Abstract: A pacemaker which generates a triphasic stimulus; the first and third phases are positive pulses, and the second is the negative stimulus. After-potentials are so low that reliable sensing of evoked signals are possible. The rapidity of the charge balancing is not affected by the stimulus amplitude because the relative amplitudes of the three phases are maintained independent of the stimulus amplitude.

Abstract: An implantable pacemaker which stores in memory the representation of an ECG signal by compressing the data. Whenever the input signal changes by a threshold amount from the last time data was recorded, a representation of the time interval which has elapsed is recorded. In a maximimally efficient system, the only information which must be stored are the successive elapsed times, along with indications of when the input signal changes slope.

Abstract: A metabolic-demand pacemaker in which the standby rate is a function of minute volume. Electrodes are placed in a blood vessel in the vicinity of the patient's pleural cavity, a known current field is established in the blood, and the impedance in the field is measured. The impedance is a function of the pleural pressure which, in turn, is a function of the patient's minute volume. The system also includes a mechanism for calibrating the standby rate to equal the nominal standby rate for a minute volume which equals a long-term average value, with the standby rate being changed in accordance with the deviation of the minute volume from the long-term average value.

Abstract: A tachycardia control pacer for which placing a magnet over the patient's chest results in the generation of two pulses, the time separation between which is an indication of the battery potential. Application of the magnet in this way also holds the device off, after the two pulses are generated, so that if the device is causing him discomfort the patient can temporarily disable it until the physician can program it off. Application of a magnet to the patient's chest, or programming of the device, resets two scanned inter-pulse time intervals to the values programmed by the physician. The next scanning begins with the programmed time values. In this way the physician, after inducing tachycardia, can verify the programmed time parameters rapidly by observing the patient's ECG waveform, without having to wait several minutes until scanning from the previously retained successful values would otherwise progress to the programmed values.

Abstract: A tachycardia control pacer for which placing a magnet over the patient's chest results in the generation of two pulses, the time separation between which is an indication of the battery potential. Application of the magnet in this way also holds the device off, after the two pulses are generated, so that if the device is causing him discomfort the patient can temporarily disable it until the physician can program it off. Application of a magnet to the patient's chest, or programming of the device, resets two scanned inter-pulse time intervals to the values programmed by the physician. The next scanning begins with the programmed time values. In this way the physician, after inducing tachycardia, can verify the programmed time parameters rapidly by observing the patient's ECG waveform, without having to wait several minutes until scanning from the previously retained successful values would otherwise progress to the programmed values.

Abstract: A heart pacer in which the magnitude of the end-of-life test current source is programmable. This effectively allows the physician to program the condition which will control a switch-over to end-of-life operation. It also allows the physician to override end-of-life operation after it initially takes place following a failing of the end-of-life test. The pacer also includes an additional end-of-life test involving the continuous monitoring of the supply potential and a switch-over to end-of-life operation should the pacer powering potential momentarily fall below a threshold level.

Abstract: A delta modulator for a heart pacer which not only allows sensed signals to be monitored, but also facilitates measurements of DC operating potential levels. The DC levels, and changes in them, can be measured accurately by equilibrating the modulator with the application to it of a suitable reference potential as the initial step in a measurement sequence. This same technique allows small signal variations to be tracked even if they are superimposed on large signals.

Abstract: A dual-chamber heart pacer whose ventricular pacing rate is closely matched to the physiological requirements of the patient. A "true" atrial rate is determined by counting over a 3-second interval the number of sensed atrial beats, including those which occur during atrial refractory periods. When the atrial rate rises to a threshold level, the ventricular pacing rate decreases gradually from the Wenckebach rate to a fall-back rate independent of atrial sensing. During this decline, atrial pacing pulses may be generated simultaneously with ventricular pacing pulses in an effort to terminate tachycardia. The controlled decline in ventricular pacing rate begins after a 3:2 block has resulted, but before a 2:1 block would otherwise result. The fall-back rate is higher than the standby rate to compensate for the lack of atrial pacing when the system operates at the fall-back rate.

