Abstract: A data telemetry system for use with implanted medical devices for transmitting digital and analog data to a remote receiver by enabling different combinations of fixed and variable value current sources according to a telemetry logic code to energize a tank coil and produce a ringing type of variable frequency RF signal.

Abstract: The programming of pulse intervals and the inhibition of the output of an implanted cardiac pacemaker are disclosed. The occurrence of either an output pulse from the implanted unit or of cardiac activity allows for synchronization of the programming unit with the implanted device so the external programmer can control the pulse timing sequence of the implanted unit. The implanted unit can be programmed after each pulse, or as required, to obtain a pulse sequence which may be used to provoke, or terminate, tachyarrhythmias, thus enabling non-invasive electrophysiologic studies, or therapeutic stimulation.

Abstract: A waveform detection system for use in a pacemaker for distinguishing normal beats from ectopic or abnormal beats for example, such as those involving ventricular tachycardia, ventricular flutter or fribrillation, premature ventricular beats, supraventricular tachycardia, retrograde conduction; and in dual chamber or atrial applications those involving atrial tachycardia and atrial flutter or fibrillation. The term "abnormal" is employed herein to mean all abnormal beats including those specified above. In the system of the illustrated embodiment a sense amplifier is employed for initiating a counter in response to a detected cardiac event and a voltage controlled oscillator is used for converting the instantaneous value of the applied waveform to a bit rate delivered to the counter. The morphology or shape of the physiological waveform is represented by a number present in the counter at the end of the counting cycle which allows for a therapy decision to be made.

Abstract: A programmer for a pacemaker which has telemetric capabilities is disclosed. The programmer, in addition to being able to program the pacemaker through telemetric transmission of programming codes can receive digital and analog (including marker) information from the pacemaker for remote display and utilization, and for program modification in response thereto, if desired. Implementation of the programmer is accomplished partly by circuitry which includes pulse duration measurement circuitry for measuring time duration intervals of incoming RF telemetric signals and partly by a firmware program stored in the programmer.

Abstract: An apparatus for treating a patient which induces an electric current in the body through external application of an electromagnetic field. The apparatus includes means for controlling the magnitude of the induced electric current by sensing the electromagnetic field and automatically controlling its strength. The sensing may be accomplished through time multiplexed use of the field inducing coil or through the use of a separated, dedicated coil.

Abstract: An implantable medical device to deliver cardioverting energy to cardiac tissue in synchrony with detected ventricular depolarizations having a DC-DC flyback converter. The primary coil of the converter is periodically coupled and decoupled to ground by a timing circuit to effect charging of a high voltage output capacitor from a low voltage source through the secondary coil. A supply voltage detector alters the time period of the timing circuit to regulate the amount of current drawn by the primary coil. As the low voltage power supply depletes, its impedance increases tending to prolong the charging time of the output capacitor. Further regulating circuitry alters the one-shot time period to avoid loading down the supply voltage which could affect operation of other circuits.

Abstract: A cardiac output monitor of the type including an ultrasound crystal for use as a doppler flowmeter. The monitor is designed for mounting directly to a blood vessel, and is provided with a novel fixation apparatus which allows for easy and secure attachment to the blood vessel. The fixation apparatus includes two parallel fixation wires especially adapted for location in the blood vessel wall, without the danger of piercing the vessel wall.

Abstract: A magnetic-field, noise-cancelling transceiver is provided by a dual-coil antenna circuit. In the receive mode, two identical coils, connected in series opposition, cancel noise signals common to both coils and receive desired signals present at only one coil. Capacitance in parallel with the series-opposed coils establishes the resonant frequency of the receiver, antenna circuit. In the transmit mode, the two coils, connected in series opposition, have their non-adjacent terminals clamped to ground via two pairs of oppositely-poled diodes, one pair on each non-adjacent terminal. The transmitter signal, coupled to the junction of the two coils through a capacitor, generates additive magnetic fields by causing equal currents to flow in each coil from the common junction, to their respective diode junctions, to ground through the respective, oppositely-poled diode pairs. Series resonance is established by the transmitter coupling capacitance and the parallel combination of the two coils.

Abstract: A tissue stimulator of the type which provides short intervals of stimulation followed by longer intervals of rest is provided with a fail-safe system for turning off the stimulator if the stimulation interval exceeds a predetermined maximum interval. A timer times each "on" interval. If the "on" interval exceeds the predetermined maximum, the timer times out and shuts off stimulation.

Abstract: A threaded pacing electrode assembly for use in implantable electrical leads. The electrode is provided with an exposed portion adapted to make electrical contact with body tissue and with a cylindrical portion proximal to the exposed portion provided with a helical screw thread. A conductor coil which has an inner diameter smaller than the outer diameter of the cylindrical portion is mounted to the exterior of the cylindrical portion, coiled within the screw thread. A transparent insulating sleeve covers the cylindrical portion, is frictionally retained by the thread, and assists in maintaining the conductor coils in contact with the cylindrical portion.

