1. Field of the Invention
The present invention generally relates to the field of implantable heart stimulation devices, such as pacemakers, and similar cardiac stimulation devices that also are capable of monitoring and detecting electrical activities and events within the heart. More specifically, the present invention relates to an implantable medical device and a method for monitoring ventricular synchronicity of a heart.
2. Description of the Prior Art
Implantable heart stimulators that provide stimulation pulses to selected locations in the heart, e.g. selected chambers have been developed for the treatment of cardiac diseases and dysfunctions. Heart stimulators have also been developed that affect the manner and degree to which the heart chambers contract during a cardiac cycle in order to promote the efficient pumping of blood.
Furthermore, the heart will pump more effectively when a coordinated contraction of both atria and ventricles can be provided. In a healthy heart, the coordinated contraction is provided through conduction pathways in both the atria and the ventricles that enable a very rapid conduction of electrical signals to contractile tissue throughout the myocardium to effectuate the atrial and ventricular contractions. If these conduction pathways do not function properly, a slight or severe delay in the propagation of electrical pulses may arise, causing asynchronous contraction of the ventricles which would greatly diminish the pumping efficiency of the heart. Patients, who exhibit pathology of these conduction pathways, such as patients with bundle branch blocks, etc., can thus suffer from compromised pumping performance. For example, asynchronous movements of the valve planes of the right and left side of the heart, e.g. an asynchronous opening and/or closure of the aortic and pulmonary valves, is such an asynchrony that affects the pumping performance in a negative way. This may be caused by right bundle branch block (RBBB), left bundle branch block (LBBB), or A-V block. In a well functioning heart, the left and right side of the heart contract more or less simultaneously starting with the contraction of the atria flushing down the blood through the valves separating the atria from the ventricles, in the right side of the heart through the tricuspid valve and in the left side of the heart through the mitral valve. Shortly after the atrial contraction the ventricles contract, which results in an increasing blood pressure inside the ventricles that first closes the one way valves to the atria and after that forces the outflow valves to open. In the right side of the heart it is the pulmonary valves that separate the right ventricle from the pulmonary artery that leads the blood to the lung, which is opened. In the left side of the heart the aortic valve separates the left ventricle from the aorta that transports blood to the whole body. The outflow valves, the pulmonary valve and aortic valve, open when the pressure inside the ventricle exceeds the pressure in the pulmonary artery and aorta, respectively. The ventricles are separated by the intra-ventricular elastic septum. Hence, for a well functioning heart a substantially synchronous operation of the left and right hand side of the heart, e.g. a synchronous opening and/or closure of the aortic and pulmonary, is of a high importance.
When functioning properly, the heart maintains its own intrinsic rhythm. However, patients suffering from cardiac arrhythmias, i.e. irregular cardiac rhythms, and/or from poor spatial coordination of heart contractions often need assistance in form of a cardiac function management system to improve the rhythm and/or spatial coordination of the heart contractions. Such systems are often implanted in the patient and deliver therapy to the heart, such as electrical stimulation pulses that evoke or coordinate heart chamber contractions. Thus, implantable heart stimulators that provide stimulation pulses to selected locations in the heart, e.g. selected chambers, have been developed for the treatment of cardiac diseases and dysfunctions. Heart stimulators have also been developed that affect the manner and degree to which the heart chambers contract during a cardiac cycle in order to promote the efficient pumping of blood.
In particular, various prior art procedures have been developed for addressing disorders related to asynchronous function of the heart. For instance, cardiac resynchronization therapy (CRT) can be used for effectuating synchronous atrial and/or ventricular contractions. Furthermore, cardiac stimulators may be provided that deliver stimulation pulses at several locations in the heart simultaneously, such as biventricular stimulators. For example, patients with heart failure symptoms and dyssynchronized cardiac chambers are often offered such a CRT device that synchronizes the right and left ventricle to obtain an improved cardiac functional performance and quality of life. The CRT settings should be optimized in terms of VV interval and AV interval for optimized pumping performance. In the majority of CRT patients this optimizing of CRT parameters is normally performed at implant and perhaps at one regular follow-up. Ideally, this optimization should be performed more frequently to match the actual need of the patient.
