the following is a description of exemplifying embodiments in accordance with the present invention . this description is not to be taken in a limiting sense , but is made merely for the purpose of describing the general principles of the invention . thus , although particular types of heart stimulators will be described , such as biventricular pacemakers with or without atrial sensing and / or stimulation , the invention is also applicable to other types of cardiac stimulators , such as univentricular or dual chamber pacemakers , implantable cardioverter defibrillators ( icd &# 39 ; s ), etc . with reference first to fig1 , there is shown a stimulation device 10 in electrical communication with a patient &# 39 ; s heart 1 via two leads 20 and 30 suitable for delivering multi - chamber stimulation ( and possible shock therapy ). the heart illustrated portions of the heart 1 include the right atrium ra , the right ventricle rv , the left atrium la , the left ventricle lv , cardiac walls 2 , the ventricular septum 4 , the valve plane 6 , and the apex 8 . the valve plane 6 refers to the annulus fibrosis plane separating the ventricles from the atria and containing all four heart valves , i . e . the aortic , pulmonary , mitral , and tricuspid valves . in order to sense right ventricular cardiac signals and to provide stimulation therapy to the right ventricle rv , the stimulation device 10 is coupled to an implantable right ventricular lead 20 having a ventricular tip electrode 22 , a ventricular annular or ring electrode 24 , and a cardiac wall movement sensor 21 . the ring electrode 24 is arranged for sensing electrical activity , intrinsic or evoked , in the right ventricle rv . the right ventricular tip electrode 22 is 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 the cardiac wall and follows the cardiac wall movements , which movements can be sensed by the sensor 21 arranged near the tip electrode . in this example , the sensor is fixedly mounted in a distal header portion of the lead 20 , in which the tip electrode 22 is also fixedly mounted . furthermore in this example , the sensor is in the form of an accelerometer . however , other arrangements sensor types are contemplated for the cardiac wall motion sensor 21 . in order to sense left ventricular cardiac signals and to provide pacing therapy for the left ventricle lv , the stimulation 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 . also , additional electrode ( s ) ( not shown ) could thereby be positioned adjacent to the left atrium . 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 comprises an annular ring electrode 34 for sensing electrical activity related to the left ventricle lv of the heart . furthermore , a cardiac wall movement sensor 31 is arranged at the tip electrode 32 for sensing left ventricular lv cardiac wall movements . turning briefly to fig2 and 3 , two alternative embodiments for placement of cardiac leads , cardiac electrodes and sensors for sensing cardiac wall movements related to longitudinal valve plane movements are illustrated . in fig2 , the rv and lv leads 20 , 30 have been supplemented with a right atrial ra lead 80 . the lead comprises an ra tip electrode 82 positioned in the patient &# 39 ; s right atrial appendage for delivering electrical stimuli to the right atrium , and an ra ring electrode 84 for sensing and conducting cardiac signals from the right atrium to the cardiac stimulator . a cardiac wall motion sensor is provided at the ra tip electrode 82 for sensing cardiac wall movements of the ra wall . furthermore , the lv lead 30 is provided with an additional cardiac wall movement sensor 33 arranged at the valve plane 6 , as well as an additional stimulating electrode , of the ring type , arranged distally of the movement sensor 33 . thereby , cardiac wall movements related to longitudinal valve plane movements at a plurality of locations , i . e . three or four , may be sensed and conducted via the cardiac leads 20 , 30 , 80 to the cardiac stimulator . furthermore , fig3 illustrates yet another example of lead , electrode and sensor placements . here , the rv , ra and lv leads 20 , 30 and 80 have been supplemented by , an external epicardial lead 90 connected to the implantable stimulator 10 . the epicardial lead 90 may be arranged for delivering stimulation pulses to the left ventricle lv of the heart , but is in this example only arranged for sensing cardiac wall movements related to longitudinal valve plane movements and comprises a cardiac wall motion sensor 91 . thus , even though the lv lead 30 terminates and the stimulation electrode 32 for stimulation of the left ventricle arranged at a position near the valve plane 6 of the heart , local wall movements occurring in the lv cardiac wall further down towards the apex 8 may still be sensed . although three examples have been illustrated in fig1 - 3 , the invention is not restricted to the illustrated examples of lead , electrode and sensor placement . for example , several epicardial electrodes and / or wall motion sensors could be used , wall motion sensors could be arranged at plural positions in the ventricles only , all wall motion sensors could be arranged in the same ventricle , plural atrial wall sensors could be used , etc . also , in the illustrated examples , the wall motion sensors are of accelerometer type . however , other