Detection of cardiac arrhythmias using template matching by signature analysis
First Claim
1. A method of detecting cardiac arrhythmias in a patient'"'"'s heart, comprising the steps of:
- sampling a cardiac electrical signal when the heart is functioning in a known cardiac state;
defining, for each sample of the known state cardiac electrical signal occurring within a predetermined time of interest, an amplitude window of signal amplitudes bracketing the amplitude of the known state cardiac electrical signal sample;
storing a template sequence of amplitude window samples encompassing the predetermined time of interest;
monitoring a time sequence of cardiac electrical signal samples when the heart is functioning in an unknown cardiac state;
time aligning samples of the unknown cardiac state sequence with respect to samples of the template sequence of amplitude window samples;
comparing, sample by sample, the samples of the unknown cardiac state sequence to the template sequence of amplitude window samples to determine the relative proportion of unknown cardiac state samples with amplitudes falling outside the amplitude window in comparison to unknown cardiac state samples with amplitudes falling inside the amplitude window; and
classifying the functioning of the patient'"'"'s heart as other than the known cardiac state when the determined relative proportion meets a predetermined criteria and, otherwise, classifying the functioning of the patient'"'"'s heart as the known cardiac state.
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Accused Products
Abstract
A method and apparatus for detecting cardiac arrhythmias are disclosed. The detecting method and apparatus sense cardiac electrical signals when the heart is functioning in a known cardiac state, such as a physiologically normal cardiac state, then define and store an array of amplitude windows wherein each sample in the array of amplitude windows corresponds to a sample of the known cardiac signal. Each amplitude window delineates a range of signal amplitudes bracketing the amplitude of the known cardiac electrical signal sample. The array of amplitude windows corresponds in time to periodically occurring known cardiac signal samples occurring within a predetermined time of interest. Subsequently, when the heart is functioning in an unknown cardiac state, the method and apparatus monitor cardiac electrical signals by time aligning samples and comparing, on a sample by sample basis, the amplitude of unknown state cardiac signal samples with the amplitude range within the stored array of amplitude window samples. The relative number of samples falling outside the amplitude windows is the basis for analyzing cardiac signal morphology for the purpose of detecting cardiac arrhythmias.
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Citations
30 Claims
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1. A method of detecting cardiac arrhythmias in a patient'"'"'s heart, comprising the steps of:
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sampling a cardiac electrical signal when the heart is functioning in a known cardiac state; defining, for each sample of the known state cardiac electrical signal occurring within a predetermined time of interest, an amplitude window of signal amplitudes bracketing the amplitude of the known state cardiac electrical signal sample; storing a template sequence of amplitude window samples encompassing the predetermined time of interest; monitoring a time sequence of cardiac electrical signal samples when the heart is functioning in an unknown cardiac state; time aligning samples of the unknown cardiac state sequence with respect to samples of the template sequence of amplitude window samples; comparing, sample by sample, the samples of the unknown cardiac state sequence to the template sequence of amplitude window samples to determine the relative proportion of unknown cardiac state samples with amplitudes falling outside the amplitude window in comparison to unknown cardiac state samples with amplitudes falling inside the amplitude window; and classifying the functioning of the patient'"'"'s heart as other than the known cardiac state when the determined relative proportion meets a predetermined criteria and, otherwise, classifying the functioning of the patient'"'"'s heart as the known cardiac state. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of detecting cardiac arrhythmias in a patient'"'"'s heart, comprising the steps of:
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sensing cardiac electrical signals when the heart is functioning in a known cardiac state; characterizing cardiac electrical signal samples occurring within a predetermined time of interest when the heart is functioning in said known cardiac state; storing said known cardiac state samples as a time sequence of template samples; defining an array of amplitude ranges bracketing said timing sequence of template samples; storing said array of amplitude ranges in a time sequence of window ranges corresponding sample by sample to said time sequence of template samples; subsequently monitoring a time sequence of cardiac electrical signal samples when the heart is functioning in an unknown cardiac state; reconstructing a template sequence of amplitude window samples from said stored time sequence of template samples and said time sequence of window amplitude ranges; time aligning samples of said unknown cardiac state sequence with respect to said reconstructed template sequence of amplitude window samples; comparing time aligned samples of said unknown cardiac state sequence with said reconstructed template sequence of amplitude window samples; ascertaining the number of the compared time aligned samples of said unknown cardiac state sequence having amplitudes outside of said reconstructed template sequence of amplitude window samples; comparing said ascertained number of unknown cardiac state sequence samples having amplitudes outside said template sequence of amplitude window samples with a threshold value; and classifying said unknown cardiac state sequence within said known cardiac state when the ascertained number of monitored samples having amplitudes outside said template sequence of amplitude window samples is less than said threshold value, and classifying said unknown cardiac state as other than said known cardiac state when the ascertained number of monitored samples having amplitudes outside said template sequence of amplitude window samples is greater than said threshold value. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A cardiac arrhythmia detector for detecting cardiac arrhythmias in a patient'"'"'s heart, comprising:
