Sensing for heart failure management

Abstract

In some examples, determining a heart failure status includes using an implantable medical device configured for subcutaneous implantation and comprising a plurality of electrodes and an optical sensor. Processing circuitry of a system comprising the device may determine, for a patient, a current tissue oxygen saturation value based on a signal received from the at least one optical sensor, a current tissue impedance value based on a subcutaneous tissue impedance signal received from the electrodes, and a current pulse transit time value based on a cardiac electrogram signal received from the electrodes and at least one of the signal received from the optical sensor and the subcutaneous tissue impedance signal. The processing circuitry may further compare the current tissue oxygen saturation value, current tissue impedance value, and current pulse transit time value to corresponding baseline values, and determine the heart failure status of the patient based on the comparison.

What is claimed is: 
     
         1 . A method for determining a heart failure status of a patient using an implantable medical device configured for subcutaneous implantation outside of a thorax of the patient, the implantable medical device comprising a plurality of electrodes and at least one optical sensor, the method comprising, by processing circuitry of a medical device system comprising the implantable medical device:
 determining a current tissue oxygen saturation value of the patient based on a signal received from the at least one optical sensor;   determining a current tissue impedance value of the patient based on a subcutaneous tissue impedance signal received from a first at least two of the plurality of electrodes;   determining a current pulse transit time value of the patient based on a cardiac electrogram signal received from a second at least two of the plurality of electrodes and at least one of the signal received from the at least one optical sensor and the subcutaneous tissue impedance signal;   comparing the current tissue oxygen saturation value, the current tissue impedance value, and the current pulse transit time value to corresponding ones of a baseline tissue oxygenation saturation value, a baseline tissue impedance value, and a baseline pulse transit time value; and   determining the heart failure status of the patient based on the comparison.   
     
     
         2 . The method of  claim 1 , wherein comparing the current tissue oxygen saturation value, the current tissue impedance value, and the current pulse transit time value to the corresponding ones of the baseline tissue oxygenation saturation value, the baseline tissue impedance value, and the baseline pulse transit time value comprises:
 determining whether a difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value satisfies a tissue oxygen saturation threshold value that is associated with a change in a tissue perfusion status of the patient;   determining whether a difference between the current tissue impedance value and the baseline tissue impedance value satisfies a tissue impedance threshold value that is associated with a change in a congestion status of the patient; and   determining whether a difference between the current pulse transit time value and the baseline pulse transit time value satisfies a threshold pulse transit time value that is associated with a change in a blood pressure status of the patient.   
     
     
         3 . The method of  claim 1 , further comprising, by the processing circuitry:
 transmitting the heart failure status of the patient to a remote computer;   receiving, from the remote computer, instructions for a medical intervention based on the heart failure status of the patient; and   transmitting the instructions for the medical intervention to a user interface.   
     
     
         4 . The method of  claim 3 , wherein the instructions for the medical intervention comprise at least one of a change in a drug selection, a change in a drug dosage, instructions to schedule a visit with a clinician, and instructions for the patient to seek medical attention. 
     
     
         5 . The method of  claim 1 , wherein determining the heart failure status of the patient based on the comparison comprises determining, by the processing circuitry, a diagnostic score based on the comparison, wherein the diagnostic score is associated with a likelihood that the patient will experience an adverse medical event. 
     
     
         6 . The method of  claim 5 , wherein the heart failure status of the patient is an updated heart failure status, and wherein determining the updated heart failure status comprises comparing, by the processing circuitry, a current diagnostic score to a baseline diagnostic score of the patient. 
     
     
         7 . The method of  claim 6 , further comprising, by the processing circuitry, determining the current diagnostic score by at least:
 determining a weighted value of the difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value;   determining a weighted value of the difference between the current tissue impedance value and the baseline tissue impedance value;   determining a weighted value of the difference between the current pulse transit time value and the baseline pulse transit time value; and   combining the weighted value of the difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value, the weighted value of the difference between the current tissue impedance value and the baseline tissue impedance value, and the weighted value of the difference between the current pulse transit time value and the baseline pulse transit time value.   
     
