Abstract: An implantable medical device for electrically stimulating the heart to beat including a pulse generator, a logic and control unit, and an atrial sense circuit. The atrial sense circuit processes signals from electrodes implanted in an atrial chamber of the heart. The atrial sense circuit provides an atrial sense signal to the logic and control unit when the magnitude of electrical activity in the atria exceeds a threshold. The medical device preferably paces the ventricles in response to detected electrical activity in the atria indicative of atrial contraction. Immediately following ventricular pacing, the medical device initiates an absolute atrial blanking period followed by an atrial sensing period and a programmable blanking period. During both the absolute atrial blanking period and the programmable blanking period, atrial sensing is disabled, while during the atrial sense period, atrial sensing is enabled.

Abstract: A cardiac stimulator lead and sleeve for anchoring the lead at its point of entry into a vein. More particularly, the present invention comprises a helical coil made of a resilient material that is capable of being uncoiled and wrapped around the lead and/or the vein such that it is biased to resume its fully coiled state and thereby frictionally engages the vein and or lead and functions as an anchoring device for the lead.

Abstract: An implantable medical device, such as a cardiac pacer, defibrillator or drug delivery system, includes a container housing the required power source and circuitry and a header portion molded or glued to the container housing. Sensors, including physiological parameter sensors as may be necessary to control and implement the operation of the implantable device, or a telemetry link, or both, are disposed and sealed within the header. The header may include electromagnetic focusing devices to enhance the performance of the sensors. The sensors may include two pulse oximetry sensors that provide differential measurements to improve detection of arterial blood flow.

Abstract: A method and apparatus for measuring impedance of heart tissue or the leads associated with a cardiac stimulation apparatus involves charging a capacitor, storing the value of the voltage across the capacitor when charged, discharging the capacitor into said lead/heart system and storing the voltage on said capacitor when discharged. The two voltages may then be used to determine the combined impedance of the lead and the heart tissue. This may be advantageously accomplished by using separate circuits to measure each of the voltages of the capacitor and storing those voltages. These voltages then may be applied to an analog-to-digital converter which converts the ratio of said voltages to digital form. This value can then be used to calculate the combined impedance of the heart tissue or the lead. If one of the two impedances is known the other can then be easily determined.

Abstract: A method and apparatus for determining the origin of a cardiac signal in the heart of a patient. A cardiac stimulator includes a multiple-chamber electrode arrangement having at least two electrodes positioned to sense and/or pace different chambers of the heart. The electrodes switch from a bipolar configuration to a unipolar configuration in order to verify the point of origin for the cardiac signal and in order to determine whether propagation of the cardiac signal occurs. The apparatus allows simultaneous and timed pacing of left and right chambers.

Abstract: An implantable cardiac stimulator for detecting capture or adjusting the strength or duration of pacing pulses by using an evoked response detector and periodically tuning the evoked response detector. When the electric evoked response detector is to be tuned, capture is verified by detecting the mechanical evoked response. As the magnitude of the stimulating pulse is adjusted to isolate the threshold as detected by the mechanical response detector. At the same time, the electrical evoked response is also monitored. The difference between the detected electrical signal following capture as detected by the mechanical response detector and the signal following non-capture is used to tune the electrical evoked response detection apparatus and algorithm. The energy of the pacing pulse can then be optimized by adjusting both strength and duration.

Abstract: A data communication system for control of transcutaneous energy transmission to an implantable medical device is disclosed having an implantable medical device with rechargeable batteries and a single coil that is employed both for energy transmission and data telemetry. Control circuitry in the implantable device senses battery voltage and current through the battery, encodes those values by use of a multiplexer, and transmits the sensed and encoded values through the coil to an external energy transmission device. The external device includes a coil that is electromagnetically coupled to the coil in the implantable device for receiving the encoded signals and for transmitting energy to the implantable device. The external device decodes the transmitted values and transmits those to a controller for controlling energy transmission.

Abstract: A method and apparatus for detecting loss of cardiac pacing pulse amplitude includes a comparator for comparing the actual pulse voltage to a reference voltage. In one advantageous embodiment, the reference voltage is determined as a percentage of the programmed pulse amplitude. The comparison of the reference voltage and the actual voltage is latched at the time when a pulse is actually created to produce a signal indicative of whether the amplitude of the actual pulse exceeds the reference. When the amplitude falls below the reference, the system may take corrective action.

Abstract: A method and apparatus for analyzing cardiac information involves recording both atrial and ventricular information related to a recognized event. This information can then be transmitted by telemetry to the physician and graphed on a common graph which plots both atrial and ventricular information over the time period of the event. This technique allows greater ability to discern the true nature of these events, including whether a given event is a sinus tachycardia due to exercise or a ventricular tachycardia which might necessitate treatment. Therefore, the present invention enables more accurate analysis of cardiac information and thereby makes possible the more appropriate application of treatment.

Abstract: A method and apparatus for monitoring balanced biphasic current pulses used for measuring impedance in cardiac stimulators involves detecting imbalances between the pulses of opposite polarity. Such imbalances are potentially harmful to cardiac stimulator users. By converting the two different pulse phases into potentials, a determination can be made as to whether adequately balanced pulses are being generated. If an imbalance is detected, corrective action can be taken quickly enough to avoid harmful effects to the stimulator user.

Abstract: An implantable device which acquires physiological data and status information. The physiological data is compressed, reducing the memory requirement of the implantable device and/or increasing the amount of data that can be stored. The compression technique uses variable resolution while maintaining desired accuracy. The physiological data, such as heart beat interval time, is converted into a digital value. The digital representation then is divided into sub-ranges, and various resolution values are assigned to each sub-range. Each resolution is selected to stay within the desired accuracy. The interval time is divided by the particular resolution to obtain a digital value for the interval time within that range. The digital value then is corrected based upon the sub-range to obtain the compressed encoded digital value, which can then be stored in memory together with other desired data.

Abstract: A cardiac simulation system including a patient warning apparatus. The cardiac stimulator is an implantable pacemaker or defibrillator or combination which can be programmed to automatically alter the voltage of its output stimulus, in particular, to increase the voltage of the output stimulus whenever a condition exists requiring patient notification or warning. A specialized auxiliary lead with a shunt circuit can be connected to a standard socket of a cardiac stimulator header and a standard lead, such as a cardiac pacemaker lead, can then be connected to the auxiliary lead. The auxiliary lead allows a stimulation electrode to be implanted near excitable tissue in a secure fashion to assure stimulation of tissue. The auxiliary lead includes an apparatus for shunting electrical current from the standard stimulation electrode implanted in or near the patient's heart to the auxiliary electrode in the presence of a stimulation pulse with a voltage at or above a preselected level.

Abstract: An implantable subcutaneous data port for transferring data received from a sensor implanted within a subject. The data port electrically connects to the sensor and includes a control circuit electrically connected to an access port. The control circuit includes a current loop transmitter which modulates a current loop signal with voltage outputs from the sensor. This current loop signal transmits through the access port to an externally located current loop receiver which converts the current loop signal into an output voltage. Needle electrodes are insertable through the skin of the subject to the access port and provide an electrical interface between the control circuit and current loop receiver.

Abstract: An improved transcutaneous energy transmission device is disclosed for charging rechargeable batteries in an implanted medical device and to minimize peak temperature rises in the implanted device. A current with a sinusoidal waveform is applied to a resonant circuit comprising a primary coil and a capacitor. Current is induced in a secondary coil attached to the implanted medical device. Two solid state switches are used to generate the sinusoidal waveform by alternately switching on and off input voltage to the resonant circuit. The present invention charges the batteries using a charging protocol that either reduces instantaneous charging current or duty cycle of a fixed charging current as the charge level in the battery increases. Peak temperature rises are less while delivering comparable electrical charge of the battery than for prior charging systems.

Abstract: An optically-controlled high-voltage switch for an implantable defibrillator. A three-terminal high-voltage-tolerant semiconductor switch exhibits high conductivity between its high-voltage terminal and its common terminal in response to a low control voltage applied between its control terminal and its common terminal, where the low control voltage exceeds a characteristic threshold value, and exhibits low conductivity between same where the control voltage is less than the characteristic threshold value. A photovoltaic coupler/isolator having a light emitting device and a photovoltaic device, optically coupled to and electrically isolated from each other, is in circuit communication across the control and common terminals. A low voltage current source drives the light emitting device of the photovoltaic coupler/isolator.

Abstract: An improved transcutaneous energy transmission device is disclosed for charging rechargeable batteries in an implanted medical device. A current with a sinusoidal waveform is applied to a resonant circuit comprising a primary coil and a capacitor. Current is induced in a secondary coil attached to the implanted medical device. Two solid state switches are used to generate the sinusoidal waveform by alternately switching on and off input voltage to the resonant circuit. The sinusoidal waveform reduces eddy current effects in the implanted device which detrimentally increases the temperature of the implanted device. The present invention charges the batteries using a charging protocol that reduces charging current as the charge level in the battery increases. The controller preferably is constructed as a pulse width modulation device with a variable duty cycle to control the current level applied to the primary coil.

Abstract: A method for making a lead body for use in a conductive insulated lead for a cardiac stimulator. Alternating layers of conductive and insulative thermosetting polymers are extruded through successively arranged heated nozzles of increasing outlet diameter. As the inner layer emerges from its nozzle in a thermoset state, it is passed through a following nozzle while surrounded by another thermosetting polymer that is extruded through that following nozzle. The second polymer becomes thermoset and bonded to the already thermoset inner layer. Successive nozzles can be provided to form successive layers of alternating conductive and insulative polymers, where the conductive layers serve as the electrical conductors of the lead.

Abstract: An implantable cardiac stimulation system having a patient warning system and an elongated electrode mounted near the can of the system for providing reliable stimulation for warning. The electrode has an extended length and a short width. The length is preferably at least double the width and more preferably at least four times the width. This extended length increases the probability that contact with the surrounding tissue will be achieved. The short width and rounded profile of the width, forming an "edge", on the other hand, increases the probability that a high enough current density will be achieved, causing stimulation to occur. The electrode may also be curved along its length, which tends to promote a "point" or small area contact between the electrode and the patient's tissue. The electrode may be mounted directly on the can or header of the cardiac stimulator or may be part of a separate pin electrode.

Abstract: A cardiac simulation system with a patient warning apparatus, including a pin electrode insertable into a standard female socket in the header of a dual chamber pacer or multi-function cardiac stimulator. The cardiac stimulator has at least two sockets in a header, such as is commonly found in a dual chamber pacemaker. Rather than stimulating both chambers of the heart, the dual chamber pacemaker is programmed to function as a single chamber pacemaker, with a standard lead connecting one socket and its associated circuitry to a selected chamber of the heart, usually the ventricle. The pin electrode is inserted in the other socket, usually used for the sensing and stimulation of the atrium, and additional programming is provided to the pacemaker or stimulator to automatically produce an output stimulus through the atrial socket to the pin electrode whenever a condition exists requiring patient notification or warning. The pin electrode includes a hood which fits around a selected part of a header.