Apparatus for identifying the circulatory effects of...

Surgery – Diagnostic testing – Cardiovascular

Reexamination Certificate

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C600S508000, C600S509000, C600S513000

Reexamination Certificate

active

06571120

ABSTRACT:

The invention concerns a cardiological device having a sensor, adapted to pick up at least one cardiac signal, and signal processing means including first detection means connected to the sensor, adapted to detect an individual signal or a feature parameter of the cardiac signal.
BACKGROUND OF THE ART
The state of the art discloses devices having at least one sensor in order to obtain conclusions about the activity of the heart, from the electrophysiological measurement signal which is obtained with the sensor.
The previous devices are based on the notion that the occurrence of normal inherent excitation of the heart can be viewed as a direct and time-related reference to the functional capability of the heart as a mechanical pump for maintaining the stability of circulation. Extrasystoles are heart actions which do not occur in the normal rhythm of the cardiac activity. Depending on the location of excitation formation, they are subdivided into supraventricular or atrial extrasystoles and ventricular extrasystoles and are considered from the point of view of the frequency with which they occur. Occurrence in large numbers permits diagnostic conclusions to be drawn. Modern electrical cardiac pacemakers have devices for recognizing or identifying extrasystoles in order to take them into account in terms of the regular substitute function in respect of heart stimulation, appropriate to the task involved.
The known devices cannot implement more extensive investigation of the action which cardiological events such as extrasystoles have on the circulation and the behavior thereof immediately after they have occurred.
The object of the present invention is to provide a device which is capable of detecting the effect of cardiophysiological events such as extrasystoles or already indicating such events before they occur. In particular, the object of the invention is to provide a device which is suitable for detecting the effect of extrasystoles on the circulatory system including the heart and on the activity of the physiological systems controlling the circulatory system, and supplying more extensive information which can be used for diagnosis, for risk monitoring, for supporting therapy implementation and for improving items of electrical equipment, in particular electrical pacemakers.
SUMMARY OF THE INVENTION
In accordance with the invention, that object is attained by a device of the kind set forth in the opening part of this specification, the signal processing means of which additionally include:
averaging means connected to the first detection means, adapted to form an average value over a plurality of values of the feature parameter or over a plurality of individual signals,
second detection means connected to the sensor, adapted to detect cardiological events, in particular extrasystoles, and
first comparison means which are connected to the second detection means, the averaging means and the first detection means and which are adapted to ascertain a deviation of at least one feature parameter or individual signal ascertained in the immediate time relationship with an event such as extrasystole from the corresponding average value.
The signal processing means also preferably additionally include second comparison means which are connected to the first comparison means and which are adapted to compare the deviation to a limit value, and signal means which are connected to the second comparison means and which are adapted to output a signal if the difference exceeds the limit value.
Preferably, that individual signal or that or those feature parameter or parameters directly following the event are used as the individual signal or signals in immediate time relationship with the event or as the feature parameter in immediate time relationship with the event.
Herein the term “cardiac signal” or “individual signal” are used in particular to denote a signal portion for example of an ECG signal, as occurs between two periodically recurring signal features, for example mutually corresponding zero-passages. An ECG signal in that sense comprises a train of individual signals which are delimited from each other by periodically recurring signal features.
The detection and storage of such signal portions or individual signals and also the formation of average values over a plurality of signal portions on the basis of predetermined time evaluation functions is already described in DE 199 38 376 to the present inventor, which is not a prior publication. The methods and means provided therein are also used in relation to the device described herein.
The invention involves the realization that, when recognizing or identifying the action of extrasystoles on the circulation and its performance and behavior, it is also necessary to observe those relationships which extend beyond an immediate association with the mechanical output of the heart. In particular, the invention takes account of the established realization that individual particularities such as the shape and size of the heart, the location of origin of the electrophysiological excitation of the heart, which is linked to extrasystoles, and pathophysiological changes in the circulatory system, can have an effect on the configuration of the measurement signal.
The invention is further based on the realization that signals which occur in immediate succession in a biological system never involve precisely the same fine signal structure but certain deviations can occur, the causes of which do not exclusively have to be related to the occurrence of extrasystoles.
Extrasystoles are heart excitations which occur earlier than is to be expected in the normal rhythm of the heart, having regard to other causes such as for example respiration or fluctuations in the activity of the autonomous nervous system. The immediate effect of extrasystoles can be diverse. A ventricular extrasystole can occur so early in the course of the normal cardiac cycle that the ventricle is only incompletely filled due to the atrium contraction which has not yet concluded at that time. Depending on the location at which the ventricular extrasystole is produced, it is also possible for the time-coordinated course of the ventricular contraction to be influenced. Many situations involve a more or less reduced beat volume and thus, as a further consequence, give rise to altered state parameters in the cardiovascular system which are established by existing physiological sensors, for example the pressor receptors in the aortic arch and in the carotid sinus and result in reactions on the behavior of the cardiovascular system. Atrial extrasystoles can also have an effect on the circulation by virtue of the fact that they occur prematurely in comparison with the normal rhythm of the heart, and because the ventricle is not completely filled, as a result. In general, atrial extrasystoles are distinguished in that the subsequent pause up to the next normal systole (the so-called post-extrasystolic pause) is longer than the pause which occurs in the normal rhythm of the heart. As a consequence of the prolonged pause, filling of the ventricle and thus the beat volume after an extrasystole can rather become somewhat greater, but at the same time the longer pause means that the situation can involve greater emptying of the vessel portions which are immediately downstream of the heart, with effects on the intravasal pressure which obtains there. In addition, there can be effects on different hormone systems, as a consequence of fluctuations in terms of circulatory effect. In addition, there is the action of the Frank Starling mechanism which describes a relationship, founded in the properties of the cardiac muscle, between filling of the heart and the beat volume. The various effects caused by extrasystoles are distinguished by different time constants which are reflected in the transitional characteristics in respect of time of the cardiovascular system until the original state is attained.
When matters are considered from a technical aspect, extrasystoles which have an effect on the c

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