pacemaker device 1, as schematically indicated in FIG. 1, for providing for a ventricular pacing action.

(23) Whereas common leadless pacemaker devices are designed to sense a ventricular activity by receiving electrical signals from the ventricle RV, LV they are placed in, it may be desirable to provide for a pacing action which achieves atrioventricular (AV) synchrony by providing a pacing in the ventricle in synchrony with an intrinsic atrial activity. For such pacing mode, also denoted as atrial tracking, it is required to sense atrial activity and identify atrial events relating to atrial contractions in order to base a ventricular pacing on such atrial events.

(24) Referring now to FIGS. 2 and 3, in one embodiment a leadless pacemaker device 1 configured to provide for an intra-cardiac pacing, in particular employing an atrial tracking, comprises a housing 10 enclosing electrical and electronic components for operating the leadless pacemaker device 1. In particular, enclosed within the housing 10 is a processing circuitry 15, comprising for example also a communication interface for communicating with an external device, such as a programmer wand. In addition, electrical and electronic components such as an energy storage in the shape of a battery are confined in the housing 10. The housing 10 provides for an encapsulation of components received therein, the housing 10 having the shape of, e.g., a cylindrical shaft having a length of for example a few centimeters.

(25) The leadless pacemaker device 1 is to be implanted on intra-cardiac tissue M first. For this, the leadless pacemaker device 1 comprises, in the region of the tip 100, a fixation device 14 for example in the shape of nitinol wires to engage with intra-cardiac tissue M for fixedly holding the leadless pacemaker device 1 on the tissue in an implanted state.

(26) The leadless pacemaker device 1 does not comprise leads, but receives signals relating to a cardiac activity, in the illustrated embodiment, by means of an electrode arrangement arranged on the housing 10 and also emits stimulation signals by means of such electrode arrangement. In the embodiment of FIGS. 2 and 3, the leadless pacemaker device 1 comprises different electrodes 11, 12, 13 making up the electrode arrangement and serving to emit pacing signals towards intra-cardiac tissue M for providing a pacing and to sense electrical signals indicative of a cardiac activity, in particular indicative of atrial and ventricular contractions.

(27) A first electrode 11 herein is denoted as pacing electrode. The first electrode 11 is placed at a tip 100 of the housing 10 and is configured to engage with cardiac tissue M.

(28) A second electrode 12 serves as a counter-electrode for the first electrode 11, a signal vector P arising between the first electrode 11 and the second electrode 12 providing for a pacing vector for emitting pacing signals towards the intra-cardiac tissue M.

(29) In addition, the second electrode 12 may serve as a sensing electrode for sensing signals, in particular relating to ventricular contractions, a signal vector V arising between the second electrode 12 and the first electrode 11, the signal vector V being denoted as near-field vector.

(30) The second electrode 12 is placed at a distance from the first electrode 11 and for example has the shape of a ring extending circumferentially about the housing 10. The second electrode 12 is for example placed at a distance of about 1 cm from the tip 100 of the housing 10 at which the first electrode 11 is placed.

(31) The leadless pacemaker device 1, in the embodiment of FIGS. 2 and 3, in addition comprises a third electrode 13 placed at a far end 101 of the housing 10, the third electrode 13 serving as a sensing electrode for sensing signals indicative of cardiac activity in the far-field. In particular, a signal vector A arises between the third electrode 13 and the first electrode 11, the signal vector A picking up signals being indicative for example of atrial contractions and being denoted as far-field vector.

(32) The electrodes 11, 12, 13 are in operative connection with the processing circuitry 15, the processing circuitry 15 being configured to cause the first electrode 11 and the second electrode 12 to emit a pacing signal for providing a stimulation at the ventricle. The processing circuitry 15 furthermore is configured to process signals received via the electrodes 11, 12, 13 to provide for a sensing of cardiac activity, in particular atrial and ventricular contractions.

