the invention will now be described purely with the purpose of providing an example of application , without this application , however , in any way constituting a limit for the invention . in fig1 block 1 represents an electronic interface device according to the invention having the purpose of sensing myocardial acceleration in at least one isovolumetric phase and of processing parameters derived therefrom . in a manner which will be described in more detail hereafter , electronic interface 1 receives , amplifies and filters the signal generated by the accelerometer and , triggered by endocardial ecg or pacing pulse , computes the peak endocardial acceleration during the isovolumetric phase according to a design known to those of skill in the art . this device is to be implanted in the body of a patient p . block 11 represents a conventional bi - directional transmission module for bi - directional data transmission between the inside and outside of the body of the patient for the purpose of monitoring myocardial acceleration and derived parameters of cardiac functionality , and for the purpose of programming operation of block 1 . such devices have been commonly employed for programming and for transcutaneously transmitting and receiving data from cardiac pacers and implantable defibrillators . blocks 1 and 11 are preferably integrated in a single implantable device and are intended to operate together with a therapeutic device d , which may be a cardiac pacer , a pcd or a drug infusion pump . device d is preferably implantable and , if possible , integrated with the device consisting of blocks 1 and 11 . the device d is intended to carry out on the patient p a drug - administration intervention and / or an intervention of an electrical nature according to the processing of the myocardial acceleration and of the endocardial ecg performed by block 1 and block 11 . it is , however , possible to create an implantable device consisting solely of blocks 1 and 11 with the exclusive aim of monitoring myocardial function . the device d can be replaced , for example , by a rate - responsive cardiac pacemaker or by an implantable cardiac defibrillator , or by a device for dosed administration of drugs . in any case , the characteristics and modes of operation of the device d are known to those of skill in the art . the characteristics of the device d , as well as the way in which it is connected to the body of the patient p , are not of themselves important for the purpose of understanding the invention . in general , block 1 is connected to a lead , having a tip c inserted in the myocardium of patient p according to known criteria . the connection is made via input terminals 2 where , in 2a , there is present an endocardial ecg signal , and in 2b , an endocardial acceleration , nha ( t ), measured by a sensor , such as the one described in u . s . pat . no . 5 , 304 , 208 . these signals are referred to a second reference electrode consisting of a ring located on the lead or of the metal container of the therapeutic device d , normally implanted subcutaneously . typical patterns of the signals are shown in diagrams a1 and b1 ( ecg ), and a2 and b2 ( nha ( t )) of fig3 . diagrams a3 and b3 represent the right ventricular pressure signal ( rvp ) sensed with a known transducer external with respect to the system described . the time scales of the superimposed diagrams coincide with one another . these signals were obtained in the course of experimental tests on animals ( sheep ) and refer to a situation of rest ( diagrams a1 , a2 and a3 ) and to a pharmacological pacing phase carried out with intravenous injection of dobutamine ( diagrams b1 , b2 and b3 ). the diagram of fig4 illustrates schematically the pattern over time of blood pressure ( mm hg on the ordinate ) in the right hand side of the heart during one complete heart cycle . in particular , the solid line indicates the right ventricular pressure ( rvp ), while the dashed line and the dashed - and - dotted line indicate the pressure in the atrium and in the pulmonary artery , respectively . points p1 and p2 identify the phase of isovolumetric contraction ( ci ), while points p3 and p4 identify the phase of isovolumetric relaxation ( ri ). in fig2 the signals 2a and 2b are operably coupled to analog - digital interface 3 . the interface 3 transfers the signals supplied by the electrode 2a and the accelerometer 2b , converted into digital form , to the input of microprocessor 4 . the latter constitutes , together with the respective memories , for instance of a rom 5 and ram 6 , a control and processing system 7 . processing system 7 is the computing system of the device and operates to process the signals received ( 2a and 2b ) according to the algorithm and programmed data stored in the memories . its design is known to those of skill in the art . associated with microprocessor 4 is clock 8 and output interface module 9 intended for driving , by means of corresponding output terminals 10 , therapeutic device d . bi - directional telemetric device 11 comprises receiver / transmitter interface 12 connected to the micro - processor 4 , as well as radio - frequency transceiver 13 , connected in bi - directional transmission to interface 12 and to transceiver antenna 14 . the process and control circuit 7 superintends all the operating phases of the device and processes the data coming from the adjacent interfaces . for this purpose , the rom memory 5 serves preferentially as a program memory , while the ram memory 6 serves preferentially as a memory for processing and maintaining the data programmed and saved by the microprocessor 4 itself , according to the processing carried out . transceiver 11 carries out the exchange of information between external programmer device 15 and control system 7 . in particular , it performs the functions of receiving programmed parameters form outside and of transmitting the stored values to the ram memory 6 . typically , the data transmitted regard the parameters processed by the system , measurements made or checks on the correctness of interaction between the external programmer and the implanted device itself . the transmission and receipt of data between the implantable device and the external programmer 15 takes place at radio frequencies . the processes referred to are achieved according to technical characteristics which are themselves well - known to those working in this sector . clock 8 , which is also programmable , is able to supply the programming system with the time reference essential for a correct time base that refers to all the measurements . analog / digital interface 3 is typically equipped with a circuit for ventricular sensing which is able to recognize the electrical activity of the right ventricle and to discriminate it from interference coming from other sources , as well as with a circuit for amplification and analog - digital conversion of the signal of heart acceleration coming from the accelerometer located in the tip of the lead . this interface , therefore , sets in communication the endocardial sensing lead and the acceleration sensor with the device for processing and controlling information 7 . in particular , the device connected to the terminal 2a is built using the same technology utilized by current cardiac pacemakers and by pcds for performing the same function , while the device connected to the terminal 2b is built as illustrated in u . s . pat . no . 5 , 304 , 208 . the processing operations performed by the system 7 on the signals coming from the terminals 2a and 2b have , in the first place , the purpose of analyzing the ecg signal ( terminal 2a ) in order to identify phases and / or events that are significant from the electrological point of view , for example , qrs and / or the t wave , measuring both amplitude and duration . also sensed are parameters such as the frequency and period of the beat . all this is achieved on the basis of criteria which in themselves are known . starting from the analysis of the ecg signal , the system 7 processes the nha ( t ) signal , isolating , within the signal , certain given time phases ( segments ) that constitute phases having an important haemodynamic meaning , for instance , isovolumetric contraction or isovolumetric relaxation , these being phases in which the dynamics of the heart wall is not perturbed by overall movements of the entire cardiac mass as a reaction to the ejection phases . for example , the control and processing system 7 is able to identify , in the context of the acceleration nha ( t ), a segment t ( see fig3 ) immediately subsequent to the spontaneous qrs , within which the isovolumetric contraction phase occurs . in the presence of the cardiac pacing function , the system 7 identifies a segment ( t + δt , where δt is of the order of approximately fifty msec ) from the possible ventricular pacing spike , which contains the isovolumetric contraction phase . in the case where the segment corresponding to isovolumetric relaxation is isolated , the system 7 refers to the t wave of the ecg , both in the event of a spontaneous beat and in the presence of pacing . the time duration of the segment t that is isolated is not necessarily fixed . for instance , in the case where the segment within which the isovolumetric contraction phase occurs is isolated , it is possible to configure the system 7 to vary the duration t , in order to associate with an increase in the beat rate ( whether spontaneous or stimulated ) a reduction , which may be even quite considerable , in this duration , or conversely , to associate with a reduction in the former an increase in the latter . an example of a therapeutic device utilizing the nha signal segments , as isolated above , is a rate responsive pacemaker . the pacemaker may be either a single or dual chamber pacer . such a pacemaker would include a pulse generator , an acceleration sensor , an ecg sensor and appropriate pacing electrodes for providing stimulation pulses to the atrium , the ventricle or both , depending on the patients &# 39 ; needs . the features of such a pacemaker have been generally discussed above in connection with fig1 and 2 . the nha signal is processed to calculate the peak - to - peak value . the peak - to - peak value as measured inside a time window containing an isolated phase of the cardiac cycle , such as the isovolumetric contraction phase , is