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Transthoracic cardiac stimulation therapies provide for detection and treatment of cardiac asystole subsequent to delivery of a defibrillation therapy. A pacing therapy is transthoracicly delivered to terminate detected cardiac asystole using residual energy from a defibrillation energy storage sour

Transthoracic cardiac stimulation therapies provide for detection and treatment of cardiac asystole subsequent to delivery of a defibrillation therapy. A pacing therapy is transthoracicly delivered to terminate detected cardiac asystole using residual energy from a defibrillation energy storage source. The residual energy usable for the pacing therapy is sufficient to transthoracicly deliver at least one pacing pulse, and is typically sufficient to deliver a series of pacing pulses, prior to depletion of the defibrillation energy storage source. Detection of cardiac asystole is performed following delivery of each pacing pulse, and subcutaneous pacing support is terminated in response to detecting cardiac asystole termination.

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What is claimed is: 1. A method of providing subcutaneous cardiac stimulation, comprising: detecting from a subcutaneous, non-intrathoracic vector, cardiac asystole subsequent to delivery of a defibrillation therapy, energy for the defibrillation therapy provided by a subcutaneous, non-intrathoraci

What is claimed is: 1. A method of providing subcutaneous cardiac stimulation, comprising: detecting from a subcutaneous, non-intrathoracic vector, cardiac asystole subsequent to delivery of a defibrillation therapy, energy for the defibrillation therapy provided by a subcutaneous, non-intrathoracic defibrillation energy storage source; and delivering, from the same or different subcutaneous, non-intrathoracic vector, a pacing therapy to terminate the detected cardiac asystole using residual energy from the defibrillation energy storage source. 2. The method of claim 1, wherein the residual energy usable for the pacing therapy delivery represents less than about 10% of energy initially stored in the defibrillation storage source prior to defibrillation therapy delivery. 3. The method of claim 1, wherein the residual energy usable for the pacing therapy is sufficient to transthoracicly deliver a plurality of pacing pulses. 4. The method of claim 3, further comprising detecting for cardiac asystole termination following delivery of each of the pacing pulses, and terminating subcutaneous pacing support in response to detecting cardiac asystole termination. 5. The method of claim 1, wherein the defibrillation therapy reduces a voltage of the defibrillation energy storage source from a first voltage level to a second voltage level, and the pacing therapy is effected at a voltage level equal to or less than the second voltage level. 6. The method of claim 1, wherein delivering the pacing therapy comprises using the residual energy until either the pacing therapy terminates the detected cardiac asystole or the defibrillation energy storage source is depleted of the residual energy. 7. The method of claim 6, further comprising recharging the defibrillation energy storage source in response to depletion of the residual energy. 8. The method of claim 7, further comprising re-delivering the pacing therapy or an alternative transthoracic pacing therapy in response to recharging the defibrillation energy storage source, wherein re-delivering the pacing therapy or the alternative transthoracic pacing therapy is initiated after recharging the defibrillation energy storage source to a level less than that associated with the defibrillation therapy. 9. The method of claim 1, wherein the residual energy used for delivering the pacing therapy is sufficient to transthoracicly deliver a single pacing pulse. 10. The method of claim 9, further comprising recharging, following delivery of the single pacing pulse, the defibrillation energy storage source to a recharge level less than a level associated with defibrillation therapy delivery. 11. The method of claim 10, wherein the recharge level of the defibrillation energy storage source is sufficient to support delivery of a subsequent single pacing pulse. 12. The method of claim 10, wherein the recharge level of the defibrillation energy storage source is sufficient to support delivery of a plurality of pacing pulses. 13. The method of claim 1, wherein delivering the pacing therapy comprises delivering one or more pacing pulses each having a peak current no greater than about 500 mA. 14. The method of claim 1, wherein delivering the pacing therapy comprises delivering one or more pacing pulses each having a pulse width of about 20 ms. 15. The method of claim 1, wherein delivering the pacing therapy comprises delivering one or more pacing pulses each having a pulse width varying between about 10 ms and about 30 ms. 16. The method of claim 1, wherein a defibrillation waveform generated from the defibrillation therapy has an overall tilt of about 0% to about 90%. 17. The method of claim 1, wherein a defibrillation waveform generated from the defibrillation therapy has an overall tilt of about 40% to about 90%. 