METHOD AND SYSTEM FOR COMMUNICATION BETWEEN A PLURALITY OF IMPLANTABLE MEDICAL DEVICES

A method of communication in a system comprising plurality of implantable medical devices, where a first device comprises a means for detection of a signal representative of atrial activity, a transmitter, and a controller, and a second device independent of the first device, the second device comprising a receiver and a controller. The method comprises synchronizing the first device with the second device, determining the duration of a cardiac cycle, determining a synchronization interval, the duration of the synchronization interval determined as a function of the duration of the cardiac cycle, the synchronization interval being shorter than the duration of the cardiac cycle, and the start of the synchronization interval is determined as a function of the synchronization signal, and activating the receiver of the second device during the synchronization interval, wherein the receiver of the second device is deactivated outside of the synchronization interval.

BACKGROUND

The present invention relates to a method and a system for communication between a plurality of implantable medical devices.

Cardiac contractions ensure blood circulation. These contractions are produced by an electrical impulse called a stimulus. In a healthy heart, the stimulus originates in the sinus node located in the wall of the right atrium. From the sinus node, the stimulus travels first to the atria, which contract to force blood out of the atria into the resting ventricles and fill them.

In turn, after a delay called atrioventricular delay, the ventricles are excited by the stimulus and contract. This atrioventricular delay is essential for optimal function of the heart.

In patients with cardiac disorders, the origin of the stimulus and/or its pathway through the heart may be disrupted due to dysfunctions in the stimulus conduction system. This causes alterations in the heart rhythm, known as arrhythmias.

When the rhythm of the heart is too weak to meet the oxygenation needs of the body, it is called bradyarrhythmia.

In order to treat bradyarrhythmia, when drugs are not sufficient, it is known to resort to artificial pacing of the heart making use of implantable devices such as pacemakers. In particular, it is known to use a pacing system called double chamber pacemaker, which consists of a device that is implanted subcutaneously and which is connected to two leads that are used to deliver an artificial stimulus. The leads are implanted intravenously to join the right atrium and the right ventricle. When the leads are connected to the same implantable medical device such as a traditional pacemaker, synchronization between the leads can be achieved directly by the electronic circuitry of the implantable medical device. The use of intravenous leads does, however, present risks. Lead fracture is one of the most common causes of pacemaker malfunction. Removal of an implanted intravenous lead (or of a pacemaker) is a procedure with serious morbidity and high mortality, and is therefore, usually only carried out in cases of severe systemic infection that cannot be treated with antibiotics. In the majority of cases, fractured leads will be disconnected from the device and left in the heart. A new lead is then implanted next to the old one and connected to the automatic implantable defibrillator. However, this solution is only possible if there is still enough space in the vein, inasmuch as the presence of further leads can lead to a vein occlusion. As a consequence, the use of intracardiac leads is not ideally suited for young patients, who may require multiple leads over the course of their lives.

One solution to the problems associated with intracardiac leads, listed above, is to replace them with subcutaneous leads and/or autonomous pacemakers.

One of the main advantages of autonomous pacemakers is the absence of a housing and the reduction of foreign materials such as leads, which absence reduces the risk of infections.

However, autonomous pacemakers, can only be used for single chamber therapies, which limits the number of patients that are treatable.

SUMMARY

The present invention relates, in particular, to a pacemaker system comprising at least one autonomous leadless cardiac pacemaker. A leadless cardiac pacemaker consists of an energy source such as a battery unit, sensors, a current generator and a telemetry module. In particular, it is conceived to be implanted on the inside of the right ventricle and may be used as an alternative to implantable single chamber pacemakers.

To increase the percentage of the population that can benefit from an autonomous pacemaker, one solution is to have a system of a plurality of implantable medical devices, where a wireless communication between the devices is required in order to send and receive physiological information such as the detection of PQRST complex waves. This information is, in particular, required in order to provide synchronized therapy. Thus, a synchronization signal representing the detection of a PQRST complex wave may be sent by a device implanted in one chamber to synchronize the therapy of another device implanted in another chamber.

However, wireless methods of communication for implantable medical devices, such as radio frequency, intra-body communication (IBC) and inductive coupling, are energy hogs and reduce battery life.

The problem is all the more critical for the device that is configured to receive the synchronization signal inasmuch as it requires that the receiving means of the device remain activated while awaiting a signal to be received, further reducing the capacity of the battery.

Therefore, it is a task of the present invention to improve the wireless communication of such implantable device systems in order to reduce their power consumption and thereby extend their life.

The task of the present invention is achieved by a method of communication in a system comprising a plurality of implantable medical devices, wherein a first device comprises at least one means for detection of a signal that is representative of atrial activity, a transmitter means, and a controller configured to analyze a signal representative of the atrial activity, and a second device, that is independent of the first implantable medical device, comprising at least one receiving means and a controller. The method comprises: A) a step for time synchronization of the first device with the second device, by sending a synchronization signal from the transmitter means of the first device to the second device, the synchronization signal being sent following the identification, by means of the controller of the first device, of a predefined electrical wave of the PQRS complex of a signal representative of the atrial activity, B) a step for determination of the duration of a cardiac cycle. Steps A and B being followed by: C) a step for determination of a synchronization interval, the duration of which synchronization interval is determined as a function of the duration of the cardiac cycle so as to be shorter than the duration of the cardiac cycle, and the start of which synchronization interval is determined as a function of the synchronization signal, D) a step for activation of the receiving means of the second device during the synchronization interval, wherein the receiving means of the second device is deactivated outside of the synchronization interval by the controller of the second device.

The method of communication is improved because the receiving means of the second device is not continuously activated, but rather only for a time interval shorter than the duration of a cardiac cycle.

The partial activation of the receiving means of the second device during each cardiac cycle is sufficient for the purpose of synchronization of the system, inasmuch as the synchronization interval takes into consideration the time marker which is related to the detection of one of the electrical waves of the PQRS complex. The detection of one of the electrical waves of the PQRS complex permits the identification of a cardiac event. The synchronization interval is therefore determined according to physiological information that is useful for the synchronization of the system and related to the cardiac rhythm of the patient. The synchronization interval is therefore advantageously adjusted according to the physiological characteristics of the patient.