identified as the peak endocardial acceleration ( pea ). the pea has been found in normal hearts to have excellent correlation with both dp / dt maximum of the right ventricle ( rv ) and dp / dt maximum of the left ventricle ( lv ). rv dp / dt maximum has been previously used in the field of cardiac pacing for driving the pacing rate in rate responsive pacemakers . however , the contractile function of the whole heart is largely dependent on the left ventricle where most of the muscular mass is found . there are some conditions of the heart where lv dp / dt maximum does not correlate with rv dp / dt maximum . thus , during these conditions rv dp / dt maximum does not provide a reliable indication of the contractile function of the heart . fig5 a and 5b show data taken during experiments with an anesthetized sheep . fig5 a shows rv dp / dt maximum and lv dp / dt maximum measured over a period of 15 minutes during positive inotropic stimulation with a dobutamine infusion . pea was measured with a sensor in the apex of the right ventricle over the same period of time . fig5 a shows a direct correlation between pea , rv dp / dt maximum and lv dp / dt maximum over the 15 minute time period under normal heart conditions . during the same experiment a condition of acute rv pressure overload and inadequate lv filling was created by occluding the pulmonary artery with a balloon . fig5 b shows rv dp / dt maximum and lv dp / dt maximum measured over a period of 60 seconds during the occlusion . pea was again measured over the same 60 second period . the data in fig5 b shows a direct correlation between lv dp / dt maximum and pea and demonstrates the dominance of lv contractility in modulating the pea changes . the data supports the conclusion that pea measured from a sensor in the right ventricle provides an accurate indication of the contractile function of the whole heart , even under conditions where rv dp / dt maximum and lv dp / dt maximum do not correlate . it has also been shown experimentally that pea shows considerable correlation to heart rate under adrenergic stimulation such as during physical and mental stress tests . however , it has also been shown experimentally that pea is not significantly dependent on heart rate variations induced by pacing at rest . this data supports the use of pea as an effective physiological parameter upon which a rate responsive pacing system can be based . fig6 illustrates the graph of an algorithm based on the use of pea to adjust the pacing rate of a rate responsive pacemaker similar to that discussed with respect to fig1 and 2 . a pea reference value ( pearef ) is selected to reflect the basal condition of the heart . pearef may be a programmable constant , or , preferably , is obtained by measuring pea on a cycle - by - cycle basis and using a mobile averaging process with a long time constant . thus , pearef is a floating value updated on a continuing basis based upon the average pea value over a long period which may be from one hour or less to 48 hours or more . by selecting a sufficiently long time period over which to average pea , the pearef value provides an accurate pea basal value of the contractile function of the heart unaffected by short episodes of physical activity and / or mental stress . the system is self adjusting such that the value of pearef will change to accommodate long term changes in the basal state of the heart . as seen in fig6 the pacing rate adjusts from a lower limit or rest rate to an upper rate limit . in this case the rest rate is selected as 50 pulses per minute ( ppm ) and the upper rate is 140 ppm . these limits may be fully programmable so that they may be adjusted according to the needs or conditions of the patient . the basic rate is indicative of the value of the pacing rate under basal conditions , i . e . free of stress or physical activity . the rest rate may be programmed as an option to allow a lower heart rate at that point where the current value of pea is just below pearef . in this example , the basic rate is set at 10 ppm over the rest rate . the rest rate is believed to be desirable to enable the heart rate to adjust to a lower value than the normal basal rate ( basic rate ) such as during periods of sleep . it should be noted however , that the difference between the basic rate and the rest rate can be programmed from zero to greater than 10 ppm . the slope 100 between the basic rate and the upper rate serves as the rate response curve establishing the relationship between currently measured pea and pacing rate . although shown as being linear , slope 100 can be programmed to effect any desired nonlinear relationship between pacing rate and pea . the pacing rate is calculated cycle - by - cycle as a function of the difference between the currently measured pea and pearef . for example , as illustrated in fig6 if the current pea is constant and equal to 3 g , the pacing rate will be approximately 112 ppm . fig7 illustrates the effect of a change in pearef on the pacing rate . if pearef decreases from 1 g to 0 . 6 g , slope 100 shifts to the left to the position of slope 100a . in that case a currently measured pea of 3 g results in a pacing rate of approximately 122 ppm . if the pearef increases to approximately 1 . 