18. The method of claim 1, wherein a defibrillation waveform generated from the defibrillation therapy comprises a monophasic waveform. 19. The method of claim 1, wherein a defibrillation waveform generated from the defibrillation therapy comprises a biphasic waveform. 20. The method of claim 1, wherein a defibrillation waveform generated from the defibrillation therapy comprises a multiphasic waveform. 21. The method of claim 1, wherein the pacing therapy is delivered using defibrillation electrodes. 22. The method of claim 1, wherein the pacing therapy is delivered using pacing electrodes. 23. A method of providing subcutaneous cardiac stimulation, comprising: detecting, from within a patient, cardiac asystole subsequent to delivery of a defibrillation therapy; and transthoracicly delivering, from within the patient, a non-physiologic, life sustaining pacing therapy at a rate substantially lower than a bradycardia pacing rate to terminate the detected cardiac asystole. 24. The method of claim 23, wherein delivering the pacing therapy comprises delivering a first pace pulse about 5 to 20 seconds subsequent to detection of the cardiac asystole. 25. The method of claim 23, wherein delivering the pacing therapy comprises delivering a first pace pulse about 20 to 30 seconds subsequent to detection of the cardiac asystole. 26. The method of claim 23, wherein delivering the pacing therapy comprises delivering a plurality of pacing pulses at a progressively increasing rate. 27. The method of claim 23, wherein delivering the pacing therapy comprises delivering a plurality of pacing pulses at a substantially constant rate. 28. The method of claim 23, wherein delivering the pacing therapy comprises delivering a series of pacing pulses, the series of pacing pulses comprising at least one sequence delivered at a variable rate and at least one sequence delivered at a substantially constant rate. 29. The method of claim 23, wherein delivering the pacing therapy comprises: delivering a first pace pulse after a first duration subsequent to detection of the cardiac asystole; and delivering a second pace pulse after a second duration subsequent to the first pace pulse, the second duration being about one-third to about three-fourths of the first duration. 30. The method of claim 23, wherein delivering the pacing therapy comprises: delivering a first pace pulse after a first duration subsequent to detection of the cardiac asystole; and delivering a second pace pulse after a second duration subsequent to the first pace pulse, the second duration being shorter than the first duration by a fixed amount. 31. The method of claim 30, wherein the fixed amount ranges between about 5 seconds and about 15 seconds. 32. The method of claim 23, wherein delivering the pacing therapy comprises delivering pacing pulses at a rate varying between about 2 and about 40 pulses per minute. 33. The method of claim 23, wherein the defibrillation therapy and the pacing therapy derive energy from a defibrillation energy storage source. 34. The method of claim 23, wherein the defibrillation therapy derives energy from a defibrillation energy storage source, and the pacing therapy derives energy from a pacing circuitry power source. 35. A method of providing subcutaneous cardiac stimulation, comprising: detecting, from with a patient, cardiac asystole subsequent to delivery of a defibrillation therapy; and transthoracicly delivering, from within the patient, a life sustaining pacing therapy at a rate insufficient to restore full patient consciousness to terminate the detected cardiac asystole. 36. The method of claim 35, wherein delivering the pacing therapy comprises delivering pacing pulses at a rate substantially lower than a bradycardia pacing rate. 37. The method of claim 35, wherein delivering the pacing therapy comprises delivering pacing pulses at a rate varying between about 2 and about 40 pulses per minute. 38. The method of claim 35, wherein delivering the pacing therapy comprises delivering a first pace pulse about 5 to 20 seconds subsequent to detection of the cardiac asystole. 39. The method of claim 35, wherein delivering the pacing therapy comprises delivering a first pace pulse about 20 to 30 seconds subsequent to detection of the cardiac asystole. 40. The method of claim 35, wherein delivering the pacing therapy comprises delivering a plurality of pacing pulses at a progressively increasing rate. 41. The method of claim 35, wherein delivering the pacing therapy comprises delivering a plurality of pacing pulses at a substantially constant rate. 42. The method of claim 35, wherein delivering the pacing therapy comprises delivering a series of pacing pulses, the series of pacing pulses comprising at least one sequence delivered at a variable rate and at least one sequence delivered at a substantially constant rate. 43. A method of providing subcutaneous cardiac stimulation, comprising: delivering, from a subcutaneous, non-intrathoracic vector, a pacing therapy in response to detecting a condition necessitating pacing therapy delivery, energy for the pacing therapy delivery provided by a subcutaneous, non-intrathoracic cardioversion/defibrillation energy storage source; and delivering, from the same or a different subcutaneous, non-intrathoracic vector, a cardioversion or defibrillation therapy in response to detecting a cardiac arrhythmia necessitating the cardioversion or defibrillation therapy, energy for the cardioversion or defibrillation therapy provided by the subcutaneous, non-intrathoracic cardioversion/defibrillation energy storage source. 