Information about the mechanical functioning of a heart can be obtained by means electrical signals produced by the heart. In a healthy heart the sinus node, situated in the right atrium, generates electrical signals which propagates throughout the heart and control its mechanical movement. Some medical conditions, however, affect the relationship between the electrical and mechanical activity of the heart and, therefore, measurements of the electrical activity only cannot be relied upon as indicative of the true status of the heart or as suitable for triggering stimulation of the heart.
Consequently, there is a need within the art of methods and devices for obtaining accurate and reliable signals reflecting different aspects of mechanical functioning of the heart.
Impedance measurements, e.g. of the intra-cardiac impedance, has been shown to provide reliable information regarding the mechanical functioning of the heart. For example, through the impedance measurements, blood volume changes are detectable. Blood has a higher conductivity (lower impedance) than myocardial tissue and lungs. The relationship between impedance-volume is inverse, i.e. the more blood—the smaller impedance.
In US 2007/0066905, a system for optimizing a cardiac synchronization based on measure impedance signals is shown. In one embodiment of the system, the left ventricular impedance is measured, which reflects the contraction and expansion of the left ventricle. The obtained impedance signals are used to compute the impedance-indicated peak-to-peak volume indication of the left ventricle and/or an impedance-indicated maximum rate of change in the left ventricular volume. These parameters are then used to control a cardiac resynchronization. In US 2006/0271119 a similar optimization system is described.
Furthermore, in U.S. Pat. No. 7,330,759 a cardiac pacemaker for bi-ventricular stimulation where impedance signals is used to obtain a synchronization of the left and right ventricles is shown. In particular, the second derivative of the intra-cardiac impedance pattern of a cardiac cycle is determined and maximized. This is based on the assumption that the intra-cardiac impedance pattern respectively reflects the volume of blood in a heart, the maximum acceleration to which the blood is subjected to in the heart is to be gauged from the maximum of the second derivative of that intra-cardiac impedance pattern, which value is correlated to contractility of the left ventricle.
However, the parameters used for the optimization in the prior art is often dependent on the physiological system including, inter alia, the heart and the vascular system which, for example, may entail that a response to a change of the stimulation parameters in terms of a change of a monitored parameter will be able to detect with a delay. This may, for example, lead to an overcompensation of the stimulation parameters. Furthermore, it cannot be ascertained that the monitored parameters reflect only the hemodynamical performance of the heart, which, in turn, may lead to a stimulation parameter setting that in the long-term is not optimal with respect to the hemodynamic performance of the heart.
In order to be able to optimize the functioning of the heart it is of paramount interest to obtain information that may provide a complete picture of the mechanical functioning and the pumping action of the heart and that provides accurate and reliable information of the mechanical functioning and the pumping action of the heart.
Moreover, in order to be able to optimize the functioning of the heart it is also of paramount interest to obtain information that may enable a fast and reliable optimization of the hemodynamic performance of the heart and, in particular, a fast and reliable synchronization of the ventricles, i.e. a coordinated contraction of the ventricles.
In addition, in order to be able to optimize the functioning of the heart it is further of high interest to obtain information that enables, in the long-term, an optimal synchronization of the ventricles, i.e. a coordinated contraction of the ventricles, with respect to the hemodynamic performance of the heart.
An object of the present invention is to present an improved device and method for obtaining information that reflects the mechanical functioning and the pumping action of the heart, and, in particular, that reflects the synchronicity of the ventricle contractions in an accurate and reliable manner.
Another object of the present invention is to provide a device and method that are capable of monitoring a ventricular synchronicity of the heart in an accurate and reliable way.
