Cordis Corporation

Telectronics Pacing Systems, Inc.

Telectronics N.v.

Robert DeCote, Jr

John H Livingston

Peter P Tarjan

A cardiac sense amplifier network includes a differential amplifier, a bandpass filter, a comparator network, a microprocessor, an analog-to-digital converter, and a random-access memory. The differential amplifier is responsive to incoming electrical signals containing cardiac signals and noise signals for amplifying the electrical signals and for producing amplified electrical signals. The filter is used to filter the amplified electrical signals and for producing filtered electrical signals. The comparator network compares the filtered electrical signals with first and second reference voltages and produces a flag signal indicative of when the filtered electrical signals exceed the first or second reference voltages. The microprocessor is responsive to the flag signal for initializing the same and for generating a control signal. The analog-to-digital converter is responsive to the control signal for converting the filtered electrical signals to digital data corresponding to the cardiac signals and noise signals. The random-access-memory is used to store data representative of noise signals and for storing program instructions for causing the microprocessor to subtract the noise signals from the digital data signals in order to obtain the cardiac signals which are free of noise.

Cardiac sense amplifier with pattern recognition capabilities

A digital data system for processing analog electrogram (EGM) signals includes an A/D converter for developing a series of digital data signals (bytes) at a given rate R1. A first whole integer plurality of signals (group N1) is processed for the maximum absolute value thereof. A second whole integer plurality (group N2) is thereafter similarly processed for the maximum absolute value thereof. By alternately outputting each such result, the effective output data stream of the system is at a new sampling rate R2, where R2=R1(N1+N2)/2. By using more than two groupings, various ratios including non-integer ratios can be implemented.

EGM data sampling system

A cardiac pacer is described which includes a pulse generator for providing pacing pulses and an electrical lead for bilateral (or bidirectional) (i.e., sense and pace) connection to a chamber of the heart. A fixed gain, tuned sensing amplifier senses selected activity of the heart chamber. The output of the sensing amplifier is connected to a pair of voltage comparators. One of the voltage comparators has a slightly lower threshold and thus a slightly higher sensitivity level than the other voltage comparator. Under closed loop control, the thresholds of the respective voltage comparators are automatically adjusted so that one of the voltage comparators will sense the selected activity of the heart chamber and the other voltage comparator will not sense the selected activity.

Automatic sensitivity control for implantable cardiac pacemakers

A low-power cardiac pacer and method includes an automatic capture threshold determination system wherein the minimum pulse energy required to reliably stimulate contractions of a patient's heart is periodically determined. The energy level of pacing pulses generated by the pacer is automatically set in accordance with the determined capture threshold level to reduce battery current drain and thereby extend the pacer's useful life.

Cardiac pacer and method providing means for periodically determining

An automatic capture threshold determination system and method apply pacing pulses to a patient's heart while simultaneously monitoring intracardiac electrical activity to detect evoked cardiac contractions. The system and method automatically adjust the energy of the applied pacing pulses in accordance with a prearranged routine, until capture is obtained, thereby determining the minimum pulse amplitude required to reliably stimulate the heart.

Automatic cardiac capture threshold determination system and method

An unsaturable cardiac sense amplifier includes first and second amplifying stages, each of which is subject to saturation by excessive input voltage. Input voltage to the first amplifier stage is limited to less than a saturating level by means of a pair of parallel, oppositely sensed, diodes. Saturation of the second amplifier stage is prevented by a degenerative feedback loop formed by a pair of serially connected zener diodes. An artifact squelch circuit, connected to the output of the second amplifier stage, limits the maximum output voltage of the sense amplifier.

Unsaturable sense amplifier for pacer system analyzer

A low-power consumption implantable pacer includes a system for detecting evoked cardiac contractions in which pacing pulses are initially applied to a patient's heart in pairs such that at most only one pulse of a pair can induce capture. The lead recovery waveforms produced in response to each of the pulses of a pair are detected and compared. By selectively varying the pulse energy level, the patient's capture threshold is determined. Pulse energy is then increased such that the first pulse of each pair induces capture and the lead recovery waveform resulting from the second, non-capturing pulse is stored. To conserve battery current, single pacing pulses are then supplied to the heart, and the lead recovery waveforms developed by the single pulses are compared against the stored waveform to yield a reference difference signal which verifies capture. When a significant change in difference signals is detected, the pacer automatically repeats the foregoing paired-pulse autocapture threshold determination and output level adjustment algorithm.

Low-power consumption cardiac pacer based on automatic verification of

A system and method for detecting evoked cardiac contractions applies pacing pulses to a patient's heart while simultaneously monitoring intracardiac electrical activity to detect evoked cardiac contractions. Pacing pulses are generated in pairs such that at most only one pulse of each pair can induce capture. The lead recovery waveforms produced in response to each of the pulses within a pair are electronically subtracted to yield a difference signal indicative of induced cardiac response.

System and method for detecting evoked cardiac contractions

The sense margin evaluation system and method for use of same is based upon (1) the interposition of a variable broad-band attenuator between an implanted cardiac pacer lead set and a pacer which is about to be implanted and (2) the inclusion of a pacer pulse detector at the pacer port. In use, the pacer is first programmed to a standby mode and a condition of 100% inhibition with the attenuator set to 0 dB. This affirms that the pacer's sense amplifier can sense the cardiac signal. Then, attenuation is incrementally added until the pacer just begins to output. The attenuation ratio (input/output) at this point is a direct measure of the ratio effective between the patient's cardiac signal and the pacer's sensing threshold, i.e., the sense margin. The advantage of this technique is that by using a broad-band attenuator, measurement inaccuracies due to the convolution of the cardiac signal's spectral content with a pacer system analyzer and a pacer sense amplifier's disparate narrow-band frequency response are avoided. The patient's cardiac signal serves as the test waveform generator for the pacer that is about to be implanted in his body and the sense amplifier'frequency response is identically that of the pacer about to be implanted.

Sense margin evaluation system and method for use same

An external pacer having a plurality of user-selectable output current levels includes a user-actuable push button switch for reducing the selected output current level by a factor of 10. By observing the absence or presence of an R-wave while operating at the reduced current level the stimulation threshold level of the heart can be determined without the need for additional level selections, and without subjecting the heart to sustained periods of low current. In the illustrated embodiment of the invention for typical output current levels of 2-20 milliamperes threshold levels of 0.2-2.0 milliamperes are obtained.

Cardiac pacer having stimulation threshold measurement circuit

To prevent crosstalk between atrial and ventricular channels in a dual chamber cardiac pacer with bipolar leads, the atrial and ventricular leads are multiplexed at about 2 kHz. This chopping rate is well above the sense amplifier's upper frequency response. Solid state switches provide that during stimulation on a given channel, only the corresponding leads are connected. Between output pulses, only one of the bipolar lead pairs is connected to the pacer at any instant of time. Circuitry is included to provide break-before-make action. Thus, at no instant of time are both channel lead pairs connected to the pacer.

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Miami Beach, FL, United States of America

Robert DeCote, Jr