     
         8 . The method of  claim 1 , wherein the signals are current signals, the method further comprising:
 receiving a baseline signal from the at least one optical sensor;   receiving a baseline subcutaneous tissue impedance signal from the first at least two of the plurality of electrodes;   receiving a baseline cardiac electrogram signal from the second at least two of the plurality of electrodes;   determining at least one of the baseline tissue oxygen saturation value or the tissue oxygen saturation threshold value based on the baseline signal received from the at least one optical sensor;   determining at least one of the baseline tissue impedance value or the tissue impedance threshold value based on the baseline subcutaneous tissue impedance signal from the first at least two of the plurality of electrodes; and   determining at least one of the baseline pulse transit time value or the threshold pulse transit time value based on the baseline cardiac electrogram signal and at least one of the baseline signal received from the at least one optical sensor or the baseline subcutaneous tissue impedance signal.   
     
     
         9 . The method of  claim 1 , wherein the first at least two of the plurality of electrodes and the second at least two of the plurality of electrodes include at least one electrode of the plurality of electrodes in common. 
     
     
         10 . The method of  claim 1 , wherein the implantable medical device comprises a housing configured for subcutaneous implantation outside the thorax, and wherein the at least one optical sensor and the plurality of electrodes are positioned on the housing. 
     
     
         11 . The method of  claim 1 , wherein the implantable medical device comprises a leadless implantable medical device. 
     
     
         12 . A system for determining a heart failure status of a patient using an implantable medical device configured for subcutaneous implantation outside of a thorax of the patient, the system comprising:
 the implantable medical device comprising:
 at least one optical sensor; and 
 a plurality of electrodes; and 
   processing circuitry configured to:
 determine a current tissue oxygen saturation value of the patient based on a signal received from the at least one optical sensor; 
 determine a current tissue impedance value of the patient based on a subcutaneous tissue impedance signal received from a first at least two of the plurality of electrodes; 
 determine a current pulse transit time value of the patient based on a cardiac electrogram signal received from a second at least two of the plurality of electrodes and at least one of the signal received from the at least one optical sensor and the subcutaneous tissue impedance signal; 
 compare the current tissue oxygen saturation value, the current tissue impedance value, and the current pulse transit time value to corresponding ones of a baseline tissue oxygenation saturation value, a baseline tissue impedance value, and a baseline pulse transit time value; and 
 determine the heart failure status of the patient based on the comparison. 
   
     
     
         13 . The system of  claim 12 , wherein the processing circuitry is configured to compare the current tissue oxygen saturation value, the current tissue impedance value, and the current pulse transit time value to the corresponding ones of the baseline tissue oxygenation saturation value, the baseline tissue impedance value, and the baseline pulse transit time value by at least:
 determining whether a difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value satisfies a tissue oxygen saturation threshold value that is associated with a change in a tissue perfusion status of the patient;   determining whether a difference between the current tissue impedance value and the baseline tissue impedance value satisfies a tissue impedance threshold value that is associated with a change in a congestion status of the patient; and   determining whether a difference between the current pulse transit time value and the baseline pulse transit time value satisfies a threshold pulse transit time value that is associated with a change in a blood pressure status of the patient.   
     
     
         14 . The system of  claim 12 , wherein the processing circuitry is further configured to:
 transmit the heart failure status of the patient to a remote computer;   receive, from the remote computer, instructions for a medical intervention based on the heart failure status of the patient; and   transmit the instructions for the medical intervention to a user interface.   
     
     
         15 . The system of  claim 14 , wherein the instructions for the medical intervention comprise at least one of a change in a drug selection, a change in a drug dosage, instructions to schedule a visit with a clinician, and instructions for the patient to seek medical attention. 
     
     
         16 . The system of  claim 12 , wherein the processing circuitry is configured to determine the heart failure status of the patient based on the comparison by at least determining a diagnostic score based on the comparison, wherein the diagnostic score is associated with a likelihood that the patient will experience an adverse medical event. 
     
