Abstract:
A method for operating an implantable medical device to control a stimulation therapy includes the steps of: sensing an acoustic energy; producing acoustic signals indicative of heart sounds of the heart of the patient over predetermined periods of a cardiac cycle during successive cardiac cycles; extracting a signal corresponding to a first heart sound (S 1 ) from a measured acoustic signal; calculating an energy value corresponding to the extracted signal; storing the energy value corresponding to the first heart sound; and initiating an optimization procedure, the optimization procedure comprising the steps of: iteratively controlling a delivery of the pacing pulses based on successive energy values corresponding to successive first heart sound signals and determining an optimal PV interval or AV interval with respect to the energy values. A medical device and a computer readable medium to implement the method.

Description:
This application is a National Stage entry of PCT/SE2005/001956, filed Dec. 16, 2005. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to implantable medical devices, such as cardiac pacemakers and implantable cardioverter/defibrillators, and in particular to a method, a medical device, a computer program product and a computer readable medium for controlling a stimulation therapy using detected heart sounds. 
     2. Description of the Prior Art 
     Auscultation is an important diagnostic method for obtaining information of the heart sounds, which is well established as diagnostic information of the cardiac function. The sounds are often described as S 1 -S 4 . During the working cycle of the heart mechanical vibrations are produced in the heart muscle and the major blood vessels. Acceleration and retardation of tissue cause the vibrations when kinetic energy is transformed to sound energy, e.g. at valve closing. Vibrations can also arise from turbulent blood flow, e.g. at stenosis and regurgitation. These vibrations may be listened to using a stethoscope or registered electronically using phonocardiography, i.e. graphical registration of the heart sounds by means of a heart microphone placed on the skin of the patient&#39;s thorax. Auscultation using a stethoscope is, to a large extent, built on practical experience and long practice since the technique is based on the doctor&#39;s interpretations of the hearing impressions of heart sounds. When applying phonocardiography, as mentioned above, a heart microphone is placed on the skin of the patient&#39;s thorax. In other words, it may be cumbersome and time-consuming to obtain knowledge of the heart sounds and the mechanical energy during the heart cycle using these manual or partly manual methods and, in addition, the obtained knowledge of the heart sounds may be inexact due to the fact that the knowledge is, at least to some extent, subjective. 
     The first tone S 1  coincides with closure of the Mitral and Tricuspid valves at the beginning of systole. Under certain circumstances, the first tone S 1  can be split into two components. An abnormally loud S 1  may be found in conditions associated with increased cardiac output (e.g. fever, exercise, hyperthyroidism, and anemia), tachycardia and left ventricular hyperthrophy. A loud S 1  is also characteristically heard with mitral stenosis and when the P-R interval of the EKG is short. An abnormally soft S 1  may be heard with mitral regurgitation, heart failure and first degree A-V block (prolonged P-R interval). A broad or split S 1  is frequently heard along the left lower sternal border. It is a rather normal finding, but a prominent widely split S 1  may be associated with right bundle branch block (RBBB). Beat-to-beat variation in the loudness of S 1  may occur in atrial fibrillation and third degree A-V block. 
     The second heart sound S 2  coincides with closure of the aortic and pulmonary valves at the end of systole. S 2  is normally split into two components (aortic and pulmonary valves at the end of systole) during inspiration. Splitting of S 2  in expiration is abnormal. An abnormally loud S 2  is commonly associated with systemic and pulmonary hypertension. A soft S 2  may be heard in the later stages of aortic or pulmonary stenosis. Reversed S 2  splitting (S 2  split in expiration—single sound in inspiration) may be heard in some cases of aortic stenosis but is also common in left bundle branch block (LBBB). Wide (persistent) S 2  splitting (S 2  split during both inspiration and expiration) is associated with right bundle branch block, pulmonary stenosis, pulmonary hypertension, or atrial septal defect. 
     The third heart sound S 3  coincides with rapid ventricular filling in early diastole. The third heart sound S 3  may be found normally in children and adolescents. It is considered abnormal over the age of 40 and is associated with conditions in which the ventricular contractile function is depressed (e.g. CHF and cardiomyopathy). It also occurs in those conditions associated with volume overloading and dilation of the ventricles during diastole (e.g. mitral/tricuspid regurgitation or ventricular septal defect). S 3  may be heard in the absence of heart disease in conditions associated with increased cardiac output (e.g. fever, anemia, and hyperthyroidism). 
     The fourth heart sound S 4  coincides with atrial contraction in late diastole. S 4  is associated with conditions where the ventricles have lost their compliance and have become “stiff”. S 4  may be heard during acute myocardial infarction. It is commonly heard in conditions associated with hyperthrophy of the ventricles (e.g. systemic or pulmonary hypertension, aortic or pulmonary stenosis, and some cases of cardiomyopathy). The fourth heart sound S 4  may also be heard in patients suffering from CHF. 