8 g slope 100 shifts to the right to the position of slope 100b . at that position the pacing rate at a currently measured pea of 3 g is approximately 91 ppm . it is important to note the differential nature of the algorithm upon which the pacing rate is based . thus , for example , an increase in pea of 1 g , i . e . from 2 g to 3 g , will cause the pacing rate to increase by the same amount whether the slope is in the position of slope 100a , 100 or 100b . as seen in fig8 a and 8b , the rate response curve may be programmed to have a higher or lower response depending on the needs of the patient . fig8 a illustrates a group of response curves 100c , 100d and 100e . curve 100c has a higher pacing rate response than curve 100d , which in turn has a higher response than curve 100e . fig8 b illustrates a group of nonlinear rate response curves 100f , 100g and 100h having response rates varying from very fast ( 100f ) to medium ( 100g ) to slow ( 100h ). fig8 a and 8b show just a few examples of the way the pacemaker may be programmed to achieve the particular response desired for a patient . in a further embodiment of the invention it is believed that pea will serve as an effective parameter with which to control av delay for those patients suffering from some form of heart conduction disease which may be associated with cardiomiopathy . it is known that cardiac output ( co ), heart rate ( hr ) and stroke volume ( sv ) are related according to the following formula : since stroke volume is dependent in part upon av delay it is clear that cardiac output will be optimized when the av delay is set to allow optimal time for filling of the ventricles . it is believed that there is a correlation between av delay and pea . therefore , an algorithm based upon the relationship between av delay and pea may be used to set av delay between upper and lower programmable limits . the algorithm would be used to optimize av delay as a function of the currently measured pea . this feature could be used alone or in combination with the rate responsive feature discussed above . thus , the pacemaker would be able to adjust pacing rate and / or av delay to provide a system which optimizes cardiac output according to a patient &# 39 ; s needs . another important function of endocardial ecg analysis is the recognition of specific arrhythmic events , for example , ventricular extrasystoles which , since they alter the normal mechanics of heart contractions , could lead to an incorrect interpretation of the nha signal . in this case , the identification of these events , based on the analysis of the ecg , makes it possible to exclude the mechanical effects of these anomalous events on the nha signal from the subsequent processings . in the case of cardiac pacing , associating an effective nha signal to the spike in the time interval set may enable the efficiency of the pacing to be ascertained . the endocardial ecg signal may be processed not only for recognizing arrhythmias , but also for determining the pattern of heart rate , which is a very important parameter associated to nha for evaluating the cardiac function . in particular , the system 7 proves able to evaluate the nha / rate ratio , thus enabling identification of conditions of depression of the cardiac function in which to an increase in heart rate there corresponds an inadequate increase , or even a decrease in nha . the availability of the ecg signal is moreover important for determining the so - called heart rate variability ( hrv ) for measuring the sympathetic - vagal balance , as described in patent no . ep - a - 0 565 909 . on the nha signal segments thus isolated , the system 7 can carry out the prescribed mathematical processing ( calculation of peak - to - peak value , calculation of peak value , calculation of rectified mean value , or rms , etc .). in the control and processing system 7 are contained the decision - making mechanisms and the algorithms , obviously differentiated , which allow the application of a possible therapeutic phase whether of an electrical or of a pharmacological nature . the output interface 9 transmits the command for intervention to the therapeutic device d , together with the values processed from the nha and from the endocardial ecg , which are able to quantify the deviation from the optimal reference values , so allowing the device to intervene effectively . in all due respect of the principle of the invention , the details and forms of implementation can be amply varied with regard to what has been described and illustrated above , without this entailing a departure from the sphere of the present invention .
the device senses natural heart acceleration , isolating at least one segment thereof corresponding to an isovolumetric phase , such as isovolumetric contraction and / or isovolumetric relaxation . preferentially , the action of isolation of the aforesaid segment is made starting from the electrocardiogram signal . among other things , the device may be used to carry out pacing functions and / or to pick up , possibly by telemetry , data on the myocardial function and / or also to control a system of drug administration .