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Techniques are provided for detecting and evaluating ventricular dyssynchrony based on morphological features of the T-wave and for controlling therapy in response thereto. For example, the number of peaks in the T-wave, the area under the peaks, the number of points of inflection, and the slope of

Techniques are provided for detecting and evaluating ventricular dyssynchrony based on morphological features of the T-wave and for controlling therapy in response thereto. For example, the number of peaks in the T-wave, the area under the peaks, the number of points of inflection, and the slope of the T-wave can be used to detect ventricular dyssynchrony and evaluate its severity. As ventricular dyssynchrony often arises due to heart failure, the degree of dyssynchrony may also be used as a proxy for tracking the progression of heart failure. Pacing therapy is automatically and adaptively adjusted based on the degree of ventricular dyssynchrony so as to reduce the dyssynchrony and thereby improve cardiac function.

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What is claimed is: 1. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical ca

What is claimed is: 1. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical cardiac signal; evaluating a morphological feature of the repolarization event that is affected by ventricular dyssynchrony; detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event, wherein detecting ventricular dyssynchrony within the patient includes detecting ventricular dyssynchrony based on the presence of two or more peaks within an individual repolarization event; and evaluating a degree of severity of ventricular dyssynchrony within the patient based on the number of peaks within individual repolarization events. 2. The method of claim 1 wherein: sensing an electrical cardiac signal within the patient includes sensing an intracardiac electrogram (IEGM); identifying the ventricular repolarization event within the electrical cardiac signal includes identifying one or more T-waves within the IEGM; and detecting ventricular dyssynchrony within the patient includes detecting ventricular dyssynchrony based on the presence of two or more peaks within an individual T-wave. 3. The method of claim 1 wherein evaluating a degree of severity of ventricular dyssynchrony within the patient includes: counting the number of peaks within individual repolarization events; and associating a greater number of peaks as being indicative of a greater severity of ventricular dyssynchrony. 4. The method of claim 1 further including adjusting pacing timing parameters to reduce the number of peaks within individual repolarization events. 5. The method of claim 1 wherein evaluating the degree of severity of ventricular dyssynchrony within the patient includes: determining a time delay between peaks within individual repolarization events; and associating a greater time delay as being indicative of a greater severity of ventricular dyssynchrony. 6. The method of claim 5 wherein the time delay is determined between peaks observed within an individual repolarization event within an individual cardiac signal; and wherein the corresponding ventricular dyssynchrony is an intraventricular dyssynchrony. 7. The method of claim 6 wherein the individual cardiac signal is a left ventricular IEGM. 8. The method of claim 6 wherein the individual cardiac signal is a right ventricular IEGM. 9. The method of claim 5 wherein the time delay is determined between peaks observed within separate cardiac signals; and wherein the corresponding ventricular dyssynchrony is an interventricular dyssynchrony. 10. The method of claim 9 wherein the separate cardiac signals include a left ventricular IEGM and a right ventricular IEGM. 11. The method of claim 5 further including adjusting pacing timing parameters to reduce the time delay between peaks within individual repolarization events. 12. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical cardiac signal; evaluating a morphological feature of the repolarization event that is affected by ventricular dyssynchrony, wherein evaluating a morphological feature of the repolarization event includes evaluating an area associated with the repolarization event; detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event, wherein detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event includes: evaluating a numerical area associated with at least a portion of an individual repolarization event curve relative to an isoelectric line; comparing the area against a baseline area indicative of a lack of ventricular dyssynchrony; and associating a larger amount of area relative to the baseline area as being indicative of ventricular dyssynchrony; and evaluating the degree of severity of ventricular dyssynchrony within the patient based on the area. 13. The method of claim 12 wherein: sensing an electrical cardiac signal within the patient includes sensing an intracardiac electrogram (IEGM); identifying the ventricular repolarization event within the electrical cardiac signal includes identifying one or more T-waves within the IEGM; and detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event includes: evaluating a numerical area associated with at least a portion of the T-wave relative to an isoelectric line; comparing the area against a baseline area indicative of a lack of ventricular dyssynchrony; and associating a larger amount of area relative to the baseline area as being indicative of ventricular dyssynchrony. 14. The method of claim 12 wherein evaluating the degree of severity of ventricular dyssynchrony within the patient includes: determining a difference between the area calculated for the repolarization event and the baseline area; and associating a greater difference as being indicative of a greater severity of ventricular dyssynchrony. 15. The method of claim 14 further including adjusting pacing timing parameters to reduce the difference. 