Patent Publication Number: US-2015088005-A1

Title: Apparatus and method for outputting heart sounds

Description:
CLAIM OF PRIORITY 
     This application is a continuation of application Ser. No. 14/080,454, filed on November 14, 2013, which is a continuation of application Ser. No. 13/928,674, filed on Jun. 27, 2013, now U.S. Pat. No. 8,663,123, which is a continuation of application Ser. No. 13/456,795, filed on Apr. 26, 2012, now U.S. Pat. No. 8,478,391, which a continuation of application Ser. No. 13/004,543, filed on Jan. 11, 2011, now U.S. Pat. No. 8,167,811, which is a continuation of application Ser. No. 11/037,276, filed on Jan. 18, 2005, now U.S. Pat. No. 7,883,470, which is a continuation of application Ser. No. 09/833,229, filed on Apr. 11, 2001, now U.S. Pat. No. 7,052,466, the specifications of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of cardiac monitoring, and more particularly relates to detecting heart sounds using an implanted sensor, transmitting data indicative of the heart sounds to an external system, and outputting the heart sound data. 
     BACKGROUND 
     Cardiac pacemakers generally (provide functions including sensing electrical signals generated by the heart, controlling stimulation of excitable tissues in the heart, sensing the response of the heart to such stimulation, and responding to inadequate or inappropriate stimulus or response (e.g., dysrhythmia) to deliver therapeutic stimuli to the heart. Some existing cardiac pacemakers also function to communicate with an external programmer device to support a variety of monitoring, diagnostic and configuration functions. 
     Certain cardiac pacemakers include an internal accelerometer for measuring the level of activity of the patient (e.g., movement caused by walking around, or by muscle twitches). Such pacemakers process (e.g., filter) the accelerometer signals to reduce noise interfering with the measurement of the patient&#39;s activity, such as the sounds generated by the heart itself, and then use the processed signals as inputs to algorithms for generating the signals used to control the stimulation of the heart. For example, if accelerometer signals indicate that a patient is walking briskly, the s pacemaker may stimulate the heart to beat at a faster rate (often subject to an upper rate limit) than when the patient is at rest. While the accelerometer signal is used internally to control the heart rate, this signal is not transmitted by the pacemaker to an external programmer for subsequent display on a display device. Thus, the accelerometer signal itself is an internal signal which is not output to the user. 
     A common method of diagnosing heart problems involves comparing the electrical operation of the heart to its mechanical operation, and identifying electrical-mechanical disassociation. Typically, a physician listens to a patient&#39;s heart using a stethoscope placed on the surface of the patient&#39;s body, and compares the heart sounds to an electrocardiograph (ECG) trace generated by an ECG machine coupled to probes placed on the patient&#39;s chest. This method suffers from several disadvantages, including the need to use the stethoscope, the effect of various factors (e.g., the placement of the stethoscope, body fat, etc.) on the heart sounds, the need to electrically couple ECG probes to the patient&#39;s chest, the difficulties faced by the physician in accurately comparing the sounds heard using the stethoscope to the traces displayed by the ECG machine, and the relatively high level of skill needed to perform this comparison (especially if a physician is not available). This method also does not continuously monitor for electrical-mechanical disassociation, thus making it difficult to detect disassociation occurring between visits to the physician, and does not provide the ability to produce a written record showing a detected disassociation. 
     Thus, it would be desirable to provide a method and apparatus for outputting heart sounds, and/or for comparing electrical operation of the heart to mechanical operation of the heart, that overcome one or more of the above-described disadvantages. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, an implantable system includes a sensor for detecting heart sounds and generating sensed signals representative thereof, an interface circuit for communicating with an external system, and a control circuit coupled to the sensor and the interface circuit. The control circuit receives the sensed signals, generates data representative of the heart sounds therefrom, and transmits the data to the external system via the interface circuit. The sensor, interface circuit and control circuit are implantable. In another aspect, an implantable system also includes a second sensor for detecting cardiac electrical signals and generating second sensed to signals representative thereof, and the control circuit also receives the second sensed signals, generates second data representative of the cardiac electrical signals therefrom, and transmits the second data to the external system. In another aspect, an implantable system also includes a third implantable sensor for detecting second cardiac electrical signals and generating third sensed signals representative thereof, and the control circuit receives the third sensed signals, generates third data representative of the second cardiac electrical signals therefrom, and transmits the third data to the external system. 
     According to another aspect, an external system includes an interface circuit to communicate with an implanted system, an output device, and a control circuit coupled to the interface circuit and output device. The control circuit receives data representing heart sounds detected by the implanted system, and generates control signals that, when applied to the output device, cause the output device to generate outputs which represent the heart sounds. In another aspect, a control circuit also receives data representing cardiac electrical signals from the implanted system, and generates control signals to cause the output device to generate outputs representing the heart sounds and cardiac electrical signals. In another aspect, a control circuit receives data representing second cardiac electrical signals from the implanted system, and causes the output device to generate outputs representing the heart sounds and the two cardiac electrical signals. 
     According to another aspect, a method of outputting heart sounds includes detecting heart sounds using an implanted sensor, and transmitting data representing the heart sounds to an external system. In another aspect, a method also includes detecting cardiac electrical signals using an implanted sensor and transmitting data representing the cardiac electrical signals to an external device. In another aspect, a method also includes detecting second cardiac electrical signals using an implanted sensor, and also transmitting data representing the second cardiac electrical signals to an external device. 
     According to another aspect, a method of outputting heart sounds includes receiving data representing heart sounds detected by an implanted system, generating control signals using the data, and applying the control signals to an output device to cause the output device to generate outputs which represent the heart sounds. In another aspect, a method also includes receiving second data representing cardiac electrical signals from the implanted system, and generating the control signals using the second data to cause the outputs generated by the output device to represent the cardiac signals. In another aspect, a method also includes receiving third data representing second cardiac electrical signals from the implanted system, and generating the control signals using the third data to cause the outputs to also represent the second cardiac signals. Other aspects of the present invention will be apparent upon reading the following detailed description of the invention and viewing the drawings that form a part thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary system for detecting heart sounds using an implanted sensor, transmitting data representing the heart sounds to an external system, and outputting the heart sound data, according to one embodiment of the invention; 
         FIG. 2  is a flow chart illustrating one embodiment of the processing performed by the controller of the implantable device shown in  FIG. 1 ; 
         FIG. 3  is a flow chart illustrating one embodiment of the processing performed by the controller of the external device shown in  FIG. 1 ; 
         FIG. 4  is a block diagram illustrating one embodiment of the signal processing performed on the heart sound signals detected by the exemplary system shown in  FIG. 1 ; 
         FIG. 5  is an exemplary output display screen that is generated by the external device shown in  FIG. 1 ; 
         FIG. 6  is another exemplary output display screen that is generated by the external device shown in  FIG. 1 ;  FIG. 7  is a flow chart showing another embodiment of the processing performed by the controller of the implantable device shown in  FIG. 1 , including a logbook feature; and 
         FIG. 8  is a block diagram of another exemplary system for outputting heart sounds. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the present invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. 
     Referring to  FIG. 1 , an exemplary system  100  for outputting heart sounds in accordance with one embodiment of the present invention comprises an implantable system  102  and an external system  104 . Implantable system  102  and external system  104  are configured to communicate via a communications link  106 . In one embodiment, link  106  uses radio-frequency (RF) signals. In another embodiment, link  106  uses optical signals. These communications may support monitoring, diagnostic and configuration functions. 
     Implantable system  102  includes an implantable device  108  operatively coupled to a patient&#39;s heart  110  by a pacing lead  112 . The components of implantable device  108  include an atrial sense amplifier  114 , a ventricular sense amplifier  116 , an atrial stimulating circuit  118 , a ventricular stimulating circuit  120 , a. controller  122 , a memory  124 , an accelerometer  126 , an analog pre-processing circuit  128 , an analog-to-digital (A/D) converter  130 , and an input/output (I/O) interface  132 . The components of implantable device  108  are housed within an implantable housing (indicated by the broken lined box in  FIG. 1 .) which is implanted within the patient&#39;s chest cavity (e.g., in the pectoral region). 
     Atrial sense amplifier  114 , ventricular sense amplifier  1116 , atrial stimulating circuit  118  and ventricular stimulating circuit  120  are operatively coupled to pacing lead  112  via a pair of conductors  134 . Pacing lead  112  includes an atrial sensing electrode  136  and an atrial stimulating electrode  138  adapted to be disposed in the right atrial chamber of heart  110 , and a ventricular sensing electrode  140  and a ventricular stimulating electrode  142  adapted to be disposed in the right ventricular chamber of heart  110 . Sensed atrial and ventricular electrical signals generated by sensing electrodes  136  and  140  are applied to atrial and ventricular sense amplifiers  114  and  116 , respectively, and atrial and ventricular stimulating signals generated by atrial and ventricular stimulating circuits  118  and  120  are applied to atrial and ventricular stimulating electrodes  138  and  142 , respectively. Atrial sense amplifier  114 , ventricular sense amplifier  116 , atrial stimulating circuit  118 , and ventricular stimulating circuit  120 , are each also operatively coupled to controller  122 . 
     In other embodiments, other sensing electrode configurations are used for internally sensing one or more electrical signals of heart  110 . In one example, only one of sensing electrodes  136  and  140  is used. In another example, one or more electrodes placed within the body but outside of heart  110  are used for generating sensed cardiac electrical signals. In yet another example, a sensing electrode is placed within the implantable housing. in each of these examples, the sensing electrodes are operatively coupled to controller  122 . 
     In the embodiment shown in  FIG. 1 , the sensing electrodes  136  and  140  and the stimulating electrodes  138  and  142  are disposed in the right side of heart  110 . In other embodiments, one or more sensing electrode(s) and one or more stimulating electrode(s) are disposed in the left side of the heart (in lieu of being disposed in the right side of the heart, or in addition to sensing electrode(s) and stimulating electrode(s) disposed in the right side of the heart). The addition of left heart sensing may advantageously allow for the resolution of ambiguities due to disassociation of right and left heart conduction. 
     Controller  122  includes a micro-controller or microprocessor which is configured to execute a program stored in a read-only memory (ROM) portion of memory  124 , and to read and write data to and from a random access memory (RAM) portion of memory  124 . By executing the program stored in memory  124 , controller  122  is configured to process the atrial and ventricular electrical signals from atrial and ventricular sense amplifiers  114  and  116 , and to provide control signals to atrial and ventricular stimulating circuits  118  and  120 . in response, stimulating circuits  118  and  120  provide stimulating pulses to heart  110  via atrial and ventricular stimulating electrodes  138  and  142  at appropriate times. In other embodiments, controller  122  may include other types of control logic elements or circuitry. 
     Implantable device  108  may be referred to as a dual-chamber pacemaker since pacemaking functions are provided to both atrial and ventricular chambers of heart  110 . In another embodiment, the implantable system includes a single-chamber pacemaker that senses electrical signals and provides stimulating pulses to a single chamber of heart  110 . In yet another embodiment, the implantable system does not provide any stimulation of heart tissues, but includes one or more sensing electrodes for sensing one or more electrical signals of heart  110 , and for providing corresponding sensed signals to controller  122 . In still another embodiment, the implantable system does not provide any sensing electrodes for sensing any cardiac electrical signals, but is configured to sense and transmit signals representing heart sounds using a sensor such as accelerometer  126 , as described below. 