(33) In order to provide for a pacing in the ventricle in which the leadless pacemaker device 1 is placed, in particular to enable a pacing using an atrial tracking, a sensing of atrial activity is required to provide for detected atrial sense markers in order to time a pacing in the ventricle in atrioventricular (AV) synchrony. For this, a far-field signal from in particular the right atrium RA (see FIG. 1) shall be sensed in order to allow for a synchronous pacing in the right ventricle RV by means of the leadless pacemaker device 1 being implanted on intra-cardiac tissue M in the right ventricle RV.

(34) Generally, when a competent sinus rhythm is available, it is preferable to use such sinus rhythm in order to time a ventricular pacing based on the sinus rhythm. Because the pacemaker device 1 is placed in the ventricle, however, signals allowing for a detection of an atrial sense rate being indicative of intrinsic atrial activity may not always be reliably available because received signals may be low in amplitude. In addition, a pacing in the ventricle based on and in synchrony with atrial signals is potentially not suitable if a detected atrial sense rate is too slow or too fast. If atrial events detected based on a signal received from the atrium are too far apart, this may represent a failure of the intrinsic atrial sinus functionality, a development of atrial fibrillation, or a failure in the detection mechanism. If in contrast atrial events are too close together, this may represent an atrial tachycardia or an intrinsic conduction disturbance associated with atrial extrasystoles, in which case the atrial sense rate may be too fast for the ventricle and an atrial tracking should be avoided in order to prevent an inefficient ventricular pumping or ventricular fatigue.

(35) Hence, a switching between an atrial tracking mode and a mode in which the atrial tracking is disabled may be required. In the atrial tracking mode the pacing in the ventricle takes place based on a detected atrial sense rate. In contrast, if the atrial tracking mode is disabled the ventricular pacing takes place by employing another mechanism, such as a rate response mechanism in which the ventricular pacing rate is governed and varies for example in dependence on a detected physical activity of a patient, which may for example be derived from sensor readings such as accelerometer readings or the like.

(36) In general, if the atrial sense rate is too small or too large (i.e., the atrial sense rate is smaller than a lower threshold or larger than an upper threshold), or if no reliable atrial sense rate can be derived from atrial signal, an atrial tracking mode should be disabled. Instead, if an atrial sense rate can be reliably detected because atrial events are continuously received and allow to determine a stable atrial rate, and if in addition the atrial sense rate is in between the lower threshold and the upper threshold, the atrial tracking mode should be enabled.

(37) If the atrial tracking mode is enabled, the ventricular pacing rate should be adapted to the atrial sense rate. Herein, prior to enabling the atrial tracking mode the ventricular pacing rate has been controlled according to another mechanism and hence may substantially differ from the now available atrial sense rate, such that the enabling of the atrial tracking mode involves a control of the ventricular pacing rate such that it now takes account of the atrial sense rate.

(38) In order to avoid a sudden switching from one ventricular pacing rate to another at the time of enabling the atrial tracking mode, it herein is proposed to progressively adjust the ventricular pacing rate such that it is progressively adapted to resemble and follow the atrial sense rate. The progressive adjustment may take into account programmed attack and decay limits such that a slope of the adaption of the ventricular pacing rate does not exceed predefined limits.

(39) In one embodiment, the adjustment of the ventricular pacing rate towards the now available atrial sense rate may follow the principles of a phase-locked loop, the control mechanism being such that a correction value is determined according to a difference between a phase of the atrial sense rate and the current ventricular pacing rate, the correction value being then used to correct the ventricular pacing rate such that it is adjusted towards the atrial sense rate.

(40) In one embodiment, when switching to the atrial tracking mode, an (ideal) atrioventricular delay AV, as illustrated in FIG. 4A according to an example of an intra-cardiac electrogram IEGM, is determined. The calculation of the atrioventricular delay AV may for example make use of an average of an atrial interval TA between two successive atrial events As, the average for example being taken over multiple cycles. The averaged atrioventricular delay AV may then be used, together with the current interval of the ventricular pacing TV, to calculate a ventricular-atrial delay VA being indicative of a predicted time at which an atrial event As should follow a ventricular pacing or sense event Vs (if the ventricular pacing rate and the atrial sense rate are in synchrony.

