Automatic sensitivity adjust for cardiac pacemakers
First Claim
1. A pacemaker, comprising:
- a pulse generator, for producing cardiac pacing pulses;
a sense amplifier for receiving and amplifying electrical cardiac signals, said sense amplifier having a sensitivity threshold adjustable by means of sensitivity control input signals, and said sense amplifier producing a sensed event output pulse whenever said electrical cardiac signals exceed said adjustable sensitivity threshold;
a pacing lead, coupled to a patient'"'"'s heart, for conveying said cardiac pacing pulses from said pulse generator to the heart, and for conveying said electrical cardiac signals from the heart to said sense amplifier;
a pressure sensor for producing a pressure sensor output signal;
peak sense and threshold measurement means, for detecting a voltage peak of said pressure sensor output signal and for determining whether said voltage peak exceeds a predetermined pressure threshold, said peak sense and threshold measurement means producing a pressure event indicator signal when said voltage peak exceeds said predetermined pressure threshold;
sensitivity adjustment circuitry, receiving said sensed event output pulses and said pressure event indicator signals, for generating said sensitivity control input signals;
wherein said sensitivity adjustment circuitry comprises timing means defining an auto-sensitivity timing period;
and wherein said sensitivity adjustment circuitry further comprises counting means for determining a count of sensed event output pulses and a count of pressure event indicator signals occurring during said auto-sensitivity timing period, said sensitivity adjustment circuitry issuing sensitivity control input signals upon expiration of said auto-sensitivity timing period;
said sensitivity control input signals causing said sensitivity threshold to be increased unless said count of pressure event indicator signals exceeds said count of sensed event output pulses by more than a predetermined margin, and otherwise causing said sensitivity threshold to be decreased.
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Accused Products
Abstract
A pacemaker capable of automatically adjusting the sensitivity of its sense amplifier to electrical cardiac signals is disclosed. In one embodiment, a pacemaker having a pressure sensor disposed on the distal end of its pacing/sensing lead counts the number of pressure events and electrical events which occur during an autosensitivity timing period. If the number of electrical events exceeds the number of pressure events by more than a predetermined margin, the sense amplifier'"'"'s sensitivity threshold is decreased. If the number of electrical events does not exceed the number of pressure events by more than the predetermined margin, the sense amplifier'"'"'s sensitivity threshold is increased. In another embodiment, the pacemaker maintains a running average of the peak voltages of sensed electrical events over a predetermined history period. Periodically, the pacemaker computes the ratio of the running average of peak voltages to a preprogrammed sense margin value, and adjusts the sensitivity threshold of the sense amplifier according to this computation. By basing the adjustment of the sense amplifier'"'"'s sensitivity threshold on a long-term average of peak sense values, the effects of cycle-to-cycle variation in sensed values are minimized. In still another embodiment of the invention, a pressure sensor alone is employed to detect natural cardiac events.
94 Citations
11 Claims
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1. A pacemaker, comprising:
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a pulse generator, for producing cardiac pacing pulses; a sense amplifier for receiving and amplifying electrical cardiac signals, said sense amplifier having a sensitivity threshold adjustable by means of sensitivity control input signals, and said sense amplifier producing a sensed event output pulse whenever said electrical cardiac signals exceed said adjustable sensitivity threshold; a pacing lead, coupled to a patient'"'"'s heart, for conveying said cardiac pacing pulses from said pulse generator to the heart, and for conveying said electrical cardiac signals from the heart to said sense amplifier; a pressure sensor for producing a pressure sensor output signal; peak sense and threshold measurement means, for detecting a voltage peak of said pressure sensor output signal and for determining whether said voltage peak exceeds a predetermined pressure threshold, said peak sense and threshold measurement means producing a pressure event indicator signal when said voltage peak exceeds said predetermined pressure threshold; sensitivity adjustment circuitry, receiving said sensed event output pulses and said pressure event indicator signals, for generating said sensitivity control input signals; wherein said sensitivity adjustment circuitry comprises timing means defining an auto-sensitivity timing period; and wherein said sensitivity adjustment circuitry further comprises counting means for determining a count of sensed event output pulses and a count of pressure event indicator signals occurring during said auto-sensitivity timing period, said sensitivity adjustment circuitry issuing sensitivity control input signals upon expiration of said auto-sensitivity timing period; said sensitivity control input signals causing said sensitivity threshold to be increased unless said count of pressure event indicator signals exceeds said count of sensed event output pulses by more than a predetermined margin, and otherwise causing said sensitivity threshold to be decreased. - View Dependent Claims (2)
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3. A method of operating a cardiac pacemaker coupled to the heart of a patient, comprising the steps of:
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(a) defining a timing interval; (b) detecting pressure inside the patient'"'"'s heart; (c) determining a pressure event count corresponding to the number of times during said timing interval that the pressure inside the heart exceeds a predetermined pressure threshold value; (d) detecting electrical cardiac signals from the patient'"'"'s heart; (e) determining an electrical event count corresponding to the number of times during said timing interval that the electrical cardiac signals from the patient'"'"'s heart exceeds an adjustable threshold voltage level; (f) upon expiration of said timing interval, increasing said adjustable threshold voltage level if said electrical event count exceeds said pressure event count by more than a predetermined margin, and decreasing said adjustable threshold voltage level otherwise. - View Dependent Claims (4)
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5. A pacemaker, comprising:
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a pulse generator, for producing pacing pulses; a sense amplifier for receiving and amplifying electrical cardiac signals, said sense amplifier having a sensitivity threshold adjustable by means of sensitivity control input signals, said sense amplifier producing a sensed event output pulse whenever said electrical cardiac signals exceed said adjustable sensitivity threshold; a pacing lead, coupled to a patient'"'"'s heart, for conveying said cardiac pacing pulses from said pulse generator to the heart, and for conveying said electrical cardiac signals from the heart to said sense amplifier; sensitivity adjustment circuitry, receiving said sensed event output pulses, for generating said sensitivity control input signals; peak voltage detection means, for determining a peak voltage of said electrical cardiac signals whenever said signals exceed said adjustable sensitivity threshold; sensitivity threshold measuring means, for determining a current sense amplifier sensitivity threshold value when said electrical cardiac signals exceed said adjustable sensitivity threshold; wherein said sensitivity adjustment circuitry comprises averaging means for maintaining a running average of a plurality of previously determined ones of said peak voltages over a predetermined history period; and wherein said sensitivity adjustment circuitry further comprises computing means for periodically determining a new sense amplifier sensitivity threshold value by computing a ratio of said running average of peak voltages to said current sense amplifier sensitivity threshold value; such that said sensitivity adjustment circuitry issues sensitivity control input signals for causing said sensitivity threshold to be adjusted from said current sensitivity threshold value to said new sense amplifier sensitivity threshold value.
