Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2001-03-29
2003-07-15
Wolfe, Willis R. (Department: 3747)
Surgery
Diagnostic testing
Cardiovascular
C600S521000
Reexamination Certificate
active
06594520
ABSTRACT:
The invention concerns an apparatus for processing physiological signals, which includes a signal pick-up unit for picking up physiological measurement signals, in particular for picking up electrical signals of a heart, and first detection means which are connected to the signal pick-up unit and include signal processing means such as a filter and a first threshold value store and a comparison unit which is connected thereto and which is adapted to output a first marker signal if the amplitude of the measurement signal exceeds a threshold value stored in the first threshold value store, and second detection means which are connected to the signal pick-up unit and include a second threshold value store and a second comparison unit which is connected thereto and which is adapted to output a second marker signal if the amplitude of the measurement signal exceeds a threshold value stored in the second threshold value store.
BACKGROUND OF THE ART
Signal processing apparatuses of that kind can for example be a component part of a cardiac pacemaker, a cardioverter and/or a defibrillator. A specific purpose of such signal processing apparatuses is the detection of chamber fibrillation phenomena, in particular the detection of ventricular fibrillation, which require anti-tachycardia therapy or cardioversion.
In particular the detection of ventricular fibrillation phenomena, that is to say physiologically disproportionately high heart rates involves some problems. It is known in principle for the heart rates to be determined by reference to an electrocardiogram by a procedure whereby the R-spikes of the QRS-complexes contained in the electrocardiogram are detected and the frequency at which the R-spikes occur, the RR-rate, is determined. A problem in that respect involves in particular a greatly fluctuating amplitude of the R-spikes of an electrocardiogram and the differing width of the QRS-complexes.
The state of the art discloses various apparatuses for the detection of ventricular fibrillation. U.S. Pat. No. 4,393,877, to Imran, teaches providing two input channels for detecting measurement signals, which involve a differing level of sensitivity for the rise gradient of ECG-signals and linking signal features of the two channels, which are recognised by way of the rise gradient, by way of an ‘exclusive-or’ function. Baker, in U.S. Pat. No. 4,880,004, describes a heart stimulator which has two input channels with differing band pass characteristics, of which one serves for the detection of cardiac events and the second serves for automatic adaptation of the level of detection sensitivity of the first input channel.
White, in U.S. Pat. No. 5,562,709, teaches an atrial defibrillator having two input channels for R-spike detection, which have different band pass characteristics and which operate with respectively specific amplitude threshold values for R-spike detection. The detection results of the two input channels are logically ‘and’-linked for producing a synchronisation signal. For resetting an interval timer the detection results of the two input channels are logically ‘or’ linked. A third separate input channel is provided for the detection of atrial fibrillation.
It has been found that the detection in particular of ventricular fibrillation, which is possible by means of the known apparatuses, leaves something to be desired in particular in terms of reliability.
Therefore the object of the present invention is to provide an apparatus for processing physiological signals, which with means of the utmost simplicity permits reliable detection of events contained in particular in cardiac signals and/or given states of the heart such as the presence of ventricular fibrillation.
SUMMARY OF THE INVENTION
In accordance with the invention that object is attained by means of an apparatus of the kind set forth in the opening part of this specification, including an evaluation unit which is connected to the first and second detection means for taking over a respective series of the first and second marker signals and for processing the series of marker signals to afford a single series of combined marker signals, for analysis of the time succession of the marker signals, in particular the intervals between marker signals of the combined series, and output of a recognition signal which is dependent on the analysis.
In the context of the invention, the recognition signal is a signal which identifies a state of the heart that is to be detected, and not an event such as an R-spike as such. Analysis of the combined series is thus not directed to the respective individual events such as R-spikes, but to the time succession of events, which is represented by the marker signals, in particular the intervals between the marker signals as a reproduction, which is already filtered, of the events. That analysis is aimed at the detection of such states as fibrillation. An apparatus of that kind advantageously makes it possible to determine RR-intervals and thus heart rates by analysis of the intervals between marker signals of a combined series of marker signals, wherein the combined series contains marker signals which originate from input channels having different detection properties. In particular an apparatus of that kind makes it possible on the one hand for the parameters of the detection means, which are crucial in terms of the detection of events and output of corresponding marker signals, such as input sensitivity, frequency characteristic and magnitude of the threshold value, and on the other hand the manner and way in which the series of marker signals obtained in two different ways are combined to form a series by suitable means to be so selected and matched to each other that the recognition of heart rates and thus also fibrillation recognition can be reliably implemented.
For analysis of the combined series of marker signals, the evaluation unit may include a counter that counts the marker signals or the intervals between marker signals within a predetermined portion of the filtered series of marker signals. That alone already makes it possible to determine the heart rate for the respective measurement signal portion. In combination with analysis of the interval lengths within the respective portion of the combined series of marker signals, it is possible to form a reliable criterion in regard to the presence of fibrillation, as is described in greater detail hereinafter.
A typical analysis is one for which a given number of for example 48 intervals is counted off and a check is made to ascertain how many of those 48 intervals are shorter than a comparison interval. A recognition signal indicating fibrillation is outputted when 36 of the 48 compared intervals are shorter than the comparison interval. In that case the evaluation unit includes for example means for counting a total number of intervals and for counting those intervals within that total number of intervals, which are shorter than a comparison interval. In addition the evaluation unit includes means for comparing the counted values to corresponding comparison values and means for outputting the recognition signal in dependence on the comparison result.
In many embodiments of the apparatus, the first selection means includes a first absolute value unit which is adapted to form the absolute value of the measurement signal. That absolute value unit may be connected upstream of the first comparison unit. In relation to the measurement signal, this means that negative measurement signal values are used with inverted signs for the threshold value comparison operation while positive measurement signal values retain their sign. It has been found that this markedly improves the reliability of fibrillation recognition.
In many embodiments, the second detection means also includes a second absolute value unit that is connected upstream of the second comparison unit.
In addition, many embodiments will be provided with a high pass filter for the measurement signal, which is either already arranged in the signal pick-up unit or which is ass
Bauer Peter Thomas
Schomburg Richard A.
Biotronik Mess-und Therapiegeraete GmbH & Co. Ingenieurbuero Ber
Grant Stephen L.
Hahn Loeser + Parks LLP
Wolfe Willis R.
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