(41) FIG. 4B shows schematically a sequence 41 of atrial sensed events As and the sequence 42 of ventricular paced events Vp according to the atrial sensed events. According to an aspect of the invention, the ventricular pacing rate can be changed to match the atrial sense rate. The atrial pacing rate in sequence 41 of FIG. 4B amounts 60 bpm due to atrial-to-atrial intervals of 1000 ms. Via changing the ventricular pacing rate by a small amount in one cardiac cycle and then returning to the previous rate in the next cycle, the phase relationship of the pace interval and the atrial interval can be adjusted. For example, if the atrial rate is 60 bpm as in sequence 41, and the ventricular pacing rate is 60 ppm, the time duration between the atrial sense and the ventricular pace may be, say, 180 ms (43 in FIG. 4B). If it is desired to adjust the AV delay instead to 200 ms, it is possible to generate a longer ventricular-to-ventricular pacing interval for one cycle (44 in FIG. 4B) and then set the ventricular-to-ventricular interval interval back to 1000 ms (cycle 45 in FIG. 4B) in order to achieve a temporal shift the Vp with respect to the As. If the AV delay is measured every cycle and compared to the desired delay, such small corrections can be used to continuously keep the AV delay at the proper value even if the atrial rate drifts up and down. A side effect is that the ventricular rate will track the drift in the atrial rate.

(42) Based on the calculated ventricular-atrial delay VA.sub.calc as indicated in FIG. 5, and based on a measurement of the true time of occurrence of the next atrial event As following a ventricular pacing or sense event Vs, a correction of the ventricular pacing rate may be performed.

(43) In particular, at the time of a ventricular event Vx (which may be a pacing event Vp or which may be an intrinsic ventricular sense event Vs) a timer is started. At the time of the next atrial event As the timer time TT is stored such that the true time of occurrence of the atrial event As following the prior ventricular event Vs is obtained.

(44) The true time of occurrence of the atrial event As may now be compared to the calculated ventricular-atrial delay VA.sub.calc, and from such comparison a correction value may be determined.

(45) In particular, in one embodiment, as illustrated in FIG. 5 a number of time bins B.sub.−3 . . . B.sub.+2 may be defined, the time bins B.sub.−3 . . . B.sub.+2 being distributed around the calculated ventricular-atrial delay VA.sub.calc such that a central time bin B.sub.0 contains the calculated ventricular-atrial delay VA.sub.calc, i.e., the predicted time of occurrence of the atrial event As if the ventricular rate and the atrial sense rate were in synchrony.

(46) Each time bin B.sub.−3 . . . B.sub.+2 herein is bounded by a lower bound L.sub.1 . . . L.sub.6 and an upper bound L.sub.2 . . . L.sub.7, the time bins B.sub.−3 . . . B.sub.+2 having for example identical widths.

(47) Each time bin B.sub.−3 . . . B.sub.+2 is associated with a particular setting value. The central time bin B.sub.0 has a setting value of 0. The time bins B.sub.−3 . . . B.sub.−1 preceding the central time bin B.sub.0 have a positive setting value, whereas the time bins B.sub.−1, B.sub.+2 succeeding the central time bin B.sub.0 have a negative setting value.

(48) Based on the measured true time of occurrence of the atrial event As it is now determined into which time bin B.sub.−3 . . . B.sub.+2 the atrial event As falls. The correction value is then set according to the setting value of the corresponding time bin B.sub.−3 . . . B.sub.+2. If the atrial event As falls into the central time bin B.sub.0, the correction value hence is set to 0. If the atrial event As falls into a time bin B.sub.−3 . . . B.sub.−1 preceding the central time bin B.sub.0, the correction value is set to a positive value according to the specific setting value of the time bin B.sub.−3 . . . B.sub.−1 the true time of occurrence of the atrial event As falls into, wherein the setting values of the time bins B.sub.−3 . . . B.sub.−1 progressively increase the farther away the time bin B.sub.−3 . . . B.sub.−1 is from the central time bin B.sub.0. If the atrial event As falls into a time bin B.sub.+1, B.sub.+2 succeeding the central time bin B.sub.0, the correction value is set to a negative value according to the specific setting value of the time bin B.sub.+1, B.sub.+2 the true time of occurrence of the atrial event As falls into, the magnitude of the setting value of the time bin B.sub.+1, B.sub.+2 a again increasing the farther the time bin B.sub.+1, B.sub.+2 is away from the central time bin B.sub.0.