According to a first aspect of the present invention, there is provided an implantable medical device for monitoring ventricular synchrony of a heart including a pace pulse generator adapted to produce cardiac stimulating pacing pulses and being connectable to at least one medical lead for delivering stimulation pulses to cardiac tissue of the heart. The medical device includes an impedance measuring unit adapted to, during impedance measuring sessions, measure impedance signals obtained by an electrode configuration being located such that the impedance signals substantially reflects septal wall movements, wherein the electrodes of the electrode configuration are connectable to the device and are located at a right side of the heart, an impedance peak detecting unit adapted to process the impedance signals to determine an impedance signal morphology and to detect impedance amplitude peaks in the impedance signal morphology; and a synchronicity index determining unit adapted to determine a synchronicity index indicating a degree of synchronicity based on detected impedance peaks, wherein at least two impedance peaks detected within a predetermined time window including a cardiac cycle or a part of a cardiac cycle indicates an increased dyssynchronicity in the ventricular contractions.
According to a second aspect of the present invention, there is provided a method for monitoring ventricular synchrony of a heart in an implantable medical device comprising a pace pulse generator adapted to produce cardiac stimulating pacing pulses and being connectable to at least one medical lead for delivering stimulation pulses to cardiac tissue of the heart. The method includes, during impedance measuring sessions, measuring impedance signals obtained by an electrode configuration being located such that the impedance signals substantially reflects septal wall movements, wherein the electrodes of the electrode configuration are connectable to the implantable medical device and are located at a right side of the heart, processing the impedance signals to determine an impedance signal morphology and to detect impedance amplitude peaks in the impedance signal morphology; and determining a synchronicity index indicating a degree of synchronicity based on detected impedance peaks, wherein at least two impedance peaks detected within a predetermined time window including a cardiac cycle or a part of a cardiac cycle indicates an increased dyssynchronicity in the ventricular contractions.
The present invention is based on the insight that certain characteristics of the morphology of the measured cardiogenic impedance reflect the septal movements or the mechanical movements of the septal wall. These characteristics may, in turn, be used to monitor ventricular dyssynchronicity. That is, certain features of the waveform morphology of the cardiogenic impedance reflect the mechanical movements of the septal wall, which movements are indicative of the synchronicity or dyssynchronicity of the ventricles of the heart. Asynchronous or dyssynchronous depolarization of the ventricles results in asynchronous myocardial contractions with regional dyskinetic cardiac tissue. The cardiac performance is very sensitive to small asynchronous cardiac movements, as the overall heart cycle is disturbed. One consequence is that not only the systolic part of the heart cycle will be less effective; the diastolic part (the filling part) will also be greatly tampered. In particular, the present invention is based on the insight that the cardiogenic impedance reaches a maximum value in connection with the end of the systolic phase of the ventricles and that a synchronized contraction of the ventricles is manifested in the impedance morphology by one pronounced impedance peak. An asynchrony in the functioning of the ventricles will, on the other hand, be reflected as a division of the impedance peak into (at least) two impedance peaks, which can be detected so as to monitor or identify the asynchrony of the contractions of the ventricles. These findings form the basis of the present invention and are utilized to construe a synchronicity measure which indicates a degree of synchronicity (or dyssynchronicity) between the right and left ventricle.
This approach for monitoring a synchronicity of the ventricles has a number of advantages. For example, since the information, i.e. the cardiogenic impedance morphology, used in the monitoring reflects the mechanical functioning and the pumping action of the heart, and, in particular, reflects the synchronicity of the ventricle contractions in an accurate and reliable manner, a device and method that are capable of monitoring a ventricular synchronicity of the heart in an accurate and reliable way can be achieved.
According to an embodiment of the present invention, points of maximum and/or minimum the impedance signal morphology are detected in the predetermined time window, which time window corresponding to a systolic and/or diastolic phase of a cardiac cycle.
In an embodiment of the present invention, a first derivative of the impedance signal is calculated and points of local minima and/or local maxima of the first derivative are determined to be impedance peaks.
The implantable medical device according to preceding claims, further comprising a VV delay determining unit adapted to initiate an optimization procedure, wherein the pace pulse generator is controlled to, based on the synchronicity index, iteratively adjust a VV-interval so as to minimize the synchronicity index in the predetermined time window to obtain substantially synchronized ventricle contractions. Using information of the impedance peaks as basis for the determination of the synchronicity index also enables, in the long-term, an optimal synchronization of the ventricles, i.e. a coordinated contraction of the ventricles, with respect to the hemodynamic performance of the heart. Thus, the advantage of a fast and reliable optimization of the hemodynamic performance of the heart and, in particular, a fast and reliable synchronization of the ventricles, i.e. a coordinated contraction of the ventricles, can be achieved.
