Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-04-24
2003-04-29
Evanisko, George R. (Department: 3762)
Surgery
Diagnostic testing
Cardiovascular
C607S009000
Reexamination Certificate
active
06556859
ABSTRACT:
THE FIELD OF THE INVENTION
The present invention relates to cardiac pacing systems capable of recognizing and classifying sensed cardiac signals. More specifically, the present invention relates to a signal classification system for recognizing and classifying P-wave signals and far field R-wave signals based upon a form of the signal through use of a form factor histogram.
BACKGROUND OF THE INVENTION
Implantable cardiac pacemakers have been devised which closely emulate the electrical activity of the heart. In such pacemakers, means are provided for sensing both atrial and ventricular depolarization signals and for generating pacing signals for both the atrium and the ventricle. The energy content of the QRS complex occurring during depolarization of the ventricle due to a R-wave signal is significantly higher than that of the P-wave signal, the R-wave or ventricle pacing spike often appears as a contaminate on the atrial sensing lead. Oversensing of the QRS on the atrial pacemaker lead is common.
Implantable cardiac pacemakers need to accurately process sensed signal information to determine when a genuine cardiac signal has in fact been sensed, and then to accurately identify, or classify, the signal. Separating cardiac signals from polarization effects and other noise artifact has always been a substantial problem in this field, and a great deal of effort has been placed on improving input circuits for this purpose. Additionally, it is often important to classify a sensed or acquired signal to determine whether the signal is, for example, a P-wave, a far field R-wave (FFRW), or an evoked response R-wave. Many prior art techniques have been developed for signal classification, but improvement is still needed.
One prior art technique is to establish a variable timing window, and classify the event in terms of a timing of a signal received during the window. However, early beats, estopic signals, etc. can fool such a technique, and noise can still mask the signal, which is sensed within the window. Other known techniques include morphology analysis, comparisons in the time and frequency domain, etc. While many of these techniques provide reasonably good results, they can involve considerable circuit complexity and frequently do not eliminate the probably of error due to detection of noise or other artifacts.
The advent of digital signal processing (DSP) has provided a tool, which can be very useful in the environment of an implantable medical device, such as an implantable cardiac pacemaker. In DSP technology, the incoming sense signal is converted to a digital signal, e.g., an 8-bit signal at a specified rate. Success of digital signals can be processed with high reliability, in a manner which is essentially hardware-controlled by the DSP circuitry. More recently DSP technology has advanced so as to provide the possibility of a low current chip, which can be used in an implantable cardiac pacemaker to provide significant sense signal processing capability.
The utilization of a DSP chip for an implantable cardiac pacemaker makes available an enhanced capacity of processing sensed signals, so as to enable more accurate classification of the signal. Such DSP processing, together with a microprocessor and an appropriate signal classification algorithm, provides a powerful tool for accurately sensing and classifying intercardiac signals. The patents listed in Table 1 are examples of different methods and systems for classifying and distinguishing sensed signals.
U.S. Pat. No.
Inventor
Issue Date
4,799,486
DuFault
01/24/89
5,549,647
Stoop et al.
08/27/96
5,755,739
Sun et al.
05/26/98
5,817,133
Houben
10/06/98
6,029,087
Wohlgemuth
02/22/00
All patents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments, and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.
In addition to the combined hardware and software capabilities discussed above, there is a need to provide an optimum decision algorithm for using the DSP-generated signal parameters so as to accurately and reliably classify sensed intercardiac signals. More specifically, there is a need for an optimum decision algorithm which can classify sensed signals as P-waves or far field R-waves based upon a form of the sensed signals.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior art by providing a method of and system for classifying signals sensed from an electrode of an implantable cardiac pacing system positioned within an atrium of a heart of a patient.
The present invention has certain objects. That is, the present invention provides solutions to certain problems existing in the prior art such as: (a) an inability to classify atrial sensed signals based upon a form of the sensed signal; (b) an inability to generate a representative form factor histogram of sensed P-wave signals and far field R-wave signals; (c) an inability to distinguish P-wave signals from far filed R-wave signals through use of a form factor histogram; (d) an inability to control the operation of a pulse generator based upon a form factor histogram; (e) an inability to control parameters of an implantable cardiac pacing system via a computer readable medium; and (f) an inability to reject atrial event signals due to interference or unsettled conditions.
The system and method of the present invention provides certain advantages, including: (a) the ability to classify atrial sensed signals based upon a form of the sensed signal; (b) the ability to generate a representative form factor histogram of sensed P-wave signals and far field R-wave signals; (c) the ability to distinguish P-wave signals from far filed R-wave signals through use of a form factor histogram; (d) the ability to control the operation of a pulse generator based upon a form factor histogram; (e) the ability to control parameters of an implantable cardiac pacing system via a computer readable medium; and (f) the ability to reject atrial event signals points due to interference or unsettled conditions.
A system and method of the present invention has certain features, including a computer readable medium containing instructions for controlling a computer system. The instructions of the computer readable medium prompt the computer system to collect atrial event signals consisting of P-wave signals and far field R-wave signals. An interim form factor histogram is generated based upon a form of collected atrial event signals. The interim form factor histogram includes an interim P-wave form factor histogram and an interim far field R-wave form factor histogram, each having bins of atrial event signals. A previously generated form factor histogram is weighted and combined with the interim form factor histogram to create a representative form factor histogram. Atrial event signals are classified as P-wave signals or far field R-wave signals by form based upon the representative form factor histogram.
Another feature of the present invention is that collected atrial event signals are rejected if the pacemaker is not operating under normal conditions. Additionally, bins of atrial sensed events within the interim form factor histogram are discarded if a discard level is not met. Further, the representative form factor histogram is analyzed to determine if a minimum safety margin is present between the representative P-wave form factor histogram and the representative far field R-wave form factor histogram such that the form factor histogram includes two distinguishable classifications. Yet another feature of the present invention is that a controller controls the operation of a pulse generator of the cardiac pacing system based upon a form of the representative form factor histogram.
Other objects, advantages, and features of the invention will be
Munneke Dave
Rouw Mattias
Stoop Gustaaf
Westendorp Henk
Wohlgemuth Peter W.
Berry Tom G.
Evanisko George R.
Medtronic Inc.
Oropeza Frances P.
Waldkoetter Eric R.
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