(49) A positive correction value causes an increase in the ventricular pacing rate such that the ventricular pacing takes place at a faster rate. A negative correction value causes a reduction in the ventricular pacing rate such that the ventricular pacing is slowed down. In the instant embodiment, because the correction value is progressively set based on a difference between the ventricular rate and the atrial sense rate, determined by comparing a true time of occur of occurrence of an atrial event As (following a prior ventricular event Vs) with a predicted time of occurrence (represented by the calculated ventricular-atrial delay VA.sub.calc), the ventricular pacing rate is progressively changed until it has converged to the atrial sense rate, hence avoiding a sudden switching between distinct ventricular pacing rates when switching from one pacing mode to another.

(50) The principle of adjusting the ventricular pacing rate when enabling the atrial tracking mode (and likewise when disabling the atrial tracking mode causing a switch to another pacing mode) may be compared with a phase-locked loop technique, as it is generally illustrated in FIG. 6.

(51) Within such technique, an input 1, namely in the instant case the atrial sense rate, is compared in a comparator 150 to an output rate O, in the instant case the ventricular pacing rate. The comparator 150 in particular determines a difference in the phase between the input rate I, namely the atrial sense rate, and the output rate O, namely the ventricular pacing rate, and provides the difference towards a filtering unit 151 which may provide for a filtering in order to improve stability of the control mechanism. The filtered difference is then forwarded to an adjustment unit 152 which, according to the difference, determines a correction value for correcting the output rate O, namely the ventricular pacing rate, and adjusts the output rate O accordingly. The now corrected output rate O, namely the ventricular pacing rate, is fed back to the input, such that a feedback mechanism is provided for progressively adjusting the output rate O, namely the ventricular pacing rate, according to an input rate I, namely the atrial sense rate.

(52) The adjustment of the ventricular pacing rate hence takes place according to predefined attack and decay limits for a rate of change such that the change in the ventricular pacing rate takes place progressively. This is illustrated in FIG. 7.

(53) Herein, prior to a time T1 the ventricular pacing rate is controlled according to a pacing mechanism other than an atrial tracking. The ventricular pacing rate may, for example, be controlled according to a rate response mechanism in which the ventricular pacing rate is varied according to a physical activity of a patient to assume a rate response rate FR, such that the ventricular pacing rate is reduced in times of inactivity, for example, during sleep, and is increased in times of heavy activity, for example during heavy physical exercise.

(54) Prior to time T1 no atrial sense rate is available or suitable for pacing. At time T1 a suitable atrial sense rate FA becomes available, such that the pacemaker device 1 switches to an atrial tracking mode in which the ventricular pacing rate is controlled according to a detected atrial sense rate FA.

(55) In a first phase, herein, between times T1 and T2 the ventricular pacing rate is ramped up according to a ramping function R1 until it is in synchrony with the atrial sense rate FA at time T2 and from that time on is controlled in synchrony with the atrial sense rate FA. The ramping function R1 is defined by the progressive adjustment of the ventricular rate using an iterative application of suitable correction values as described, for one embodiment, above.

(56) At time T3 a suitable atrial sense rate no longer is available, either because of an undersensing of atrial signals or because the atrial sense rate has become too small or too high. In that case the pacemaker device 1 switches back to another pacing mode, for example to a pacing mode making use of a rate response mechanism. Again, in order to avoid a sudden switching of the ventricular pacing rate, the ventricular pacing rate is progressively adapted by applying a ramping function R2 until it has converged towards the rate response rate FR.