     Thus, the systolic and diastolic heart functions are reflected in the heart sound. The power of energy value of the heart sounds and their relation may carry information of the workload and status of the heart. For example, as discussed above, patients with a wide QRS complex due to e.g. right bundle branch block (RBBB) or A-V block are associated with a widened or split first heart sound S 1 . Furthermore, changes of the energy of e.g. S 1  over time can be a useful tool, for example, in diagnosis of different conditions. A high variability of the energy parameters during otherwise constant conditions indicates, for example, that filling is altering due to e.g. arrhythmia or conduction disorder. As can be understood from the above-mentioned, knowledge of the heart sounds and the corresponding mechanical energy can be used for diagnosis/monitoring and controlling pacing therapy of patients. In addition, this knowledge can also be used to optimize a stimulation therapy and to verify that the stimulation output evokes a desired response in a selected region of the heart. In patients suffering from heart failure, such as Congestive Heart Failure (CHF), the knowledge of the heart sounds and the corresponding energy parameters can be used to estimate the severity of the condition and/or to optimize the AV delay. Consequently, it would be beneficial if signals related to the heart sounds and the corresponding energy could be collected and used for controlling/optimizing pacing therapy in an automated manner. 
     The known technique presents a number of automated systems for controlling/optimizing stimulation therapy. For example, medical devices and methods in such devices for optimizing AV delay are known. In U.S. Pat. No. 5,700,283, a method and apparatus for pacing patients with severe congestive heart failure is shown. The heart sounds are sensed and used to derive a mechanical AV delay of the patient&#39;s heart. The pacemaker applied AV delay is adjusted until the measured AV falls in a predetermined range of between 180 ms to 250 ms. This solution may require extensive signal processing in order to derive the mechanical AV delay of the heart from the sensed heart sounds. In U.S. Pat. No. 6,044,298, a method and apparatus for optimizing a pacing mode of a cardiac pacemaker for patients having CHF are shown. The Total Acoustic Noise (TAN) is measured and an optimum pacing mode is determined by detecting the particular mode associated with the minimum TAN, wherein the integrated value of the acoustic signal during a single heart beat cycle (from P-wave to P-wave or from R-wave to R-wave) is referred to as the total acoustic noise (TAN). However, the total acoustic noise is blunt tool in the optimization of the AV interval due to the fact that it comprises noise from of a large number of sources including, for example, the first heart sound to the fourth heart sound (S 1 -S 4 ). In addition, other factors such as activity level of the patient, position of the patient, etc. also affect and/or contribute to the noise. This may, for example, introduce errors since it may be difficult to identify which noise source that contributes to the total noise signal and to what extent different sources contribute to it, which, in turn, may entail unreliable optimization results. Hence, the optimization may be based, at least in part, on erroneous information. In WO 01/56651 a system and method for adjusting AV delay by monitoring heart sounds S 1  and S 2  is disclosed. The presence or absence of one or more of the heart sounds S 1  and S 2  in the sensor signal indicates whether a stimulation pulse evokes the desired response in the patient&#39;s heart. This solution is thus directed to monitoring whether a desired response was obtained where the presence of a predetermined heart sound indicates capture rather than optimizing the AV delay. 
     Thus, there is a need of a method and a medical device that are capable of automatically controlling the stimulation therapy, and in particular the AV or PV delay, and that provide reliable optimization results using detected heart sounds. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the present invention is to provide a method and medical device that are capable of automatically controlling the stimulation therapy, in particular the AV or PV delay. 
     Another object of the invention is to provide reliable and accurate optimization results using detected heart sounds. 
     According to an aspect of the present invention, there is provided an implantable medical device including a pulse generator adapted to produce cardiac stimulating pacing pulses, the device being connectable to at least one lead comprising electrodes for delivering the pulses to cardiac tissue in at least one atrium and/or in at least one ventricle of a heart of a patient. The device has a signal processing circuit adapted to extract a signal corresponding to a first heart sound (S 1 ) from a measured acoustic signal, which signal has been received from an acoustic sensor adapted to sense an acoustic energy and to produce acoustic signals indicative of heart sounds of the heart of the patient over predetermined periods of a cardiac cycle during successive cardiac cycles, and to calculate an energy value corresponding to the extracted signal; a storage unit that stores the energy value corresponding to the first heart sound and/or the extracted signal; and a controller adapted to initiate an optimization procedure, wherein a delivery of the pacing pulses is controlled iteratively based on successive energy values corresponding to successive first heart sound signals to determine an optimal PV interval or AV interval with respect to the energy values. 
