Abstract: An implantable pacemaker having circuit means for indicating, by pulse width modulation of the delivered pacing pulses, the programmable control states which control the selected pacemaker operating perameters. The circuitry includes a parallel to serial shift register adapted to receive the control states from a pacer circuit and to generate a serial multiple bit word when the pacemaker is switched to a magnetic mode. The shift register is clocked by stimulus timing signals, and the multiple bit word drives a one shot generator, the output of which is combined with the timing pulses to produce pulse width modulated pacing pulses.

Abstract: An epicardial lead with an insertion assembly for attaching same into good stimulating contact with the heart wall, the lead having movable fixation means for fixing the distal electrode head to the heart wall in combination with a stimulating probe electrode for delivering stimulus signals to the heart. The fixation element is preferably of a corkscrew configuration, oriented normal to the lead axis, and is normally contained within an enclosed electrode chamber. The insertion assembly provides means for releasably holding the electrode head while screwing the fixation member into the epicardial wall. Since the fixation member is free to move with respect to the electrode head, the lead can remain free to be hooked to an external pacer during the fixation step.

Abstract: A programmable digital atrio-ventricular pacer is provided whereby a single programming circuit is utilized for providing program control signals for control of separate ventricular and atrial pacing circuits. The atrial stimulus circuitry is controlled by a multiple bit control signal to cause derivation of atrial timing signals from the same clock signal as used for deriving ventricular stimulus pulses. A programmable digital multiplier is employed in combination with a counter to set the atrial escape interval independent of the timing of the ventricular stimulus pulses.

Abstract: A circuit for indicating at a remote location the control states of a fully implantable heart pacer includes a parallel to serial converter which receives the control states from a register which controls the parameters of the associated pacer. When the pacer is switched to an asynchronous or to a magnetic mode, the data is shifted through the parallel to serial converter. A delay is added between pulses when a particular logic state appears, and no delay is added if the complement of that logic state appears. The parameters can therefore be determined externally by observing the successive periods between stimulation pulses in the asynchronous or magnetic mode of the pacer.

Abstract: A programmable implantable pacer is provided for performing the dual functions of demand pacing as well as standby tachycardia breakup. A command parameter control is used for programmably controlling parameters of the pacer operation as well as of the tachycardia recognition and response to same. Upon recognition of tachycardia, a series of stimulus pulses of predetermined rate and number are delivered, the tachycardia breakup pulses being generated and delivered through an output circuit utilized commonly with the demand pacer circuitry.

Abstract: A heart pacer employing a digital parameter controlling circuit is controlled by externally transmitted magnetic pulses of width corresponding to the desired ultimate parameter controlling signal. In the embodiment shown, a magnetic pulse of width about 5.1 milliseconds corresponds to a digital "0", and a pulse of about 20.5 milliseconds corresponds to a digital "1". Circuits for generating and transmitting the pulses as well as for receiving and controlling the pacer parameters in accordance with the pulses are shown.

Abstract: A heart pacer employing a digital parameter controlling circuit is controlled by data received from an external source, the data preferably being in the form of magnetic pulses of width corresponding to the desired logic state of the parameter controlling signal. The externally transmitted signal which is received by the pacer comprises both parameter data for controlling selected pacer parameter operation and access data which is processed by the pacer for determining whether the parameter data is accepted for control purposes. The access and parameter data components of the externally generated signal are intermixed so that when receipt of the signal is enabled by the pacer, proper receipt of the parameter data is also ensured.

Abstract: An implantable cardiac pacer is instructable to vary the stimulation pulse interval, the stimulation pulse width, the stimulation pulse amplitude, the pacer sensitivity, the refractory period and the mode (demand or asynchronous).A master parameter control circuit is provided to vary selected parameters of the heart pacer in accordance with an externally applied control signal.An external control unit produces two sequential series of pulses, the first series being an access comprising at least one digital "0" state which must be detected by an access code detecting circuit within the master parameter control before the following parameter code will be accepted to vary the pacer parameters. The parameter code, generated subsequently to the access code, determines the selected set of pacer parameters, and can be selected from external controls upon the external control unit.

Abstract: A digital cardiac pacer has an asynchronous interval counter to count clock pulses to establish a stimulation interval at the end of which it produces a pulse for initiating a stimulation pulse. A control counter to which amplified naturally occurring heat pulses or stimulation pulses are applied controls the delivery of a resetting pulse to the asynchronous interval counter to reinitiate its count. If the stimulation, heart, or an interference pulse is detected during the count of a "refractory period," the control counter is reset and the refractory period is extended. If another stimulation, heart, or interference, pulse is detected during the extended refractory period, no resetting pulse is delivered, and the asynchronous interval counter continues its normal count. If during the period of time following the extended refractory period a stimulation, heart, or interference pulse is received, the control counter produces a resetting pulse to reset the asynchronous interval counter.

Abstract: A cardiac pacer includes means connected to electrodes adapted to be connected to a patient's heart for detecting and amplifying naturally occurring heart pulses. First and second counters are provided to receive periodic pulses from a clock pulse generator to time a refractory period and a stimulation pulse period, respectively. A rate limiting circuit limits the stimulation pulse rate to a predetermined rate, above which, the pacer is precluded from producing stimulation pulses. A test circuit is selectively connectable to produce a visual indication of the production of a stimulation pulse.