According to an embodiment of the present invention, the synchronicity is index based on a peak distance between two detected peaks in the differentiated impedance signal within the time window, for example, in systole and/or diastole. An increased peak distance corresponds to an increased value of the synchronicity index. For example, a synchronicity index for systole or diastole may be based on the difference between a local maximum point and a local minimum point. The higher difference between the respective peaks the higher synchronicity index. A higher synchronicity index indicates a higher degree of dyssynchronicity. During an optimization procedure, the VV-interval that minimizes the synchronicity index is identified in an iterative procedure. Dependent on patient condition, the synchronization may be optimized during diastole, during systole or for both systole and diastole. For example, one synchronicity index may be determined for systole and one index for diastole and the optimization may be performed on basis of a weighted total index based on the two indices associated with different weights, i.e. the weighted total index is minimized. Alternatively, the indices may be optimized separately to obtain a minimized index in systole and in diastole, respectively.
According to an embodiment of the present invention, the synchronicity index may be based on the number of detected peaks in differentiated impedance signal within the predetermined time window, for example, systole and/diastole, wherein an increased number of peaks corresponds to an increased value of the synchronicity index.
In an embodiment of the present invention, the synchronicity index may be based on a total peak area of one or several detected peaks of the differentiated impedance signal within the predetermined time window for example, systole and/or diastole measured above a predetermined threshold, wherein an increased peak area corresponds to an increased value of the synchronicity index. In a further alternative, the synchronicity index may be the total area of the peaks in both systole and diastole, or a weighted value of all peaks where different peaks may be associated with different weights.
According to an embodiment of the present invention, the synchronicity index may be based on a variability of the amplitude of detected peaks in systole and/or diastole, wherein increased amplitude variability corresponds to an increased value of the synchronicity index.
In an embodiment, the synchronicity index may be based on variability of the difference between peaks, for example, in systole and/or diastole, wherein increased variability corresponds to an increased value of the synchronicity index.
Moreover, in a further embodiment of the present invention, the synchronicity index is based on an absolute value of total peak amplitude of one or more of the detected peaks within the predetermined time window, for example, in systole and/or diastole, wherein increased total peak amplitude corresponds to an increased value of the synchronicity index. In a further alternative, the synchronicity index may be the total area of the peaks in both systole and diastole, or a weighted value of all peaks where different peaks may be associated with different weights.
According to an embodiment of the present invention, a breath rate sensor is adapted to sense a breathing cycle of the patient, wherein the synchronicity index can be determined in synchronism with an event of a breathing cycle or respiration cycle of the patient or as an average value over a predetermined number of breathing cycles. Thereby, the accuracy of the synchronicity index can be significantly improved. This is due to the fact that the cardiogenic impedance is greatly affected by the respiration. Therefore, by synchronizing the determination of the synchronicity index with a particular event in the respiration cycle or by determining the index as an average value over a number of respiration cycles, the influence of the respiration on the impedance causing variability in the impedance signal can be eliminated or at least significantly reduced.
In a further embodiment of the present invention, a body posture sensor is adapted to sense a body posture of the patient, wherein the synchronicity index can be determined in synchronism with a predetermined body posture of the patient, or as an average value of the synchronicity index of at least two body postures. Thereby, the accuracy of the synchronicity index can be significantly improved. This is due to the fact that the cardiogenic impedance is greatly affected by the body posture of the patient. Therefore, by synchronizing the determination of the synchronicity index with a particular body posture or by determining the index as an average value over a more than one body posture, the influence of the body posture on the impedance causing variability in the impedance signal can be eliminated or at least significantly reduced.
Further embodiments include an activity sensor adapted to sense an activity level of the patient and a heart rate sensor adapted to sense a heart rate of the patient, respectively, and the synchronicity index may thus be determined in synchronism with a predetermined activity level of the patient or in synchronism with a predetermined heart rate or heart rate interval of the patient.
