Cardiac stimulator with data converter for cardiac signal
First Claim
1. An implantable cardiac stimulator comprising:
- means for stimulating the heart;
means for sensing intrinsic cardiac waveforms in the heart;
means for converting said intrinsic cardiac waveforms from analog to digital form, said converting means consisting oftiming means for defining measurement cycles;
sampling means for sampling the analog value of said cardiac waveform in a measurement cycle;
means for comparing at least two sampled analog values of said cardiac waveforms;
means for determining an analog difference having a predicted probability of occurrence between said two sampled cardiac waveforms;
means for assigning a digital code to said analog difference, said digital code being of predetermined, variable size, said size being proportional to the predicted probability of occurrence of said difference.
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Abstract
An implantable cardiac stimulator with an analog-to-digital converter which comprises timing means for defining measurement cycles. During successive cycles, the value of a cardiac waveform is sampled. The difference between sampled values in two different measurement cycles produces a value whose probability is predicted. A digital code is assigned to each expected difference value such that difference values with a high expected probability have a shorter code and values with a low probability have a longer code. Means are provided for assigning a digital code based on the determined difference, the digital code being of predetermined variable size, the size of the code being proportional to the predicted probability of occurrence of a particular difference. The variability in code length permits the resulting digital representation of the waveform to be compressed and the energy required for conversion to be reduced. Different codes can be assigned to a detected difference depending on the type of waveform (normal, tachycardia, fibrillation) which is being detected.
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Citations
22 Claims
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1. An implantable cardiac stimulator comprising:
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means for stimulating the heart; means for sensing intrinsic cardiac waveforms in the heart; means for converting said intrinsic cardiac waveforms from analog to digital form, said converting means consisting of timing means for defining measurement cycles; sampling means for sampling the analog value of said cardiac waveform in a measurement cycle; means for comparing at least two sampled analog values of said cardiac waveforms; means for determining an analog difference having a predicted probability of occurrence between said two sampled cardiac waveforms; means for assigning a digital code to said analog difference, said digital code being of predetermined, variable size, said size being proportional to the predicted probability of occurrence of said difference. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. An analog-to-digital converter for cardiac waveforms comprising:
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means for sensing intrinsic cardiac waveforms in the heart; means for converting said intrinsic cardiac waveforms from analog to digital form, said converting means consisting of timing means for defining measurement cycles; sampling means for sampling the analog value of said cardiac waveform in a measurement cycle; means for comparing at least two sampled analog values of said cardiac waveforms; means for determining an analog difference between said two sampled cardiac waveforms; means for assigning a digital code to said analog difference, said digital code being of predetermined, variable size, said size being proportional to the predicted probability of occurrence of said difference. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification