Dual-use sensor for rate responsive pacing and heart sound monitoring

Abstract

An implantable medical device includes a dual-use sensor such as a single accelerometer that senses an acceleration signal. A sensor processing circuit processes the acceleration signal to produce an activity level signal and a heart sound signal. The implantable medical device provides for rate responsive pacing in which at least one pacing parameter, such as the pacing interval, is dynamically adjusted based on the physical activity level. The implantable medical device also uses the heart sounds for pacing control purposes or transmits a heart sound signal to an external system for pacing control and/or diagnostic purposes.

1 . An implantable medical device, comprising:
 a pacing circuit configured to deliver pacing pulses;   an accelerometer configured to sense an acceleration signal indicative of physical activities and heart sounds;   a preconditioning circuit coupled to the accelerometer and configured to digitize the acceleration signal;   a sensor processing circuit coupled to the preconditioning circuit and programmable for producing an activity level signal and a heart sound signal using the preconditioned acceleration signal, the activity level signal indicative of a level of the physical activities, the heart sound signal indicative of the heart sounds, the sensor processing circuit including a first set of cutoff frequencies suitable for producing the activity level signal and a second set of cutoff frequencies suitable for producing the heart sound signal;   a controller coupled to the pacing circuit and the sensor processing circuit, the controller configured to program the sensor processing circuit and control the delivery of the pacing pulses using the activity level signal and the heart sound signal; and   an implantable housing encapsulating at least the pacing circuit, the preconditioning circuit, the sensor processing circuit, and the controller.   
     
     
         2 . The device of  claim 1 , wherein the controller comprises a sensor processing circuit programming module configured to program the sensor processing circuit to produce the activity level signal using the first set of cutoff frequencies during a first time period and produce the heart sound signal using the second set of cutoff frequencies during a second time period, wherein the first time period and the second time period do not overlap. 
     
     
         3 . The device of  claim 1 , wherein the controller comprises a sensor processing circuit programming module configured to program the sensor processing circuit for producing the activity level signal and the heart sound signal concurrently. 
     
     
         4 . The device of  claim 1 , wherein the accelerometer comprises an integrated circuit accelerometer and is encapsulated in the implantable housing. 
     
     
         5 . The device of  claim 4 , wherein the sensor processing circuit comprises a first band-pass filter having the first set of cutoff frequencies and a second band-pass filter having the second set of cutoff frequencies. 
     
     
         6 . The device of  claim 4 , wherein the sensor processing circuit comprises a band-pass filter having cutoff frequencies programmable to one of the first set of cutoff frequencies and the second set of cutoff frequencies after implantation of the implantable medical device. 
     
     
         7 . The device of  claim 4 , wherein the first set of cutoff frequencies comprises a first low cutoff frequency programmable in a range of 0.5 Hz to 2 Hz and a first high cutoff frequency programmable in a range of 5 Hz to 15 Hz. 
     
     
         8 . The system of  claim 7 , wherein the second set of cutoff frequencies comprises a second low cutoff frequency programmable in a range of 5 Hz to 10 Hz and a second high cutoff frequency programmable in a range of 50 Hz to 200 Hz. 
     
     
         9 . The device of  claim 4 , comprising a heart sound detector coupled to the sensor processing circuit, encapsulated in the implantable housing, and configured to detect at least one type of heart sound from the heart sound signal. 
     
     
         10 . The device of  claim 9 , wherein the controller comprises a rate responsive pacing algorithm execution module adapted to dynamically adjust at least a pacing interval using the activity level signal. 
     
     
         11 . A method for operating an implantable medical device, the method comprising:
 sensing an acceleration signal indicative of physical activities and heart sounds using an accelerometer;   digitizing the acceleration signal;   producing an activity level signal by filtering the digitized acceleration signal using a first set of cutoff frequencies, the activity level signal indicative of a level of the physical activities;   producing a heart sound signal by filtering the digitized acceleration signal using a second set of cutoff frequencies, the heart sound signal indicative of the heart sounds; and   controlling delivery of cardiac pacing pulses from the implantable medical device using the activity level signal and the heart sound signal.   
     
     
         12 . The method of  claim 11 , comprising:
 producing the activity level signal and the heart sound signal using a band-pass filter having programmable cutoff frequencies;   programming the programmable cutoff frequencies to the first set of cutoff frequencies for a first time period; and   programming the programmable cutoff frequencies to the second set of cutoff frequencies for a second time period that does overlap with the first time period.   
     
     
         13 . The method of  claim 11 , comprising:
 producing the activity level signal using a first band-pass filter having the first set of cutoff frequencies; and   producing the activity level signal using a second band-pass filter having the second set of cutoff frequencies.   
     
     
         14 . The method of  claim 11 , comprising detecting at least one type of heart sounds from the heart sound signal using a heart sound detector in the implantable medical device. 
     
     
         15 . The method of  claim 14 , comprising executing a rate responsive pacing algorithm dynamically adjusting at least one pacing parameter using the activity level signal. 
     
     
         16 . The method of  claim 14 , further comprising:
 measuring one or more parameters associated with the detected heart sounds; and   trending the one or more parameters.   
     
     
         17 . The method of  claim 16 , further comprising transmitting one or more of the acceleration signal, the activity level signal, and the heart sound signal from the implantable medical device to an external system in real time. 
     
     
         18 . An implantable medical device, comprising:
 means for sensing an acceleration signal indicative of physical activities and heart sounds using an accelerometer;   means for digitizing the acceleration signal;   means producing an activity level signal by filtering the digitized acceleration signal using a first set of cutoff frequencies and producing a heart sound signal by filtering the digitized acceleration signal using a second set of cutoff frequencies, the activity level signal indicative of a level of the physical activities, the heart sound signal indicative of the heart sounds; and   means for controlling delivery of cardiac pacing pulses from the implantable medical device using the activity level signal and the heart sound signal.   
     
     
         19 . The device of  claim 18 , comprising means for producing the activity level signal during a first time period and producing the heart sound signal during a second time period that does overlap with the first time period. 
     
     
         20 . The device of  claim 18 , comprising means for producing the activity level signal and the heart sound signal concurrently.