(57) For the switching back to the rate response rate FR a similar mechanism as for the switching to synchronize with the atrial sense rate may be applied.

(58) The ventricular pacing may be continuous such that a pacing signal is generated and injected into cardiac tissue independent of intrinsic ventricular activity. Alternatively, intrinsic signals may be sensed and taken into account in order to avoid a ventricular pacing in case intrinsic ventricular signals are present. For this, at each ventricular event Vs, may it be a ventricular pacing event or a ventricular sense event due to intrinsic ventricular activity, a ventricular pacing rate timer may be started, the timer defining a maximum time until which an intrinsic ventricular event must occur in order to avoid a ventricular pacing signal. If the timer has not timed out when an intrinsic ventricular event Vs is detected, the generation of a ventricular pacing signal is skipped. If the timer does timeout, a ventricular pacing signal is generated and injected.

(59) As illustrated above according to FIGS. 2 and 3, for detecting atrial signals to derive an atrial sense rate, beneficially a far-field vector in between electrodes 11, 13 being farthest away on the housing 10 of the pacemaker device 1 is used. Such large vector is preferred in order to accentuate variations in the electromagnetic field paths from the right atrial tissue to the electrodes 11, 13, allowing for a detection of a differential signal indicative of atrial activity.

(60) The measured signal should be filtered in order to differentiate atrial signals from other signals, in particular ventricular signals, and a blanking mechanism may in addition be employed to blank out signals not related to atrial activity.

(61) This is illustrated, in an example, in FIGS. 8A and 8B, illustrating an intra-cardiac electrogram IEGM measured in the ventricle prior to filtering and blanking (FIG. 8A) and after filtering and blanking (FIG. 8B). In particular, a blanking window T.sub.blank may be employed to blank out such periods of the signals which may relate to activity in the heart other than atrial activity.

(62) The processed and filtered signal is then used to determine atrial events As.

(63) Atrial events As may in particular be determined by employing a processor or state-machine logic. In particular, for determining an atrial event Vs a signal may be analyzed, as illustrated in FIG. 9, for determining a maximum positive peak PP, a maximum negative peak PN, an average value AP of positive signal portions above a baseline B, and an average value AN of negative portions below the baseline B. An atrial event As may then for example be determined according to a crossing of a threshold D, wherein one or multiple thresholds may be employed, for example a positive threshold and a negative threshold, the thresholds being for example calculated according to the characteristics determined from the processed signal.

(64) Generally, if intrinsic ventricular activity is present, beneficially such intrinsic signals should not be interrupted by an artificial pacing, dependent on however whether the intrinsic ventricular activity is in synchrony with atrial activity. If a synchronous intrinsic ventricular activity is present, the pacemaker device I should be operated in an intrinsic conduction mode in which the heart operates naturally making use of its intrinsic conduction mechanism.

(65) In the intrinsic conduction mode the pacemaker device 1 observes ventricular activity in particular with respect to its synchrony with atrial activity. For this, time windows W1, W2 as illustrated in FIG. 10 may be established in order to monitor the time duration between a ventricular event Vs and a following atrial event As.

(66) The windows W1, W2 herein may be established based on a calculated ventricular-atrial delay VA.sub.calc as referred to above (see in particular FIGS. 4 and 5 and the corresponding description), the calculated ventricular-atrial delay VA.sub.calc indicating the time at which an atrial event As should follow a prior ventricular event Vs if the ventricular rate and the atrial rate are in synchrony.

(67) The windows W1, W2 in particular may be centered about the ventricular-atrial delay VA.sub.calc, wherein at each intrinsic ventricular event. Vs a timer is started and a true time of occurrence of an atrial event As (timer time TT) is determined and stored. If the true time of occurrence of the atrial event As falls into the inner window W1, it is assumed that the ventricular rate and the atrial rate are in synchrony, and the pacemaker device remains in the intrinsic conduction mode, hence not providing any artificial pacing.