     In the remainder of this description, implantable device  108  is described as a dual-chamber pacemaker since the present system may be used with patients who have already had a pacemaker implanted in their bodies, thereby alleviating the need to implant a device solely for the purpose of monitoring heart sounds and/or intra-cardial electrical signals, it is to be understood, however, that implantable system  102  need not provide the stimulation functions described herein, and may provide other functions which are not described herein. 
     Accelerometer  126  is configured to provide sensed signals to analog pre-processing circuit  128 , which generates an analog output signal which is digitized by A/D converter  130 . The digitized accelerometer signal is received by controller  122 . In the embodiment of  FIG. 1 , accelerometer  126  is located internally to the housing of implantable device  108 . In another embodiment, accelerometer  126  is located. externally to the implantable housing. Accelerometer  126  may include, for example, a. piezo-electric crystal accelerometer sensor of the type used by pacemakers to sense the level of activity of the patient, or may include other types of accelerometers that are packaged to fit in the implantable housing. To detect heart sounds, other types of sound-detecting sensors or microphones may also be used, such as pressure sensors or vibration sensors configured to respond to sounds made by the heart. 
     In another embodiment, system  100  includes a plurality (two or more) of sound-detecting sensors. In this embodiment, the plurality of sensed heart sound signals from the plurality of sensors may be individually transmitted to external system  104  for display as individual traces, may be combined (e.g., averaged) by external system  104  before being displayed as a single trace, or may be combined by controller  122  before being transmitted to external system  104  as a single heart sound signal. These sensors may include different types of sensors, sensors that are located in different locations, or sensors that generate sensed signals which receive different forms of signal processing. 
     In one embodiment, accelerometer  126  is configured to generate sensed signals representative of two distinct physical parameters: (1) the level of activity of the patient; and (2) the heart sounds generated by heart  110 . Accordingly, analog pre-processing circuit  128  is configured to pre-process the sensed signals from s accelerometer  126  in a manner which conforms to the signal characteristics of both of these physical parameters. For example, if the frequencies of interest for measuring the patient&#39;s level of activity are below 10 Hz, while the frequencies of interest for detecting heart sounds are between 0.05 Hz and 50 Hz, then analog pre-processing circuit  128  may include a low-pass filter having a cutoff frequency of 50 Hz. Controller  122  may then perform additional filtering in software using, for example, a low-pass filter with a cutoff frequency of 10 Hz to detect the level of activity of the patient, and a band-pass filter with cutoff frequencies of 0.05 Hz and 50 Hz to detect the heart sounds, although these signal processing functions could also be performed by external system  104 . Along with filtering, analog pre-processing circuit  128  may perform other processing functions including automatic gain control (AGC) functions. 
     In another embodiment, implantable device  108  has two pre-processing channels for receiving sensed signals from accelerometer  126 . In still another embodiment, implantable device  108  includes two accelerometers, with one accelerometer configured to generate sensed signals representative of the level of activity of the patient and the other accelerometer configured to generate sensed signals representative of heart sounds, In these latter two embodiments, any hardware and/or software processing performed on the sensed signals can conform to the specific characteristics of the respective sensed signals. For example, the analog pre-processing circuit used for the level-of-activity sensed signals can provide a low-pass filter with a cutoff frequency of 10 Hz, while the analog pre-processing circuit for the heart-sound sensed signals can provide a band-pass filter with cutoff frequencies of 0.05 and 50 Hz. In the latter case, each accelerometer can be selected, located and/or oriented to maximize the detection of the respective physical parameter. In yet another embodiment, if the implantable device does not need to sense the level of activity of the patient, accelerometer  126  may measure only the sounds made by heart  110 . 
     Controller  122  is capable of bi-directional communications with external system  104  via I/O interface  132 . In one embodiment I/O interface  132  communicates using RF signals, In other embodiments, I/O interface  132  communicates using optical signals, or a combination of RF and optical signals (e.g., RE signals for receiving data from external system  104  and optical signals for transmitting data to external system  104 , or vice-versa). Controller  122  uses I/O interface  132  for bi-directional communications with external system  104  to support conventional monitoring, diagnostic and configuration pacemaker functions. 
     Controller  122  also uses I/O interface  132  to telemeter data representative of the heart sounds sensed by accelerometer  126  to external system  104 . In various embodiments, controller  122  further uses I/O interface  132  to telemeter data representative of cardiac electrical signals (i.e., electrogram or EGM signals), which may include data representative of atrial electrical signals (i.e., A EGM signals) sensed by atrial sensing electrode  136 , and/or data representative of ventricular electrical signals (i.e., V EGM signals) sensed by ventricular sensing electrode  140 . Thus, implantable system  102  is capable of sensing heart sounds, atrial electrical signals and ventricular electrical signals, and of telemetering data representative of the heart sounds and/or cardiac electrical signals to external system  104 . In other embodiments, controller  122  telemeters data representative of cardiac electrical signals which were sensed by other configurations of internal cardiac sensing electrodes. 
     In one embodiment, external system  104  includes an external device  142  and a surface electrocardiograph (ECG) system  144 . External device  142  includes an external controller  146 , an I/O interface  148 , user input device(s)  150 , and user output device(s)  152 . Using I/O interface  148 , external controller  146  is configured for bi-directional communications with implantable device  108 , for receiving input signals from input device(s)  150 , and for applying control signals to output device(s)  152 . Input device(s)  150  include at least one input device which allows a user (e.g., a physician, nurse, medical technician, etc.) to generate input signals to control the operation of external device  142 , such as at least one user-actuatable switch, knob, keyboard, pointing device e.g., mouse), touch-screen, voice-recognition circuit, etc. Output device(s)  152  include at least one display device (e.g., CRT, fiat-panel display, etc.), audio device (e.g., speaker, headphone), or other output device which generates user-perceivable outputs (e.g., visual displays, sounds, etc.) in response to control signals. External controller  146  is configured to receive the data representative of heart sounds, atrial electrical signals and/or ventricular electrical signals from implantable system  102 , and to generate control signals that, when applied to output device(s)  152 , cause the output device(s) to generate outputs that are representative of the heart sounds, the atrial electrical signals and/or the ventricular electrical signals. 
     Surface ECG system  144  includes electrodes adapted to be electrically coupled to the surface of the patient&#39;s chest for sensing cardiac electrical signals, and is configured to produce ECG output signals which are coupled to I/O interface circuit  148 . External controller  146  is configured to receive the ECG signals from I/O interface circuit  148 , and to generate control signals which, when applied to output device(s)  152 , cause the output device(s) to also generate outputs representative of the patient&#39;s ECG. Alternatively, in other embodiments, surface ECG electrodes are coupled directly to external device  142 , rather than being supplied by a surface ECG system. In another embodiment, external device  142  does not receive surface ECG signals, and does not output such ECG signals. (Note: “ECG” is used herein to refer to cardiac electrical signals measured from the surface of the body, and “EGM” is used to refer to internally-measured cardiac electrical signals.) 
     In one embodiment, external device  142  comprises an external programming device for a cardiac pacemaker, such as the ZOOM™ external programmer available from the Guidant Corporation, except that the external programmer is configured (i.e., programmed or otherwise set up) to perform the various functions described in the present application. 
     In one embodiment, system  100  further includes a remote system  154  operatively coupled to communicate with external system  104  via transmission media  156 . Remote system  154  includes one or more user input device(s)  158 , and one or more user output device(s)  160 , which allow a remote user to interact with remote system  154 . Transmission media  156  includes, for example, a telephone line, electrical or optical cable, RF interface, satellite link, local area network (LAN), wide area network (WAN) such as the Internet, etc. Remote system  154  cooperates with external system  104  to allow a user located at a remote location to perform any of the diagnostic or monitoring functions that may be performed by a user located at external system  104 . For example, data representative of heart sounds and/or cardiac electrical signals are communicated by external system  104  to remote system  154  via transmission media  156  to provide a visual display and/or an audio output on output device(s)  160 , thereby allowing a physician at the remote location to aid in the diagnosis of a patient. System  154  is “remote” in the sense that a user of remote system  154  is not physically capable of actuating input device(s)  150  and/or of directly perceiving outputs generated by output device(s)  152 . For example, system  154  may be located in another room, another floor, another building, another city or other geographic entity, across a body of water, at another altitude, etc., from external system  104 . 
     Referring to  FIG. 2 , in one embodiment, the processing  200  performed by controller  122  of implantable device  108  includes detecting heart sounds by receiving sensed signals representative of the heart sounds from accelerometer  126  (at  202 ), detecting atrial electrical signals by receiving sensed signals representative of the atrial electrical signals from atrial sensing electrode  136  (at  204 ), detecting ventricular electrical signals by receiving sensed signals representative of the ventricular electrical signals from ventricular sensing electrode  140  (at  206 ), and transmitting data representative of the heart sounds, atrial electrical signals, and ventricular electrical signals to external device  142  (at  208 ). 
     In another embodiment, processing  200  further includes signal processing the accelerometer, atrial and ventricular sensed signals to generate processed sensed signals (between  206  and  208 ), and then transmitting the processed sensed signals to external device  142  (at  208 ). The signal processing may also be performed on only one or two of these sensed signals. However, performing the signal processing in implantable device  108  (rather than in external device  142 , as described below relative to  FIG. 3 ) may increase the computational requirements for implantable device  108 , and may also increase the transmission load between devices  108  and  142 . It is to be understood that the division of signal processing between implantable device  108  and external device  142  could be modified from that disclosed herein, as would be apparent to a person of skill in the art. 
     In another embodiment, processing  200  also includes storing one or more of the raw or processed sensed signals in memory  124  for later retrieval by external device  142 . In still another embodiment, the processing performed by controller  122  does not include detecting the atrial electrical signals (at  204 ) and/or the ventricular electrical signals (at  206 ), in which case the corresponding EGM data is not transmitted to external device  142  (at  208 ). In yet another embodiment, the processing performed by controller  122  includes detecting other cardiac electrical signals sensed by other cardiac electrical signal sensors, and transmitting data representative of these other cardiac signals to external device  142 . 
     Referring to  FIG. 3 , in one embodiment, the processing  300  performed by external controller  146  of external device  142  includes receiving the data representative of the heart sounds, atrial electrical signals and ventricular electrical signals from implantable device  108  (at  302 ), receiving surface ECG data from surface ECG system  144  or directly from surface ECG leads (at  304 ), processing the accelerometer, atrial electrical signals, ventricular electrical signals and surface ECG data (at  306 ), and generating output control signals to simultaneously output the raw and/or processed accelerometer, atrial electrical signals, ventricular electrical signals, and surface ECG signals on output device(s)  152  (at  308 ). Processing  300  may also include receiving timing comparison command signals from input device(s)  150  (at  310 ), and generating control signals to output timing comparison information on output device(s)  152  (at  312 ). Processing  300  may also include storing one or more of the raw or processed sensed signals in memory for later analysis. 
     In other embodiments, the processing performed by external controller  146  does not include receiving the atrial and/or ventricular electrical signals (at  302 ), or receiving surface ECG data (at  304 ), in which case the corresponding EGM data or surface ECG data is not processed (at  306 ) or output (at  308 ). Further, it is contemplated that external controller  146  may not perform any processing of the accelerometer, atrial electrical signals and/or ventricular electrical signals (at  306 ), and may instead receive corresponding processed data (rather than raw data) from implantable device  108 . The processing of these signals (at  306 ) is illustrated in  FIG. 3 , however, to indicate that the processing described below in relation to  FIG. 4  may well be performed by external device  142  rather than implantable device  108 , thereby reducing the computational requirements for implantable device  108 . iii Referring to  FIG. 4 , the signal processing  400  performed on the heart sound data by external controller  146  in accordance with one embodiment of the invention is shown. In other embodiments, some or all of this signal processing could instead be performed by controller  122  of implantable device  108 , or by either external or implantable hardware. Signal processing  400  includes a first processing path  402  used for machine detection of heart sounds, and a second processing path  404  used for visual display of heart sounds. Alternatively, only one of heart sound signal processing paths  402  and  404  is provided. 
     First processing path  402  includes a band-pass filter  406 , a rectifier  408 , a low-pass filter  410 , and an ensemble averager  412 , coupled in series. Raw accelerometer data  414  (representative of the heart sounds) is applied to band-pass filter  406 , which has lower and upper cutoff frequencies set to pass frequencies indicative of heart sounds, to produce band-pass filtered data  416 . In one example, the lower and upper cutoff frequencies are 0.05 Hz and 50 Hz, respectively. The cutoff frequencies are also set to reject frequencies due to movement of the patient (e.g., walking around, muscle twitches, etc.) to the extent that the heart sound signals still pass. Band-pass filtered data  416  is then applied to rectifier  408  to produce rectified data  418  that is, in turn, applied to low-pass filter  410  to produce filtered data  420 . In one example, the cutoff frequency for low-pass filter  410  is 10 Hz. 
     Filtered data  420  is applied to ensemble averager  412  to produce processed accelerometer data  422 , which is used for machine detection of heart sounds. Ensemble averager  412  is triggered by an output  424  of a systole detector  426 , which is asserted to open a window of interest when the start of a cardiac cycle is detected based upon the electrical systole (which may be detected using the A EGM, V EGM and/or surface ECG signals). Ensemble averager  412  causes the repetitive heart sound data to be averaged over a number of cardiac cycles to accentuate the heart sounds (which are correlated to a particular frequency) while filtering out random or spurious noise (which are not correlated to a particular frequency). For example, ensemble averager  412  may average sequential heart sounds over a period of between 2 and 128 cardiac cycles, although other periods may also be used. In other embodiments, heart sounds are sequentially averaged over a period of time (e.g., one minute), or over the course of an event or condition (e.g., while the patient is performing an exercise), in which case only completed cardiac cycles will be averaged. Note that signal averaging the heart sound data includes the superposition and the summation of successive temporal samples of the pulsatile heart sound waveform. Second processing path  404  includes a band-pass filter  428  and an ensemble averager  430 , coupled in series. Raw accelerometer data  414  (representative of the heart sounds) is applied to band-pass filter  428 , which has lower and upper cutoff frequencies set to pass frequencies indicative of heart sounds, to produce band-pass filtered data  432 . In one example, the lower and upper cutoff frequencies are 0.05 Hz and 50 Hz, respectively. The cutoff frequencies are also set to reject frequencies due to patient movement to the extent that the heart sound signals still pass. Band-pass filtered data  432  is then applied to ensemble averager  430  to produce processed accelerometer data  434 , which is used for visual display of heart sounds. Ensemble averager  430  is triggered by output  424  of systole detector  426 , which is asserted to open a window of interest when the start of a cardiac cycle is detected based upon the electrical systole. Ensemble averager  430  causes the heart sound data to be averaged over a number of cardiac cycles (e.g., between 2 and 128 cardiac cycles, or other range) to accentuate the heart sounds while filtering out random or spurious noise. By eliminating the rectifier and low-pass filter of processing path  402 , processing path  404  avoids eliminating information from the visual display of the heart sound data which may be useful to a physician, nurse, medical technician or other user of system  100 . 
     In one embodiment, ensemble averager  430  includes logic to reject data from cardiac cycles outside the range of normal as such cycles may be of non-physiologic origin (e.g., PVC&#39;s). However, in the case of frequent PVC&#39;s, the PVC interval may become the norm. Thus, this logic may be adaptive so as to include such PVC&#39;s. 
     The signal processing for the heart sound data illustrated in  FIG. 4  is merely exemplary, and other types of signal processing may be used. For example, the cutoff frequencies described above for the band-pass and low-pass filters may be varied, one or both of these filters may be eliminated, or other filters may be added. In one embodiment, the raw accelerometer data could be applied directly to an ensemble averager. 
     Referring to  FIG. 5 , an exemplary output screen display  500  generated by external device  142  on an output device  152  is shown. In this example, it is assumed implantable system  102  includes accelerometer  126 , atrial sensing electrode  136 , and ventricular sensing electrode  140 , and that implantable system  102  transmits the raw sensed signals from each of these sensors to external device  142 . It is also assumed that external device  142  generates display control signals that are output to a display to generate these outputs. 
     Output screen display  500  includes multiple horizontal traces, including a surface ECG trace  502  a raw accelerometer trace  504  a processed accelerometer trace  506 , an atrial electrical signal (“A EGM”) trace  508 , and a ventricular electrical signal (“V EGM”) trace  510 . Alternatively, one or more of traces  502 - 510  may not be displayed. For example, since raw accelerometer trace  504  includes a relatively large amount of noise, this trace may not be displayed since it may not be easily interpreted by a user. Thus, display  500  simultaneously shows a visual trace of all five of these signals, which may be used by a user (e.g., a physician) to diagnose an electrical/mechanical disassociation of heart  110 . Note that, if it is desirable for a user at a remote location to aid in the diagnosis of heart  110 , the data representative of the heart sounds and electrical signals may be communicated by external device  142  to remote system  154  for display on one of output device(s)  160 . 
     In one embodiment, display  500  includes one or more traces for displaying one or more cardiac electrical signals that were sensed from the left side of the heart, such as an “LV EGM” signal sensed by a sensing electrode disposed in the left ventricle. 
     In one embodiment, to help the user determine timing relationships between the signals shown in  FIG. 5 , external system  142  (and/or remote system  154 ) generates timing comparison control signals which, when applied to the display device, cause the display device to output timing comparison information indicating timing between the displayed signals. For example, system  142  (and/or system  154 ) may generate control signals which cause the display device to display a pair of vertical lines or calipers  512 A and  512 B, which can be moved horizontally by the user via a pair of input devices  150  (or input devices  158 ), with each input device controlling the position of one caliper. The calipers can help the user to compare timing between any of the displayed signals. To further aid the user, external system  142  (and/or remote system  154 ) may cause the display device to display a visual indicia  160  indicating the time period between the calipers. For example, indicia  160  indicates that the distance between calipers  512 A and  512 B represents 50 msec. 
     In one embodiment, to further aid the user in interpreting the display, heart sound data is automatically processed to identify one or more heart sounds, and visual indicia indicative of the identified sounds are also displayed on display  500 . For example, external controller  146  may automatically process the sensed accelerometer data (e.g., processed accelerometer data  422 ) to detect the S1 and S2 heart sounds (and possibly the S3 heart sound), and to generate the display control signals so as to cause visual indicia (e.g., “S1” and “S2”) to be displayed in association with the locations of the heart sounds on processed accelerometer trace  506  (or on raw accelerometer trace  504 ), as in  FIG. 5 . The S1 heart sound is associated with the closure of the AV valve and opening of the aortic valve in the heart, the S2 heart sound is associated with the subsequent closure of the aortic valve, and the S3 heart sound (less pronounced than the S1 and S2 sounds) is associated with the end of the heart&#39;s fast-filling phase during diastole. An exemplary method for automatically processing accelerometer signals to detect S1, S2 and S3 heart sounds is disclosed in U.S. Pat. No. 5,792,195, issued to Carlson et al. on Aug. 11, 1998, and incorporated by reference herein in its entirety. The heart sound indicia may help users to quickly and accurately identify these sounds, and may be especially helpful to less experienced users. 
     In one embodiment, to provide still additional aid to the user, the intra-cardiac EGM and/or surface ECG data may be automatically processed to identify one or more electrical cardiac events, and visual indicia indicative of the identified events may be displayed on display  500 . For example, external controller  146  may be configured to automatically process the sensed atrial electrical data, ventricular electrical data, and/or surface ECG data to identify the P waves, QRS complexes, T waves, U waves, or other electrical cardiac events, and to generate the display control signals so as to cause visual indicia (e.g., “P”, “QRS”, “T”, “U”, etc.) to be displayed in association with the locations of the corresponding events on A EGM trace  508 , V EGM trace  510 , and/or surface ECG trace  502 . The electrical cardiac event indicia may help users to quickly and accurately identify the electrical cardiac events, and may be especially helpful to less experienced users. External controller  146  may also provide additional processing (e.g., filtering) of the A EGM, V EGM and/or surface ECG signal to further delineate the events of interest (e.g., by low-pass filtering these signals to eliminate everything but the higher signal peaks). 
     To provide the user with additional operational control, the generation oft heart sound indicia and/or electrical cardiac event indicia on display  500  may be controlled by one or more of input devices  150  (or input devices  158 ). For example, a first input device (e.g., a switch) may be provided to allow the user to turn the heart sound indicia on or off and a second input device may be provided to turn the electrical event indicia on or off 
     In other embodiments, external device  142  performs additional processing to aid the user in interpreting display  500 . For example, in one embodiment, external device  142  automatically calculates timing differences (e.g., electrical-to-mechanical time delay) for each heart beat, and outputs (e.g., lists, plots, etc.) the timing differences on a beat-to-beat basis. The user can examine the outputs to determine how the electrical-to-mechanical time delay changes over time (e.g., over a number of heart beats). In situations where electrical-to-mechanical disassociation occurs only in limited circumstances (e.g., when the patient is exercising), showing such timing differences over time may be useful to a physician. 
     In another embodiment, external controller  146  calculates and displays timing differences between automatically detected cardiac events, such as between automatically detected heart sounds, between automatically detected heart sounds and electrical cardiac events, between automatically detected electrical cardiac events, etc. For example, external controller  146  may calculate timing differences between the S1 and S2 heart sounds, between the QRS complex and S1 heart sound, or between the P wave and QRS complex, and then generate output control signals to cause visual indicia indicative of these timing differences (e.g., “n msec”) to be displayed on display  500 . In one embodiment, the timing differences that are displayed on display  500  are selected by the user based upon input signals generated by user input device(s)  150  (or input device(s)  158 ). In one example, a user employs a mouse to select a particular timing interval from a pull-down list of timing intervals that he or she would like to see calculated and displayed on display  500 . 
     In one embodiment, one or more of output devices  152  (or output devices  160 ) comprises an audio device for generating audio outputs representative of the heart sounds. For example, raw accelerometer data  414  may be applied to a speaker to allow the user to hear and identify heart abnormalities. Alternatively, processed accelerometer data, such as processed accelerometer data  422  or  434 , may be applied to an audio device to allow the user to hear and identify heart abnormalities. Other types of processed accelerometer data, including filtered and signal-averaged accelerometer data, may also be applied to an audio device to allow the user to hear and identify heart abnormalities. In each case, the user is presented with the heart sounds in the audio domain, which may more familiar to a physician or other user who is used to listening to heart sounds using a stethoscope. In each case, the user may also be presented with any or all of the traces shown in  FIG. 5 , such that the user may receive cardiac information in both the visual and the audio domains. 
     Referring to  FIG. 6 , another exemplary output screen display  600  generated by external device  142  on an output device  152  is shown. In this example, it is again assumed that implantable system  102  includes accelerometer  126 , atrial sensing electrode  136 , and ventricular sensing electrode  140 , that implantable system  102  transmits the raw sensed signals from each of these sensors to external device  142 , and that external device  142  generates display control signals that are output to a display to generate these outputs. The displayed traces include a processed accelerometer trace  602 , an atrial electrical signal (“A EGM”) trace  604 , and a ventricular electrical signal (“V EGM”) trace  606 . Other traces, such as a surface ECG trace and/or a raw accelerometer trace, could also be displayed. 
     In this embodiment, to help the user determine timing relationships between the traces shown in  FIG. 6 , external device  142  (and/or remote system  154 ) is configured to generate timing comparison control signals which cause the display device to vertically move one or more of the traces under the control of the user via one or more of input devices  150  (or input devices  158 ). For example, each input device may control the vertical position of one trace. By vertically moving one or more of the traces, the user can superimpose the traces over one another to show timing comparisons. For example, as illustrated by the dashed lines in  FIG. 6 , the user has used an input device  150  to move A EGM trace  604  upward to superimpose this trace over processed accelerometer trace  602 . By doing so, timing comparisons between traces  602  and  604  become readily apparent. Thus, in this embodiment, visual outputs of heart sounds may be superimposed over visual outputs of cardiac electrical signals to show timing comparisons therebetween. Note that, since display  600  does not indicate which superimposed signal was moved “over” another, superimposing trace A “over” trace B is the same as superimposing trace B “over” trace A. 
     Referring to  FIG. 7 , in another embodiment, implantable device  108  includes an arrhythmia logbook feature. With this feature, if an arrhythmia (e.g., an abnormally fast heart rate) detected, implantable device  108  records data in memory for later examination by a physician for use in making a diagnosis. Implantable device  108  may, for example, continually record 10 seconds of data in an area of memory  124 , and may simply rewrite over that area of memory. if however, an arrhythmia is detected (e.g., the V EGM signal indicates that heart  110  is beating at an abnormally high rate of 180 beats/minute), the 10 seconds of recorded data is saved in another area of memory  124 , along with an additional 20 seconds of data recorded after the arrhythmia. Other arrhythmia events may also be logged. Then, on the next visit of the patient to a doctor, the doctor can use external device  142  to read the data from the logbook, and can examine the data to look for arrhythmia events. For example, the logbook may indicate that, in the three months since the patient was last seen, heart  110  experienced five episodes of fast atrial heart beat, three atrial flutters, and one ventricular fibrillation. The data recorded by implantable device  108  in association with each arrhythmia event may include heart rate data, A EGM data, V EGM data and, in accordance with the present system, raw and/or processed heart sound data. 
     To provide the arrhythmia logbook feature, in one embodiment, controller  122  of implantable device  108  performs the processing  700  shown in  FIG. 7 . In particular, controller  122  detects heart sounds by receiving sensed signals representative of the heart sounds from accelerometer  126  (at  702 ), detects atrial electrical signals by receiving sensed signals representative of the atrial electrical signals from atrial sensing electrode  136  (at  704 ), detects ventricular electrical signals by receiving sensed signals representative of the ventricular electrical signals from ventricular sensing electrode  140  (at  706 ), and stores the accelerometer, atrial EGM and ventricular EGM data in memory  124  (at  708 ). In one embodiment, controller  122  continually stores 10 seconds of such data (along with other desired data, such as heart rate data) in a particular area of memory  124 . If controller  122  determines that an arrhythmia has not occurred (at  712 ) and that no arrhythmia logbook playback request has been received from external device  142  (at  714 ), controller  122  loops back (to  702 ), and repeats these operations. As new data is collected and stored in memory  124 , the oldest data is re-written by the new data such that the particular area of memory always stores the last 10 seconds of data. If an arrhythmia is detected (at  712 ), however, controller  122  creates a record in another area of memory (i.e., the arrhythmia logbook), and copies the last  10  seconds of data into that record. Then, for the next 20 seconds, controller  122  continues to monitor data, and stores this data within that same record. Thus, for each detected arrhythmia, controller  122  creates a record in memory  124  that contains data for the  110  seconds leading up to the arrhythmia, and the  20  seconds after the arrhythmia. In other embodiments, less than or more than this amount of data is stored either before or after each arrhythmia occurs. Then, when controller  122  determines that an arrhythmia logbook playback command is received from external device  142 , controller  122  transmits the records from memory  124  to external device  142 . External device  142  then outputs the data from these records to output device(s)  152  (or output device(s)  160 ). The physician can then examine the recorded data for each arrhythmia to aid in making a diagnosis. Thus, by using the arrhythmia logbook feature of the system, the physician is provided with heart sound information from both before and after the arrhythmia. 
     In one embodiment, system  100  may provide more sophisticated signal processing in cases of cardiac arrhythmia. For example, in the case of bigeminy, system  100  may be configured to use two averaging processes in order that like events are averaged separately. Exemplary signal processing techniques that could be employed by system  100  include, for example, those described in U.S. Pat. Nos. 4,799,493, 4,799,486, 4,793,361 and 4,721,114. In another embodiment, implantable device  108  may be configured to detect heart murmurs or extra heart sounds, to count such extra heart sounds, and to transmit such counts to external device  142  for output on one of output device(s)  150  (or devices  160 ). 
     Referring to  FIG. 8 , an exemplary system  800  for outputting heart sounds according to another embodiment comprises an implantable device  802  coupled to a patient&#39;s heart (not shown) by a pacing lead  804  and one or more heart electrode(s)  806 , and operatively coupled to an external device (not shown) via a communications link  808 . In one embodiment, heart electrode(s)  806  includes an atrial sensing electrode, ventricular sensing electrode, atrial stimulating electrode and ventricular stimulating electrode as in  FIG. 1 . 
     Implantable device  802  includes one or more cardiac sense amplifier(s)  810  and one or more cardiac stimulating circuit(s)  812  operatively coupled to heart electrode(s)  806  via lead  804 . In another embodiment, where device  802  does not provide heart stimulation, device  802  does not include cardiac stimulating circuit(s)  812 . Device  802  also includes a controller  814 , a memory  816  operatively coupled to controller  814 , an activity level detecting path  818 , a heart sound detecting path  820 , a systole detector  822 , and an I/O interface  824 . Activity level detecting path  818  includes an activity level sensor  826  fir sensing patient activity, an analog pre-processing circuit  828  for pre-processing signals generated by activity level sensor  826 , an A/D converter  830  for digitizing the activity level signals, and an activity level filter  832  for filtering the digitized signals to eliminate sources of noise such as those caused by heart sounds. Heart sound detecting path  820  includes a heart sound sensor  834  for sensing heart sounds, an analog pre-processing circuit  836  for pre-processing signals generated by heart sound sensor  834 , A/D converter  830  for digitizing the heart sound signals (e.g., using a different channel than the channel used for the activity level signals), a heart sound filter  838  for filtering the digitized signals to eliminate sources of noise such as those caused by patient activity, an S1 heart sound detector  840  for detecting the S1 heart sound, an S2 heart sound detector  842  for detecting the S2 heart sound, and an S3 heart sound detector  844  for detecting the S3 heart sound. Controller  814  transmits data representing the patient&#39;s activity level and the S1, S2 and S3 heart sounds to the external device via I/O interface  824 . Where S1, S2 and S3 heart sound detectors  840 ,  842  and  844  ensemble average the heart sound signals, controller  814  provides an output signal indicative of the start of a cardiac cycle from systole detector  822  to heart sound detectors  840 ,  842  and  844  for use as a trigger. In one embodiment, the outputs from S1, S2 and S3 heart sound detectors  840 - 844  comprise a sequence of pulses, each pulse representing a detected heart sound. The external device receives the heart sound and cardiac electrical signal data via link  808 , and simultaneously outputs this data. 
     In one embodiment, activity level filter  832 , heart sounds filter  838 , heart sound detectors  840 - 844  and systole detector  822  are implemented by controller  814  through appropriate programming commands. In another embodiment, one or more of filters  832  and  838 , and detectors  840 - 844 ,  822 , are implemented by one or more hardware circuits. In another embodiment, sonic or all of the processing functions of 
       FIG. 8  are performed by the external device instead of device  802 . In another embodiment, system  800  includes S1 and S2 detectors  840  and  842 , but does not include S3 detector  844 . In another embodiment, system  800  includes other sound detectors for detecting other heart sounds. In another embodiment, when an electrical-mechanical disassociation is detected, stimulation timing provided by stimulating electrodes  138  and  142  is changed. 
     CONCLUSION 
     Thus, exemplary embodiments of an improved apparatus and method for outputting heart sounds, and/or for comparing electrical operation of the heart to mechanical operation of the heart, are disclosed herein. The disclosed apparatus and method for outputting heart sounds do not require the use of a stethoscope placed on the body of the patient, and are not subject to various factors which affect the heart sounds heard using a stethoscope. The disclosed apparatus and method for comparing electrical and mechanical operations of the heart also do not require the use of a stethoscope, are not subject to various factors which affect the heart sounds heard using a stethoscope, do not require ECG probes to be electrically coupled to the patient&#39;s chest, increase the accuracy of comparisons between heart sounds and electrical signals, decrease the level of skill needed to identify electrical-mechanical disassociation, provide for continuous monitoring of such electrical-mechanical disassociation, and are capable of producing a written record showing such disassociation. 
     As indicated above, the outputs generated by system  100  may be used by a physician to diagnose problems with heart  110  such as electrical-mechanical disassociation, or problems leading to cardiac arrhythmia. The outputs may also be used by a physician located remotely from the patient to diagnose the patient by checking the patient&#39;s heart sounds through a telephone, Internet or other communication connection. The sensed heart sound signals generated by system  100  may also be used for other purposes. For example, the heart sound signals may be useful in optimization of timing for CHF pacing, for determining the best AV delay, or for identifying the upper rate limit for a pacemaker. 
     Also, while the above description has focused on the relative timing of the various cardiac signals, the morphology or amplitude of the heart sound and cardiac electrical signals may also provide diagnostic information. For example, a heart sound signal with an amplitude lower than normal may be suggestive of certain heart abnormalities. 
     The above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of ordinary skill in the art upon reviewing the present specification. For example, the implantable device described herein need not be a cardiac pacemaker, but may be another type of implantable device. Also, the external device described herein need not be an external pacemaker programmer, but may be another type of external device such as a cardiac monitor. The processing described herein as being performed by external controller  146  may also be performed by the implantable device, or by other combinations of hardware and software. Other signal processing routines may also be used. Further, while the system described herein outputs heart sounds, A EGM, V EGM and surface ECG signals, one or more of these signals need not be output, or may be replaced by the output of another internal or external cardiac signal. The scope of the present invention should therefore be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.