     
         17 . The system of  claim 16 , wherein the heart failure status of the patient is an updated heart failure status, and wherein the processing circuitry is configured to determine the updated heart failure status by at least comparing a current diagnostic score to a baseline diagnostic score of the patient. 
     
     
         18 . The system of  claim 17 , wherein the processing circuitry is further configured to determine the current diagnostic score by at least:
 determining a weighted value of the difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value;   determining a weighted value of the difference between the current tissue impedance value and the baseline tissue impedance value;   determining a weighted value of the difference between the current pulse transit time value and the baseline pulse transit time value; and   combining the weighted value of the difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value, the weighted value of the difference between the current tissue impedance value and the baseline tissue impedance value, and the weighted value of the difference between the current pulse transit time value and the baseline pulse transit time value.   
     
     
         19 . The system of  claim 12 , wherein the signals are current signals, and wherein the processing circuitry is further configured to:
 receive a baseline signal from the at least one optical sensor,   receive a baseline subcutaneous tissue impedance signal from the first at least two of the plurality of electrodes,   receive a baseline cardiac electrogram signal from the second at least two of the plurality of electrodes,   determine at least one of the baseline tissue oxygen saturation value or the tissue oxygen saturation threshold value based on the baseline signal received from the at least one optical sensor,   determine at least one of the baseline tissue impedance value or the tissue impedance threshold value based on the baseline subcutaneous tissue impedance signal from the first at least two of the plurality of electrodes, and   determine at least one of the baseline pulse transit time value or the threshold pulse transit time value based on the baseline cardiac electrogram signal and at least one of the baseline signal received from the at least one optical sensor or the baseline subcutaneous tissue impedance signal.   
     
     
         20 . The system of  claim 12 , wherein the first at least two of the plurality of electrodes and the second at least two of the plurality of electrodes include at least one electrode of the plurality of electrodes in common. 
     
     
         21 . The system of  claim 12 , wherein the implantable medical device comprises a housing configured for subcutaneous implantation outside the thorax, and wherein the at least one optical sensor and the plurality of electrodes are positioned on the housing. 
     
     
         22 . The system of  claim 12 , wherein the implantable medical device comprises a leadless implantable medical device. 
     
     
         23 . A system for determining a heart failure status of a patient using an implantable medical device configured for subcutaneous implantation outside of a thorax of the patient, the system comprising:
 the implantable medical device, comprising:
 at least one optical sensor; 
 a plurality of electrodes; and 
 processing circuitry configured to:
 determine a current tissue oxygen saturation value of the patient based on the signal received from the at least one optical sensor; 
 determine a current tissue impedance value of the patient based on a subcutaneous tissue impedance signal received from a first at least two of the plurality of electrodes; 
 determine a current pulse transit time value of the patient based on a cardiac electrogram signal received from a second at least two of the plurality of electrodes and at least one of the signal received from the at least one optical sensor and the subcutaneous tissue impedance signal; 
 determine whether a difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value satisfies a tissue oxygen saturation threshold value that is associated with a change in a tissue-perfusion status of the patient; 
 determine whether a difference between the current tissue impedance value and the baseline tissue impedance value satisfies a tissue impedance threshold value that is associated with a change in a congestion status of the patient; 
 determine whether a difference between the current pulse transit time value and the baseline pulse transit time value satisfies a threshold pulse transit time value that is associated with a change in a blood-pressure status of the patient; 
 determine the heart failure status of the patient based on at least one of the difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value, the difference between the current tissue impedance value and the baseline tissue impedance value, and the difference between the current pulse transit time and the baseline pulse transit time; and 
 transmit the heart failure status of the patient to a remote computer; and 
 
   the remote computer, wherein the remote computer comprises processing circuitry configured to:
 receive the heart failure status of the patient transmitted by the processing circuitry of the implantable medical device; and 
 transmit the instructions for the medical intervention to a user interface. 
   
     
     
         24 . A system for determining a heart failure status of a patient, the system comprising:
 means for determining a current tissue oxygen saturation value of the patient based on a signal received from at least one optical sensor;   means for determining a current tissue impedance value of the patient based on a subcutaneous tissue impedance signal received from a first at least two of a plurality of electrodes;   means for determining a current pulse transit time value of the patient based on a cardiac electrogram signal received from a second at least two of the plurality of electrodes and at least one of the signal received from the at least one optical sensor and the subcutaneous tissue impedance signal;   means for comparing the current tissue oxygen saturation value, the current tissue impedance value, and the current pulse transit time value to corresponding ones of a baseline tissue oxygenation saturation value, a baseline tissue impedance value, and a baseline pulse transit time value; and   means for determining the heart failure status of the patient based on the comparison.   
     
     
         25 . The system of  claim 24 , wherein the means for comparing the current tissue oxygen saturation value, the current tissue impedance value, and the current pulse transit time value to the corresponding ones of the baseline tissue oxygenation saturation value, the baseline tissue impedance value, and the baseline pulse transit time value comprises:
 means for determining whether a difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value satisfies a tissue oxygen saturation threshold value that is associated with a change in a tissue perfusion status of the patient;   means for determining whether a difference between the current tissue impedance value and the baseline tissue impedance value satisfies a tissue impedance threshold value that is associated with a change in a congestion status of the patient; and   means for determining whether a difference between the current pulse transit time value and the baseline pulse transit time value satisfies a threshold pulse transit time value that is associated with a change in a blood pressure status of the patient.   
     
     
         26 . A non-transitory computer-readable medium storing instructions for causing processing circuitry to perform a method for determining a heart failure status of a patient using an implantable medical device configured for subcutaneous implantation outside of a thorax of the patient, the implantable medical device comprising a plurality of electrodes and at least one optical sensor, the method comprising:
 determining a current tissue oxygen saturation value of the patient based on a signal received from the at least one optical sensor;   determining a current tissue impedance value of the patient based on a subcutaneous tissue impedance signal received from a first at least two of the plurality of electrodes;   determining a current pulse transit time value of the patient based on a cardiac electrogram signal received from a second at least two of the plurality of electrodes and at least one of the signal received from the at least one optical sensor and the subcutaneous tissue impedance signal;   comparing the current tissue oxygen saturation value, the current tissue impedance value, and the current pulse transit time value to corresponding ones of a baseline tissue oxygenation saturation value, a baseline tissue impedance value, and a baseline pulse transit time value; and   determining the heart failure status of the patient based on the comparison.   
     
     
         27 . The non-transitory computer-readable medium of  claim 26 , wherein the method further comprises:
 determining whether a difference between the current tissue oxygen saturation value and the baseline tissue oxygen saturation value satisfies a tissue oxygen saturation threshold value that is associated with a change in a tissue perfusion status of the patient;   determining whether a difference between the current tissue impedance value and the baseline tissue impedance value satisfies a tissue impedance threshold value that is associated with a change in a congestion status of the patient; and   determining whether a difference between the current pulse transit time value and the baseline pulse transit time value satisfies a threshold pulse transit time value that is associated with a change in a blood pressure status of the patient.   
     
     
         28 . A system for determining a heart failure status of a patient, the system comprising: one or more sensors configured to monitor one or more parameters of the patient; and processing circuitry configured to:
 determine current values of the one or more parameters of the patient based on one or more signals received from the one or more sensors, the one or more parameters comprising a surrogate parameter for congestion, a surrogate parameter for tissue perfusion, and a surrogate parameter for blood pressure;   compare the current value of the surrogate parameter for congestion, the current value of the surrogate parameter for tissue perfusion, and the current value of the surrogate parameter for blood pressure to corresponding ones of a baseline value of the surrogate parameter for congestion, a baseline value of the surrogate parameter for tissue perfusion, and a baseline value of the surrogate parameter for blood pressure; and   determine the heart failure status of the patient based on the comparison.