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means for sampling a cardiac electrical signal when the heart is functioning in a known cardiac state; means for defining, for each sample of the known state cardiac electrical signal occurring within a predetermined time of interest, an amplitude window of signal amplitudes bracketing the amplitude of the known state cardiac electrical signal sample; means for storing a template sequence of amplitude window samples encompassing the predetermined time of interest; means for monitoring a time sequence of cardiac electrical signal samples when the heart is functioning in an unknown cardiac state; means for time aligning samples of the unknown cardiac state sequence with respect to samples of the template sequence of amplitude window samples; means for comparing, sample by sample, the samples of the unknown cardiac state sequence to the template sequence of amplitude window samples to determine the relative proportion of unknown cardiac state samples with amplitudes falling outside the amplitude window in comparison to unknown cardiac state samples with amplitudes falling inside the amplitude window; and means for classifying the functioning of the patient'"'"'s heart as other than the known cardiac state when the determined relative proportion meets a predetermined criteria and, otherwise, classifying the functioning of the patient'"'"'s heart as the known cardiac state. - View Dependent Claims (17, 18, 19, 20, 21)
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22. A cardiac arrhythmia detector for detecting cardiac arrhythmias in a patient'"'"'s heart, comprising:
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means for sensing cardiac electrical signals when the heart is functioning in a known cardiac state; means for characterizing cardiac electrical signal samples occurring within a predetermined time of interest when the heart is functioning in said known cardiac state; means for storing said known cardiac state samples as a time sequence of template samples; means for defining an array of amplitude ranges bracketing said time sequence of template samples; means for storing said array of amplitude ranges in a time sequence of window ranges corresponding sample by sample to said time sequence of template samples; means for subsequently monitoring a time sequence of cardiac electrical signal samples when the heart is functioning in an unknown cardiac state; means for reconstructing a template sequence of amplitude window samples from said stored time sequence of template samples and said time sequence of window amplitude ranges; means for time aligning samples of said unknown cardiac state sequence with respect to said reconstructed template sequence of amplitude window samples; means for comparing time aligned samples of said unknown cardiac state sequence with said reconstructed template sequence of amplitude window samples; means for ascertaining the number of the compared time aligned samples of said unknown cardiac state sequence having amplitudes outside of said reconstructed template sequence of amplitude window samples; means for comparing said ascertained number of unknown cardiac state sequence samples having amplitudes outside said template sequence of amplitude window samples with a threshold value; and means for classifying said unknown cardiac state sequence within said known cardiac state when the ascertained number of monitored samples having amplitudes outside said template sequence of amplitude window samples is less than said threshold value, and classifying said unknown cardiac state as other than said known cardiac state when the ascertained number of monitored samples having amplitudes outside said template sequence of amplitude window samples is greater than said threshold value. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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29. A method of detecting cardiac arrhythmias in a patient'"'"'s heart, comprising the steps of:
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selecting samples of the patient'"'"'s physiologically normal cardiac electrical signal; defining for each of the selected samples an amplitude window delineating a range of signal amplitudes bracketing the amplitude of the normal cardiac electrical signal sample; subsequently monitoring the patient'"'"'s cardiac electrical signal when the heart is operating in an unknown cardiac state by sampling said cardiac electrical signals, comparing said samples to time-corresponding defined amplitude windows and counting the relative number of samples wherein the sample amplitude falls outside the amplitude window; and classifying said unknown cardiac state as either a normal state or an arrhythmia state as a function of said relative number of samples.
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30. A cardiac arrhythmia detector for detecting cardiac arrhythmias in a patient'"'"'s heart, comprising:
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a sensor for sensing, amplifying and digitizing cardiac electrical signals, said cardiac electrical signals being indicative of a normal physiological state at certain times and being indicative of an arrhythmia cardiac state at other times, and a controller, said controller further comprising; means for selecting samples of the patient'"'"'s physiologically normal cardiac electrical signal; means for defining for each of the selected samples an amplitude window delineating a range of signal amplitudes bracketing the amplitude of the normal cardiac electrical signal sample; means for subsequently monitoring the patient'"'"'s cardiac electrical signal when the heart is operating in an unknown cardiac state by sampling said cardiac electrical signals and by calculating a signature function by comparing said samples to time-corresponding defined amplitude windows and counting the relative number of samples wherein the sample amplitude falls outside the amplitude window; and means for classifying said unknown cardiac state as either a normal state or an arrhythmia state as a function of said signature function.
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Specification