Deriving Patient Activity Information from Sensed Body Electrical Information

Abstract

Electrodes of a subcutaneous monitoring system receive body electrical signals that indicate both cardiac and non-cardiac muscle activity. In general, non-cardiac muscle activity is often correlated with physical activity, and physical activity is typically a strong indicator of patient health. Exemplary systems and methods that detect non-cardiac muscle activity information in sensed body electrical waveforms may provide a diagnostic tool for monitoring physical activity level over time in patients that have subcutaneous monitoring systems. In an illustrative embodiment, systems and methods for presenting patient activity information in a graphical format over intervals of time include processing ECG waveform information to identify and to accumulate non-cardiac muscular activity information during each of the intervals of time. In various implementations, number, intensity, and/or duration of the events that are identified during a time interval may be accumulated and stored for subsequent recall.

1 . A method of storing information indicative of patient activity, the method comprising:
 a) receiving an electrical waveform using subcutaneous electrodes, the received electrical waveform comprising electrical signals generated by electrical activity of a heart in a patient during a selected time period;   b) determining a value to represent a level of physical activity of the patient by identifying portions of the received electrical waveform that include signals indicative of non-cardiac muscular activity in the patient; and   c) storing the determined value in a data store for subsequent retrieval as an indicator of a level of physical activity of the patient during the selected time period.   
     
     
         2 . The method of  claim 1  further comprising sending the stored determined value for display on a display device in a histogram format to represent a measure of patient activity during the selected time period. 
     
     
         3 . The method of  claim 1  further comprising telemetering information indicative of non-cardiac muscle activity from a transmit module implanted in the patient to a receiver module external to the patient. 
     
     
         4 . The method of  claim 3  wherein the telemetered information comprises the stored determined value. 
     
     
         5 . The method of  claim 1  further comprising sending for display on a display device information about the values determined for each of a plurality of selected time periods. 
     
     
         6 . A system for presenting physical activity information for an individual by detecting non-cardiac muscle noise in electrocardiogram (ECG) waveform information collected by an implanted device, the system comprising:
 a) an implantable waveform acquisition module operable to acquire ECG waveforms from subcutaneous electrodes implanted in a body;   b) a processing module to process the acquired ECG waveforms to identify non-cardiac muscle activity events;   c) an accumulation module to determine an activity level for each of a plurality of time intervals, each activity level being determined from an aggregation of the identified non-cardiac muscle activity events; and   d) a format module to render a graphical representation of the determined activity level for each of the plurality of time intervals.   
     
     
         7 . The system of  claim 6  further comprising a housing that contains the implantable waveform acquisition module and the processing module, the housing having an electrically conductive exterior portion that forms at least one of the subcutaneous electrodes. 
     
     
         8 . The system of  claim 7  wherein at least a portion of the electrically conductive exterior portion of the housing is adapted to make substantially direct electrical contact with non-cardiac muscle tissue. 
     
     
         9 . The system of  claim 8  wherein the non-cardiac muscle tissue comprises fascia. 
     
     
         10 . The system of  claim 7  wherein at least a portion of the electrically conductive exterior portion of the housing is substantially free of any electrically insulating coating when implanted in a body of a patient. 
     
     
         11 . The system of  claim 6  wherein the processing module receives the acquired ECG waveform from a receiver module located external to the body. 
     
     
         12 . The system of  claim 6  wherein the processing module is substantially remote from the body. 
     
     
         13 . The system of  claim 6  wherein the graphical representation comprises a histogram. 
     
     
         14 . A method of controlling a rate of application of electrical stimulation to a heart of a patient based on patient activity as determined from non-cardiac muscle electrical signals in electrocardiogram (ECG) waveform information collected by an implanted device, the method comprising:
 a) receiving an electrical waveform using subcutaneous electrodes, the received electrical waveform comprising electrical signals generated by electrical activity of a heart in a patient during a selected time period;   b) determining a level of physical activity of the patient by identifying portions of the received electrical waveform that include signals indicative of non-cardiac muscular activity in the patient during the selected time period; and   c) adjusting a rate of electrical stimulation applied to the heart in response to changes in the determined level of physical activity.   
     
     
         15 . The method of  claim 14  wherein the determining step comprises post-processing the received electrical waveform to determine a level of activity of the patient during a portion of the selected time periods by identifying non-cardiac muscle activity events in the received electrical waveform and aggregating the identified activity events. 
     
     
         16 . The method of  claim 15  wherein the determining step further comprises counting the identified activity events to determine the level of activity of the patient. 
     
     
         17 . The method of  claim 15  wherein the determined level of activity of the patient is a function of an amplitude of each of the identified activity events. 
     
     
         18 . The method of  claim 15  wherein the determined level of activity of the patient is a function of a duration of one or more of the identified activity events. 
     
     
         19 . The method of  claim 14  wherein the adjusting step comprises adjusting the rate of electrical stimulation applied to the heart in response to a moving average of the determined physical activity level. 
     
     
         20 . A system for applying electrical stimulus to an organ in a patient, the stimulation being responsive to patient physical activity information determined by detecting non-cardiac muscle noise in electrocardiogram (ECG) waveform information collected by a device implanted in the patient, the system comprising:
 a) an implantable waveform acquisition module operable to acquire ECG waveforms from subcutaneous electrodes implanted in a body;   b) a first processing module to process the acquired ECG waveforms to identify non-cardiac muscle activity events; a second processing module to determine an activity level from an aggregation of the identified non-cardiac muscle activity events; and   c) a stimulation module to generate electrical stimulation to apply to an organ in the body based on the determined activity level.   
     
     
         21 . The system of  claim 20  wherein the implantable waveform acquisition module comprises a housing having an electrically conductive exterior portion that forms at least one of the subcutaneous electrodes. 
     
     
         22 . The system of  claim 21  wherein at least a portion of the electrically conductive exterior portion of the housing is adapted to make substantially direct electrical contact with non-cardiac muscle tissue. 
     
     
         23 . The system of  claim 22  wherein the non-cardiac muscle tissue comprises fascia. 
     
     
         24 . The system of  claim 20  wherein at least a portion of the electrically conductive exterior portion of the housing is substantially free of any electrically insulating coating when implanted in the body.