Abstract: A rate responsive cardiac pacing system is provided. In the illustrative embodiment, electrical stimulus pulses are applied to the heart ventricle and the evoked potential of the applied electrical stimulus pulses is detected. The detected potential is integrated over time to obtain a depolarization gradient magnitude. The depolarization gradient magnitude is compared with a corresponding depolarization gradient magnitude of at least one previous cardiac cycle. The rate of the electrical stimulus pulses is controlled in response to this comparison.

Abstract: A rate responsive cardiac pacing system is provided. In the illustrative embodiment, electrical stimulus pulses are applied to the heart ventricle and the evoked potential of the applied electrical stimulus pulses is detected. The detected potential is integrated over time to obtain a repolarization gradient magnitude. The repolarization gradient magnitude is compared with a corresponding repolarization gradient magnitude of at least one previous cardiac cycle. The rate of the electrical stimulus pulses is controlled in response to this comparison.

Abstract: A rate responsive cardiac pacing system is provided. In the illustrative embodiment, electrical stimulus pulses are applied to the heart ventricle and the evoked potential of the applied electrical stimulus pulses is detected. The detected potential is integrated over time to obtain a depolarization gradient and a repolarization gradient. A peak to peak time interval is determined from the peak of the depolarization gradient to the peak of the repolarization gradient. The peak to peak time interval is compared to the peak to peak time interval of at least one previous cardiac cycle. The rate of the electrical stimulus pulses is controlled in response to this comparison.

Abstract: A telemetry system for transmitting digital data from an implanted pacer to an external programming/receiver unit includes a voltage-controlled pulse generator having an output period proportional to its input voltage magnitude. The external receiver unit includes a pulse period detector to generate a reconstructed analog signal whose amplitude is proportional to each pulse-to-pulse time interval from the pulse generator. The pulse generator requires only minimum width pulses and thus there is minimum system drain because the signal information is contained only in the pulse-to-pulse interval and not in the pulsewidth.

Abstract: The apparatus for pacing a heart in accordance with the heart rate needed to produce a required cardiac output while the person is exercising, comprises a pacer adapted to be implanted in a human body and having a pulse generator and control circuitry (e.g. including a microprocessor) therein, a pacing lead adapted to be implanted in a right ventricle in a heart and having a distal electrode adapted to engage and supply pacing pulses to the apex of the right ventricle and a pressure sensor or impedance sensing electrode mounted in or on the lead.

Abstract: A multi-programmable ROM-less cardiac pacer employs an intermittent microprocessor turned ON and OFF by a pacer timer clockwise independent of the processor to time intervals preset by the processor. Sensed activity and external communications restart the processor with an interrupt request. Five antitachycardia mechanism are externally programmable: programmed burst, burst rate scanning, automatic overdrive, programmed critically timed and critically timed scanning. In scanning mechanisms, the interval changes progressively until the tachycardia is terminated by a successful interval which is stored. Runaway protection is executed in the software. For telemetry, the pacer collects the following monitored pacing data over a programmable period of time: percent pacing, average rate, maximum rate, number of tachycardia episodes and maximum tachycardia duration.

Abstract: The apparatus for pacing a heart in accordance with the heart rate needed to produce a required cardiac output relative to the partial pressure of carbon dioxide in the blood, pCO.sub.2, while the person is exercising comprises a pacer adapted to be implanted in a human body and having a pulse generator and control circuitry (e.g. including a microprocessor) therein, a pacing lead adapted to be implanted in a heart and having a distal electrode adapted to engage and supply pacing pulses to a right ventricle of a heart and a pCO.sub.2 sensor for sensing pCO.sub.2 of the blood in the heart. An algorithm and routine utilizing same are stored in the control circuitry (microprocessor) and are adapted to relate pCO.sub.2 with the required heart rate or change in rate, .DELTA.R, needed to supply a desired cardiac output and to cause the pacer to pace the heart at the required heart rate when the heart is not naturally paced.