Abstract: A tachycardia control pacer in which at least one scanned pulse is generated following each tachycardia confirmation, and the last-used pulse timing is retained following the next tachycardia termination for subsequent first use following the next tachycardia confirmation. The tachycardia termination detecting circuit does not respond to the time interval between at least the first two heartbeats following a generated pulse, to prevent a false determination of tachycardia termination due to the excessive pauses which sometimes occur immediately after pacing despite the fact that tachycardia has not terminated.

Abstract: An improved pacer for controlling tachycardia. Placing a magnet over the patient's chest results in the generation of two pulses, the time separation between which is an indication of the battery potential. Application of the magnet in this way also holds the device off, after the two pulses are generated, so that if the device is causing him discomfort the patient can temporarily disable it until the physician can program it off. Application of a magnet to the patient's chest, or programming of the device, also resets two start-of-scan time intervals to the values programmed by the physician. The next scanning begins with the programmed time values. In this way the physician, after inducing tachycardia, can verify the programmed time parameters rapidly by observing the patient's ECG waveform, without having to wait several minutes until scanning from previously retained successful values would otherwise progress to the programmed values.

Abstract: There is disclosed an improved pacer for controlling tachycardia. Following each tachycardia confirmation, a burst of stimulating pulses is generated. The rates of the bursts increase from cycle to cycle; thus following each tachycardia confirmation, a pulse burst at a different rate is generated. The number of pulses in a burst is similarly scanned, a complete rate scan taking place for each pulse number in a scan. The rate of a burst and the number of pulses in it which are successful in terminating tachycardia are stored, and following the next tachycardia confirmation the stored rate and pulse number are used for the first burst which is generated. In this manner, there is a greater likelihood that tachycardia will be terminated following the first burst since a previously successful rate and pulse number are used. Only if success is not achieved does scanning of the burst rate and pulse number ensue, starting with the previously successful rate and pulse number.

Abstract: There is disclosed an improved pacer for controlling tachycardia. Following each tachycardia confirmation, a burst of a programmed number (e.g., 15) of stimulating pulses is generated. The rates of the bursts increase from cycle to cycle; thus following each tachycardia confirmation, a pulse burst at a different rate is generated. The rate of a burst which is successful in terminating tachycardia is stored, and following the next tachycardia confirmation the stored rate is used for the first burst which is generated. In this manner, there is a greater likelihood that tachycardia will be terminated following the first burst since a previously successful rate is used. Only if success is not achieved does scanning of the burst rate ensue, starting with the previously successful rate.

Abstract: There is disclosed an event counting and reporting heart pacer which is useful for patients who suffer from bradycardia. The pacer operates in a demand mode with a 2.5-second escape interval. A count is maintained of the number of pauses each of which exceeds this escape interval. Four successive pauses, each of which exceeds 2.0 seconds but is less than 2.5 seconds, are treated as a single 2.5-second pause. Following the detection of each pause, the escape interval is reduced to 1.2 seconds and the counter is inhibited from further operation; the counter is enabled and the 2.5-second escape interval applies once again only after a spontaneous heartbeat is detected within 1.2 seconds of the preceding beat. When a maximum count of 128 pauses is reached, the system thereafter operates with fixed 1.2-second escape interval.

Abstract: A pacer for controlling tachycardia, in which the coupled interval is scanned as well as the initial delay. The time parameters which are successful in terminating the condition are stored so that upon confirmation of another tachycardia event, the previously successful time parameters are the first ones to be tried. The unit also allows tachycardia to be induced by the physician so that the parameters which are programmable can be adjusted for optimum performance following a subsequent naturally occurring tachycardia confirmation.

Abstract: There is disclosed a dual chamber pacer which offers several advantages over prior art devices. Although the pacer requires for its operation AV delay and VA delay parameter values, most physicians characterize dual chamber pacers in terms of AV delay and ventricular pacing rate. The pacer of the invention can be programmed under external control by the physician setting values for the parameters with which he is most familiar. A subtractor in the pacer forms the difference between the reciprocal of the ventricular pacing rate and the AV delay to derive the value of the VA delay. The pacer is also characterized by active recharge of the atrial output capacitor so that a very short ventricular refractory period following atrial pacing may be provided. A single maximum rate timer prevents the generation of excessively fast ventricular stimuli, whether due to the ventricular or atrial sub-systems, or even if atrial contractions are being sensed at too rapid a rate.