44. The method of claim 43, wherein the condition necessitating pacing therapy comprises a bradycardia condition. 45. The method of claim 43, wherein the condition necessitating pacing therapy comprises a tachycardia condition. 46. An apparatus for providing subcutaneous cardiac stimulation, comprising: an implantable housing; energy delivery circuitry provided in the housing, the energy delivery circuitry comprising a defibrillation energy storage source; first and second electrodes respectively coupled to the energy delivery circuitry and arranged in a spaced relationship with respect to cardiac tissue and vasculature for subcutaneous, non-intrathoracic cardiac sensing and energy delivery; and detectionlcontrol circuitry provided in the housing and coupled to the energy delivery circuitry, the detection/control circuitry detecting cardiac asystole subsequent to delivery of a defibrillation therapy and transthoracicly delivering a pacing therapy via the energy delivery circuitry to terminate the detected cardiac asystole using residual energy from the defibrillation energy storage source, wherein the residual energy used for delivering the pacing therapy is sufficient to transthoracicly deliver a single pacing pulse, and the detection/control circuitry, following delivery of the single pacing pulse, initiates recharging of the defibrillation energy storage source to a recharge level less than a level associated with defibrillation therapy delivery. 47. The apparatus of claim 46, wherein the residual energy usable for the pacing therapy delivery represents less than about 10% of energy initially stored in the defibrillation storage source prior to defibrillation therapy delivery. 48. The apparatus of claim 46, wherein the residual energy usable for the pacing therapy is sufficient to transthoracicly deliver a plurality of pacing pulses. 49. The apparatus of claim 46, wherein the detection/control circuitry comprises a detector for detecting cardiac asystole termination following delivery of each of a plurality of pacing pulses, the detection/control circuitry terminating subcutaneous pacing support in response to the detector detecting cardiac asystole termination. 50. The apparatus of claim 46, wherein the energy delivery circuitry delivers the pacing therapy using the residual energy until either the detection/control circuitry detects cardiac asystole termination or the defibrillation energy storage source is depleted of the residual energy. 51. The apparatus of claim 50, wherein the detection/control circuitry initiates recharging of the defibrillation energy storage source in response to depletion of the residual energy. 52. The apparatus of claim 46, wherein the detection/control circuitry initiates re-delivery of the pacing therapy or an alternative transthoracic pacing therapy in response to recharging of the defibrillation energy storage source, wherein re-delivery of the pacing therapy or the alternative transthoracic pacing therapy is initiated after recharging the defibrillation energy storage source to a level less than that associated with the defibrillation therapy. 53. The apparatus of claim 46, wherein the pacing therapy delivered by the energy delivery circuitry comprises one or more pacing pulses each having a peak current no greater than about 500 mA. 54. The apparatus of claim 46, wherein the pacing therapy delivered by the energy delivery circuitry comprises one or more pacing pulses each having a pulse width of between about 10 ms and 30 ms. 55. The apparatus of claim 46, wherein a defibrillation waveform generated by the energy delivery circuitry has an overall tilt of about 0% to about 90%. 56. The apparatus of claim 46, wherein the energy delivery circuitry delivers pacing pulses at a rate varying between about 2 and about 40 pulses per minute. 57. The apparatus of claim 46, wherein the energy delivery circuitry delivers a first pace pulse after a first duration subsequent to detection of the cardiac asystole, and delivers a second pace pulse after a second duration subsequent to the first pace pulse, the second duration being about one-third to about three-fourths of the first duration. 58. The apparatus of claim 46, wherein the energy delivery circuitry delivers a first pace pulse after a first duration subsequent to detection of the cardiac asystole, and delivers a second pace pulse after a second duration subsequent to the first pace pulse, the second duration being shorter than the first duration by a fixed amount. 59. The apparatus of claim 58, wherein the fixed amount ranges between about 5 seconds and about 15 seconds. 60. The apparatus of claim 46, wherein a defibrillation waveform generated by the energy delivery circuitry comprises a monophasic waveform. 