(68) If the true time of occurrence of the atrial event As, instead, is outside the inner window W1, but still falls within the outer, wider window W2 (also referred to as drift window) it is assumed that atrioventricular synchrony is lost. The processing circuitry 15 of the pacemaker device 1 hence switches into an atrial tracking mode and controls the ventricular rate by generating and injecting, pacing signals. For adjusting the ventricular pacing rate to the atrial sense rate, herein, an algorithm as described above according to FIG. 5 may be employed, hence adjusting the ventricular pacing rate analogously to a phase-locked loop control.

(69) If a predetermined number of consecutive ventricular senses occurs in synchrony with the atrial rate, the control logic may switch back to the intrinsic conduction mode.

(70) If within the windows W1, W2 no atrial events As occur, the control logic of the processing circuitry 15 may switch to a searching mode in which it is searched for atrial events As. Within such searching mode the ventricular rate may be controlled according to another pacing mechanism, such as a rate response mechanism, wherein the ventricular pacing rate may be progressively adjusted to approach the rate as controlled by the rate response mechanism.

(71) A search for atrial events As is initiated when the processing circuitry 15 is in the searching mode. In the searching mode the processing circuitry 15 may analyze an intra-cardiac electrogram reading for potential atrial events and may determine characteristic values such as peak values and average values to evaluate potential candidates for atrial events. Bandpass filters may be employed to cover a frequency range of a supported atrial sensing, wherein frequencies may be sorted into a continuous range of filter bins. A digital data stream which is analyzed by the processing circuitry may feed into such filter bins, wherein threshold detectors may be enabled at the output of each filter (except the filter that covers the rate interval that corresponds with the current ventricular rate). The threshold value employed by the threshold detectors may be a common value that can be controlled by the search algorithm. The threshold value herein may be raised or lowered until just one detector is active during a predetermined number of consecutive ventricular cycles. An interval associated with this detector is then used to reload a ventricular timer at each ventricular event Vs. If this results in stable candidate atrial events within the calculated ventricular-atrial delay VA.sub.calc, it is assumed that an atrial sense rate now again is picked up and the control logic may switch back to the intrinsic conduction mode or to the atrial tracking mode. If in contrast within the calculated ventricular-atrial delay VA.sub.calc no stable candidate atrial event As is detected, the search circuitry may be disabled to save power and pacing continues for example according to a rate response mechanism.

(72) If a search has not been successful in identifying stable atrial events As, a predetermined search delay may be initiated for temporarily pause searching. The control logic, during the search delay, uses an adaptive rate according to the rate response mechanism to reload the ventricular timer, and at the end of the search delay the search circuitry may be enabled again to perform another search. This may repeat indefinitely as long as no stable candidate atrial events As are detected and hence no reliable atrial sense rate is picked up.

(73) Between searches, the control logic may monitor for consistent candidate atrial events As within the ventricular-atrial delay window (window W1 in FIG. 10), and if stable atrial events As are detected, the control logic switches back to the intrinsic conduction mode.

(74) The switching between different modes is illustrated, according to an embodiment, in FIG. 11. If an atrial sense rate is detected and is in synchrony with a ventricular rate of intrinsic ventricular event Vs, the pacemaker device 1 is in the intrinsic conduction mode S1. If synchrony is lost because the ventricular rate and the atrial rate drift out of synchrony, the pacemaker device 1 switches into the tracking mode S2. If either in the intrinsic conduction mode S1 or the tracking mode S2 no stable atrial senses allowing for a detection of an atrial sense rate are available, the device switches into the searching mode S3. If a search is performed, but is not successful in identifying stable atrial events As, the device may switch into a delay mode S4 in which a search is paused and a search circuitry is powered off an order to save energy, until at the end of the search delay the device switches back to the searching mode S3. If again a reliable atrial sense rate in synchrony with a ventricular rate is detected, the device switches back to the intrinsic conduction mode S1 (or, if the atrial sense rate is not in synchrony with the ventricular rate, to the tracking mode S2).

(75) A general schematic of the switching between an atrioventricular synchronous mode, involving an atrial tracking, and an asynchronous mode is illustrated in FIGS. 12 and 13.

(76) In the synchronous mode an atrial tracking is employed, the ventricular pacing rate hence following the intrinsic atrial sense rate. If, in the synchronous mode (state N1 in FIG. 12), atrial features are detected and an atrial sense rate hence is reliably picked up, the device remains in the synchronous mode (state N2). If instead no atrial event As is detected, it may be checked whether an atrial event As cannot be detected for a predetermined number of cycles N.sub.asynch, for example 10 consecutive cycles. If indeed no atrial event As can be detected for such predetermined number of cycles N.sub.asynch (state N3), it is switched to the asynchronous pacing mode (state N4). If atrial events As are again picked up prior to reaching the predefined number of consecutive cycles N.sub.asynch in state N3, the device remains in the synchronous mode (state N5).

(77) If the device is in the asynchronous mode (state M1 as illustrated in FIG. 13), it is checked whether an atrial feature As is detected. If this is the case, it may be checked if atrial events As can be stably detected for a predetermined number of cycles N.sub.sync, for example 10 cycles (state M2). If this is the case, it is switched to the synchronous mode (state M3).

(78) If in state M1 no atrial features are detected, the device remains in the asynchronous pacing mode (state M4). If in state M2 stable atrial events As cannot be detected for the predetermined number of cycles N.sub.synch, the device also remains in the asynchronous pacing mode (state M5).

(79) The predetermined number of cycles N.sub.asynch for switching to the asynchronous mode (state N3 in FIG. 12) and the predetermined number of cycles N.sub.synch for switching from the asynchronous mode to the synchronous mode (state M2 in FIG. 13) may be equal or may differ from each other. The predetermined number of cycles N.sub.asynch, N.sub.synch may be for example 10, but may also be larger or smaller.

(80) Algorithms and procedures to control a pacing rate and to switch from one mode to another are implemented in the processing circuitry 15 of the pacemaker device 1 for example by software run on one or multiple suitable processors.

(81) It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teaching. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.

LIST OF REFERENCE NUMERALS

(82) 1 Leadless pacemaker device

(83) 10 Housing

(84) 100 Tip

(85) 101 Far end

(86) 11 First electrode (pacing electrode)

(87) 12 Second electrode (pacing ring)

(88) 13 Third electrode

(89) 14 Fixation device

(90) 15 Processing circuitry

(91) 150 Comparator

(92) 151 Filtering unit

(93) 152 Adjustment unit

(94) A Atrial vector

(95) AN Negative average

(96) AP Positive average

(97) As Atrial event

(98) AV Atrial-ventricular delay

(99) AVN Atrioventricular node

(100) Baseline

(101) B.sub.0, B.sub.−1, B.sub.−2, B.sub.−3, B.sub.+1, B.sub.+2 Time bin

(102) CV Correction value

(103) D Threshold value

(104) FA Atrial rate

(105) FR Rate response rate

(106) FV Ventricular rate

(107) H HIS bundle

(108) L1-L7 Limit

(109) LA Left atrium

(110) LBB Left bundle branch

(111) LV Left ventricle

(112) M Intra-cardiac tissue (myocardium)

(113) P Pacing vector

(114) PN Negative peak value

(115) PP Positive peak value

(116) R1, R2 Ramping function

(117) RA Right atrium

(118) RBB Right bundle branch

(119) RV Right ventricle

(120) S1-S4 Modes

(121) T1-T4 Time

(122) TA Atrial interval

(123) TV Ventricular interval

(124) T.sub.blank Blanking window

(125) TT Timer time

(126) SAN Sinoatrial node

(127) V Ventricular vector

(128) VA Ventricular-atrial delay

(129) VA.sub.calc Calculated ventricular-atrial delay

(130) Vs Ventricular event

(131) W1, W2 Window