Abstract: A demand heart pacer which includes an oscillator, an amplifier for receiving and amplifying naturally occurring heart pulses, a monostable multivibrator activated by amplified naturally occurring heart pulses to generate a disabling pulse, and means for disabling the oscillator upon occurrence of a disabling pulse is of complimentary metal oxide semiconductor devices to present a capability of operating with low power dissipation to facilitate implantable heart pacer use having an enhanced power supply lifetime. The heart pacer produces stimulation pulses in an "inhibit mode" at a first frequency and stimulation pulses in a "fixed rate mode" at a second frequency, the difference in the first and second frequencies being indicative of the power supply voltage to provide a monitor of its state or condition.

Abstract: A circuit for measuring the sensitivity of a cardiac pacer includes a generator for producing a signal which varies as a function of the sine.sup.2 of a predetermined frequency. The signal is generated by an intermediate step of generating a waveform having the value of 1/2 [1-COS(.theta./2)]. The waveform is applied to an input of a cardiac pacer, and the amplitude varied in a measurable manner. The output of the cardiac pacer is observed in response to the signals applied to its input, and the amplitude of the voltage waveform which just inhibits the operation of the pacer is directly read from the amplitude varying control.

Abstract: A circuit for measuring the refractory period of a heart pacer includes first, second and third monostable multivibrators. The first monostable multivibrator is reset by the reception of a pacer stimulation pulse to produce a state change for a time period longer than the stimulation pulse interval of the pacer. The second monostable multivibrator is triggered by the trailing edge of the stimulation pulse, and has a variable time constant to produce a state change for a controlled period of time. The third monostable multivibrator applies a pulse to the pacer at the conclusion of the state change of the second monostable multivibrator. A counter is provided which counts the stimulation pulses produced by the pacer, and is connected to a resistive time constant circuit, to add additional time controlling resistors into the time constant circuit of the second monostable multivibrator.

Abstract: An infant grows rapidly enough that the distance between the heart and the location for the implantation of a cardiac pacer can change during the few years between surgical investigations of the implanted apparatus. The lead connecting the pacer with the heart follows a large spiral path around the pacer so that the spiral can tighten to a smaller spiral to accommodate the greater distance between the heart and the pacer as the infant grows. Such spiral portion of the lead is within a plastic bag permitting such contraction of the spiral without the lead adhering to tissue. The association of the plug at the end of the lead with the cylindrical socket in the end face of the pacer helps to direct the lead toward its initial large spiral path. Such socket is encapsulated in a plastic shield at one of the four corners of the two side faces of the pacer. Adequate battery life is achieved by one or more cells having the combination of a lithium anode and thionyl chloride-containing electrolyte.

Abstract: In a thermoelectric generator, a component comprises a ceramic insulator, having over limited areas thereof, each area corresponding to a terminal end of thermoelectric wires, a coating of a first metal which adheres to the insulator, and an electrical thermoelectric junction including a second metal which wets said first metal and adheres to said terminal ends but does not wet said insulator, and a cloth composed of electrically insulating threads interlaced with thermoelectric wires.

Abstract: Threads are interlaced with thermoelectric wires to provide a woven cloth in tape form, there being an intermediate layer of heat radiation reflecting material (e.g., aluminum foil) insulated electrically from said wires, which are of opposite thermoelectric polarity and connected as a plurality of thermocouples.

Abstract: An electrical generator having an Isotopic Heat Capsule including radioactive fuel rod 21 as a primary heat source and Thermoelectric Modules 41 and 43 as converters. The Biological Shield for the Capsule is suspended from Spiders at each end each consisting of pretensioned rods 237 and 239 defining planes at right angles to each other. The Modules are mounted in cups 171 of transition members 173 of a heat rejection Fin Assembly whose fins 195 and 197 extend from both sides of the transition member 173 for effective cooling.

Abstract: A cylindrical casing has a central shielded capsule of radioisotope fuel. A plurality of thermonuclear modules are axially arranged with their hot junctions resiliently pressed toward the shield and with their cold junctions adjacent a transition member having fins radiating heat to the environment. For each module, the assembly of transition member and fins is hinged to the casing for swinging to permit access to and removal of such module. A ceramic plate having gold layers on opposite faces prevents diffusion bonding of the hot junction to the shield.

Abstract: Apparatus for generating electrical stimulation pulses in the absence of naturally occurring "R" heart waves includes a free running multivibrator for generating pulses at the desired heart stimulation rate and an output amplifier and voltage multiplier for amplifying the generated pulses for application to the heart. A plural stage filter-amplifier amplifies any naturally occurring "R" waves to trigger a normally nonconducting multivibrator to activate disabling transistors, in turn, which discharge the timing capacitors of the free running multivibrator.The apparatus can be used with either a chemical or nuclear battery or other load dependent low voltage source.

Abstract: A heat-to-electricity converter is disclosed which includes a radioactive heat source and a thermoelectric element of relatively short overall length capable of delivering a low voltage of the order of a few tenths of a volt. Such a thermoelectric element operates at a higher efficiency than longer higher-voltage elements; for example, elements producing 6 volts. In the generation of required power, thermoelectric element drives a solid-state converter which is controlled by input current rather than input voltage and operates efficiently for a high signal-plus-noise to signal ratio of current. The solid-state converter has the voltage gain necessary to deliver the required voltage at the low input of the thermoelectric element.