Implantable medical devices using heuristic filtering in cardiac event detection
First Claim
1. A method of cardiac signal analysis comprising:
- capturing a cardiac signal using implanted electrodes;
conditioning and amplifying the signal;
performing analog-to-digital conversion on the signal; and
applying a heuristic filter to the captured cardiac signal by repeatedly performing the following at a predetermined interval;
a) calculating an actual quiescent point of the analog-to-digital converted signal; and
b) adjusting the analog-to-digital conversion of the signal to modify the actual quiescent point toward a desired quiescent point; and
adjusting the predetermined interval by calculating a quiescent distance between the actual quiescent point and the desired quiescent point; and
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x) reducing the predetermined interval if the quiescent distance is greater than a first threshold;
y) increasing the predetermined interval if the quiescent distance is less than a second threshold;
orz) if the quiescent distance is between the first and second thresholds, making no adjustment to the predetermined interval.
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Accused Products
Abstract
Methods for performing cardiac signal analysis in an implanted medical device, and devices configured to perform illustrative methods of cardiac signal analysis. A cardiac signal is captured by an implanted device using implanted electrodes and, during at least certain conditions, the cardiac signal undergoes heuristic filtering. In some embodiments, heuristic filtering is achieved by modifying a signal or value that is used as an indicator of received signal amplitude. In an illustrative example, the heuristic filtering includes periodically incrementing or decrementing the signal or value toward a desired quiescent point, where the heuristic filter period is significantly longer than the sampling period for the signal itself. In another illustrative example, the heuristic filter frequency can be adjusted dynamically to keep the signal average near the desired quiescent point.
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Citations
12 Claims
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1. A method of cardiac signal analysis comprising:
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capturing a cardiac signal using implanted electrodes; conditioning and amplifying the signal; performing analog-to-digital conversion on the signal; and applying a heuristic filter to the captured cardiac signal by repeatedly performing the following at a predetermined interval; a) calculating an actual quiescent point of the analog-to-digital converted signal; and b) adjusting the analog-to-digital conversion of the signal to modify the actual quiescent point toward a desired quiescent point; and adjusting the predetermined interval by calculating a quiescent distance between the actual quiescent point and the desired quiescent point; and
;x) reducing the predetermined interval if the quiescent distance is greater than a first threshold; y) increasing the predetermined interval if the quiescent distance is less than a second threshold;
orz) if the quiescent distance is between the first and second thresholds, making no adjustment to the predetermined interval. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of cardiac signal analysis comprising:
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capturing a cardiac signal between implanted electrodes; conditioning the cardiac signal for use in analysis, including sampling the cardiac signal; creating an adjusted signal, the adjusted signal representing a series of samples of the conditioned cardiac signal added to an offset; repeatedly performing at predefined intervals; a) calculating an average of the adjusted signal over a predetermined period of time; and b) modifying the offset depending upon whether the average of the adjusted signal is greater than or less than a predetermined value; and using the calculated average of the adjusted signal to adjust the predefined intervals by; increasing the duration of the predefined intervals if the calculated average is close to a desired quiescent point;
ordecreasing the duration of the predefined intervals if the calculated average is greater than a desired quiescent point. - View Dependent Claims (8, 9)
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10. An implantable cardiac rhythm management device comprising:
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at least a pair of sensing electrodes; an analog-to-digital converter (ADC) configured to convert a signal received from the sensing electrodes into a digital representation; and control circuitry coupled to the ADC that is configured to; a) perform the following steps repeatedly at a predefined interval; calculate an actual quiescent point of the ADC output; calculate a quiescent distance from the actual quiescent point to a desired quiescent point; and increment or decrement a counter in the ADC to reduce the quiescent distance; and b) at a fixed interval, compare the quiescent distance to a first threshold and a second threshold and if the quiescent distance is shorter than the first threshold, increase the duration of the predetermined interval; if the quiescent distance is longer than the second threshold, decrease the duration of the predetermined interval;
elseleave the predetermined interval unchanged. - View Dependent Claims (11, 12)
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Specification