types of sensors for sensing and measuring wall movements related to longitudinal valve plane movements are to be comprised in the scope of the present application . further examples of sensor placements will be presented in relation to the further embodiments that will be described below . turning now to fig4 , the heart stimulator 10 of fig1 is shown in a block diagram form . for illustrative purposes , reference is made to fig1 for the elements of the leads that are intended for positioning in or at the heart . the heart stimulator 10 is connected to a heart 1 in order to sense heart signals and emit stimulation pulses to the heart 1 . a first tip electrode 22 is anchored in the right ventricle rv of the heart 1 and connected , via a first electrode conductor in the lead 20 , to a first pulse generator 26 in the heart stimulator 2 . a first ring electrode 24 is connected near the first tip electrode 22 and , via a second electrode conductor in the first lead 20 , to the first pulse generator 26 . a stimulation pulse to the right ventricle can be delivered to heart tissue by the first pulse generator via the first lead 20 and the first tip electrode 22 . the stimulation pulse is then returned , via the first ring electrode 24 and the first lead 20 , to the first pulse generator 26 . alternately , the stimulation pulse can be delivered via the first tip electrode 22 and an indifferent electrode 12 which , in this instance , consists of the enclosure of the heart stimulator 10 but can also consist of a separate electrode located somewhere in the body . the indifferent electrode 12 is connected to the first pulse generator 26 via an electrode conductor 14 in order to return stimulation pulses from the right ventricle . a first detector 28 is connected in parallel across the output terminal of the first pulse generator 26 in order to sense right ventricular activity in the heart . in corresponding manner , a second tip electrode 32 is positioned in a vein distally of the coronary sinus and , thus , connected to the left ventricle lv of the heart 1 , and , via a conductor in the second lead 30 , to a second pulse generator 36 . a second ring electrode 34 is located near the second tip electrode 32 and connected , via a further conductor in the second electrode lead 30 , to the second pulse generator 36 . delivery of a stimulation pulse to the ventricle can be bipolar via the second tip electrode 32 and the second ring electrode 34 , or unipolar via the second tip electrode 32 and the indifferent electrode 12 . a second detector 38 is connected in parallel across the output terminal of the second pulse generator 36 in order to sense left ventricular activity in the heart . the pulse generators 26 and 36 and the detectors 28 and 38 are controlled by a control unit 40 which regulates the stimulation pulses with respect to amplitude , duration and stimulation interval , the sensitivity of the detectors 28 and 38 etc . a physician using an extracorporeal programmer 56 can , via a telemetry unit 54 , communicate with the heart stimulator 10 and thereby obtain information on identified conditions and also reprogram the different functions of the heart stimulator 10 . fig4 further shows a first embodiment of an analysis device . the analysis device 50 is connected via the first electrode lead 20 to a first cardiac wall motion sensor 21 for sensing cardiac wall movements related to longitudinal valve plane movements , and via the second electrode lead 30 to a second cardiac wall motion sensor 31 for sensing cardiac wall movements related to longitudinal valve plane movements . the analysis device 50 includes a measurement unit 52 which is capable of selectively receiving signals from any of the sensors , and which filters and amplifies the incoming signals in an appropriate manner . the output signal from the measurement unit 52 , which is proportional to the measurement signal , is then sent to a buffer 54 and to a differentiating circuit 56 . buffering is performed so that the differentiated signal is in phase with the proportional signal when they are sent to a calculator unit 58 . the calculator unit 58 calculates a synchronization or synchrony value or signal based on the output signals from the respective sensors . the calculated synchronization signal 58 is sent to a comparator 60 for comparison with a threshold value , for instance indicative of when insufficient cardiac synchrony is present . the output signal from the comparator comprises information of whether the synchronization signal passes the threshold value , or one of the threshold values for embodiments where a number of threshold values are utilized , and is forwarded to a microprocessor 62 which communicates with the control unit 40 . if , e . g ., an asynchrony is identified , the control device 40 can institute therapeutic treatment with stimulation pulses in order to restore cardiac synchrony . the microprocessor 62 further controls the measurement unit 52 with respect to the measurement signal to be sent to the analysis device 50 and can also control the comparator 60 , for example for varying threshold values in response to altered pacing therapy or due to altered settings by the physician . with reference now to fig5 , there is shown an alternative analysis device 51 . this alternative analysis device 51 basically comprises the same or similar