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6. A method of operating a programmable cardiac pacemaker coupled to a patient'"'"'s heart via a pacing and sensing lead, comprising the steps of:
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(a) selecting one of a plurality of programmable sense amplifier sensitivity threshold voltage settings, each said threshold setting defining limits in which a resulting actual sensitivity threshold voltage will fall, said selected sense amplifier threshold setting being designated CTS and said resulting actual sensitivity threshold voltage being designated SATM; (b) receiving electrical cardiac signals from the patient'"'"'s heart at an input of said sense amplifier; (c) each time said electrical cardiac signals exceed said SATM, determining a peak voltage level of said electrical cardiac signals; (d) each time said electrical cardiac signals exceed said SATM, measuring said SATM; (e) maintaining a running average of said peak voltage levels, said running average being designated APSV; (f) selecting one of a plurality of programmable percent safety margin settings, said selected percent safety margin setting being designated as PSM; (g) periodically computing a new sense amplifier threshold setting value, designated SATS, according to the formula;
##EQU2## (h) periodically resetting said CTS to said SATS;
(i) each time said electrical cardiac signals exceed said SATM, delivering a cardiac stimulating pulse to the heart if electrical cardiac signals exceeding said current threshold setting are not detected within a predetermined time period thereafter.
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7. A pacemaker, comprising:
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a pulse generator, for producing cardiac pacing pulses; a sense amplifier for receiving and amplifying electrical cardiac signals, said sense amplifier having a sensitivity threshold adjustable by means of sensitivity control input signals, and said sense amplifier producing a sensed electrical event output pulse whenever said electrical cardiac signals exceed said adjustable sensitivity threshold; a pacing lead, coupled to a patient'"'"'s heart, for conveying said cardiac pacing pulses from said pulse generator to the heart, and for conveying said electrical cardiac signals from the heart to said sense amplifier; a mechanical sensor for producing a sensed mechanical event output signal whenever said mechanical sensor detects mechanical activity corresponding to an intrinsic cardiac event; sensitivity adjustment circuitry, receiving said sensed electrical event output pulses and said sensed mechanical event signal, for generating said sensitivity control input signals; wherein said sensitivity adjustment circuitry comprises timing means defining an auto-sensitivity timing period; and wherein said sensitivity adjustment circuitry further comprises counting means for determining a count of sensed electrical event output pulses and a count of sensed mechanical event output signals occurring during said auto-sensitivity timing period, said sensitivity adjustment circuitry issuing sensitivity control input signals upon expiration of said auto-sensitivity timing period; said sensitivity control input signals causing said sensitivity threshold to be increased unless said count of sensed mechanical event output signals exceeds said count of sensed electrical event output pulses by more than a predetermined margin, and otherwise causing said sensitivity threshold to be decreased.
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8. A pacemaker, comprising:
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a pulse generator, for producing cardiac stimulating pulses; a pressure sensor, coupled to said pacemaker and disposed within the right ventricle of a patient'"'"'s heart, for detecting pressure in the right ventricle, said pressure sensor producing an electrical pressure signal the voltage of which corresponds to said pressure in the right ventricle; a pressure detection circuit, receiving said pressure signal, for producing an output signal whenever said pressure signal exceeds a predetermined threshold voltage; a digital control circuit, receiving said output signals from said pressure detection circuit, said digital control circuit being coupled to said pulse generator and controlling the timing of delivery of said cardiac stimulating pulses by said pulse generator.
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9. A pacemaker, comprising:
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a pulse generator, for producing cardiac stimulating pulses; a mechanical sensor, coupled to said pacemaker and disposed within a patient'"'"'s heart, for detecting cardiac mechanical activity, said mechanical sensor producing an electrical sensor signal the voltage of which corresponds to said cardiac mechanical activity; a detection circuit, receiving said sensor signal, for producing an output pulse whenever said sensor signal exceeds a predetermined threshold voltage; a digital control circuit, receiving said output pulses from said detection circuit, said digital control circuit being coupled to said pulse generator and controlling the timing of delivery of said cardiac stimulating pulses by said pulse generator.
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10. A method of operating a cardiac pacemaker, comprising the steps of:
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(a) measuring pressure in the right ventricle of a patient'"'"'s heart; (b) establishing a current pressure threshold value; (c) initiating a timing interval when said pressure exceeds said current pressure threshold value; (d) delivering a cardiac stimulating pulse to the patient'"'"'s heart if said pressure does net exceed said current pressure threshold during said timing interval; (e) inhibiting delivery of a cardiac stimulating pulse to the patient'"'"'s heart if said pressure exceeds said current pressure threshold during said timing interval; and (f) periodically resetting said current pressure threshold value to a new level. - View Dependent Claims (11)
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Specification