Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-05-11
2001-02-20
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06192275
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates generally to a device for stimulating cardiac tissue, and more particularly relates to an implantable cardiac rhythm management device and method for automatically adjusting the evoked response detection threshold. Without limitation, during automatic capture verification the cardiac rhythm management device receives and digitizes an electrocardiogram signal of the patient's heart and adjusts the evoked response detection threshold dependant upon modulation or changes in the amplitude of the evoked response from beat-to-beat. Several factors influence the modulation of the amplitude associated with the evoked response including respiration of the patient. The respiration of the patient affects the amplitude of the evoked response for each R-wave, increasing and decreasing the amplitude in a cyclic fashion. Other factors further modulate the amplitude of the evoked response for each R-wave. The present invention accordingly adjusts the evoked response detection threshold in relation to the modulation of the amplitude of the evoked response.
II. Discussion of the Prior Art
For the most part, prior art implantable cardiac rhythm management devices, including bradycardia and tachycardia pacemakers and cardiac defibrillators, have sense amplifier circuits for amplifying and filtering electrogram signals detected by electrodes placed in or on the heart and which are coupled by suitable leads to the implantable cardiac rhythm management device. Typically, the signals emanating from the sense amplifier are applied to one input of a comparator circuit whose other input is connected to a source or reference potential. Only when an electrogram signal from the sense amplifier exceeds the preprogrammed reference potential threshold will it be treated as a cardiac paced or sensed beat. The source reference potential may be referred to as an evoked response detection threshold.
Typically, the reference potential threshold is set at a fixed amount that is expected to exceed the maximum amplitude of artifact. If, however, the threshold is not set high enough, then artifact may result in malsensing. Further, if the reference potential threshold is set too high, then the amplitude associated with an R-wave may not be sufficient to trigger the reference potential threshold.
The inventors of the present invention have determined that several factors influence the amplitude associated with R-waves. For example, respiration of the patient fluctuates the amplitude of the evoked response in a cyclic fashion increasing and decreasing over several beats. This fluctuation makes it even less desirable for the reference potential threshold to be set at a fixed amount. Other factors, described in greater detail below, affect the amplitude of the evoked response. Thus, a need exists for a cardiac rhythm management device that automatically adjusts the evoked response detection threshold in conjunction with fluctuations in the amplitude associated with a particular R-wave, taking into account the modulation of the amplitude corresponding to the evoked response for each R-wave. The present invention meets these and other needs that will become apparent from a review of the description of the present invention.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for automatically adjusting an evoked response sensing/detection threshold (ER threshold) in a cardiac rhythm management device, wherein the ER threshold is set dependant upon a determined modulation of the amplitude corresponding to evoked response R-wave. The automatic adjustment of the ER threshold in accordance with the present invention is particularly useful during an automatic capture verification pacing sequence. The rhythm management device of the present invention may include a sense amplifier for amplifying and filtering electrocardiogram signals detected by electrodes of a lead that is coupled to the sense amplifier. Also included is a power supply, peak detector, timing circuit, controller coupled to receive the sensed electrogram signals and means controlled by the controller for applying cardiac stimulation pulses to a patient's heart. The stimulation pulses are applied in response to control signals from the controller. The sense amplifier may include a 4-150 Hz wide-band pass filter.
The rhythm management device includes detecting means, means for determining a value associated with modulation and adjusting means each of which may be constructed of separate suitable components or may be internal to the controller. The controller may be in any of several forms including a dedicated state device or a microprocessor with code, and may include ROM memory for storing programs to be executed by the controller and RAM memory for storing operands used in carrying out the computations by the controller.
The controller and components contained therein or coupled thereto detect and distinguish cardiac depolarization deflections from the electrocardiogram signal. A peak detector, for example, is utilized to in affect determine the amplitudes of the cardiac depolarization deflections or evoked response. A value associated with modulation of the amplitude of the evoked response is determined from several cardiac depolarization deflections. The evoked response detection threshold is adjusted dependant upon the determined value associated with modulation.
In the preferred embodiment, during a mode of automatic capture verification the implantable cardiac rhythm management device is capable of automatically sensing an evoked response of a patient's heart and has an adjustable evoked response detection threshold. The cardiac rhythm management device includes a pulse generator, a controller that activates the pulse generator, conduction means for conducting an electrocardiogram signal including electrical impulses corresponding to a cardiac depolarization and noise, and detecting means coupled to the conduction means for detecting from the electrocardiogram signal an evoked response of the patient's heart. The detecting means includes an adjustable evoked response detection threshold, means for determining a value associated with modulation of the amplitude of the evoked response, and adjusting means for adjusting the detection threshold dependant upon a determined value associated with modulation.
The implantable cardiac rhythm management device may also include an evoked response filter means for determining an amount or value associated with a maximum amplitude of the detected evoked response over a predetermined number of beats and an amplitude of an immediately prior determined maximum amplitude of the detected evoked response. The adjusting means for adjusting the evoked response detection threshold may also adjust the threshold dependant upon the value associated with the evoked response filter means. Further, the adjusting means may incorporate a respiration modulation index that is determined from a measured mean maximum amplitude of the detected evoked response over a predetermined number of beats and a minimum maximum amplitude of the detected evoked response over the predetermined number of beats. Also, an amount associated with an evoked response minimum is determined by the controller from the determined respiration modulation index and an amount derived from the evoked response filter. Additionally, the implantable cardiac rhythm management device may include a means for determining an amount associated with an artifact baseline of the electrocardiogram signal, wherein the amplitude of the ER detection threshold is set greater than the amount associated with the maximum amplitude of the artifact baseline and less than an evoked response minimum.
In use, the cardiac rhythm management device includes a preset protocol for automatically adjusting the evoked response detection threshold utilizing the controller and associated components. The peak detector and controller, for example, may determine a maximum amplitude from
Gryzwa Mark
Olive Arthur
Zhang Geng
Zhu Qingsheng
Cardiac Pacemakers Inc.
Getzow Scott M.
Nikolai Mersereau & Dietz, P.A.
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