Surgery – Diagnostic testing
Reexamination Certificate
2001-04-30
2004-04-13
Jastrzab, Jeffrey R. (Department: 3762)
Surgery
Diagnostic testing
C607S004000, C600S509000
Reexamination Certificate
active
06719689
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of medical devices with limited data storage capacity. More particularly, the present invention relates to implantable devices, such as cardiac pacing systems, that are capable of compressing and storing data, especially cardiac signal data such as episodes of intracardiac electro cardiogram (IEGM).
BACKGROUND OF THE INVENTION
Medical devices with limited data storage capacity are well known in the art. Two common examples are hearing aids and pacemakers. In the latter case, some pacemakers, or other such implantable pulse generators (IPGs) include means for storing data related to cardiac events. These cardiac events may include, for example, episodes of spontaneous heart rate that are higher or lower than an acceptable or previously established rate. Stored data related to one or more cardiac events are useful in assessing the functioning of the IPG and in monitoring the progress of the patient.
Digital signal processing (DSP) has proved to be a useful tool in the environment of medical devices such as implantable pulse generators. Using DSP technology, an incoming sensed heart signal may be converted to a digital signal, e.g., an 8-bit signal. This conversion may occur at a predetermined sample rate. For example, episodes of IEGM may be processed using DSP. The IEGM is one type of signal in which heart contractions may be identified.
Typically an input signal from an IPG is amplified. The signal may then be converted to a digital signal (using, for example, analog to digital (A/D) converters). Then the signal may be digitally processed, generally by filtering the resulting digital data streams. The result from this process is generally a number of digital data streams. Each data stream is more or less a digitally processed representation of an IPG input signal. Based upon the information in these streams, DSP technology may be used to determine heart contractions. As stated above, a physician may use information about these contractions to assess and monitor the efficacy of IPG therapy.
Typically, data is collected continuously while the patient is using the IPG. However, a physician is only able to view the data when the patient and the IPG are available for evaluation, e.g. when the patient is in the physician's office. Usually, the IPG is linked to an interrogation device with a display, which shows the data being collected at the time the patient is being examined.
However, the most interesting episodes of IEGM generally occur when the patient is proceeding about his normal business, away from the physician's office. Thus, current IPGs (and other implantable therapeutic devices) have the capability to store data, such as an IEGM, for later viewing by the physician. At the time of viewing, the IPG may be linked to an interrogation device with a display that communicates the stored data. Because implantable devices are, of necessity, small enough for implantation in a human body, their available storage space is limited. Thus, the signal, such as a digital IEGM, needs to be compressed as much as possible without losing the sense of the original signal. Moreover, the type of information stored is also important in analysis of the efficacy of IPG therapy. For example, storage of an episode may begin when a preset condition, or “trigger”, has been met, e.g. the IPG senses a particular heart rate indicative of a cardiac event such as an atrial fibrillation. Although data representing the cardiac event, or trigger, itself may be of interest to the physician, analysis of the data representing cardiac conditions prior to the event may be more useful in assessing the device's performance and the disease's progress. Thus, the ability to store data prior to the “trigger” event is also desirable. The longer the stored episode, particularly prior to the “trigger”, the more useful the data is to the physician. Again, efficient compression would allow longer episodes to be stored.
Thus, a need exists in the medical arts for compressing and storing data in an implantable medical device.
Several methods have been proposed in the prior art for improving compression and storage in an implantable medical device.
For example, U.S. Pat. No. 5,603,331 to Heemels et al., entitled “Data Logging System For Implantable Cardiac Device” discloses the compression of heart rate variability data via logarithmic data compression and the storing of the results as time-related histograms with a standard deviation.
U.S. Pat. No. 5,819,740 to Muhlenberg entitled “System and Method for Compressing Digitalized Signals in Implantable and Battery-Powered Devices” discloses the compression of data using non-linear sampling. A time varying threshold is used and the signal of interest is compared to the threshold.
U.S. Pat. No. 5,836,982 to Muhlenberg et al., entitled “System and Method of Data Compression and Non-Linear Sampling from Implantable and Battery-Powered Devices” discloses compressing a data block by storing the change, or delta, from one sample to another sample.
U.S. Pat. No. 5,312,446 to Holschbach et al., entitled “Compressed Storage of Data in Cardiac Peacemakers” discloses compression of data using an analog implementation of a turning point algorithm.
U.S. Pat. No. 5,623,935 to Faisandier entitled “Data Compression Methods and Apparatus for Use with Physiological Data” discloses compression of data by generating the first and second derivatives of an analog signal. The first and second derivatives of an analog signal are generated and one of three modes of encoding is selected. Either one of the derivative values is then encoded using one of the three modes based upon maximum compression.
U.S. Pat. No. 5,709,216 to Woodson entitled “Data Reduction of Sensed Values in an Implantable Medical Device Through the Use of a Variable Resolution Technique” discloses compression of data using variable resolution. The variable resolution is based upon pre-selected sub-ranges, i.e., smaller values or intervals have finer resolutions.
U.S. Pat. No. 5,215,098 to Steinhause et al., entitled “Data Compression of Cardiac Electrical Signals Using Scanning Correlation and Temporal Data Compression” discloses data compression by storing pre-recorded (i.e. learned) signal templates.
U.S. Pat. No. 5,217,021 to Steinhause et al., entitled “Detection of Cardiac Arrhythmias Using Correlation of a Cardiac Electrical Signal and Temporal Data Compression” also discloses data compression using stored pre-recorded signal templates.
U.S. Pat. No. 5,836,889 to Wyborny et al., entitled “Method and Apparatus for Storing Signals in an Implantable Medical Device” discloses compression of data for storing a straight-line connection between the last stored value and new data. Data is stored when the first derivative exceeds a threshold.
U.S. Pat. No. 4,716,903 to Hanson et al., entitled “Storage in a Pacemaker Memory” discloses data compression by storing the time to the next sample. The time is stored when the samples are near the baseline. An additional flag is added for turning points.
U.S. Pat. No. 5,263,486 to Jeffreys entitled “Apparatus and Method for Electrocardiogram Data Compression” discloses data compression by varying the sampling period dynamically. The variation is based upon signal rate of change value.
U.S. Pat. No. 4,920,489 to Hubelbank et al., entitled “Apparatus and Method for Solid State Storage of Episodic Signals” discloses compression of data by storing the derivative value, which is defined as data differing from the last stored value. The resolution is also changed based upon the magnitude of rate change.
U.S. Pat. No. 5,735,285 to Albert et al., entitled “Method and Hand-Held Apparatus for Demodulating and Viewing Frequency Modulated Biomedical Signals” discloses transmission of data using A-Law encoding and decoding.
U.S. Pat. No. 5,694,356 to Wong et al., entitled “High Resolution Analog Storage EPROM and Flash EPROM” discloses compression of a signal using A-Law or U-Law log arrhythmic relationships.
As discussed abo
Kerver Harry B. A.
Munneke Dave
Jastrzab Jeffrey R.
Medtronic Inc.
Wolde-Michael Girma
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