Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.