     According to a second aspect of the present invention, there is provided method for operating an implantable medical device to control a stimulation therapy, which device includes a pulse generator adapted to produce cardiac stimulating pacing pulses and which device is connectable to at least one lead comprising electrodes for delivering the pulses to cardiac tissue in at least one atrium and/or in at least one ventricle of a heart of a patient. The method includes the steps of sensing an acoustic energy; producing acoustic signals indicative of heart sounds of the heart of the patient over predetermined periods of a cardiac cycle during successive cardiac cycles; extracting a signal corresponding to a first heart sound (S 1 ) from a measured acoustic signal; calculating an energy value corresponding to the extracted signal; storing the energy value corresponding to the first heart sound; and initiating an optimization procedure, the optimization procedure comprising the steps of: iteratively controlling a delivery of the pacing pulses based on successive energy values corresponding to successive first heart sound signals and determining an optimal PV interval or AV interval with respect to the energy values. 
     According to a further aspect of the present invention, there is provided a computer readable medium encoded with programming instructions that cause a computer to perform a method according to the second aspect of the present invention. 
     Thus, the invention is based on the insight that the amplitude of the E1 signal, i.e. the energy value corresponding to the first heart sound (S 1 ), is closely related to the length of the AV or PV interval. In particular, the E1 signal depends highly on the AV or PV interval in that a too short AV interval gives an abnormally high E1 value while a long AV interval gives a low E1 value. Moreover, a certain amplitude of the E1 signal is associated with a specific activity level or activity level range at a normal cardiac function. That is, at a certain cardiac function there exists a suitable or optimal energy value or range for each activity level or activity level range. Thus, the optimization of the AV or PV interval according to the present invention is based on the above-mentioned findings in that a delivery of pacing pulses is iteratively controlled based on successive energy values corresponding to successive first heart sound signals and an optimal PV interval or AV interval is determined with respect to the energy values. 
     The present invention provides several advantages. For example, one advantage is that the optimization procedure for identifying an optimal AV or PV delay with respect to the energy value can be performed on a continuous and automated basis. 
     Another advantage is that the optimization can adapt to changing conditions of a heart of patient in a fast and reliable way since intrinsic information of the heart, i.e. the heart sounds, is used as input to the optimization procedure. The optimization is also accurate due to the facts that the systolic and diastolic heart functions are reflected in the heart sound, and that the heart sounds and their relations thus carry information of the workload and status of the heart. 
     The fact that the heart sounds are obtained by means of an implantable medical device connectable to an acoustic sensor that senses sounds or vibrations inside or outside the heart also contributes to higher degree of accuracy and reliability. 
     A further advantage of the present invention is that it is possible to study changes of the energy over time, which may provide useful information regarding, for example, the variability of the energy parameters. This information can, in turn, be used as an indicator of, for example, a changed filling due to e.g. arrhythmia or conduction disorder. Furthermore, the collected energy information can be used to estimate the severity of congestive heart failure and thus to optimize the AV delay with respect to this condition. In addition, the collected energy information may be used to tune a combination of drugs given to the patient. 
     According to an embodiment of the present invention, the PV interval or AV interval is gradually adjusted until the optimal PV interval or AV interval with respect to the energy values can be determined. The fact that the E1 signal depends highly on the AV or PV interval in that a too short AV interval gives an abnormally high E1 value while a long AV interval gives a low E1 value is used. The PV interval or AV interval may be gradually adjusted until a present energy level is within a predetermined energy value range. Thereby, a fast and reliable optimization procedure can be obtained. 
     In another embodiment of the present invention, the optimization procedure comprises the steps of, upon initiation of the optimization procedure, select a first PV or AV interval and gradually reduce the first PV interval or AV interval; compare an energy value corresponding to the first heart sound resulting from delivered pacing pulses in accordance with a latest PV or AV interval with an energy value corresponding to the first heart sound resulting from delivered pacing pulses in accordance with a preceding PV or AV interval and determine a PV or AV interval to be optimal when the comparison between successive energy values indicates an increase of energy level of the first heart sounds. 
     According to yet another embodiments of the present invention, a delivery of ventricular pacing pulses is controlled such that a VV interval is kept substantially constant during the optimization procedure and the PV or AV interval is determined to be optimal for the present VV interval. 
     In another embodiment of the present invention, an activity level of the patient is sensed and upon initiation of the optimization procedure, a first PV or AV interval is selected and the first PV interval or AV interval is gradually adjusted until an energy value corresponding to the first heart sound resulting from at least one delivered pacing pulse in accordance with a latest PV or AV interval is within a predetermined energy value range associated with the sensed activity level. The fact that, at a certain cardiac function, there exists a suitable or optimal energy value or energy value range for each activity level or activity level range is used. Thereby, a fast and reliable optimization procedure can be obtained. In addition, by performing this optimization procedure at two or more activity levels, it is possible to extrapolate the data to obtain a rate adaptive AV or PV delay. 