The present method thus makes it possible to reduce the time period during which the receiving means of the second device must be activated to allow wireless communication to take place. As a consequence, it is made possible to save on the power requirements of the second device and thus extend its lifetime.

The present invention, related to a method of communication, can be further improved thanks to the following embodiments.

According to one embodiment, for one cardiac cycle, a first time marker marking the sending of the synchronization signal by the transmitter means of the first device may be determined, and a second time marker marking the receipt of the synchronization signal by the receiving means of the second device may be determined, and the synchronization interval of the first device for a subsequent cardiac cycle may be determined as a function of the first time marker, the synchronization interval of the second device for a subsequent cardiac cycle may be determined as a function of the second time marker.

Thus, the synchronization interval of the second device is a function of the second time marker which is itself related to a physiological characteristic of the patient, such as the P wave, wherein the P wave is one of the electrical waves of the PQRST complex.

According to one embodiment, during the synchronization interval of the second device, the receiving means of the second device may be activated during a plurality of predefined activation time slots and may be deactivated during a plurality of predefined deactivation time slots, the plurality of predefined activation time slots of the second device being distributed over the synchronization interval of the second device so as to be synchronized with signal pulse slots of the first device as a function of the first time marker and the second time marker.

Thus, the power consumption of the receiving means of the second device can be further advantageously reduced because the receiving means is not activated over the entire synchronization interval but only on a slot by slot basis. This does not in any way interfere with the receipt of a synchronization signal since the activation slots are advantageously adjusted in relation to the first time marker, which marks the sending of the synchronization signal by the first device.

According to one embodiment, the transmitter means of the first device may be configured to send a single synchronization signal per cardiac cycle.

Thus, the method of communication does not require that a series of pulses is transmitted by the first device. In effect, the present method allows the single synchronization signal sent by the first device to “fall” within an activation time slot of the receiving means of the second device due to the synchronization of the first and second time markers.

According to one embodiment, each of the predefined activation time slots may be of the same duration and each of the predefined deactivation time slots may be of the same duration and each of the predefined activation and deactivation time slots may alternatingly succeed each other in the synchronization interval.

The succession of the activation and deactivation time slots is thus periodic, further promoting the likelihood that a synchronization signal will be received during the synchronization interval.

According to one embodiment, the duration of an activation time slot may be shorter than or equal to the duration of a deactivation time slot.

Thus, the power consumption of the receiving means of the second device may be further reduced.

According to one embodiment, the duration of an activation time slot may represent between 0.3 and 50% of the duration of a deactivation time slot, in particular 5 to 10%.

Thus, the power consumption of the receiving means of the second device may be reduced as much as possible.

According to one embodiment, the duration of a pulse during which the transmitter means of the first device can be configured to transmit a synchronization signal corresponds to 25 to 80% of the duration of an activation time slot, in particular 50%.

Thus, the activation time slots that correspond to the time slots during which the receiving means of the second device is activated to “listen” and detect a synchronization signal are longer than the duration of transmission of a synchronization signal. Thus, there is a greater chance that receipt of the synchronization signal will occur during an activation time slot of the second device.

According to one embodiment, the first time marker may mark the start or end of the sending of the synchronization signal or a predetermined time during the sending of the synchronization signal.

The adjustment of the synchronization interval for the second device with that of the first device can thus be improved, as the “timing” of the first time marker is defined with more precision.

According to one embodiment, in step A), the predefined electrical wave detected by means of the controller of the first device may correspond to the P wave of the PQRS complex.

The detection of the P wave is particularly suitable since it marks the depolarization during the contraction of the atria and thus constitutes physiologically relevant information for the atrioventricular delay and synchronization.

According to one embodiment, in step A), the predefined electrical wave may be detected by means of the controller of the first device by the analysis of an electrogram, an electrocardiogram, of data measured by an accelerometer, of data measured by cardiographic impedance or of data measured by an acoustic sensor.

The method can thus advantageously be implemented with different detection means.

According to one embodiment, over at least two successive cardiac cycles, the first device and the second device can communicate with each other in an asynchronous manner during steps A and B and the receiving means of the second device is activated in a continuous manner during the at least two successive cardiac cycles.

Thus, the first device and the second device are configured to each independently determine a time marker in order to determine and adjust the synchronization interval.

According to one embodiment, the controller of the second device may be configured to deactivate the receiving means of the second device during the remaining time of the synchronization interval of the second device after receipt of the synchronization signal.

Thus, the power consumption of the receiving means of the second device may be reduced as much as possible.

According to one embodiment, the controller of the second device may be configured to send an alert signal through a transmitter means of the second device to a receiving means of the first device when a synchronization signal is not received by the second device during the synchronization interval of the second device.

Thus, the first device is alerted that the second device, configured to be implanted in the right ventricle, has not received the information relating to the detection of the predefined electrical wave. The first device having sent the synchronization signal (which has not been received by the second device), the first device is able to see that the signal has been lost during its journey. Local pacing of the right atrium may then be necessary.

The task of the present invention is also achieved by a system of a plurality of implantable medical devices. The system comprises a first device comprising at least one detection means, a transmitter means, and a controller configured to analyze a signal representative of the atrial activity. The system comprises a second device, independent of the first implantable medical device, comprising at least one receiving means and a controller. The receiving means of the second device is configured to be activated and deactivated by the controller of the second device. The controller of the first device and the controller of the second device are configured to implement the method according to the embodiments described above.

Thus, the multi-implantable device system is improved since the receiving means of the second device is not continuously activated, but rather only during a synchronization interval that is shorter than the duration of one cardiac cycle.

The partial activation of the receiving means of the second device during each cardiac cycle is sufficient for the purposes of synchronization of the system, inasmuch as the synchronization interval takes into consideration the time marker that is related to the detection of one of the electrical waves of the PQRS complex. The detection of one of the electrical waves of the PQRS complex enables the identification of a cardiac event. The synchronization interval is therefore determined as a function of physiological information that is useful for the synchronization of the system and related to the cardiac rhythm of the patient. The synchronization interval is therefore advantageously adjusted according to physiological characteristics of the patient.

According to one embodiment, the first implantable medical device may be an implantable subcutaneous medical device, an event loop recorder or a leadless pacemaker, and the second medical device may be a leadless pacemaker.

The system is thus suitable for dual-chamber synchronization therapy. In particular, the system is suitable for dual-chamber synchronization therapy with an implantable leadless pacemaker in the right atrium and an implantable leadless pacemaker in the right ventricle.

DETAILED DESCRIPTION

The invention will now be described in more detail using advantageous embodiments by way of example and with reference to the figures. The embodiments described are simply possible configurations and it should be kept in mind that the individual characteristics as described above may be provided independently of each other or may be omitted altogether when implementing the present invention.

The present invention relates to a method of communication for a system of a plurality of implantable medical devices, as well as to such a system.

Embodiments of such a system of a plurality of implantable medical devices are first described with reference toFIGS.1,3and4.

The method of communication according to the present invention that can be implemented by a system of a plurality of implantable medical devices is then described with reference toFIGS.5through10.

FIG.1represents a multi-device system10according to a first embodiment of the present invention comprising two implantable devices20,21.

The multi-device system10represented inFIG.1comprises a subcutaneous implantable device20and a leadless autonomous pacemaker21implanted in the right ventricle RV.

The subcutaneous implantable device20represented inFIG.1comprises a housing22and a subcutaneous lead24provided with three electrodes26,28,30and a defibrillation electrode32. Although not visible inFIG.1, the housing22comprises a transmitter means, such as a radio frequency (RF) transmitter device or uses an intra-body communication connection, and a controller. The housing22may also comprise a receiving means.

In one variant, an event recorder or an implantable loop recorder comprising at least a pair of electrodes may be used in the stead of the subcutaneous implantable device20.

The subcutaneous implantable device20is configured to detect the atrial activity using any one of the methods known in the state of the art, by way of example, by an electrocardiogram (ECG), by impedance cardiography, by an acoustic sensor, and/or by an accelerometer.

In the first embodiment of the invention, the subcutaneous implantable device20is configured to analyze data representative of an ECG. The analysis of the data representative of an ECG makes it possible to detect at least one of the five P, Q, R, S, T waves of the PQRST complex which are electrophysiological characteristics. An example of a PQRST complex is shown inFIG.2. The subcutaneous implantable device20is, in particular, configured to identify a time marker corresponding to the detection of an electrical wave of the PQRST complex. The detection of the P wave is preferred inasmuch as it marks the depolarization of the atria and thus constitutes physiologically relevant information for the atrioventricular delay and synchronization.

Detection of the P wave can, for example, be determined by identifying a local maximum.

The leadless autonomous pacemaker21comprises a tip electrode23arranged at a distal end25of the device21, and a ring electrode27arranged toward a proximal end29of the device21. The electrodes23,27may form a receiver dipole or a transmitter dipole. It should be noted that the present invention is not limited to the use of a tip electrode and a ring-type electrode but may be implemented using any type of electrode comprised in a leadless autonomous pacemaker.

The tip electrode23may be a detection electrode or a pacing electrode. In one variant, the electrode23is both a detection electrode and a pacing electrode.

Although not visible inFIG.1, the body31of the leadless autonomous pacemaker21may encapsulate a battery unit, a controller, and a receiving means, such as an RF receiving device or use an intra-body communication connection. The body31may also comprise a transmitter means.

The receiving means of the leadless autonomous pacemaker21is configured to communicate wirelessly with the transmitter means of the subcutaneous implantable device20, in particular by means of an intra-body communication connection.

The subcutaneous implantable device21may be configured to detect cardiac activity making use of any one of the methods known in the state of the art, for example, by an electrocardiogram (ECG), an electrogram (EGM), by impedance cardiography, by an acoustic sensor, and/or by an accelerometer.

In one variant, the wireless communication between the devices20,21could likewise also be achieved making use of other wireless methods of communication such as intra-body communication or inductive coupling.

In the system10, the leadless autonomous pacemaker21is thus configured to receive a signal sent from the subcutaneous implantable device20. In particular, this may be a synchronization signal containing timing information related to an atrial depolarization. Such a synchronization signal may enable synchronization of the contractions of the ventricle. The synchronization signal may be used to deliver pacing to the right ventricle based on the physiological heart activity of the patient that is detected by the subcutaneous implantable device20.

FIG.3illustrates a multi-device system40according to a second embodiment of the present invention comprising two implantable devices21,41.

The elements with the same numerical references already used for the description ofFIG.1will not be described again in detail, and reference is made to their descriptions above.

The implantable device21corresponds to the leadless autonomous pacemaker21already described in reference toFIG.1and to which reference is made.

In the second embodiment, a second leadless autonomous pacemaker41is used in the stead of the subcutaneous implantable medical device20of the first embodiment.

As illustrated inFIG.3, the leadless autonomous pacemaker41is configured to be implanted in the right atrium (RA).

The autonomous leadless pacemaker41is configured to detect atrial activity using any of the methods known in the state of the art, for example, by an electrocardiogram (ECG), by an electrogram (EGM), by impedance cardiography, by an acoustic sensor, and/or by an accelerometer.

The leadless autonomous pacemaker41is configured to analyze data that are representative of an ECG. The analysis of data that are representative of an ECG makes detection possible of at least one of the five P, Q, R, S, T waves of the PQRST complex as known in the prior art. An example of a PQRST complex is illustrated inFIG.2. The leadless autonomous pacemaker41is, in particular configured to identify a time marker corresponding to the detection of an electrical wave of the PQRST complex.

In a similar manner to the leadless autonomous pacemaker21, the leadless autonomous pacemaker41comprises a tip electrode43arranged at a distal end45of the pacemaker41, and a ring electrode47arranged toward a proximal end49of the pacemaker41. The electrodes43,47may form a receiver dipole or a transmitter dipole. It should be noted that the present invention is not limited to the use of a tip electrode and a ring-type electrode but may be implemented using any type of electrode comprised in a leadless autonomous pacemaker.

The tip electrode43may be a detection electrode or a pacing electrode. In one variant, the electrode43is both a detection electrode and a pacing electrode.

Although not visible inFIG.3, the body51of the leadless autonomous pacemaker41may encapsulate a battery unit, a processor, a controller, and a transmitter means, such as an RF transmitter device. The body51may also include a receiving means.

The transmitter means of the leadless standalone pacemaker41is configured to communicate wirelessly with the receiving means of the leadless standalone pacemaker21, in particular by means of an intra-body communication connection.

In one variant, the wireless communication between the devices21,41could also occur by means of other wireless methods of communications such as intra-body communication or inductive coupling.

In one embodiment that is not shown, a system according to the present invention comprises a subcutaneous implantable device20and two leadless pacemakers21,41.

FIG.4illustrates a multi-device system60according to a third embodiment of the present invention comprising three implantable devices21,41,61.

Elements with the same numerical references already used for the description ofFIGS.1and3will not be described again in detail, and reference is made to their descriptions above.

When compared to the second embodiment, the multi-device system60of the third embodiment comprises a third implantable medical device61. The multi-device system60is of the so-called triple-chamber resynchronization system type, also referred to as “CRT-P” for “Cardiac Resynchronization Therapy-Pacemaker.”

The implantable devices21,41correspond respectively to the leadless autonomous pacemakers21,41already described in reference toFIGS.1and3and to which reference is made.

The third device61is a leadless autonomous pacemaker61implanted in an epicardial manner on the myocardial wall.

In each of the embodiments of the present invention described in reference toFIGS.1,3and4, the implantable devices20,21,41,61may contain both receiving means and transmitter means, particularly suitable for RF communication. Thus, each of the implantable devices20,21,41,61is configured both to send a signal and to receive a signal in order to enable wireless communication in each of the systems10,40,60.

Moreover, each of the implantable devices20,21and41are capable of determining the duration of a cardiac cycle.

The wireless method of communication according to the present invention relates to the synchronization of at least two implantable devices such as20,21,41,61comprised in a system such as systems10,40or60. The wireless method of communication according to the present invention is hereinafter described. The systems10,40,60are each configured to implement said method of communication. In particular, the method of communication is hereinafter described for a system comprising a first device and a second device.

FIG.5schematically illustrates the operation of the method of communication according to a first embodiment of the present invention.

FIG.5shows three time axes102,104,106. The unit of the axes102,104,106is expressed in milliseconds (ms).

An ECG is represented on the time axis102. The ECG illustrated on the time axis102comprises a plurality of PQRST complex for each of the cardiac cycles depicted. The duration of a complete cardiac cycle can be determined as the time between two successive identical waves. InFIG.5, the duration of the cardiac cycle is represented by the interval PP, illustrated between the two local maximums representing the P wave of the cardiac cycle. Four successive cardiac cycles, n=1 to n=4, are annotated inFIG.5.

The interval PP is representative of the duration of a complete cardiac cycle, and typically lasts approximately one second or more.

A first device is configured to analyze the ECG102and to determine a characteristic of the ECG in order to identify a wave of the PQRS complex, in particular the P wave. The characteristic may be, for example, the local maximum assigned to the P wave. The first device may also be configured to record the ECG102.

The first device is configured to determine the duration of a cardiac cycle. This first device may be the subcutaneous implantable device20, a recorder, or the leadless autonomous pacemaker41configured to be implanted in the right atrium (RA). The first device inFIG.5comprises at least one transmitter means, for example, by means of an intra-body communication connection.

Detections of the P wave for each PP cycle (see “detection P1” to “detection P4”) identified by the first device are represented on the time axis104.

The time axis106refers to a second device of a multi-device system, as described with reference toFIGS.1,3and4. This second device may be the leadless autonomous pacemaker21configured to be implanted in the right ventricle (RV). The second device may be configured to determine the duration of a cardiac cycle. The second device may thus be capable of delivering ventricular pacing.

The second device ofFIG.5is independent of the first implantable medical device and comprises at least one receiving means.

The method of the present invention is a method of wireless communication between said first device and said second device constituting a multi-device system in order to allow synchronization of the devices with each other. Said method is hereinafter described.

Firstly, let us consider the first cardiac cycle n=1 illustrated inFIG.5, during which the first and second devices are not yet synchronized.

As explained above, the first device is configured to analyze the ECG and detect a P wave. During the first cardiac cycle n=1, a P wave is detected by the first device and is annotated “detection P1” on the time axis104.

Following the detection and identification of the P1wave, the transmitter means of the first device is configured to send a synchronization signal to the second device. The time marker Prefi n=1on the time axis104corresponds to the time marker that marks the sending of the synchronization signal for the first cardiac cycle illustrated inFIG.5.

This synchronization signal is received by the receiving means of the second device and is indicated by the time marker Prep n=1on the time axis106.

Then, during the next cardiac cycle n=2, a P wave is once again detected and identified by the first device and is annotated “detection P2” on the time axis104.

Following the detection and identification of the P2wave, the transmitter means of the first device is configured to send a synchronization signal to the second device. The Pref1 n=2time marker on the time axis104corresponds to the time marker that marks the sending of the synchronization signal for the second cardiac cycle n=2 illustrated inFIG.5.

This synchronization signal is received by the receiving means of the second device and is indicated by the time marker Pref2 n=2on the time axis106.

According to the present invention, the duration of the first cardiac cycle n=1 is determined between Pref1 n=1and Pref1 n=2(see “Pref1 n=1Pref1 n=2interval” inFIG.5). This allows to refer to a reference that is common to the first and second devices.

In one variant, the duration between “detection P1” and “detection P2” may allow determination of the duration of the first cardiac cycle n=1 (see “interval P1P2” inFIG.5).

Then, during the next cardiac cycle n=3, a P wave is once again detected and identified by the first device and is annotated “detection P3” on the time axis104.

