Abstract: A memory device particularly useful in size-constrained electronic products, such as cardiac stimulators. To provide additional memory for such size-constrained products, memory chips are stacked one on top of another. The memory chips are configured to facilitate bonding without crossed contacts, using aligned bonding pads, vias, or castellations. Each memory chip also includes an address selection circuit that receives signals from one or more address lines to selectively enable and disable the memory chips in the stack.

Abstract: A cardiac stimulator capable of measuring pacing impedance includes a tank capacitor for delivering charge to the heart via device leads, a shunt resistor, and high-impedance buffers for measuring pacing current through the shunt resistor. Soon after the leading edge of the stimulation pulse, the voltage across the shunt resistor, as sampled by a high-impedance buffer, indicates lead and cardiac tissue resistance. Just prior to opening the pacing switch to terminate the stimulation pulse, the voltage across the shunt resistor is sampled by a high-impedance buffer and held once again to allow the capacitance of the lead/heart tissue to be calculated. In alternative embodiments, a high-impedance buffer measures the voltage between the tank capacitor and ground immediately following the stimulation pulse to allow estimation of the lead/heart tissue capacitance.

Abstract: A technique for acquiring and accessing information from a medical implantable device is provided. Analog waveforms of interest are sensed and processed by signal acquisition circuitry. Analog parameters of interest are applied to selector switches which are controlled by a logic circuit. The logic circuit is also coupled an A/D converter for converting the analog signals to digital values. The digital values are stored in dedicated registers and are available for telemetry to an external device upon receipt of a request or prompt signal. When a digitized value is accessed and telemetered, the control logic circuit changes the conductive state of the selector switches to apply the corresponding analog signal to the A/D converter. The resulting digital value is applied to the corresponding register to refresh the accessed and telemetered value. The technique permits the external device to request and configure the implanted device to send only digitized values of interest.

Abstract: A cardiac stimulator capable of measuring pacing impedance includes a tank capacitor for delivering charge to the heart via device leads, a shunt resistor, and high-impedance buffers for measuring pacing current through the shunt resistor. Soon after the leading edge of the stimulation pulse, the voltage across the shunt resistor, as sampled by a high-impedance buffer, indicates lead and cardiac tissue resistance. Just prior to opening the pacing switch to terminate the stimulation pulse, the voltage across the shunt resistor is sampled by a high-impedance buffer and held once again to allow the capacitance of the lead/heart tissue to be calculated. In alternative embodiments, a high-impedance buffer measures the voltage between the tank capacitor and ground immediately following the stimulation pulse to allow estimation of the lead/heart tissue capacitance.

Abstract: A memory device particularly useful in size-constrained electronic products, such as cardiac stimulators. To provide additional memory for such size-constrained products, memory chips are stacked one on top of another. The memory chips are configured to facilitate bonding without crossed contacts, using aligned bonding pads, vias, or castellations. Each memory chip also includes an address selection circuit that receives signals from one or more address lines to selectively enable and disable the memory chips in the stack.

Abstract: A memory device particularly useful in size-constrained electronic products, such as cardiac stimulators. To provide additional memory for such size-constrained products, memory chips are stacked one on top of another. The memory chips are configured to facilitate bonding without crossed contacts, using aligned bonding pads, vias, or castellations. Each memory chip also includes an address selection circuit that receives signals from one or more address lines to selectively enable and disable the memory chips in the stack.

Abstract: An implantable medical device for electrically stimulating the heart to beat generally includes a processor, a plurality of electrodes, a sense amplifier, a pulse generator, and a heart status monitor. The processor can determine when the patient has entered an environment of high electromagnetic interference. When this occurs, the processor forces the implantable device into a safe noise mode. While in the same noise mode (which preferably continues while the patient is experiencing the electromagnetic interference), the implantable device paces the heart on demand and inhibits pacing during the vulnerable period. The processor determines when the vulnerable period is occurring and when the heart needs to be paced by monitoring a status signal from the heart status monitor.

Abstract: A cardiac stimulator capable of measuring pacing impedance includes a tank capacitor for delivering charge to the heart via device leads, a shunt resistor, and high-impedance buffers for measuring pacing current through the shunt resistor. Soon after the leading edge of the stimulation pulse, the voltage across the shunt resistor, as sampled by a high-impedance buffer, indicates lead and cardiac tissue resistance. Just prior to opening the pacing switch to terminate the stimulation pulse, the voltage across the shunt resistor is sampled by a high-impedance buffer and held once again to allow the capacitance of the lead/heart tissue to be calculated. In alternative embodiments, a high-impedance buffer measures the voltage between the tank capacitor and ground immediately following the stimulation pulse to allow estimation of the lead/heart tissue capacitance.

Abstract: An implantable medical device including an enclosure and a header portion attached to the enclosure. The header includes a lead cavity into which a lead can be inserted. The lead cavity includes a compression device, such as a spring, for aligning a highly visible indicator plunger at least partially hidden from view inside the volume defined by an annular electrode, or other opaque object, partially surrounding the lead cavity. The plunger includes at least a portion that is easily visible to a surgeon during implantation of the medical device. When a lead is inserted into the lead cavity, the end of the lead pushes against the indicator plunger thereby moving the plunger and compressing the spring. When the lead is fully inserted into the lead cavity, the plunger becomes visible as it is pushed away from the volume defined by the annular electrode. In this way, the plunger provides a positive indication that the lead has been fully inserted into the header.

