Shock Reduction Using Absolute Calibrated Tissue Oxygen Saturation and Total Hemoglobin Volume Fraction

• US 20100317946A1
• Filed: 06/10/2010
• Published: 12/16/2010
• Est. Priority Date: 06/10/2009
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Kuhn, Jonathan L., Cinbis, Can, Anderson, David A., Carney, James K.
• Granted Patent: US 9,126,049 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 5/02028 Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/283 Invasive
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/36557 controlled by chemical substances in blood
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

An implantable medical device for detecting and treating an arrhythmia includes an optical sensor adapted for positioning adjacent to a blood-perfused tissue volume. In one embodiment for controlling arrhythmia therapies delivered by the device, the optical sensor is controlled to emit light in response to detecting an arrhythmia, detect light scattered by the volume of blood perfused tissue including measuring an optical sensor output signal corresponding to the intensity of scattered light for at least four spaced-apart wavelengths, and compute a volume-independent measure of tissue oxygen saturation from the detected light. The hemodynamic status of the arrhythmia is detected in response to the measure of tissue oxygen saturation.

Claims

1. A method, comprising:

sensing cardiac depolarization signals;

detecting an arrhythmia in response to the depolarization signals;

controlling an optical sensor to emit light in response to the detected arrhythmia;

detecting light scattered by a volume of blood perfused tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to light attenuation of at least four spaced apart light wavelengths;

computing a measure of tissue oxygenation from the optical sensor output signal; and

detecting a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation.

2. The method of claim 1, wherein detecting a hemodynamic status comprises:

detecting a hemodynamically unstable arrhythmia in response to a decreasing measure of tissue oxygen saturation;

enabling a shock therapy for treating the arrhythmia in response to detecting the hemodynamically unstable arrhythmia; and

withholding delivering of a shock therapy for treating the arrhythmia in response to not detecting the hemodynamic status as being unstable.

3. The method of claim 1, wherein computing the measure of tissue oxygenation comprises:

computing a light attenuation for each of the at least four wavelengths;

computing a second derivative of the light attenuation with respect to two different wavelengths; and

computing a measure of tissue oxygen saturation as a ratio of the second derivatives at the two different wavelengths.

4. The method of claim 3, further comprising computing a measure of total hemoglobin volume fraction using the measure of tissue oxygen saturation, wherein detecting a hemodynamic status comprises detecting a hemodynamic status in response to both the measure of tissue oxygen saturation and the measure of total hemoglobin volume fraction.

5. The method of claim 1, further comprising:

determining a baseline measurement of tissue oxygenation prior to detecting the arrhythmia;

computing an onset measurement of tissue oxygenation corresponding to a time at which the arrhythmia is detected in response to the depolarization signals;

comparing the baseline measurement and the onset measurement; and

enabling a shock therapy in response to the onset measurement being less than the baseline measurement.

6. The method of claim 1, further comprising:

computing an onset measurement of tissue oxygenation corresponding to a time at which the arrhythmia is detected in response to the depolarization signals;

computing an episode measurement of tissue oxygenation at a time subsequent to arrhythmia detection;

comparing the onset measurement and the episode measurement; and

withholding a shock therapy in response to the comparison.

7. The method of claim 4 further comprising:

defining an acceptable measurement range for the measure of total hemoglobin volume fraction;

comparing the measure of total hemoglobin volume fraction to the acceptable measurement range; and

determining a quality of the measure of total hemoglobin volume fraction in response to the comparing.

8. The method of claim 1, wherein detecting a hemodynamic status comprises:

determining a baseline measurement of tissue oxygenation prior to detecting the arrhythmia;

defining a threshold in response to the baseline measurement; and

comparing the measure of tissue oxygenation to the threshold.

9. The method of claim 4, further comprising computing a tissue oxygenation index as a function of the measure of tissue oxygen saturation and the measure of total hemoglobin volume fraction.

10. The method of claim 1, further comprising:

sensing a signal corresponding to a patient position; and

detecting the hemodynamic status in response to the measure of tissue oxygenation and the signal corresponding to the patient position.

11. The method of claim 1, further comprising:

storing a state table relating the tissue oxygenation measurement to a cardiac status; and

determining an absolute value of the tissue oxygenation measurement and a trended value of the tissue oxygenation measurement, wherein detecting a hemodynamic status comprises determining a cardiac status stored in the state table corresponding to the absolute value and the trended value.