61. The apparatus of claim 46, wherein a defibrillation waveform generated by the energy delivery circuitry comprises a biphasic waveform. 62. The apparatus of claim 46, wherein a defibrillation waveform generated by the energy delivery circuitry comprises a multiphasic waveform. 63. The apparatus of claim 46, wherein the first electrode is provided on the housing, and the second electrode is electrically and physically coupled to the housing via a lead. 64. The apparatus of claim 46, wherein the housing defines a unitary structure, and each of the first and second electrodes is respectively provided on the housing. 65. The apparatus of claim 64, wherein the housing comprises an arcuate or angled portion, and the first and second electrodes are respectively positioned proximate opposing ends of the housing. 66. The apparatus of claim 46, wherein one or both of the first and second electrodes is provided on a support structure outwardly extending from the housing. 67. The apparatus of claim 66, further comprising a header block disposed between the support structure and the housing, the header block comprising an electrical connection arrangement for coupling electrical terminals of the housing with conductors respectively coupled to the first and second electrodes. 68. The apparatus of claim 66, wherein all or a portion of the support structure comprises a shape adjustable arrangement, whereby an orientation between the first and second electrodes is alterable in response to manual manipulation of the shape adjustable arrangement. 69. The apparatus of claim 46, wherein a longitudinal axis defined between the first and second electrodes passes through at least some of the cardiac tissue. 70. An apparatus for providing subcutaneous cardiac stimulation, comprising: an implantable housing; energy delivery circuitry provided in the housing; first and second electrodes respectively coupled to the energy delivery circuitry and arranged in a spaced relationship with respect to cardiac tissue and vasculature for subcutaneous, non-intrathoracic cardiac sensing and energy delivery, one or both of the first and second electrodes provided on a support structure outwardly extending from the housing, all or a portion of the support structure comprises a shape adjustable arrangement, whereby an orientation between the first and second electrodes is alterable in response to manual manipulation of the shape adjustable arrangement; and a detection/control circuitry provided in the housing and coupled to the energy delivery circuitry, the detection/control circuitry detecting cardiac asystole subsequent to delivery of a defibrillation therapy and transthoracicly delivering a non-physiologic, life sustaining pacing therapy to terminate the detected cardiac asystole. 71. The apparatus of claim 70, wherein the defibrillation therapy and the pacing therapy derive energy from a defibrillation energy storage source of the energy delivery circuitry. 72. The apparatus of claim 70, further comprising pacing circuitry coupled to the detection/control circuitry, wherein the energy delivery circuitry delivers the defibrillation therapy and the pacing circuitry delivers the pacing therapy. 73. The apparatus of claim 70, wherein the energy delivery circuitry delivers a pacing therapy at a rate insufficient to restore full patient consciousness. 74. The apparatus of claim 70, wherein the energy delivery circuitry delivers a pacing therapy at a rate substantially lower than a bradycardia pacing rate. 75. The apparatus of claim 70, wherein the energy delivery circuitry delivers pacing pulses at a rate varying between about 2 and about 40 pulses per minute. 76. The apparatus of claim 70, wherein the energy delivery circuitry delivers one or more pacing pulses each having a pulse width of between about 10 ms and 30 ms. 77. The apparatus of claim 70, wherein the energy delivery circuitry delivers a first pace pulse about 5 to 30 seconds subsequent to detection of the cardiac asystole. 78. The apparatus of claim 70, wherein the energy delivery circuitry delivers a plurality of pacing pulses at a progressively increasing rate. 79. The apparatus of claim 70, wherein the energy delivery circuitry delivers a plurality of pacing pulses at a substantially constant rate. 80. The apparatus of claim 70, wherein the first electrode is provided on the housing, and the second electrode is electrically and physically coupled to the housing via a lead. 81. The apparatus of claim 70, wherein the housing defines a unitary structure, and each of the first and second electrodes is respectively provided on the housing. 82. The apparatus of claim 81, wherein the housing comprises an arcuate or angled portion, and the first and second electrodes are respectively positioned proximate opposing ends of the housing. 83. The apparatus of claim 70, further comprising a header block disposed between the support structure and the housing, the header block comprising an electrical connection arrangement for coupling electrical terminals of the housing with conductors coupled to respective first and second electrodes.