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: The cardiac pacing system comprises a cardiac pacer, and a multiconductor pacing lead having a distal end and a proximal end having a plurality of spaced apart ring electrodes thereon. The pacer comprises a metal case mounting electronic/electrical circuitry, and a power supply therein and having a top side. A soft pliable elongate neck is mounted to the top side of the case. A connector assembly is located inside said neck for connecting the cardiac pacer with the proximal end of the pacing lead and comprises a plurality of spaced-apart U-shaped electrical contacts and insulated conductors extending through the top side for coupling the electrical contacts to electrical circuitry in the case. The neck has at least one elongate lumen therein into which extend the electrical contacts and has an open end for receiving the proximal end of the pacing lead.

Abstract: An implantable pacemaker in which the sensitivity is automatically controlled. The peak value of each R wave is measured, and a long-term average is derived. The gain of the sense channel is adjusted automatically in accordance with the average of the measured peak values.

Abstract: Cardiac ultrasonically marked leads produced by mounting one or more piezoelectric marker transducers into the leads and connecting the transducers by electrical conductors to appropriate electronic circuits which, upon reception of the scanner ultrasonic signals by the marker transducers, generate appropriate electrical signals which localize unambiguously the marker transducers in an ultrasonic echographic image, thereby permitting guiding of pacing leads and detection of their malfunctions.

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: The hollow cylindrical wall of the catheter is composed of flexible, electrically insulating, ultrasonically transparent material. Embedded therein are spaced tubular-shaped ultrasonic piezoelectric transducers which substantially surround the lumen. The transducers receive signals from the imaging transducer on the body surface and serve to establish catheter location within the body during a diagnostic procedure. Electrical connector leads from the transducers are embedded in the wall and connected to a signal processor which provides an output for incorporation into the display of an echocardiograph image display system.

Abstract: A combined pacemaker delta modulator and bandpass filter which requires only one active device. The sense signal is applied through a conventional delta modulator capacitor to the minus input of a differential amplifier, and the conventional current sources are connected to the minus input. Instead of simply connecting the plus input to a reference potential, however, it is also coupled, through a resistor, to the input signal, and an RC network is connected across the two inputs.

Abstract: A magnetic field sensor including a resonant circuit having a coil. The resonant frequency varies with the strength of the magnetic field which passes through the coil. The resonant circuit is energized for approximately one-half cycle of the resonant frequency which characterizes the circuit in the absence of a magnetic field. During a sensing window of predetermined duration which then immediately follows, the voltage across the coil is examined for a zero crossing. A zero crossing will occur only in the presence of a magnetic field whose amplitude exceeds a threshold value.

Abstract: A circuit for measuring the internal impedance of the cell of a heart pacer in order that the remaining life of the cell can be estimated. The test is performed by cutting off all current flow from the cell to the pacer circuitry, the pacer still being powered, however, by the conventional by-pass capacitor. When the cell impedance test is conducted, a test capacitor is placed across the cell and it charges exponentially with a time constant which is a function of the cell impedance. By measuring the time required for the test capacitor potential to reach a reference level, the cell impedance can be ascertained. The measured parameter can be telemetered out of the pacer along with other data in the conventional manner. With a typical lithium iodide cell, the internal impedance of the cell varies from less than 100 ohms when new, to tens of kilohms near the end of the cell life.

Abstract: There is disclosed a tachycardia control pacer in which there is generated a sequence of pacing pulses at intervals which are a function of the effective refractory period intrinsically associated with the rate of the patient heartbeats. If the tachycardia episode is not terminated, another sequence of pulses is generated; however, the rate of the new sequence is decreased if at least one unevoked heartbeat was sensed during the preceding pacing pulse sequence and the rate is increased in the absence of any unevoked heartbeat having been sensed during the preceding pacing pulses sequence. Also, in order to smooth the transition between the fast pulses used to terminate the tachycardia episode and subsequent beating in sinus rhythm, pacing pulses continue to be generated at increasing pacing intervals until they merge into standby pacing.