According to embodiments, one or several of the sensors including a heart rate sensor, a breath rate sensor, an activity sensor, and/or body posture sensor may be combined.
According to an embodiment, a matrix of synchronicity indices can be determined. For example, different indices for different body postures and for different activity levels may be included in the matrix. Further, different synchronicity indices may be determined for different events in the respiration cycle and for systole and diastole. During an optimization, the index corresponding to the present conditions of the patient can be selected and optimized.
In an embodiment of the present invention, IEGM signals of consecutive cardiac cycles are sensed and cardiac events are detected in the cardiac cycles using the IEGM signals. A time window is determined based on the detected cardiac events and the IEGM signals and/or impedance signals. For example, a time window including a systolic phase of the cardiac cycle can be determined to extend between a period starting at a detection of an R-wave and ending at a detection of a T-wave. Further, a time window including a diastolic phase of the cardiac cycle can be determined to extend between a period starting at a detection of a T-wave and ending at a detection of an R-wave.
According to embodiments of the present invention, the impedance signal is measured using an electrode configuration including at least a first pair of electrodes having a ring electrode and a tip electrode arranged in a medical lead located in the right ventricle or a first electrode located adjacent to the septum in the right ventricle and a second electrode located in a coronary vein on the left ventricle or the can, i.e. the housing of the implantable medical device which may function as an electrode.
In an embodiment of the present invention, points of maximum amplitude of the impedance signal morphology are detected, wherein a first detected point at which the impedance reaches a maximum value is determined to be a first impedance peak and a second detected point at which the impedance reaches a maximum value is determined to be a second impedance peak. For example, points of the impedance amplitude where a first derivative of the impedance signal is zero and a second derivative of the impedance signal is below zero are determined to be impedance amplitude peaks.
According to a third aspect of the present invention, there is provided a method for optimizing electrode locations, the electrodes being connectable to an implantable medical device comprising a pace pulse generator adapted to produce cardiac stimulating pacing pulses and being connectable to at least one medical lead for delivering stimulation pulses to cardiac tissue of the heart, in which the ideas of the present invention is utilized. In particular, the method includes:
According to a fourth aspect of the present invention, there is provided a system for optimizing lead and/or electrode locations including an implantable medical device. The implantable device includes a pace pulse generator adapted to produce cardiac stimulating pacing pulses and being connectable to at least one medical lead for delivering stimulation pulses to cardiac tissue of the heart, an impedance measuring unit adapted to, during impedance measuring sessions, measure impedance signals obtained at a first electrode configuration being located such that the impedance signals substantially reflects septal wall movements, wherein the electrodes of the electrode configuration are connectable to the device, an impedance peak detecting unit adapted to process the impedance signals to determine an impedance signal morphology and to detect impedance amplitude peaks in the impedance signal morphology, a synchronicity index determining unit adapted to determine a synchronicity index indicating a degree of synchronicity based on detected impedance peaks for the first electrode configuration, wherein at least two impedance peaks detected within a predetermined time window including a cardiac cycle or a part of a cardiac cycle indicates an increased dyssynchronicity in the ventricular contractions, and a VV delay determining unit adapted to perform an optimization procedure, wherein the pace pulse generator is controlled to, based on the synchronicity index, iteratively adjust a VV-interval so as to minimize the synchronicity index in the predetermined time window. The system further includes an external control unit connectable to the implantable medical device and being adapted to: instruct the implantable medical device to obtain a synchronicity index for at least a second electrode configuration, compare the minimum synchronicity index for each configuration to identify a overall minimum synchronicity index; and select the electrode configuration being associated with the minimum synchronicity index.
