Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-08-30
2001-10-16
Jastrzab, Jeffrey R. (Department: 3762)
Surgery
Diagnostic testing
Cardiovascular
C128S901000
Reexamination Certificate
active
06304772
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to patient monitoring and diagnostic devices, and particularly, to patient monitoring and diagnostic devices capable of acquiring multiple-lead electrocardiograph (ECG) signals and performing rhythm analysis on the signals.
It is commonly known in the art to provide patient monitoring and diagnostic devices, particularly multiple-lead capability ECG machines, with the ability to engage in complex ECG rhythm analysis. The rhythm analysis capability is usually a function of the software controlling the machine. Typically, the ECG waveform is filtered, and digitized, i.e., input to an analog-to-digital (A/D) converter. The digitized waveform is then analyzed by the rhythm analysis software. The goal of the rhythm analysis is to make an accurate diagnosis of the cardiac condition of the patient being evaluated.
It is estimated that approximately two to three percent of all patients evaluated using multiple-lead ECG machines have implanted pacemakers that assist the patient's cardiac performance. In order to provide an accurate rhythm analysis, the ECG machine must be able to detect the existence of pacemaker pulses in the ECG waveform and provide to the clinician an indication that the particular event on the ECG waveform is a pacemaker-triggered event, and not an abnormal physiological event, such as an ectopic heartbeat. Pacemaker pulses are typically seen as high frequency spikes on the ECG waveform. The timing relationship of detected pulses to features of the ECG is then used by the algorithm to determine the pacing mode of the implanted pacemaker.
Known patient monitoring and diagnostic systems perform pacemaker pulse detection prior to digitization of the ECG waveform. The detection is performed using analog signal processing techniques. In particular, a high pass filter is used to locate the presence of high frequency elements of the ECG waveform that indicate when a pacemaker pulse has occurred. The information about the detected pacemaker pulse is then passed on to the ECG analysis software by inserting artificial markers in the digitized ECG data wherever a pacemaker pulse is estimated to be. The analysis software then detects these markers and analyzes the ECG waveform with the knowledge that the event markers indicate pacemaker pulses.
SUMMARY OF THE INVENTION
The inventors have determined that there are two major drawbacks to the prior methods of detecting pacemaker pulses in an ECG waveform as set forth above. First, the analog detection circuitry used to detect the high frequency pacemaker pulses is generally susceptible to high frequency noise commonly present in clinical environments. This noise is often falsely identified as being a pacemaker pulse.
Second, because the detected pacemaker pulses are inserted into the digitized ECG waveform data, a high rate of false detection by the analog circuit will corrupt the digitized ECG data. This corruption of the digitized ECG data is irreversible and severely limits the ability of the algorithm and the clinician to accurately analyze the ECG waveform. In order to avoid corrupted data, clinicians often turn “off” the pacemaker detection capability of commonly known patient monitoring and diagnostic systems.
With analog pacemaker detection turned “off,” the rhythm analysis software has to rely on the residual pacemaker pulses remaining in the processed, digitized ECG signal. These residual pulses are generally of reduced amplitude and duration due to the low-pass filtering performed in the front-end of the device. This limits the detection performance of the software (low sensitivity). On the other hand, an interpretation algorithm attempting to detect pacemaker pulses with the analog detection turned “off” will rarely detect a false pacemaker pulse (high specificity).
Accordingly, the invention provides a method of analyzing ECG waveforms to detect pacemaker pulses and determine the pacing mode therein. The invention further provides a patient monitoring system employing the method of analyzing ECG waveforms to detect pacemaker pulses therein. The patient monitoring system acquires the physiological waveform from the patient through a front-end instrumentation amplifier. The physiological waveform is simultaneously sent to an analog pace detection circuit and an ECG processing circuit. The analog pace detection circuit includes a high pass filter that detects potential pacemaker pulses in the analog waveform. The high pass filter looks for waveform events that have a high slew rate (high frequency component) that is characteristic of a pacemaker pulse. The analog pace detection circuit transmits analog detection markers along with a measure of the energy contained in each detected pulse to an interpretation algorithm. The interpretation algorithm analyzes the timing of the analog detection markers using timing constraints and the energy of the analog detection markers to help distinguish actual pacemaker pulses from noise or other artifacts that have been erroneously identified as being potential pacemaker pulses. The interpretation algorithm eliminates the erroneously detected detection markers. Stated differently, the interpretation algorithm looks at the analog detection markers and the associated energy measure and eliminates markers that may be due to noise by ignoring consecutive runs, analog detection markers that are very close together in time, and analog markers associated with low-energy pulses. At the same time that the ECG waveform is being processed by the analog pace detection circuit, a second channel of the ECG waveform is input to an ECG processing circuit which filters and digitizes the ECG waveform. The ECG processing circuit outputs the digitized ECG data to the interpretation algorithm.
The pacemaker interpretation algorithm then independently analyzes the digitized ECG data to establish digital pace detection markers that are separate and distinct from the analog detection markers generated by the analog pace detection circuit. These markers are generated based on the detection of the residual pacemaker pulses in the digitized ECG data and are automatically registered by the algorithm as “true” pulses. The analog detection markers are compared with the registered markers from the digitized ECG. Wherever the analog detection markers correspond to the registered markers from the digitized ECG, it is clear that a pacemaker pulse has occurred. However, for each analog detection marker that does not have a corresponding registered marker from the digitized ECG, the digitized ECG data are analyzed locally to search for high-frequency evidence that substantiates the presence of a pacemaker pulse as indicated by the analog detection markers. If such evidence is found, then a new pace detection marker is registered as a “true” pulse.
Following pacemaker pulse detection, the algorithm uses the timing information of the detected pulses and compares it to the timing and morphology of certain ECG features (QRS,P wave, etc.) to determine the pacing mode of the implanted pacemaker.
It is a principal advantage of the invention to provide a highly specific, highly sensitive patient monitoring and diagnostic system for detecting pacemaker pulses in an ECG waveform.
Other features and advantages of the invention are set forth in the following drawings, detailed description and claims.
REFERENCES:
patent: 4094310 (1978-06-01), McEachern et al.
patent: 5413593 (1995-05-01), Spinelli et al.
patent: 5540232 (1996-07-01), Laney et al.
patent: 5660184 (1997-08-01), Donehoo et al.
patent: 5771898 (1998-06-01), Marinello
Reddy Shankara Bonthu
Taha Basel Hasan
GE Medical Systems Information Technologies Inc.
Jastrzab Jeffrey R.
Michael & Best & Friedrich LLP
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