Abstract: A rate responsive pacer which paces the heart at a rate dependent on detected variations in the stroke volume of the heart.

Abstract: A gain control system for verifying the programming of an implanted medical device is provided for an external programming unit which receives transmitted signals from the implanted unit and verifies if these signals represent valid "1" and "0" data bits. If the signals of an encoded message unit are valid signals then processing continues. If some of the signals are invalid due to noise interference, the gain of the receiver of the programming unit is decremented in steps as long as the error rate exceeds a predetermined number of errors per unit time.

Abstract: A physiologic cardiac pacer operable in the DVI or A-V sequential pacing mode or the DDD or fully automatic pacing mode senses for the omission of an R-wave from an implantable cardiac pacer during the A-V interval. If the pacer does not sense a R-wave during the A-V interval the V-A interval is timed out immediately following the A-V interval and an atrial pacing pulse is issued at the end of the V-A interval. In the event, however, that an R-wave is sensed during the A-V interval, a flag is set and then the entire A-V interval is to be timed out, at which time the state of the flag is determined. If an R-wave was previously issued, a ventricular pacing pulse is not issued to the pacer at the end of the A-V interval, whereas if the flag is not set it is transmitted to the pacer.

Abstract: An improved method for producing ion-selective membranes having a desired shape and of a desired plastic, for incorporation in ion-sensing electrodes, and the electrodes incorporating these membranes. This method allows the use of preformed polymeric members having the desired shape to produce ion-selective membranes, allowing simplified production of ion-sensing electrodes, as well as combination ion-sensing and reference electrodes.

Abstract: A lead for implantation in the epidural space has an inflatable balloon which is sealed against a first side of the lead so it inflates away from the first side. The balloon contacts walls of the epidural space and urges an electrode on the first side against the dura. A syringe for inflating the balloon has a spring to absorb travel of a plunger actuator when fluid pressure in the balloon exceeds tension of the spring.

Abstract: The programming of pulse intervals and the inhibition of the output of an implanted cardiac pacemaker are disclosed. The occurence of either an output pulse from the implanted unit or of cardiac activity allows for synchronization of the programming unit with the implanted device so the external programmer can control the pulse timing sequence of the implanted unit. The implanted unit can be programmed after each pulse, or as required, to obtain a pulse sequence which may be used to provoke, or terminate, tachyarrhythmics thus enabling non-invasive electrophysiologic studies, or therapeutic stimulation.

Abstract: A drug delivery catheter and storage bladder adapted for use in an implantable drug delivery system. The catheter and bladder are provided with piezoelectric layers adapted to be responsively coupled to a source of ultrasonic electrical signals. When so coupled, vibration of the piezoelectric layer dislodges any accumulation of crystallized drugs within the catheter and bladder.

Abstract: A body implantable lead for the delivery of stimulation energy to a desired body site including a drug dispenser carried by the lead which retains a drug to be dispensed while allowing the dispensing of that drug at least adjacent the desired body stimulation site. The drug may be one which is intended to counter thrombus formation, fibrosis, inflammation or arrhythmias, or any combination thereof, or to accomplish any other localized purpose. The drug is retained in a cavity within the lead, with an agency controlling dispensing of the drug. In a preferred embodiment, the drug is compounded into a solid material which is retained within a tip electrode while being exposed to body fluids through a porous elution path. The drug may also be retained on and diffused from a porous surface of the electrode, adjacent to the elution path. Preferably, the drug is compounded within a polymer carrier, mounted within the cavity in the electrode.

Abstract: A pacing system analyzer is constructed to provide verification that an implantable cardiac pacer operating in a demand mode will not itself produce tachycardia in a patient because of abnormally long patient retrograde conduction time. The analyzer when performing the retrograde conduction test provides an intercardiac electrogram, changes the ventricular sense amplifier to asynchronous and samples to determine the maximum amplitude signals over a sampling period to select an amplifier gain factor. After the gain factor is set additional signal samples are collected, peak-to-peak amplitude is measured and interpolation between data is made to provide waveform "segments" and the best waveform segment to employ for testing for retrograde conduction is selected. The time periods from pacing to these segments are measured and utilized to determine if retrograde conduction is present.

Abstract: A pacing system analyzer as connected to an implantable cardiac pacer and if an atrial pacing pulse is detected only, the analyzer sends a simulated P-wave to the pacer and determines the response of the simulated P-wave to determine if the pacing mode is AAI, AAT, or AOO. In the event a ventricular output pulse only is detected by the analyzer, a simulated R-wave is sent to the pacer and if the pacer responds either by a triggered ventricular pulse or by not changing its response, the analyzer determines that the pacer is in a VVT or VOO mode. On the other hand, if the pacer is inhibited a subsequent simulated P-wave is sent to it and the response of this P-wave determines whether or not the pacer is in a VVI or VDD mode. In the event that both atrial and ventricular pacing pulses are detected by the analyzer, the simulated R-wave is first sent to the pacer and an unchanged response determines that the pacer is in a DOO mode.