Hence, according to the third and fourth aspect of the invention, a test procedure is performed, for example, during an implantation of the implantable medical device according to the present invention so as to identify an optimal lead and/or electrode location with regard to inter alia capture and synchronized contraction of the ventricles. This may be performed by a physician using an external programmer unit connectable, via a cable or wirelessly, with the implantable medical device. During this procedure, for example, the optimal location of left ventricle electrodes can be determined. This can be achieved by starting with determined locations for a right ventricle lead and right ventricle electrodes and successively testing different locations for the left ventricle lead and/or left ventricle electrodes. At each test location, an optimization of a VV interval can be performed to identify the minimum synchronicity index for that particular location. Thereafter, each synchronicity index (i.e. the index for each location) are compared to identify the overall minimum synchronicity index, which thus will correspond to the optimal location of the left ventricle lead and left ventricle electrode (-s). Of course, this procedure can also be performed to identify the optimal location for a right ventricular lead and right ventricular electrode (-s). Location of both left and/or right ventricular leads and electrodes can be optimized using the present invention. For example, a first location of the right ventricle lead and electrodes can be selected and a number of different left ventricle lead and electrode locations can be tested to identify the minimum synchronicity index. Then, a second location of the right ventricle lead and electrodes can be selected and all locations of the left ventricle lead are tested again to identify a minimum synchronicity index for this location. This is repeated for all possible locations of the right ventricle lead and electrodes. Consequently, a matrix of minimum synchronicity indices is obtained, and the overall minimum index can be selected, which will correspond to the optimal locations for left and right ventricular leads and electrodes. However, the method according to this further aspect may also be used within an implanted medical device to optimize an electrode configuration if the leads comprise a number of possible electrode configurations.
As is apparent to those skilled in the art, steps of the methods according to the present invention, as well as preferred embodiments thereof, are suitable to realize as
a schematically shows cardiogenic impedance signal morphologies at the systolic phase during synchronous pacing/intrinsic functioning and asynchronous pacing/intrinsic functioning.
b schematically shows impedance signal morphologies at the diastolic phase during synchronous pacing/intrinsic functioning and asynchronous pacing/intrinsic functioning.
The following is a description of exemplifying embodiments in accordance with the present invention. This description is not to be taken in limiting sense, but is made merely for the purposes of describing the general principles of the invention. Thus, even though particular types of implantable medical devices such as heart stimulators will be described, e.g. biventricular pacemakers, the invention is also applicable to other types of cardiac stimulators such as dual chamber stimulators, implantable cardioverter defibrillators (ICDs), etc.
With reference first to
In order to sense right ventricular and atrial cardiac signals and impedances and to provide stimulation therapy to the right ventricle RV, the implantable medical device 10 is coupled to an implantable right ventricular lead 20, which may have a ventricular tip electrode 22 and a ventricular annular or ring electrode 24. The right ventricular tip electrode 22 is in this embodiment arranged to be implanted in the endocardium of the right ventricle, e.g. near the apex 8 of the heart. Thereby, the tip electrode 22 becomes attached to cardiac wall. In this example, the tip electrode 22 is fixedly mounted in a distal header portion of the lead 20.
Furthermore, in order to sense ventricular cardiac signals and impedances and to provide pacing therapy for the left ventricle LV, the implantable medical device 10 is coupled to a “coronary sinus” lead 30 designed for placement via the coronary sinus in veins located distally thereof, so as to place a distal electrode adjacent to the left ventricle. The coronary sinus lead 30 is designed to receive ventricular cardiac signals from the cardiac stimulator 10 and to deliver left ventricular LV pacing therapy using at least a left ventricular tip electrode 32 to the heart 1. In the illustrated example, the LV lead 30 further comprises an annular ring electrode 34 for sensing electrical activity related to the left ventricle LV of the heart.
With reference to the configuration shown in
Turning now to
As discussed above with reference to
Furthermore, an impedance measuring unit 41 is adapted to carry out impedance measurements of the cardiac impedance of the patient indicative of the septal wall 4 movements, for example, by means of the measurements vectors wherein the current is applied between the ring electrode 24 of the right ventricle and the tip electrode 22 of the right ventricle, and the resulting impedance is measured between the same electrodes. A further alternative is an impedance measurement vector where the current is applied between the ring electrode 24 of the right ventricle lead and the tip electrode 32 of the left ventricle lead. The resulting impedance is measured between the same electrodes. Asynchronous ventricular contractions cause abnormal septal movements during systole as well as during diastole. The measured impedance reflects the mechanical motion of the septal wall 4 and, hence, it is possible to obtain a measure of the ventricular synchrony/asynchrony. This will be discussed in more detail below with reference to
The impedance measuring unit 41 may comprise an amplifier (not shown) that amplifies the evoked voltage response, i.e. the measured voltage, and may be synchronized with the excitation current. Thus, the impedance measuring unit 41 obtains the cardiac impedance given by the delivered current and the evoked voltage response. The impedance measuring unit 41 may also comprise a filtering circuit (not shown), for example, a Gaussian filter.