Following the detection and identification of the P3wave, the transmitter means of the first device is configured to send a synchronization signal to the second device. The time marker Pref1 n=3on the time axis104corresponds to the time marker that marks the sending of the synchronization signal for the third cardiac cycle illustrated inFIG.5.

This synchronization signal is received by the receiving means of the second device and is indicated by the time marker Pref2 n=3on the time axis106.

According to the present invention, and by analogy with the first cycle, the duration of the second cardiac cycle n=2 is determined between Pref1 n=2and Pref1 n=3.

In one variant, the duration between “detection P2” and “detection P3” allows for the determination of the duration of the second cardiac cycle n+2.

A synchronization interval108for the second device may be determined for the third cardiac cycle n=3 starting from the time marker Pref2 n=2and the duration of the second cardiac cycle. This synchronization interval108corresponds to a listening window, which is to say, the receiving means of the second device is activated over the synchronization interval108for the purpose of receiving a synchronization signal transmitted by the first device. A signal or message may thus be received by the receiving means of the second device during the synchronization interval108.

The duration of the synchronization interval108is determined in such a manner to be shorter than the duration of the second cardiac cycle. The synchronization interval108may be less than 0.8 s in duration, in particular, less than 0.4 seconds.

The start of the synchronization interval108, indicated by the reference Dref2 n=3is determined as a function of the time marker Pref2 n=2of the preceding cardiac cycle n+2.

Since the synchronization interval108is a function of the time marker Pref2 n=2of the previous cardiac cycle n+2, this allows the synchronization interval108to be arranged over the third cycle such that the receipt of the synchronization signal occurs during said synchronization interval108.

The receipt of the synchronization signal is indicated by the time marker Pref2 n=3.

The determination of the start Dref2 n=3and the duration of the synchronization interval108over the third cardiac cycle notably takes into consideration, the maximum acceleration between beats, which generally does not exceed 10 to 40%, in particular 25 to 35% of the duration of a cardiac cycle.

Moreover, the determination of the synchronization interval108also takes into account the time it takes the myocardium to respond to atrial activity. This is a parameter that can be programmed by a physician to improve the physiological response of the heart. This parameter may correspond to 0-50%, in particular 0-30%, of the duration of a cardiac cycle.

According to the present invention, the receiving means of the second device is activated during the synchronization interval108and is deactivated outside the synchronization interval108by the controller of the second device.

Thus, the receiving means of the second device is not continuously activated for the duration of a complete cardiac cycle, which allows to reduce the power consumption of the second device. Indeed, as long as the receiving means of the second device is activated, it consumes power.

By activating the receiving means during the synchronization interval108rather than over the duration of a complete cardiac cycle, the power consumption required for wireless communication for the purpose of resynchronization can be reduced since the duration of powering up of the receiving means is limited to the duration of the synchronization interval108.

This is not, however, a matter of turning off all functionalities of the second device all at once, which second device implements other functions such as detection, timing or pacing in parallel with the functionality of the receiving means.

A synchronization interval110for the first device may likewise be determined starting from the time marker Prefi n=2and the duration of the second cardiac cycle. The start of the synchronization interval110for the third cardiac cycle n+3 is indicated by the time marker Drefi n=3. The start of the synchronization interval110Drefi n=3is thus determined, in particular, as a function of the time marker Prefi n=2.

The synchronization interval110for the first device corresponds to a sending window, which is to say, an interval during which the synchronization signal is likely to be sent, according to the identification of a P wave. For the third cardiac cycle n+3, the sending of the synchronization signal is indicated by the time marker Prefi n=3.

The determination of the synchronization intervals108,110for the fourth and subsequent cardiac cycles n+4 (which are not shown inFIG.5) is carried out in the same manner as explained above for the third cardiac cycle.

An advantage of the present method is that the communication intervals108,110are adjusted over time as a function of a cardiac event (the detection of a P wave) and are thus tailored to the physiological characteristics of a patient.

In an alternative that is not shown, the synchronization interval110may be arranged over the third cycle n+3 as a function of the time marker Prefi n=2and the duration of the second cardiac cycle in such a manner that the detection of the P wave is not comprised in the synchronization interval110. In this case, the synchronization interval110is shifted to the right of the time axis104relative to the first embodiment. In this alternative, the synchronization interval108is thus also shifted to the right of the time axis104relative to the first embodiment. This alternative is particularly suitable for sending a synchronization message containing a data set.

Let us note that the first device may send a synchronization “signal” or “message.” In the present description, a synchronization “signal” refers to a signal comprising information encoded on a single bit whereas a synchronization “message” refers to a signal comprising information encoded on multiple bits.

The difference between a synchronization “signal” and a synchronization “message” is thus related to the way the timing information of the P wave detection is encoded.

In a synchronization message, the timing of the P wave detection is encoded and thus allows more detailed information to be sent to the second device.

In a synchronization signal, the timing information of the P wave detection is implicit in the timing of the sending of said signal. Thus, a signal comprising information coded on a single bit can be sent.

The time markers Pref1and Pref2for each cycle n serve as time references to synchronize the synchronization intervals108,110with each other. In particular, the time markers Pref1and Pref2are used, in particular, to ensure that the synchronization intervals108,110overlap or even align.

Thus, the time marker Prep is used to adjust the activation of the receiving means of the second device.

FIG.6schematically illustrates the operation of the method of communication according to a second embodiment of the present invention.

In a similar manner toFIG.5,FIG.6represents three time axes202,204,206. The unit of the axes202,204,206is expressed in milliseconds (ms).

An ECG is shown on the time axis202. The ECG comprises a PQRST complex. The duration of a complete cardiac cycle can be determined as the duration between two successive identical waves.

A synchronization interval210of a first device of a multi-device system, as described with reference toFIGS.1,3and4, is shown on the time axis204.

A synchronization interval208of a second device of a multi-device system, as described with reference toFIGS.1,3and4, is shown on the time axis206. This second device may be the leadless autonomous pacemaker21configured to be implanted in the right ventricle (RV). The second device may thus be capable of delivering ventricular pacing.