elements as described in relation to the measurement unit analysis device 50 of fig4 . however , the alternative analysis device 51 is arranged for receiving output signals from three cardiac wall motion sensors via conductors 70 , 72 and 74 , the analysis device thus being arranged to provide a synchronization signal indicative of cardiac synchrony between three different locations of the heart . furthermore , a fourth conductor 76 provides an iegm signal for the measurement unit . the iegm signal may provide an indication related to when the output signals of the sensors may be used for determining cardiac synchrony for a particular portion of the heart cycle . thus , the iegm signal may for instance be used by the analysis device 50 , or rather by the differentiating circuit 54 and the calculator unit 58 , as an aid in discriminating between the systolic and the diastolic phases of the heart cycle . thereby , the analysis device can for instance be configured to process only sensor output signals provided during the diastolic phase . then , there will be no risk of misinterpreting an asynchrony that may be present in the systolic phase as an asynchrony in the diastolic phase . turning now to fig6 - 6 c and 7 a - 7 c , there will be shown in schematic form the presence and determination of cardiac synchrony and asynchrony , respectively . in fig6 a , 6 b , 7 a , and 7 b , a heart is schematically illustrated with three cardiac wall motion sensors a , b and c positioned in the left ventricle lv of the heart . in fig6 a , the position of the sensors , i . e . the cardiac wall portions in which the sensors are arranged , are illustrated at an instant when the myocardium is fully dilated , in particular during the diastolic phase of the heart cycle . thus , the sensors and the wall portions thereof are in a respective position obtained from the longitudinal or long - axis valve plane movements as a result of myocardial relaxation . in fig6 b , an instant when the myocardium is at a state of myocardial contraction is illustrated , in particular during the systolic phase of the heart cycle . thus , the movement of the sensors and the wall portions into the contracted positions have ceased and they are in a respective position obtained from the longitudinal valve plane movements as a result of myocardial contraction . the output signals of the sensors are illustrated in fig6 c , and it can be seen that the movements sensed by the three sensors are substantially simultaneous throughout the heart cycle . therefore , the processing circuitry , or analysis device , of the cardiac stimulator determines that there is cardiac synchrony . as a consequence , no further actions related to change in pacing therapy is performed . it should be noted that the determination of cardiac synchrony can be determined for the entire heart cycle , for the systolic phase , the diastolic phase , the transitions between diastolic and systolic phase , and vice versa , or any other time interval of the heart cycle that may be of particular interest for the determination of cardiac synchrony . in fig7 a , the position of the sensors and the respective cardiac wall portions thereof correspond to that of fig6 a at an instant when the myocardium is fully dilated . thus , the sensor positions are derived from the longitudinal valve plane movements resulting from myocardial relaxation . however , at the particular instant illustrated in fig7 b , only sensor b , and the cardiac wall portion to which sensor b is attached , has reached the position derived from the longitudinal valve plane movements obtained in the fully contracted state of the myocardium . hence , there is lack in synchrony between the longitudinal valve plane movements for the cardiac wall portions at which the sensor a , b and c are attached , respectively . this lack in synchrony also appears in the output signals a , b and c of the cardiac wall motion sensors a , b and c , respectively . thus , upon performing a synchronicity analysis for the output signals , for instance in the systolic phase of the heart cycle , it can be determined that cardiac asynchrony is present and that suitable measures should be taken . such measures could include restoring the cardiac synchrony or to derive an alarm signal indicative of the cardiac asynchrony . turning now to fig8 a - 8 c , there is shown a further example of the occurrence and detection of cardiac asynchrony related to longitudinal valve plane movements . in fig8 a , the positions of the cardiac wall motion sensors a , b and c at an instant where the myocardium has assumed a contracted state is shown . in fig8 b , a post - systolic contraction psc occurs in the cardiac wall portion where sensor a is arranged for sensing cardiac wall movements derived from longitudinal valve plane movements . consequently , sensor a is subjected to a longitudinal movement at an instant when sensors b and c remain substantially stationary during diastole . this appears in the combined sensor signal outputs a , b and c , and can be detected and determined as an asynchrony in the diastolic phase by the analysis device 50 of the stimulator 10 . in the signal diagram of fig8 c , the portion comprising the signal output during the psc is encircled . thus , as a result of the determined asynchrony , appropriate adjustment of the pacing therapy may be executed in order to restore the cardiac synchrony . in fig6 a through 8 b , substantially only one example of the positioning of cardiac wall motion sensors for sensing movements related to the longitudinal movements of the valve plane is provided . however , there are a vast number of sensor positioning alternatives that are contemplated within the scope of the present application . in fact , any placement of sensors for measuring cardiac wall motions occurring during the heart cycle may be used , as long as there is in fact movements of the particular portion to which the sensor is located and attached in relation to the longitudinal movements of the valve plane during the heart cycle , or any portion thereof . thus , the present application is not limited to a particular number of wall motion sensors , or to particular positioning thereof . turning to fig9 a - 9 d , further examples of wall motion sensors are provided . in these examples , the sensors a , b and c are arranged at the same ventricle , i . e . for measuring cardiac wall movements at several locations in the left ventricle lv of the heart . fig9 a is intended to illustrate the orientation of the valve plane , which is indicated by numeral 6 in fig1 . in the example illustrated in fig9 b , the sensors are positioned in the actual valve plane , which of course is suitable for detecting valve plane movements . then , the sensors could in one alternative be positioned in the actual annulus fibrosis tissue , or epicardially outside the annulus fibrosis plane . in fig9 c and 9 d , two alternative examples of sensor positionings are presented . in fig9 c , the sensors a , b and c have been positioned at equal distances from the valve plane , thus forming a sensor plane parallel to the valve plane . thereby , the sensors are assumed to be subjected to movements related to the longitudinal valve plane movements of substantially the same distance during the heart cycle , which may be beneficial when calculating and determining synchrony and possible sudden or expected appearance of asynchrony in the valve plane movements . in the example shown in fig9 d , the sensors are positioned at different levels at one ventricle along the longitudinal axis , or long - axis , of the heart . in this example , the physician has positioned the sensors at selected regions of interest , for instance regions suffering from a conductive disorder or having hibernating tissue which is expected or suspected to become active during remodulation of the heart due to progressing stimulation therapy . turning now to fig1 a to 10 d , further examples of sensor positioning are illustrated . in the examples , the sensors are arranged in or at both ventricles of the heart . first , fig1 a illustrates the valve plane and the longitudinal direction of the heart . then , fig1 b illustrates the example where the cardiac wall motion sensors are positioned and arranged to sense longitudinal cardiac wall movements of the valve plane . the benefits thereof would of course be similar to the placement in the same ventricle as illustrated in fig9 b . furthermore , in the same manner as mentioned above in relation to fig9 b , the sensors could in one alternative be positioned in the actual annulus fibrosis tissue , or epicardially outside the annulus fibrosis plane . suitably , the right ventricular sensor a is arranged endocardially in the valve plane , and the left ventricular sensor c is arranged epicardially . the sensor b arranged at the septum 4 could be arranged epicardially either directly or via a coronary vein , or endocardially , via the right atrium and ventricle . possibly , the rv sensor a arranged at the valve plane could be replaced for an ra sensor arranged in or at the valve plane , e . g . in the annulus fibrosis tissue . in fig1 c , the sensors a , b and c have been positioned in or at the right and the left ventricle , respectively , at equal distances from the valve plane , thus forming a sensor plane parallel to the valve plane . thereby , similar to the example shown in fig9 c , the sensors are assumed to be subjected to movements of substantially the same distance during the heart cycle , which may be beneficial when calculating and determining synchrony and possible sudden or expected appearance of asynchrony in the longitudinal valve plane movements . in the example illustrated in fig1 d , the sensors are positioned at different levels , in or at the right and the left ventricle , along the longitudinal axis of the heart . in this example , similar to the example shown in fig9 d , the physician has positioned the sensors at selected regions of interest , for instance regions suffering from a conductive disorder or having hibernating tissue which is expected or suspected to become active during remodulation of the heart due to progressing stimulation therapy . when the signal output from the sensors a , b and c is received by the analysis device 50 , a calculation of a synchronization index or signal is performed , which can be used for determining synchrony of the heart . in fig1 a , the output signals a , b and c , stemming from the sensors a , b and c , respectively , indicative of cardiac wall movements are illustrated in a diagram . in the portion of the diagram illustrating sensor output signal a , the sensor output signal b has been added as shown by the dotted