16. The method of claim 14 wherein evaluating the degree of severity of ventricular dyssynchrony within the patient includes: determining a ratio of the area calculated for the repolarization event compared against the baseline area; and associating a greater ratio as being indicative of a greater severity of ventricular dyssynchrony. 17. The method of claim 16 further including adjusting pacing timing parameters to reduce the ratio. 18. The method of claim 12 wherein evaluating the numerical area is performed to separately evaluate the areas associated with separate peaks of the repolarization event curve. 19. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical cardiac signal; evaluating a morphological feature of the repolarization event that is affected by ventricular dyssynchrony, wherein evaluating a morphological feature of the repolarization event includes evaluating points of inflection associated with the repolarization event; and detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event. 20. The method of claim 19 wherein: sensing an electrical cardiac signal within the patient includes sensing an intracardiac electrogram (IEGM); identifying the ventricular repolarization event within the electrical cardiac signal includes identifying one or more T-waves within the IEGM; evaluating a morphological feature of the repolarization event includes evaluating points of inflection associated with the T-wave; and detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event includes detecting ventricular dyssynchrony within the patient based on the detection of more than three points of inflection within an individual T-wave. 21. The method of claim 19 wherein detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event includes: evaluating numerical derivatives of a repolarization event curve; identifying points of inflexion within the repolarization event curve based on the numerical derivatives; and associating more than three points of inflection within a single repolarization event as being indicative of ventricular dyssynchrony. 22. The method of claim 21 further including evaluating a degree of severity of ventricular dyssynchrony within the patient based on the points of inflection. 23. The method of claim 22 further including adjusting pacing timing parameters to reduce the degree of severity of ventricular dyssynchrony within the patient by reducing the number of points of inflection. 24. The method of claim 22 wherein evaluating a degree of severity of ventricular dyssynchrony within the patient includes determining a total number of points of inflection within a individual repolarization event; and associating a greater number of points of inflection as being indicative of a greater severity of ventricular dyssynchrony. 25. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical cardiac signal; evaluating a morphological feature of the repolarization event that is affected by ventricular dyssynchrony, wherein evaluating a morphological feature of the repolarization event includes evaluating one or more slope values associated with the repolarization event; detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event; and adjusting pacing timing parameters to reduce the magnitude of the slope of individual repolarization event curves. 26. The method of claim 25 wherein: sensing an electrical cardiac signal within the patient includes sensing an intracardiac electrogram (IEGM); identifying the ventricular repolarization event within the electrical cardiac signal includes identifying one or more T-waves within the IEGM; evaluating a morphological feature of the repolarization event includes evaluating one or more slope values associated with the T-wave; detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event includes: evaluating an upslope of the T-wave; comparing the upslope against a baseline upslope indicative of a lack of ventricular dyssynchrony; and associating a significant increase in the slope relative to the baseline slope as being indicative of ventricular dyssynchrony; and adjusting pacing timing parameters includes adjusting pacing timing parameters to reduce the magnitude of the slope of T-waves. 27. The method of claim 25 wherein detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event includes: evaluating a slope of a repolarization event curve; comparing the slope against a baseline slope indicative of a lack of ventricular dyssynchrony; associating a larger magnitude slope relative to the baseline slope as being indicative of ventricular dyssynchrony. 28. The method of claim 25 wherein the slope values include one or more of upslope values and downslope values. 29. The method of claim 25 further including evaluating a degree of severity of ventricular dyssynchrony within the patient based on the slope. 30. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical cardiac signal; measuring a morphological feature of the repolarization event that is affected by ventricular dyssynchrony; detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event; evaluating a degree of severity of ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event; and evaluating progression of heart failure based on changes in the severity of ventricular dyssynchrony within the patient over time. 31. The method of claim 30 wherein: sensing an electrical cardiac signal within the patient includes sensing an intracardiac electrogram (IEGM); and identifying the ventricular repolarization event within the electrical cardiac signal includes identifying one or more T-waves within the IEGM. 32. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical cardiac signal; measuring a plurality of morphological features of the repolarization event that is affected by ventricular dyssynchrony; and detecting ventricular dyssynchrony within the patient based on the plurality of morphological features of the repolarization event. 33. The method of claim 32 wherein: sensing an electrical cardiac signal within the patient includes sensing an intracardiac electrogram (IEGM); and identifying the ventricular repolarization event within the electrical cardiac signal includes identifying one or more T-waves within the IEGM. 34. The method of claim 33 wherein the plurality of morphological features is selected from the group consisting of a number of peaks of an individual T-wave, an area under one or more peaks of an individual T-wave, a number of inflection points within an individual T-wave, a slope of an individual T-wave, and combinations thereof. 