     According to an alternative embodiment, interventricular pacing timing parameters for at least one electrode is iteratively adjusted based on the energy values. 
     In yet another embodiment of the present invention, a bandpass filter is adapted to filter off frequency components of the acoustic signal outside a predetermined frequency range. The bandpass filter may have a frequency range of 10 to 300 Hz. The filtered signal is rectified to produce a signal containing only positive or zero values and at least one local maximum point being coincident with a first heart sound signal is identified in the rectified signal. To produce the energy value corresponding to the specific heart sound, the first heart sound signal is integrated in a predetermined time window comprising the at least one local maximum point. Alternatively, a squaring procedure is performed on the filtered signal to produce a signal containing only positive or zero values. A further alternative to the rectifying is to determine absolute values of the filtered signal. At least one local maximum point being coincident with a first heart sound signal is identified in the squared signal and the first heart sound signal is integrated in a predetermined time window comprising the at least one local maximum point to produce the energy value corresponding to the specific heart sound, wherein an energy value corresponding to the first heart sound can be obtained. 
     In a further embodiment of the present invention, a part of the signal containing only positive or zero values, i.e. the rectified or squared signal, above a predetermined threshold is selected and the part of the signal above the predetermined threshold is integrated, wherein an energy value corresponding to the first heart sound can be obtained. 
     In an embodiment of the present invention, each energy value is calculated as a mean value over a predetermined number of successive energy values. Thereby, more reliable and accurate energy values can be obtained. Alternatively, a weighted average value of a predetermined number of successive energy values can be used. In still another embodiment, a moving average of a predetermined number of successive energy values of heart sound signals is utilized. 
     In another embodiment of the present invention, an activity level of the patient is sensed and it is checked whether the sensed activity level is below a predetermined activity level. If it is determined the sensed activity level is below the predetermined activity level or activity level range, the optimization procedure is initiated. By performing the optimization at stable conditions, e.g. correlating the optimization procedure with a predetermined activity level, the accuracy and reliability of the procedure can be further enhanced. This predetermined activity level can, for example, be set such that the optimization is performed at rest. That is, in this case an AV or PV delay that is optimal for situations when the patient is at rest can be obtained. 
     According to yet another embodiment of the present invention, an activity level of the patient is sensed and it is checked whether the sensed activity level is below a predetermined first activity level (or within a first range) or within a second activity level range between a second activity level and a third activity level, wherein second activity level can be equal to or higher than the first activity level or equal to or higher than an upper limit of the first range. If the sensed activity level is found to be below the predetermined first activity level, an optimization procedure is initiated to identify a first AV or PV interval for the first activity level, and if the sensed activity level is found to be within the activity level range, an optimization procedure is initiated to identify a second AV interval or PV interval for the activity level range. Thus, the optimization can be performed at two activity levels, and the AV or PV interval can be optimized, for example, at rest and at an elevated activity level (e.g. at exercise), respectively. By knowing the optimal AV or PV delay at two activity levels, it is possible to extrapolate the data to obtain a rate adaptive AV or PV delay. 
     According to an alternative embodiment, a heart rate of the patient is sensed and it is determined whether the sensed heart rate is within a predetermined heart rate interval. If it is determined that the sensed heart rate is within the predetermined heart rate interval, an optimization procedure is initiated. By performing the optimization at stable conditions, e.g. correlating the optimization procedure with a predetermined heart rate level, the accuracy and reliability of the optimization procedure can be further improved. 
     According to another embodiment, at least one body position of the patient is detected and it is determined whether the patient is in at least one predetermined specific body position. If it is determined that the patient is in the predetermined position, an optimization procedure is initiated. By performing the optimization at stable conditions, e.g. correlating the optimization procedure with a predetermined position, the accuracy and reliability of the optimization procedure can be improved. Furthermore, the optimization can be performed at two different positions, for example, when the patient is in supine (lying down) and when the patient is in an upright position and thus an optimal AV or PV delay can be obtained for the supine position and an optimal AV or PV delay can be obtained for the upright position. In this way, the AV or PV delay can be optimized during different conditions. 
     In alternative embodiments, the optimization can be synchronized with anyone, some, or all of the following: heart rate, activity level, AV delay, pacing rate, or position of patient. 