line . similarly , the sensor output signal c has been added to the portion of the diagram illustrating sensor output signal b . in this example , the difference between the sensor output signals a and b and the difference between the sensor output signals is calculated . this is performed by simply subtracting sensor output signal b from a and sensor output signal c from b . the resulting difference signals are shown in fig1 b . these signals could be further added to each other in order to arrive at the synchronization index or signal . alternatively , the difference signals could be used separately in order to provide dual synchronization indices or signals . furthermore , statistical calculations could be applied to the difference signal ( s ) to arrive at a suitable value indicative of the level of synchronization . fig1 a and 12 b illustrate a further example of deriving one or more synchronization indices or signals . here , the upper and lower portions of the diagram in fig1 a illustrates two signals obtained from two sensor output signals , respectively . one signal is indicated with a solid line , and the other one with a dotted line , respectively . these pairs of sensor output signals are cross - correlated in order to arrive at a cross - correlation result which is used as said synchronization indices or signals . in the illustrated example , two cross - correlation results in the form of synchronization index a and synchronization index b are obtained . the synchronization signals can then be compared with a threshold value , which is illustrated in fig1 b with the dotted straight line , and appropriate measures be taken when the synchronization signal exceeds the threshold level . when the monitoring of cardiac synchronization has revealed that a cardiac asynchrony has arisen , or that a reduction of cardiac synchrony has occurred , the parameters for timing of stimulation pulse delivery may be changed in order to restore or improve the cardiac synchrony . such an indication could in exemplifying embodiments of the invention be used for triggering a change in the stimulation therapy . such a change could for example refer to an adjustment in the vv - interval , e . g . for a biventricular heart stimulator ; a change in the av - interval , e . g . for a dual chamber or an av - sequential heart stimulator ; or combinations thereof . thereby , the cardiac synchrony can be monitored during remodulation of the patient &# 39 ; s heart , and the pacing therapy can be adjusted in adaptation to the remodulation of the heart . for heart stimulators in which the pacing therapy may be automatically adjusted by the heart stimulator in order to optimize or maximize cardiac output , a synchronized and elongated diastolic phase may be given priority over the optimization of cardiac output . for instance , in patients suffering from ischemic heart disease , it may be more important to ensure synchronized diastole and , thereby , adequate coronary flow at all times rather than maximized cardiac output . in further embodiments , the indication of cardiac asynchrony could be used for triggering an alarm signal to the patient . this alarm signal could be intended for prompting the patient to seek medical assistance for care or follow - up . it should be noted that the sensors may be subjected to pressures , movements and / or accelerations that are not derived from or related to the intrinsic movements of the myocardium and the cardiac walls thereof . for instance , accelerations derived from extra - cardiac movements of the patient , such as from running , vibrations in the patient environment , thoracic movements etc . however , output signal contributions deriving from intrinsic movements of the myocardial tissue can easily be discriminated from signal contributions from such extra - cardiac movements since the latter have a substantially identical impact on the respective sensor . furthermore , by designing the sensors to be sensitive for certain frequency ranges , the majority of the extra - cardiac signal contributions may be omitted . furthermore , band - pass filtering of the sensor outputs may also be used for discriminating or filter out the signal contribution from extra - cardiac movements . although modifications and changes may be suggested by those skilled in the art , it is the intention of the inventors to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of their contribution to the art .
in a system and method for monitoring cardiac synchrony in a human heart , a first sensor is positioned at a first cardiac wall location that is subject to movements related to longitudinal valve plane movements along the longitudinal axis of the heart , and measures the cardiac wall movements at the first cardiac wall location and a second sensor is positioned at a second cardiac wall location that is subject to movements related to longitudinal valve plane movements along the longitudinal axis of the heart , and measures the cardiac wall movements at the second cardiac wall location . a lead arrangement conducts respective output signals from the first and second sensors to processing circuitry that processes the first and second sensor output signals to produce a synchronization signal therefrom indicative of synchrony in the respective valve plane movements at the first and second cardiac wall locations .