Active medical device, including an implantable defibrillator, for detection of QRS complexes in a very noisy signal
An active implantable medical device (e.g., implantable pacemaker or defibrillator), for detection of QRS complexes in noisy signals. Functional units ( 12 - 16 ) collect, amplify, prefilter and convert from analog-to-digital an endocardial signal, and digital functional units ( 18 ) provide signal processing and analysis of the digitized signal, for delivery of an indicator corresponding to a signal peak detection representative of the presence of a QRS complex in the endocardial signal. A double threshold comparator ( 30 ) is employed, receiving as input ( 28 ) the digitized signal and outputting ( 40 ) the indicator of peak detection when, cumulatively: the amplitude (A) of the input signal exceeds a peak amplitude threshold (SA), and the peak amplitude threshold is exceeded for a period (W) greater than a peak width threshold (SW). The peak amplitude threshold (SA) is a variable adaptive threshold, according to a noise level calculated from the energy (RMS) of the input signal.
1. An active implantable medical device, comprising means for collecting, amplifying, prefiltering and converting from analog-to-digital an endocardial signal, means for digitally processing and analyzing the digitized endocardial signal, and for delivering an indicator of signal peak detection representative of a presence of a QRS complex in the endocardial signal,
wherein the digitized endocardiac signal has an amplitude, the means for digital processing and analyzing comprises a double threshold comparator, having as an input said digitized endocardial signal, a peak amplitude threshold and a peak width threshold and having as an output said indicator of peak detection in response to, cumulatively:
the digitized endocardiac signal amplitude exceeding said peak amplitude threshold; and
said peak amplitude threshold is exceeded for a period greater than said peak width threshold;
wherein said peak amplitude threshold is a variable adaptive threshold, and wherein the means for digitally processing and analyzing further comprises:
means for determining said peak amplitude threshold, by combining a predetermined base threshold and a variable value of noise level of the input endocardial signal; and
means for determining said variable value of noise level based upon an energy (root mean square (RMS)) of the noise present in the input signal outside of the periods of said digitized endocardial signal amplitude exceeding said peak amplitude threshold.
2. The device of claim 1 , wherein the means for determining said variable value of noise level further comprises means for calculating an energy of the endocardial input signal during a predetermined computing period during which the digitized endocardial signal amplitude does not exceed said peak amplitude threshold.
3. The device of claim 2 , further comprising means for inhibiting and resetting the means determining the variable value of noise level in response said digitized endocardial signal amplitude exceeding said peak amplitude threshold before expiration of said predetermined computing period.
4. The device of claim 1 , wherein said peak width threshold is a fixed predetermined threshold.
5. The device of claim 1 , wherein the means for digital processing and analyzing further comprises:
A low-pass filter, for filtering said input endocardial signal.
6. The device of claim 5 , wherein the means for digital processing and analyzing further comprises:
A high-pass filter and a rectifier, for filtering and rectifying the signal applied to the low-pass filter.