Furthermore, the heart stimulator 10 comprises an impedance peak detecting unit 46 adapted to determine an impedance signal morphology using measured impedance signals for consecutive cardiac cycles and to detect impedance amplitude peaks in the impedance signal morphology. The impedance peak detecting unit 46 thus identifies at least one characteristic shape feature of the impedance signal morphology being indicative of the occurrence of a synchronous/asynchronous depolarization of the left and right ventricles, respectively, i.e. amplitude peaks of the impedance. Asynchronous depolarization of the ventricles results in asynchronous myocardial contractions with regional dyskinetic cardiac tissue, which manifest in a peak split into two (or more) amplitude peaks in the impedance signal morphology.
In one embodiment of the present invention, the impedance peak detecting unit 46 is adapted differentiate the impedance signal to calculate a first derivative of the impedance signal and to detect points of local minima and/or local maxima of the first derivative as the impedance peaks (see
Further, the heart stimulator 10 further comprises a synchronicity index determining unit 48 adapted to determine a synchronicity index indicating a degree of synchronicity based on the detected impedance peaks. In one embodiment, at least two impedance peaks detected within a predetermined time window including a cardiac cycle or a part of a cardiac cycle correspond to an increased synchronicity index indicating an increased dyssynchronicity or asynchrony in the ventricular contractions.
The heart stimulator 10 also includes sensor circuits 47, for example, a respiration sensor for sensing a respiration rate or breathing rate and/or a body posture sensor for sensing a body posture of the patient. Additional sensors may include a heart rate sensor and/or an activity level sensor. The sensor circuit may be arranged in a medical lead 20, 30 or within the heart stimulator 10.
With reference now to
In
In
In
In
According to an embodiment of the present invention, the synchronicity index is based on a peak distance between two detected peaks within the time window, wherein an increased peak distance corresponds to an increased value of the synchronicity index. With reference to
According to another embodiment of the present invention, the synchronicity index is based on the number of detected peaks within the predetermined time window, wherein an increased number of peaks corresponds to an increased value of the synchronicity index. With reference to
In a further embodiment of the present invention, the synchronicity index is based on a total peak area of one or several detected peaks within the predetermined time window measured above a predetermined threshold, wherein an increased peak area corresponds to an increased value of the synchronicity index. Referring to
According to another embodiment of the present invention, the synchronicity index is based on a variability of the amplitude of detected peaks, wherein increased amplitude variability corresponds to an increased value of the synchronicity index. Further, the variability of the difference between peaks, for example, between the local maximum peaks 73 or 77 and the local minimum peak 75 shown in
Moreover, in a further embodiment of the present invention, the synchronicity index is based on an absolute value of total peak amplitude of the detected peaks within the predetermined time window, wherein increased total peak amplitude corresponds to an increased value of the synchronicity index. Referring to
With reference now to
According to another aspect of the present invention, an optimization procedure so as to find or identify the optimal lead and/or electrode location can be performed. For example, during an implantation of an implantable medical device according to the present invention, a physician can perform such an optimization. In such a case, an external programmer unit 90, with reference to
According to yet another embodiment of the present invention, a pacing analyzer for optimizing lead and/or electrode locations is connectable to at least one medical lead implantable in a heart of a patient. A pacing analyzer is used to assess the electrical performance of a lead system during implantation of a heart stimulator, e.g. a stimulator as described above with reference to
Although exemplary embodiments of the present invention has been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications, or alterations to the inventions as described herein may be made. Thus, it is to be understood that the above description of the invention and the accompanying drawings is to be regarded as a non-limiting example thereof and that the scope of protection is defined by the appended patent claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/SE08/00720 | 12/17/2008 | WO | 00 | 6/16/2011 |