The second device ofFIG.6is independent of the first implantable medical device and comprises at least one receiving means.

For a cardiac cycle n, the synchronization interval208of the second device is determined in the same manner as described for the synchronization interval108of the second device at the third cycle of the first embodiment (seeFIG.5). In other words, the start Dref2 nof the synchronization interval208of the second device illustrated inFIG.6is a function of the second time marker Pref2 n−1of the previous cardiac cycle n−1 (which is not represented inFIG.6).

Likewise, for a cardiac cycle n, the synchronization interval210of the first device is determined in the same manner as described for the synchronization interval110of the first device at the third cycle of the first embodiment (seeFIG.5). In other words, the start Dref1 nof the synchronization interval210of the first device illustrated inFIG.6is a function of the first time marker Pref1 n−1of the previous cardiac cycle n−1 (which is not shown inFIG.6).

During the synchronization interval208, the transmitter means of the first device may transmit pulses of duration Tbitspaced apart by rest periods Toffas depicted on the time axis204ofFIG.6. During the rest periods Toff, the transmitter means does not send pulses. The durations Tbitcan be equal to 500 microseconds (μs) and “Toff” can be equal to 9.5 milliseconds (ms).

Immediately upon detection of a P wave, indicated by “detection P” inFIG.6, the transmitter means of the first device uses the first available slot defined by Tbitto transmit a synchronization signal. Thus, notwithstanding thatFIG.6represents a plurality of Tbitslots, only one slot is used by the transmitter means to send the synchronization signal.

In other words, when the first device detects a P wave, the transmitter of the first device is configured to send a synchronization signal to the first block Tbitthat follows the detection of the P wave, which is indicated by the block Tbit PinFIG.6. The sending of the synchronization signal is marked by the time marker Pref1 n. The time marker Pref1 nmay indicate the start of the sending of the signal or the end of the sending of the signal.

To further reduce power consumption of the second device, in the second communication mode, the receiving means of the second device is activated and then deactivated by the controller at intervals during the synchronization interval208.

The synchronization interval208of the second device thus comprises a plurality of activation time slots “mon” and a plurality of deactivation time slots “Moff”. In other words, the synchronization interval208comprises a succession of blocks “m”, each of which comprises a slot mon and a slot moff, as illustrated inFIG.6on the time axis206.

During an activation time slot “mon”, the receiving means is activated, it is configured to receive a signal, in particular the synchronization signal transmitted by the first device.

During a deactivation time slot “Moff”, the receiving means is deactivated, which is to say it is switched off and does not consume any energy.

In the example ofFIG.6, each activation time slot “mon” is of the same duration.

In the example ofFIG.6, each deactivation time slot “moff” is of the same duration.

The duration of each slot mon may be of equal duration or shorter than the duration of each slot moff.

The synchronization intervals208,210of the cardiac cycle n are synchronized with each other on the basis of the time markers Pref2 n−1and Pref1 n−1of the previous cardiac cycle n−1, as explained with reference toFIG.5.

Moreover, the plurality of predefined activation time slots mon of the second device are synchronized to the plurality of time slots Tbitof the first device on the basis of the second time marker Pref2 n−1and the first time marker Pref1 n−1of the previous cardiac cycle n−1.

As illustrated inFIG.6, the synchronization signal is received by the receiver of the second device during the activation slot indicated by “MonP”. The receipt of the signal is marked by the time marker Prep n.

The duration of an activation time slot mon can represent between 0.3 and 50% of the duration of one deactivation time slot moff. The duration of an activation time slot mon depends on the quality of the receiver and the time it needs to detect the synchronization signal. In particular, the duration of an activation time slot mon can represent 5 to 10% of the duration of a deactivation time slot moff.

When considering a synchronization interval 208 of about 350 ms and a ratio mon=10% of m (m=mon+moff), it turns out that the improvement of the activation cycle of the receiving means of the second device for synchronization purposes can reduce power consumption by 0.1 to 3.5%. For example, a block m may be equal to a duration of 10 ms, with the block m comprising a slot mon of 1 ms and a slot moffof 9 ms.

In an advantageous variant, the receiving means of the second device is deactivated for the remainder of the given cardiac cycle, once the time marker Pref2 nhas been determined, in order to conserve further power. In the example ofFIG.6, this would translate in the deactivation of the receiving means starting out from block mon Puntil the end of the cardiac cycle n.

FIG.7illustrates initialization steps of the method implemented by the first device, by means of a flowchart300. These initialization steps are implemented in an asynchronous manner with respect to the second device. The method steps of the flowchart300apply to the embodiments described with reference toFIGS.5and6.

As illustrated by the flowchart ofFIG.7, the initialization302includes the detection of a time marker of a cardiac cycle in step304. This time marker corresponds to the detection of a predefined electrical wave of the PQRST complex. As previously explained, the first device is indeed configured to analyze data that are representative of an ECG.

Preferably, the time marker corresponds to the detection of the P wave which is the first detectable wave of the PQRST complex. The P wave appears when the stimulus (or impulse) propagates to the atrial myocardium, depolarizing the atria.

In the following, reference is thus made to the detection of the P wave, which has been chosen as the predefined electrical wave in the embodiment ofFIG.7, as indicated in step304of the flowchart300. It should be kept in mind that the choice of the P wave is however not limiting, and that another wave of the PQRST complex may be considered, in particular the R-wave.

If a P wave is detected in step304, a synchronization signal is transmitted in step306to the second device.

The synchronization signal thus represents the timing of the detection of the P wave. The synchronization signal for each cardiac cycle enables indication that a depolarization of the atria, in particular of the right atrium, has been detected.

In a step308, which follows step306, a time vector characterizing the timing at which the synchronization signal was transmitted in step306is saved. The time vector can be saved in a “first in—first out” (FIFO) memory. In other words, a time marker marking the sending of the synchronization signal is determined in step308.

Then, in a step310, the time vector is incremented in a counter in such a manner that when a plurality “n” of time markers for n cardiac cycles—and thus as many time vectors—have been incremented in a step312, they can be compared with each other to define a so-called Prefi reference time marker based on the n time markers.