Abstract: A memory device particularly useful in size-constrained electronic products, such as cardiac stimulators. To provide additional memory for such size-constrained products, memory chips are stacked one on top of another. The memory chips are configured to facilitate bonding without crossed contacts, using aligned bonding pads, vias, or castellations. Each memory chip also includes an address selection circuit that receives signals from one or more address lines to selectively enable and disable the memory chips in the stack.

Abstract: An implantable medical device for electrically stimulating the heart to beat generally includes a processor, a plurality of electrodes, a sense amplifier, a pulse generator, and a heart status monitor. The processor can determine when the patient has entered an environment of high electromagnetic interference. When this occurs, the processor forces the implantable device into a safe noise mode. While in the same noise mode (which preferably continues while the patient is experiencing the electromagnetic interference), the implantable device paces the heart on demand and inhibits pacing during the vulnerable period. The processor determines when the vulnerable period is occurring and when the heart needs to be paced by monitoring a status signal from the heart status monitor.

Abstract: A technique for acquiring and accessing information from a medical implantable device. Analog waveforms of interest are sensed and processed by signal acquisition circuitry. Analog parameters of interest are applied to selector switches which are controlled by a logic circuit. The logic circuit is also coupled to an A/D converter for converting the analog signals to digital values. The digital values are stored in dedicated registers and are available for telemetry to an external device upon receipt of a request or prompt signal. When a digitized value is accessed and telemetered, the control logic circuit changes the conductive state of the selector switches to apply the corresponding analog signal to the A/D converter. The resulting digital value is applied to the corresponding register to refresh the accessed and telemetered value. The technique permits the external device to request and configure the implanted device to send only digitized values of interest.

Abstract: An implantable medical device for electrically stimulating the heart to beat generally includes a processor, a plurality of electrodes, a sense amplifier, a pair of comparators, inner and outer target logic units, and pulse generator. The processor controls the magnitudes of inner and outer target reference signals which are generated by the inner and outer target logic units, respectively. The outer target is adjusted to be approximately equal to the peak amplitude of the cardiac signal. The processor stores representations of the outer target reference in memory. Alternatively or additionally, the processor computes a histogram of the relative or absolute number of cardiac cycles that occur over a given period of time for each outer target setting. The processor can be directed to retrieve the outer target representations and/or the histogram from memory and transmit that information to an external programmer for use by a physician.

Abstract: A training unit generally includes a processor, a magnetic field sensor, a plurality of control switches, and a message and data output device. Placing a PEIS magnet, constructed in accordance with the ISOWD 14994 standard, adjacent to or in contact with the training unit activates the magnetic field sensor, a condition detectable by the processor. Activation of the switches determines which of three modes the training unit will operate. In an instructional mode, the process provides instructional messages to the operator via the message and data output device, which preferably includes a display and an audio speaker. In a coached mode, the training unit informs the operator when to place the magnet adjacent to or in contact with the training unit and when to remove the magnet in accordance with the timing intervals of the PEIS entry code. In a practice mode, the operator initiates and completes the entry code using a PEIS magnet without coaching.

Abstract: A method and apparatus for detecting failure or impending failure of a lead and for providing a warning to a patient or a patient's physician. The impedance of the lead is repeatedly measured and compared with certain impedance limits. If the measured impedance falls outside of these impedance limits, an alarm may be given to the patient, or a warning may be given to the patient's physician.

Abstract: A cardiac stimulator with a method and apparatus for automatically switching the cardiac stimulator to its normal mode from its backup mode. A fault monitor receives fault signals and determines whether a particular fault warrants activation of the backup mode. If so, a number of attempts to reactivate the normal mode are permitted. The normal mode may be reactivated if the stored information is valid and if the circuitry is operational.

Abstract: A method and apparatus for reliably producing a pulse train includes a control system which automatically selects a secondary pulse generator circuit when high frequency pulses are needed or whenever the use of alternating pulse generators would be desirable. This secondary pulse generator may be provided for other functions or it may be dedicated to providing alternate pulses, for example, to increase the frequency of the primary pulse generator without the loss of amplitude. This system may be useful for many purposes including implementing a noninvasive programmed stimulation operation or for providing antitachycardia arrhythmia therapy.

Abstract: An implantable pacemaker with apparatus for detecting capture or adjusting the strength or duration of pacing pulses by assessing the mechanical evoked response that may be distinctly sensed through impedance sensing, pressure sensing, plethysmography or other suitable methods. When capture is to be detected or the strength or duration of the pacing pulses is to be adjusted, two pacing pulses are delivered to the heart in each cycle of a series of cardiac cycles. The first pulse is varied in strength or duration or both. The second pulse is maintained at a consistently high strength or duration to assure capture. The impedance of the heart is measured during a time window following the first pulse which is predicted to include a recognizable feature of the impedance waveform of the heart following a stimulating pulse. The magnitude of the first pulse is gradually changed until capture is lost.

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: An implantable medical device includes a giant magnetoresistance ratio (GMR) sensor is used to detect the presence of a magnet in order to command the device to enter a predetermined mode of operation. The GMR responds to a modulated magnetic field generated by the programming of a command transmitter apparatus for non-invasive programming or controlling of the implanted device. The implantable medical device also monitors for the presence of a steady magnetic field to place the implanted device in a known, safe mode.