Programmable digital cardiac pacer
First Claim
1. Implantable cardiac pacing apparatus comprising:
- electrode means adapted to couple a stimulating signal to the heart and for sensing a cardiac signal;
sensing means for sensing signals on said electrode means;
selection circuit means responsive to the signals sensed by said sensing means for detecting a predetermined component of a natural cardiac cycle;
first timing circuit means having a first timing source operating at a first rate for generating timing signals representative of time periods in a cardiac cycle including a rate time out period during which said predetermined component is expected to occur;
second timing circuit means synchronized with said first timing circuit means and having a second timing source independent of said first timing source and operating at a second, faster rate for generating a rate limit enable signal defining a predetermined mimimum period relative to the commencement of a cardiac cycle and ending during a normal cardiac rate time out period; and
generator means for generating a stimulating signal on said electrode means if said selection circuit means fails to detect said predetermined component during said rate time out period and being inhibited from generating said stimulating signal until said rate limit signal is generated by said second timing circuit means.
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Accused Products
Abstract
A cardiac pacer has separate digital filter circuits for sensing atrial and ventricular activity. Parameter data stored in memory is used by the digital filters for identifying the various components of cardiac activity, such as the P, R and T waves, as well as for identifying Premature Ventricular Contractions (PVC). A Ventricular Rate Time Out period is established from the last natural beat or stimulating pulse; and if a P wave or natural R wave is not sensed during that period, the system generates a stimulating pulse and, using T wave parameters in the ventricular filter, tests to verify capture. Loss of capture increases stimulating pulse width and amplitude to regain capture. If a P wave is sensed before the Rate Time Out period ends, the system establishes a predetermined P-R interval period to override the Ventricular Rate Time Out period in which the ventricular filter is set to detect a natural R wave in an effort to synchronize the ventricle with the atrium. Prior to the Ventricular Rate Time Out period of each cardiac cycle, the ventricular filter is set to detect Premature Ventricular Contractions. If a predetermined number of PVCs is detected, the system generates a train of stimulating signals at a rate higher than expected tachycardia in an effort to break the tachycardia cycle. Many of the system'"'"'s functions can be enabled or disabled by action of the physician; and many of the system parameters can be externally programmed, such as ventricular rate, stimulating pulse amplitude and/or duration, atrial and ventricular filter parameters, P-R delay interval and others.
57 Citations
31 Claims
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1. Implantable cardiac pacing apparatus comprising:
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electrode means adapted to couple a stimulating signal to the heart and for sensing a cardiac signal; sensing means for sensing signals on said electrode means; selection circuit means responsive to the signals sensed by said sensing means for detecting a predetermined component of a natural cardiac cycle; first timing circuit means having a first timing source operating at a first rate for generating timing signals representative of time periods in a cardiac cycle including a rate time out period during which said predetermined component is expected to occur; second timing circuit means synchronized with said first timing circuit means and having a second timing source independent of said first timing source and operating at a second, faster rate for generating a rate limit enable signal defining a predetermined mimimum period relative to the commencement of a cardiac cycle and ending during a normal cardiac rate time out period; and generator means for generating a stimulating signal on said electrode means if said selection circuit means fails to detect said predetermined component during said rate time out period and being inhibited from generating said stimulating signal until said rate limit signal is generated by said second timing circuit means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. In cardiac pacing apparatus, the combination comprising:
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first oscillator circuit means for generating a periodic signal at a first repetition rate; first divider circuit means responsive to the output signal of said first oscillator circuit means for generating a digital signal representative of lapsed time; first memory circuit means having a plurality of selectively addressable storage locations for storing digital words representative of sequentially occurring predetermined time marks relative to a commencement time; first address means for addressing the storage locations of said first memory circuit means to enable selective readout of the time mark words stored therein; first digital comparator circuit means responsive to one of said time mark words read out from said first memory means selected by said first address means representative of a predetermined time in a cardiac cycle for comparing the same with the contents of said first divider circuit means representative of lapsed time in a cardiac cycle; said first digital comparator circuit means generating an output signal when said lapsed time signal contents of said first divider circuit means is equal to a time mark word read out from said first memory circuit means; said output signal being representative of the occurrence of a predetermined time in said cardiac cycle as represented by said digital time mark word read out from said first memory circuit means. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. In cardiac pacing apparatus, including electrode means for stimulating the heart and for sensing a cardiac signal;
- detector circuit means responsive to the signal on said electrode means for detecting a predetermined component of a cardiac signal in response thereto;
timing circuit means responsive to the output of said detection circuit means for generating signals representative of a predetermined ventricular rate time out period during which a natural R wave is expected to occur in a normal cardiac cycle;pulse generator circuit means responsive to said timing circuit means for generating a stimulating signal and for coupled the same to said electrode means to stimulate the heart in the absence of a detected R wave during said ventricular rate time out period; the improvement comprising; a plurality of function circuit means each performing a predetermined cardiac function in said apparatus; status control memory means for storing a plurality of status control data words, each word representative of a desired status condition for an associated function circuit means; and state controller means responsive to the contents of said status control memory means for selectively enabling or disabling the operation and functioning of each of said function circuit means in response to an associated status data word in said status control memory means. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31)
- detector circuit means responsive to the signal on said electrode means for detecting a predetermined component of a cardiac signal in response thereto;
Specification