Frequency domain analysis to detect T wave oversensing
Detection of T wave oversensing in an ICD is accomplished in order to prevent improper application of treatment to a patient. The ICD device senses for electrical impulses representing the R waves of a beating heart. In some instances the ICD device will sense T waves that it will assume to be R waves, because the ICD device expects or assumes that such sensed signals are R waves. Time intervals between each detected, assumed R waves are measured and a list of intervals is generated. The list is transformed into its frequency domain equivalent and analyzed for peaks and randomness criteria to determine whether T wave oversensing has occurred.
1. In an implantable medical device, a method for determining T wave oversensing in cardiac electrical signals, the method comprising:
receiving, by the implantable medical device, a list of assumed R-R intervals for a beating heart;
transforming, by the implantable medical device, the list of assumed R-R intervals into a frequency domain equivalent, responsive to the list of assumed R-R intervals indicating a tachyarrhythmia; and
analyzing, by the implantable medical device, the frequency domain equivalent to determine whether the list of assumed R-R intervals includes over sensed T waves.
2. The method of claim 1 wherein the cardiac electrical signals are sensed in an implantable cardioverter/defibrillator (ICD) device, the method further comprising:
blocking treatment from the ICD device responsive to the determination of the over sensed T waves.
3. The method of claim 1 wherein the analyzing comprises:
analyzing a power level of peaks detected in the frequency domain equivalent.
4. The method of claim 3 wherein inclusion of over sensed T waves is determined based on said analyzing resulting in a plurality of low frequency peaks having substantially the same said power level.
5. The method of claim 1 wherein the analyzing comprises:
analyzing a randomness of a plurality of local peaks detected in the frequency domain equivalent.
6. The method of claim 5 wherein inclusion of over sensed T waves is determined based on said analyzing resulting in a high value of said randomness occurring in said plurality of local peaks at a higher frequency in the frequency domain equivalent.
7. The method of claim 1 wherein inclusion of the over sensed T waves is determined by discovery of at least two peaks having a same power level in the frequency domain equivalent.
8. The method of claim 1 further comprising:
sensing for wave deflections in a measurement of electrical impulses emitted from the beating heart, wherein the wave deflections are assumed to be R wave deflections;
measuring an interval between each sensed wave deflection; and
generating the list of assumed R-R intervals using each of the measured intervals.
9. The method of claim 1 wherein the transforming comprising:
processing the list of assumed R-R intervals using one of:
a fast Fourier transform (FFT);
a discrete Fourier transform (DFT);
a Laplace transform; and
a discrete wavelet transform (DWT).
10. A system for detecting T wave oversensing in cardiac electrical signals comprising:
means for receiving a list of assumed R-R intervals for a beating heart;
means, operable in response to the list of assumed R-R intervals indicating a tachyarrhythmia, for transforming the list of assumed R-R intervals into a frequency domain equivalent; and
means for analyzing the frequency domain equivalent to determine whether the list of assumed R-R intervals includes over sensed T waves.
11. The system of claim 1 wherein the cardiac electrical signals are sensed in an implantable cardioverter/defibrillator (ICD) device, the system further comprising:
means for blocking treatment from the ICD device responsive to the determination of the over sensed T waves.
12. The system of claim 1 wherein the means for analyzing the frequency domain equivalent comprises means for analyzing a power level of peaks detected in the frequency domain equivalent.
13. The system of claim 12 wherein inclusion of the over sensed T waves is determined based on said means for analyzing resulting in a plurality of low frequency peaks having substantially the same said power level.
14. The system of claim 1 wherein the means for analyzing comprises means for analyzing a randomness of a plurality of local peaks detected in the frequency domain equivalent.
15. The system of claim 14 wherein inclusion of the over sensed T waves is determined based on said means for analyzing resulting in a high value of said randomness occurring in said plurality of local peaks at a higher frequency in the frequency domain equivalent.
16. The system of claim 1 wherein inclusion of the over sensed T waves is detected when at least two peaks have a same power level in the frequency domain equivalent.
17. The system of claim 1 further comprising:
means for sensing wave deflections in a measurement of electrical impulses emitted from the beating heart, wherein the wave deflections are assumed to be R wave deflections;
means for measuring an interval between each sensed wave deflection; and
means for generating the list of assumed R-R intervals using each of the measured intervals.
18. The system of claim 1 wherein the means for transforming comprises:
means for processing the list of assumed R-R intervals using one of:
a fast Fourier transform (FFT);
a discrete Fourier transform (DFT);
a Laplace transform; and
a discrete wavelet transform (DWT).