Thus, in a step314, the determination of a reference time marker Prefi marking the sending of a synchronization signal is carried out by taking into consideration the timing of the detection of the P wave for a number n of cardiac cycles (for example, by calculating an average over n cardiac cycles), in particular n being greater than or equal to three, provided that the n cardiac cycles are considered regular cardiac cycles. Cardiac cycles are considered regular when the maximum cycle-to-cycle acceleration does not exceed 25%. For example, with an average cardiac cycle (which can be defined by an interval PP) of 1 s, an interval PP of duration greater than or equal to 750 ms is considered stable.

If no P wave is detected in step304, it is verified in step316that the duration of the cardiac cycle has not yet expired. The duration of a cardiac cycle can be determined, for example, by the duration between two successive time markers marking the sending of the signal or two successive P waves. Note that in the initialization phase, a predetermined “initialization” interval PP can be used.

According to the present invention, the duration of a cardiac cycle may also be determined by means of the first device and/or the second device via a detection means, which allows, for example, to obtain the plot of an ECG.

If the duration of the cardiac cycle is not considered to have expired in step316, then the first device continues to analyze the ECG in step304.

On the contrary, if the cardiac cycle time is considered to have expired in step316, the time vector is reset in step318and thus returns to the first initialization step302.

Following the initialization steps of the method, a reference time marker Prefi that is indicative of the timing of the sending of a synchronization signal following the detection of a P wave is thus determined in step314of the flowchart300.

This reference time marker Prefi is, for example, represented inFIGS.5and6.

FIG.8illustrates the continuation of the flowchart300ofFIG.7, which is to say, of the operational steps of the method that follow step314, in which step a reference time marker Prefi is determined. Thus, the steps of the method described by means ofFIG.8apply to the embodiments described with reference toFIGS.5and6.

During the operational steps of the method, a synchronization interval for the first device is used. Such a synchronization interval110,210has already been described in relationship withFIGS.5and6, to which reference is made.

If a P wave for the next cardiac cycle n+1 is detected in step320, then a corresponding synchronization signal is sent in a step322to the second device. The synchronization signal carries physiological information relating to the detection of the PQRST complex and enables the delivery of a synchronized therapy.

In a step324, which follows the transmission of the synchronization signal of step322, a time vector characterizing the time at which the synchronization signal was transmitted in step322is saved. The time vector can be saved in a FIFO-type memory.

It is then verified in a step326whether the synchronization interval110,210for the cardiac cycle n+1 has expired. If this is not the case, the first device continues to be activated and waits for the detection of a P wave for the cardiac cycle n+1 in order to send a synchronization signal.

If a P wave is detected in step320, a synchronization signal is transmitted in step322. Then, if it is confirmed in step326that the duration of the synchronization interval110,210has expired, then the first device is configured to activate a receiving means of the first device in step328.

Step328is further described below with reference toFIG.8a.

As illustrated inFIG.8a, the transmitter means of the first device is configured to be activated during a synchronization interval110,210. The first device may moreover comprise a receiving means configured to be activated during an interval329that is shorter than the synchronization interval110,210. The receiving means of the first device may be activated with a predetermined offset Δd, starting from the end110a,210aof the synchronization interval110,210, as illustrated on the time axis104,204ofFIG.8a.

During the interval329, the receiving means of the first device is activated to detect a possible alert signal transmitted by the second device. The transmission of an alert signal by the second device is further described below with reference toFIGS.9and10.

If, in step330, the receiving means of the first device receives an alert signal, it is determined in step332whether to reset the method and transmit a control signal in order to require delivery of pacing to the right atrium (step334) or only reset the method without requiring delivery of pacing (step336).

In the event that no alert signal is detected during the interval329in step338, the first device continues to operate in a near-synchronized manner using the synchronization interval110,210for the wireless communication with the second device.

The flowchart300illustrated inFIGS.7and8thus represents an algorithm implemented by the first device of the multi-device system.

The multi-device system according to the present invention comprises at least one second device, configured to be implanted in the right ventricle, and in which an algorithm is also implemented. The second device is independent of the first device. However, the second device implements an algorithm that is complementary to that of the first device. The algorithm implemented by the second device is hereinafter described by means of a flowchart400, illustrated inFIGS.9and10.

FIGS.9and10represent a flowchart400of the method implemented by the second device.

The flowchart400ofFIG.9represents initialization steps of the method implemented by the second device. These initialization steps are implemented in an asynchronous manner with respect to the first device. The steps of the method of the flowchart400can apply to the embodiments described with reference toFIGS.5and6.

During these initialization steps implemented by the second device, the receiving means of the second device is continuously activated since the timing of the receipt of a synchronization signal is not yet estimated.

To begin, as illustrated by the flowchart ofFIG.9, the initialization402includes activation of the receiving means of the second device in step404.

It is analyzed in step406whether a synchronization signal is received by the receiving means of the second device.

If a synchronization signal is indeed received, then, in step408, a time vector characterizing the timing at which the synchronization signal was received in step406is saved. The time vector may be saved in a FIFO-type memory.

Then, in step410, the time vector is incremented in a counter in such a manner that when a plurality n of time vectors for n cardiac cycles—and thus as many as synchronization signals received—have been incremented in step412, they can be compared with each other in order to define a so-called reference time marker Prep for the second device.

Thus, in a step414, the determination of a reference time marker Pref2is carried out by taking into consideration the timing of the receipt of the synchronization signal for a number n of cardiac cycles, wherein, in particular, n is greater than or equal to three, provided that the n cardiac cycles are considered regular cardiac cycles. Cardiac cycles are considered regular when the maximum cycle-to-cycle acceleration does not exceed 25%. For example, with an average cardiac cycle (which can be defined by an interval PP) of 1 s, an interval PP of duration greater than or equal to 750 ms is considered stable. The reference time marker Prep can, in particular, be determined by carrying out an average of the timings of the receipt of the synchronization signal for a number n of cardiac cycles.

If no synchronization signal is received in step406, it is verified in a step418that the duration of the cardiac cycle that is considered has not yet expired. The duration of a cardiac cycle may, for example, be determined by the duration between two successive P waves.

Thus, the second device may be configured to estimate the duration of a cardiac cycle by means of timing information contained in two successively received synchronization signals.

In one variant, the second device may comprise a detection means, which may, for example, permit one to obtain an ECG plotting and from the plotting derive a cardiac cycle duration. If the duration of the cardiac cycle is not considered to have expired in step418, then the second device continues to wait for receipt of a synchronization signal in step406.

On the contrary, if the cardiac cycle time is considered to have expired in step418, the time vector is reset in step420and thus returns to step406.

Following the initialization steps of the method, a reference time marker Pref2, that is indicative of the timing of the receipt of a synchronization signal and related to the detection of a P wave in the atria, is thus determined in step414of the flowchart400.

Such a reference time marker Prep is, for example, represented on the time axis106,206ofFIGS.5and6.

FIG.10illustrates the continuation of the flowchart400ofFIG.9, which is to say, of the operational steps of the method that follow step414in which the reference time marker Prep is determined. According to the second embodiment, during the operational steps of the method, in particular from step422onwards described below, the receiving means of the second device is no longer activated continuously but rather by intervals during the synchronization interval208. Reference is made to the description ofFIG.6for the activation of the receiving means in intervals during blocks mon of the synchronization interval208.

As illustrated byFIG.10, in a step422which follows step414, the second device updates and adjusts the synchronization interval208relative to the value of the reference time marker Pref2determined in step414. The synchronization interval208of a cardiac cycle n is adjusted as a function of the value of the reference time marker Prep determined at the previous cardiac cycle n−1 or as a function of the average of the values of the reference time marker Prep determined from a plurality of previous cardiac cycles.

In a step424, the receiving means is activated over the synchronization interval208during a plurality of activation time slots mon, as illustrated inFIG.6.

It is analyzed in step424whether a synchronization signal transmitted by the first device, is received by the receiving means of the second device.

If a synchronization signal is indeed received, then, in step426, a time vector characterizing the timing at which the synchronization signal was received is saved. The time vector can be saved in a memory of the first in—first out (FIFO) type.

The time vector is used in step414to update the timing of the receipt of the synchronization signal, which is to say, the reference time marker Prep that will be used for the next cardiac cycle. The reference time marker Pref2is thus updated beat-by-beat since it is calculated on the basis of the reference time markers Prep of the previous beats, for example on the basis of the two previous cardiac cycles n−2 and n−1 that preceded the cardiac cycle n under consideration.

If no synchronization signal is received in step424, it is verified in a step428that the duration of the synchronization interval208has not yet expired.

If the duration of the synchronization interval208has not yet expired in step428, then the second device continues to wait for receipt of a synchronization signal in step424.

On the contrary, if the duration of the synchronization interval208has expired in step428without a signalization signal being received, the second device is configured to send an alert signal in step430. To do so, the second device further comprises a transmitter means.

Note that the second device does not know the cause of the failure to receive a signaling signal. It may be a communication failure, or rather that a P wave was not detected by the first device. In either case, the second device sends an alert signal in step430.

Step430is further described hereinafter with reference toFIG.10a.

In step430, the second device is configured to activate a transmitter means. As shown inFIG.10a, the transmitter means of the second device is configured to be activated during an interval431that is shorter than the synchronization interval208.

The alert signal may be sent with a predetermined offset Add after the end208bof the synchronization interval208as represented on the time axis206ofFIG.10a.

Thus, during the interval431, the transmitter means of the second device is activated to send an alert signal to the first device. The activation interval431of the transmitter means of the second device is shorter than the activation interval329of the receiving means of the first device.

The activation interval431of the transmitter means of the second device can be used for two purposes: both to inform the first device of the failure of the communication (due to the lack of receipt of a synchronization signal) - the first device knowing that its transmitter means has indeed sent a synchronization signal, or to require an artificial and local pacing of the right atrium.

The method of communication of the present invention allows synchronization of the therapy delivered by the multi-device system and enables the saving of a considerable amount of energy.

However, patients fitted with such a multi-device system may suffer from episodes in which atrial activity becomes rapid and irregular, known as supraventricular tachyarrhythmia. In this case, the therapy delivered to the ventricle must be independent of the atrial activity.

Moreover, a patient suffering from atrial arrhythmia needs to temporarily uncouple the dual-chamber (or triple-chamber) therapy in order to desynchronize the ventricle (or ventricles) from the atrium.

FIG.11illustrates an alternative variant of the first and second embodiments advantageously adapted to the case of the aforementioned cardiac rhythm disorders.

FIG.11is based on diagram100ofFIG.5, to which a so-called start interval260,262that precedes the synchronization intervals208,210for each of the first device and the second device is added on each of the time axes104,106.

During the start-up interval260, the transmitter means of the first device is configured to send a start authorization signal to the receiving means of the second device.

Thus, during the start-up interval262, the receiving means of the second device is configured to receive the start-up authorization signal transmitted by the second device.

The start-up intervals260,262allow or disallow communication between the first device and the second device.

It is likewise possible that the first device waits for a receipt acknowledgement signal that is sent by a transmitter means of the second device in order to ensure that the information was correctly received by the second device.

This prevents that energy is unnecessarily dissipated to activate the receiving means of the second device, by way of example, during cardiac arrhythmia episodes.

The start-up intervals260,262may also more simply provide a “switch” function, so that they can be switched from a single-chamber mode of operation (which is to say, a mode where the devices are not synchronized) to a dual-chamber mode of operation (which requires the devices to be synchronized).

The wireless method of communication and the multi-device system configured to implement said method of the present invention allow to adjust and adapt communication windows—which correspond to the synchronization intervals—to the electrophysiological rhythm of the patient. Indeed, each device of the system is capable of determining a time marker associated with the detection of P waves (or any other wave of the PRQST complex) and of rearranging the communication window as a function of the time marker that is thus determined for each cardiac cycle.