Methods and apparatus for cardiac R-wave sensing in a subcutaneous ECG waveform
First Claim
1. A method of detecting R-waves produced by a depolarization event of a heart in an ECG waveform, comprising the steps of:
- programming a minimum threshold;
applying a first threshold for a first period of time;
applying a second threshold for a second period of time beginning at the end of the first period of time;
applying a third threshold for a third period of time beginning at the end of the second period of time;
sensing ECG signals emanating from near a heart with at least one electrode; and
recording each event as an R-wave, noise, an arrhythmia, or an asystole based on whether features of the sensed ECG waveform exceed or fail to exceed one or more of the minimum, first, second or third thresholdssensing a peak amplitude of an R-wave and,applying the peak amplitude in combination with the programmed sensitivity (PS) setting;
calculating a threshold curve; and
displaying the threshold curve in relation to a set of detected cardiac activity.
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Abstract
The present invention uses a R-wave sensing algorithm that uniquely combines an automatic threshold adjustment method with a new noise rejection technique. This algorithm has significant advantages in avoiding the sensing of T-waves, P-waves, and noise/artifacts. Detecting the presence of noise bursts uses features that determine if an R-R interval adjacent to or within the noise signal is valid. Circuitry that discriminates noise signals from R-waves can use any one of several features including, but not limited to, the following: detection events occurring so close together that they are outside normal physiologic heart rates; frequency content that is wider than that of QRS complexes; amplitudes that are different than the adjacent or encompassing R-waves; and amplitudes that display greater than normal variability. The present invention employs multiple discrete thresholds optionally with different decay constants, alone or in combination with one or more substantially constant magnitude sensing threshold.
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Citations
17 Claims
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1. A method of detecting R-waves produced by a depolarization event of a heart in an ECG waveform, comprising the steps of:
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programming a minimum threshold; applying a first threshold for a first period of time; applying a second threshold for a second period of time beginning at the end of the first period of time; applying a third threshold for a third period of time beginning at the end of the second period of time; sensing ECG signals emanating from near a heart with at least one electrode; and recording each event as an R-wave, noise, an arrhythmia, or an asystole based on whether features of the sensed ECG waveform exceed or fail to exceed one or more of the minimum, first, second or third thresholds sensing a peak amplitude of an R-wave and, applying the peak amplitude in combination with the programmed sensitivity (PS) setting; calculating a threshold curve; and displaying the threshold curve in relation to a set of detected cardiac activity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An apparatus for detecting R-waves, comprising:
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threshold setting means for providing at least two thresholds for a primary portion and a secondary portion of an ECG waveform, respectively; comparing means for comparing the at least two thresholds to the primary and second portion of the ECG waveform; logic means for determining whether each portion of the ECG waveform that exceeds a corresponding threshold is a native R-wave or is a spurious noise peak, a myopotential or other signal artifact and whether an arrhythmia or an asystole has occurred; and storage means for storing portions of the ECG waveform for which an arrhythmia or an asystole is determined to have occurred wherein the storage means operates according to a priority sequence so that in the event that a limited storage event occurs, a lower priority ECG waveform is displaced by a higher priority ECG waveform. - View Dependent Claims (17)
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Specification