     In embodiments, the acoustic sensor is arranged in a lead connectable to the device and is located e.g. in the right ventricle of the heart of the patient, in the left ventricle or in a coronary vein on the middle of the left ventricle. In addition, the sensor may be located in any suitable position in the body of a patient, e.g. vena cava, epicardially, or other places in thorax. 
     According to embodiments, the acoustic sensor is an accelerometer, a pressure sensor or a microphone. 
     In an alternative embodiment, the sensor is arranged within a housing of the implantable device. 
     As realized by the person skilled in the art, the methods of the present invention, as well as preferred embodiments thereof, are suitable to realize as a computer program or a computer readable medium. 
     The features that characterize the invention, both as to organization and to method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawings. It is to be expressly understood that the drawings is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic diagram showing a medical device implanted in a patient in which device the present invention can be implemented. 
         FIG. 2  is block diagram of the primary functional components of a first embodiment of the medical device according to the present invention. 
         FIG. 3  is a block diagram of the primary functional components of another embodiment of the medical device according to the present invention. 
         FIG. 4  is a flow chart of an embodiment of the method according to the present invention. 
         FIG. 5  shows a typical cardiac cycle, related heart sounds, and the resulting signals at a heart rate of 75 BPM. 
         FIG. 6   a  is a diagram illustrating the relationship between the energy level corresponding to the first heart sound (S 1 ) and AV-delay. 
         FIG. 6   b  is a diagram illustrating the relationship between the energy level corresponding to the first heart sound (S 1 ) and activity level. 
         FIG. 7  is a flow chart of an embodiment of the optimization procedure according to the present invention. 
         FIG. 8  is a flow chart of another embodiment of the optimization procedure according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , there is shown a schematic diagram of a medical device implanted in a patient in which device the present invention can be implemented. As seen, this embodiment of the present invention is shown in the context of a pacemaker  2  implanted in a patient (not shown). The pacemaker  2  comprises a housing being hermetically sealed and biologically inert. Normally, the housing is conductive and may, thus, serve as an electrode. The pacemaker  2  is connectable to one or more pacemaker leads, where only two are shown in  FIG. 1  namely a ventricular lead  6   a  and an atrial lead  6   b . The leads  6   a  and  6   b  can be electrically coupled to the pacemaker  2  in a conventional manner. The leads  6   a ,  6   b  extend into the heart  8  via a vein  10  of the patient. One or more conductive electrodes for receiving electrical cardiac signals and/or for delivering electrical pacing to the heart  8  are arranged near the distal ends of the leads  6   a ,  6   b . As will be apparent to those skilled in the art, the leads  6   a ,  6   b  may, for example, be implanted with their distal ends located in either the right atrium or right ventricle of the heart  8 . Moreover, they may be in form of epicardial leads attached directly at the epicardium, they may be located in the left ventricle or in a coronary vein on the middle of the left ventricle. In addition, leads comprising a sensor may be located in any suitable position in the body of a patient, e.g. vena cava, or other places in thorax. 
     With reference now to  FIG. 2 , the configuration including the primary components of an embodiment of the present invention will be described. The illustrated embodiment comprises an implantable medical device  20 , such as the pacemaker shown in  FIG. 1 . Leads  26   a  and  26   b , of the same type as the leads  6   a  and  6   b  shown in  FIG. 1 , are connectable to the device  20 . The leads  26   a ,  26   b  may be unipolar or bipolar, and may include any of the passive or active fixation means known in the art for fixation of the lead to the cardiac tissue. As an example, the lead distal tip (not shown) may include a tined tip or a fixation helix. The leads  26   a ,  26   b  carry one or more electrodes (as described with reference to  FIG. 1 ), such as a tip electrode or a ring electrode, arranged to, inter alia, measure the impedance or transmit pacing pulses for causing depolarization of cardiac tissue adjacent to the electrode (-s) generated by a pace pulse generator  25  under influence of a controller  27  including a microprocessor. The controller  27  controls, inter alia, pace pulse parameters such as output voltage and pulse duration. 
     Furthermore, an acoustic sensor  29  is arranged in or connected to one of the leads  26   a ,  26   b . Alternatively, the acoustic sensor is located within the housing of the device  20 . In one embodiment, the acoustic sensor  29  is arranged in a lead located in a right ventricle of the heart, in coronary sinus or the great cardiac vein of the patient. The acoustic sensor  29  may, for example, be an accelerometer, a pressure sensor, or a microphone. The acoustic sensor  29  is adapted to sense acoustic energy of the heart and to produce signals indicative of heart sounds of the heart of the patient. For example, the acoustic sensor  29  may sense the acoustic energy over predetermined periods of a cardiac cycle during successive cardiac cycles. In one embodiment of the present invention, a sensing session to obtain a signal indicative of a first heart sound (S 1 ) is synchronized with a detected heart event, e.g. detection of an intrinsic or paced QRS-complex. 
     Furthermore, the implantable medical device  20  comprises a signal processing circuit  23  adapted to process the sensed signal to extract a signal corresponding to a first heart sound (S 1 ) and to calculate an energy value corresponding to the extracted signal. In one embodiment, the signal processing circuit  23  includes pre-process circuits including at least one bandpass filter  30  adapted to filter off frequency components of the heart sound signal outside a predetermined frequency range, for example, 10-300 Hz, and a determining circuit  32  adapted to determine the absolute value of the bandpass filtered signal and to produce a resulting absolute value heart sound signal. The bandpass filter  30  is, for example, a digital filter of second order and the filtering process is performed as a zero-phase procedure to cancel out time delays introduced by the filter, and hence the signal is filtered twice, first in a forward direction and in then in a backward direction. As alternatives to the determining means, a rectifier can be used to rectify the filtered signal or the filtered signal can be squared to obtain the instantaneous power of the filtered signal. The signal processing circuit  23  also has an energy calculating circuit  34  adapted to calculate an energy value corresponding to the filtered signal. For example, the energy calculating circuit  34  may include an identifying circuit  36  adapted to identify at least one local maximum point being coincident with a first heart sound (S 1 ) and an integrator  38  adapted to integrate the filtered signal over a predetermined time window exhibiting the local maximum point, wherein an energy value of the filtered signal is obtained. 
     A storage unit  31  is connected to the controller  27 , which storage means  31  may include a random access memory (RAM) and/or a non-volatile memory such as a read-only memory (ROM). Detected signals from the patients heart are processed in an input circuit  33  and are forwarded to the controller  27  for use in logic timing determination in known manner. The implantable medical device  20  is powered by a battery  37 , which supplies electrical power to all electrical active components of the medical device  20 . Data contained in the storage means  31  can be transferred to a programmer (not shown) via a programmer interface (not shown) for use in analyzing system conditions, patient information, etc. 
     With reference now to  FIG. 3 , another embodiment of the present invention will be described. Like parts in  FIG. 2  and  FIG. 3  are denote with the same reference numeral and the description thereof will be omitted since they have been described with reference to  FIG. 2 . The implantable medical device  20 ′ may include activity level sensing means  41  for sensing an activity level of the patient connected to the controller  27 . The controller  27  may be adapted to determine whether a sensed activity level is within a predetermined activity level range and to, if the sensed activity level is found to be within the range, initiate an optimization procedure comprising the steps of: selecting a first PV or AV interval; and gradually adjusting the first PV interval or AV interval until an energy value corresponding to the first heart sound resulting from at least one delivered pacing pulse in accordance with a latest PV or AV interval is within a predetermined energy value range. 
     In addition, the implantable medical device  20 ′ may include heart rate sensor  43  for sensing a heart rate of the patient connected to the controller  27 . The controller  27  may be adapted to determine whether a sensed heart rate is within a predetermined heart rate interval and to initiate an optimization procedure if the sensed heart rate is determined to be within the predetermined heart rate interval. 
     Furthermore, the implantable medical device  20 ′ according to the present invention comprises a position detecting sensor  35  arranged to detect a body position of the patient. For example, the position sensor  35  can adapted to detect a predetermined specific body position. In a one embodiment of the present invention, the position detecting means is a back-position sensor arranged to sense when the patient is lying on his or her back (or on his or her face). The position detecting sensor  35  is connected to the controller  27 . 
     As the skilled man realizes, only one, some of or all of the following features: the activity level sensing means  41 , the heart rate sensor  43 , a breathing rate sensor, the position detector  35 , or the means for sensing signals related to the heart pumping activity of the patient may be included in the medical device according to the present invention. 
     Turning now to  FIG. 4 , a high-level description of the method according to the present invention will be given. First, at step  50 , the acoustic sensor  29  senses an acoustic energy and produces signals indicative of heart sounds of the heart of the patient. In  FIG. 5 , a typical cardiac cycle, related heart sounds, and the resulting signals at a heart rate of 75 BPM are shown. A surface electrocardiogram and the related heart sounds S 1 , S 2 , S 3 , and S 4  are indicated by  60  and  61 , respectively, and a time axis is indicated by  62 . In one embodiment, the acoustic sensor  29  is activated by the detection of a QRS-position, as indicated by  63 , an intrinsic detected event or a paced event indicated by  60 . The acoustic sensor  29  senses the acoustic energy in the heart sound S 1 , indicated by  61 , during a sensing session having a predetermined length, for example, during a predetermined time window, indicated by  64 . In this embodiment, the initiation of the sensing session is synchronized with the detection of the QRS-position, indicated by  63 . The length of the time window is programmable and a typical length is about 200 ms. Hence, the acoustic sensor  29  receives a triggering signal from the controller  27  upon detection of the QRS-position by the input circuit  33 . The produced signal corresponding to the first heart sound S 1  is indicated by  65 . This may be performed during successive cardiac cycles under control of the controller  27 , which thus produces a time series of successive heart sound signals. The produced signal or signals indicative of the first heart sounds are supplied to the signal processing circuit  23  where, at step  52 , a signal corresponding to a first heart sound (S 1 ) is extracted from a sensed signal by the pre-processing circuits  30 ,  32 . Optionally, this step may include performing a filtering procedure in order to filter the sensed signal. In one embodiment, frequency components of the signal outside a predetermined frequency range is filtered off and the absolute value of the sensed signal is calculated. The resulting signal is indicated by  66  in  FIG. 5 . In another embodiment, the first heart sound signal is determined to be a part of the sensed signal having an amplitude above a predetermined amplitude level. 
     Thereafter, at step  54 , an energy value corresponding to the extracted signal, indicated by  66  in  FIG. 5 , corresponding to the first heart sound is calculated in the energy calculating circuit  34 . Then, at step  55 , the calculated energy values and/or the extracted signal may be stored in the memory means  31 . If signals corresponding to the first heart sound is obtained for successive cardiac cycles, the signals and calculated energy values can be stored in the memory means  31  in consecutive time order. Subsequently, at step  58 , an optimization procedure is initiated. Optionally, a check whether conditions, such as activity level of the patient or position of the patient, are suitable for performing an optimization procedure can be performed before the optimization procedure is initiated. That is, the optimization procedure is initiated only if certain predetermined conditions are fulfilled, for example, that a sensed activity level is within a predetermined activity level range. Thus, optionally, a optimization procedure condition check step  56  may be performed before the optimization procedure is initiated. If the predetermined condition (-s) is (are) fulfilled, the optimization step  58  is initiated. On the other hand, if the predetermined condition (-s) is (are) not fulfilled, the procedure returns to step  50 . 
     With reference now to  FIGS. 6-8 , embodiments of the optimization procedure will be described. 
     Referring first to  FIG. 7 , an embodiment of the optimization procedure where the fact that the E1 signal, i.e. the energy value corresponding to the first heart sound (S 1 ), depends highly on the AV or PV interval is utilized will be described. To be precise, a too short AV interval gives an abnormally high E1 value while a long AV interval gives a low E1 value, as illustrated in  FIG. 6   a . First, at step  70 , upon initiation of the optimization procedure, a first or initial PV or AV interval is selected. This first interval or delay is preferably relatively long, which, as can be seen in  FIG. 6   a , entails that an energy value corresponding to a first heart sound (S 1 ) resulting from a delivered stimulation therapy using the first interval will be low. Then, at step  71 , the energy value corresponding to the first heart sound resulting from the delivered pacing pulse (-s) is stored, which energy value can be obtained in accordance with the procedure described above with reference to  FIG. 4 . Thereafter, at step  72 , the initial AV or PV delay is reduced. The AV or PV delay can be reduced in accordance with predetermined steps, which may be programmable. In step  73 , the resulting energy value is stored, which energy value can be obtained in accordance with the procedure described above with reference to  FIG. 4 . Subsequently, at step  74 , the latest energy value corresponding to the first heart sound resulting from the delivered pacing pulse (-s) in accordance with the latest PV or AV interval is compared with the energy value corresponding to the first heart sound resulting from delivered pacing pulse (-s) in accordance with the preceding PV or AV interval. If the latest energy value is determined to be higher than the preceding energy value with a predetermined factor, the procedure proceeds to step  75 . If the latest energy value is lower than, equal to, or higher than, but with a factor being lower than the predetermined factor, the preceding energy value, the procedure returns to step  72  where the AV or PV delay is reduced again. In an embodiment, each energy value is compared with a mean value of a predetermined number of preceding energy values, for example, a weighted mean value. At step  75 , the present AV or PV delay is identified to be the optimal delay or interval. 