35. The method of claim 33 wherein the plurality of morphological features includes the number of peaks under an individual T-wave, the area under the individual T-wave, and the slope of the individual T-wave, and wherein detecting ventricular dyssynchrony within the patient based on the plurality of morphological features of the repolarization event includes: comparing the number of peaks under an individual T-wave to a baseline value; comparing the area under the individual T-wave to a baseline value; comparing the slope of the individual T-wave to a baseline value; and detecting ventricular dyssynchrony if each of said comparisons is indicative of ventricular dyssynchrony. 36. The method of claim 33 further including adaptively adjusting pacing timing parameters to reduce fractionation of T-waves or reduce the time delay between peaks of a T-wave. 37. The method of claim 34 further including adaptively adjusting pacing timing parameters to reduce ventricular dyssynchrony by adjusting an interventricular pacing delay. 38. The method of claim 34 further including adaptively adjusting pacing timing parameters to reduce ventricular dyssynchrony by adjusting a delay between a paced or sensed atrial event and a paced ventricular event. 39. A method for use with an implantable medical device for detecting ventricular dyssynchrony, the method comprising: sensing an electrical cardiac signal within the patient in which the device is implanted; identifying a ventricular repolarization event within the electrical cardiac signal; measuring a morphological feature of the repolarization event that is affected by ventricular dyssynchrony; and detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event, wherein the device is equipped to selectively deliver pacing at any of a plurality of pacing sites and wherein pacing sites are selected so as to reduce ventricular dyssynchrony. 40. The method of claim 39 wherein: sensing an electrical cardiac signal within the patient includes sensing an intracardiac electrogram (IEGM); and identifying the ventricular repolarization event within the electrical cardiac signal includes identifying one or more T-waves within the IEGM. 41. The method of claim 30 further including the step of detecting a significant deterioration in ventricular dyssynchrony. 42. The method of claim 41 further including the step of activating a warning device in response to detection of a significant deterioration in ventricular dyssynchrony. 43. The method of claim 30 further including the step of transmitting diagnostic information pertaining to ventricular dyssynchrony to an external system. 44. The method of claim 43 wherein the diagnostic information pertaining to ventricular dyssynchrony sent to the external system includes trending information. 45. A system for use with an implantable medical device for detecting ventricular dyssynchrony, the system comprising: means for sensing an electrical cardiac signal within the patient in which the device is implanted; means for identifying a ventricular repolarization event within the electrical cardiac signal; means for evaluating at least one morphological feature of the repolarization event that is affected by ventricular dyssynchrony, wherein the morphological feature is selected from the group consisting of a number of peaks of an individual T-wave, an area under one or more peaks of an individual T-wave, a number of inflections within an individual T-wave, a slope of an individual T-wave, and combinations thereof; means for detecting ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event; means for evaluating the degree of dyssynchrony based on the morphological feature of the repolarization event; and means for adaptively adjusting the pacing parameters of the implantable medical device based on the morphological feature of the repolarization event. 46. A system for use with an implantable medical device for detecting ventricular dyssynchrony, the system comprising: an electrical cardiac signal sensing unit operative to sense electrical cardiac signals within the patient in which the device is implanted; a ventricular repolarization event detection unit operative to identify a ventricular repolarization event within the electrical cardiac signal; a ventricular repolarization event morphological feature evaluation unit operative to evaluate at least one morphological feature of the repolarization event that is affected by ventricular dyssynchrony, wherein the morphological feature is selected from the group consisting of a number of peaks of an individual T-wave, an area under one or more peaks of an individual T-wave, a number of inflections within an individual T-wave, a slope of an individual T-wave, and combinations thereof; a ventricular repolarization-based ventricular dyssynchrony evaluation system operative to detect ventricular dyssynchrony within the patient based on the morphological feature of the repolarization event; and a pacing site and timing unit for adaptively adjusting the pacing parameters of the implantable medical device based on the morphological feature of the repolarization event. 47. The system of claim 46 further including a heart failure progression tracking unit operative to track progression of heart failure in the patient based on the degree of ventricular dyssynchrony within the patient. 48. The system of claim 46 further including an implantable warning device operative to generate warnings in response to the detection of ventricular dyssynchrony within the patient. 49. The system of claim 46 further including a telemetry system operative to transmit diagnostic information pertaining to ventricular dyssynchrony to an external system for display. 50. The system of claim 49 wherein the diagnostic information includes trending information. 51. The system of claim 46 wherein the system is implantable. 52. The system of claim 51 wherein the system is a component of the implantable medical device.