12. An implantable medical device, comprising:

a cardiac electrode for sensing cardiac depolarization signals;

an optical sensor for providing a signal corresponding to light attenuation by a volume of blood perfused tissue;

a control module coupled to the optical sensor controlling the light emitted by the optical sensor;

a monitoring module receiving an optical sensor output signal and measuring light attenuation for at least four spaced-apart light wavelengths; and

a processor coupled to the cardiac electrode and the monitoring module, the processor being configured to detect an arrhythmia in response to the depolarization signals and compute a tissue oxygenation measurement in response to detecting the arrhythmia, the processor further configured to detect a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation.

13. The device of claim 12, further comprising a therapy delivery module coupled to the electrode to deliver shock therapy for treating the arrhythmia, wherein the processor is further configured to detect the hemodynamic status as unstable in response to a decreasing measure of tissue oxygenation and to enable the therapy delivery module to deliver the shock therapy in response to detecting the unstable hemodynamic status, and withhold delivery of a shock therapy by the therapy delivery module in response to not detecting the hemodynamic status as unstable.

14. The device of claim 12, wherein the processor is further configured to compute an attenuation for each of the at least four wavelengths of detected light, compute a second derivative of the light attenuation with respect to two different wavelengths, and compute a measure of tissue oxygen saturation as a ratio of the second derivatives at the two different wavelengths.

15. The device of claim 14, wherein the processor is further configured to compute a measure of total hemoglobin volume fraction using the measure of tissue oxygen saturation, and detect a hemodynamic status in response to both the measure of tissue oxygen saturation and the measure of total hemoglobin volume fraction.

16. The device of claim 12, further comprising a therapy delivery module coupled to the electrode for delivering a shock therapy to a patient, wherein the processor is further configured to determine a baseline measurement of tissue oxygenation prior to detecting the arrhythmia, compute an onset measurement of tissue oxygenation corresponding to a time at which the arrhythmia is detected in response to the depolarization signals, compare the baseline measurement and the onset measurement, and enable the therapy delivery module to deliver shock therapy in response to the onset measurement being less than the baseline measurement.

17. The device of claim 12, further comprising a therapy delivery module coupled to the electrode for delivering a shock therapy to a patient, wherein the processor is further configured to determine an onset measurement of tissue oxygenation corresponding to a time at which the arrhythmia is detected in response to the depolarization signals, compute an episode measurement of tissue oxygenation corresponding to a time subsequent to the arrhythmia being detected in response to the depolarization signals, compare the onset measurement and the episode measurement and enable the therapy delivery module to deliver a shock therapy in response to the episode measurement being less than the onset measurement.

18. The device of claim 15, further comprising a memory storing an acceptable measurement range for the measure of total hemoglobin volume fraction, wherein the processor is further configured to compare the measure of total hemoglobin volume fraction to the acceptable measurement range, and determine a quality of the measure of total hemoglobin volume fraction and the measure of tissue oxygen saturation in response to the comparing.

19. The device of claim 12, further comprising a memory for storing a threshold, wherein the processor is further configured to determine a baseline measurement of tissue oxygenation prior to detecting the arrhythmia, compute a threshold in response to the baseline measurement and store the threshold in the memory;

and compare the measure of tissue oxygenation to the threshold.

20. The device of claim 15, wherein analyzing the measure of tissue oxygen saturation and the measure of total hemoglobin volume fraction comprises computing a tissue oxygenation index as a function of the measure of tissue oxygen saturation and the measure of total hemoglobin volume fraction.

21. The device of claim 12, further comprising a sensor coupled to the processor to sense a signal corresponding to a patient position, wherein the processor is further configured to detect the hemodynamic status in response to the measure of tissue oxygenation and the signal corresponding to the patient position.

22. The device of claim 12, further comprising a memory storing a state table relating the tissue oxygenation measurement to a cardiac status, wherein the processor is further configured to determine an absolute value of the tissue oxygenation measurement and a trended value of the tissue oxygenation measurement, and detect the hemodynamic status by determining a cardiac status stored in the state table corresponding to the absolute value and the trended value.

23. A computer readable medium having computer executable instructions for performing a method comprising:

sensing cardiac depolarization signals;

detecting an arrhythmia in response to the depolarization signals;

controlling an optical sensor to emit light in response to the detected arrhythmia;

detecting light scattered by a volume of blood perfused tissue wherein detecting light comprises measuring an optical sensor output signal corresponding to light attenuation of at least four spaced apart light wavelengths;

computing a measure of tissue oxygenation from the optical sensor output signal; and

detecting a hemodynamic status of the arrhythmia in response to the measure of tissue oxygenation.