     With reference now to  FIG. 8 , an embodiment of the optimization procedure where the fact that a certain amplitude of the E1 signal, i.e. the energy value corresponding to the first heart sound (S 1 ), or a certain amplitude range is associated with a specific activity level or activity level range at a normal cardiac function. That is, at normal cardiac function there exists a suitable or optimal energy value or range for each activity level or activity level range, as illustrated in  FIG. 6   b . As can be seen, the activity level A 1  is associated with an energy value range between E1 1 , and E1 2  whereas the activity level A 2  is associated with an energy value range between E1 3  and E1 4 . First, at step  80 , an activity level of the patient is sensed. Then, at step  81 , an energy level range associated with the sensed activity level, or in fact a predetermined activity level range about the sensed activity level, is identified, i.e. the amplitude range associated with the sensed activity level or activity level range at a normal cardiac function. For example, the storage means  31  may contain a look-up table containing a list of energy level ranges each being associated with a specific activity level range and the controller  27  can be adapted to collect the energy value range corresponding to the activity level range comprising the sensed activity level. Subsequently, at step  82 , an PV or AV interval is selected. Then, at step  83 , the energy value corresponding to the first heart sound resulting from the delivered pacing pulse (-s) is stored, which energy value can be obtained in accordance with the procedure described above with reference to  FIG. 4 . Subsequently, at step  84 , the energy value corresponding to the first heart sound resulting from the delivered pacing pulse (-s) in accordance with the latest PV or AV interval is compared with the pre-stored energy value range. If the energy value is within the pre-stored energy level range, the procedure proceeds to step  85  where the present AV or PV delay is identified to be the optimal delay or interval for the sensed activity level (or activity level range about the sensed activity level). If the energy value is outside the pre-stored energy level range, the procedure proceeds to step  86  where an adjustment of the present AV or PV delay is calculated, i.e. whether the delay should be lengthened or shortened depending on whether the latest energy value is above or below the range, respectively. Then, at step  87 , a new PV or AV interval is selected based on the adjustments calculated in step  86 . 
     An ordered set of pre-set AV intervals and/or PV intervals may be programmed into the memory  31 , for example, at the time of implant by the physician, and they can also be re-programmed using a programmer via a programmer interface. This timing interval set may contain a range of AV intervals and/or PV intervals over which the controller  27  will automatically switch during an optimization procedure. 
     As described with reference to  FIG. 3 , an activity level of the patient can be sensed by means of the activity level sensor  41  and the controller  27  may be adapted to checked whether the sensed activity level is below a predetermined activity level. If it is determined the sensed activity level is below the predetermined activity level or activity level range, the optimization procedure is initiated as discussed with reference to  FIG. 4 . By performing the optimization at stable conditions, e.g. correlating the optimization procedure with a predetermined activity level, the accuracy and reliability of the procedure can be further enhanced. This predetermined activity level can, for example, be set such that the optimization is performed at rest. That is, in this case an AV or PV delay that is optimal for situations when the patient is at rest can be obtained. The controller  27  according to an alternative embodiment be adapted to check whether the sensed activity level is below a predetermined first activity level (or within a first range) or within a second activity level range between a second activity level and a third activity level, wherein second activity level can be equal to or higher than the first activity level or equal to or higher than an upper limit of the first range. If the sensed activity level is determined to be below the predetermined first activity level, an optimization procedure is initiated to identify a first AV or PV interval for the first activity level, and if the sensed activity level is found to be within the activity level range, an optimization procedure is initiated to identify a second AV interval or PV interval for the activity level range. Thus, the optimization can be performed at two activity levels, and the AV or PV interval can be optimized, for example, at rest and at an elevated activity level (e.g. at exercise), respectively. By knowing the optimal AV or PV delay at two activity levels, it is possible to extrapolate the data to obtain a rate adaptive AV or PV delay. 
     According to another embodiment, the body position of the patient is detected by means of the position sensor  35  and the controller  27  may be adapted to determine or check whether the patient is in at least one predetermined specific body position. If it is determined that the patient is in the predetermined position, an optimization procedure is initiated as discussed with reference to  FIG. 4 . By performing the optimization at stable conditions, e.g. correlating the optimization procedure with a predetermined position, the accuracy and reliability of the optimization procedure can be improved. Furthermore, the position sensor  35  may be adapted to detect two different positions of the patient and the controller  27  may be adapted to determine whether the patient is in one of this predetermined positions and initiate an optimization procedure when the patient is in one of them. Thereby, the optimization can be performed at two different positions, for example, when the patient is in supine (lying down) and when the patient is in an upright position and thus an optimal AV or PV delay can be obtained for the supine position and an optimal AV or PV delay can be obtained for the upright position. In this way, the AV or PV delay can be optimized during different conditions. 
     Although specific embodiments have been shown and described herein for purposes of illustration and exemplification, it is understood by those of ordinary skill in the art that the specific embodiments shown and described may be substituted for a wide variety of alternative and/or equivalent implementations without departing from the scope of the invention. Those of ordinary skill in the art will readily appreciate that the present invention could be implemented in a wide variety of embodiments, including hardware and software implementations, or combinations thereof. As an example, many of the functions described above may be obtained and carried out by suitable software comprised in a micro-chip or the like data carrier. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein.