Abstract: A system and method for measuring and storing parametric data pertaining to the operating characteristics of an implantable medical device are provided. The parametric data may include the impedance of a lead that is attached to a patient's heart, and the internal impedance of a battery used to power the implantable medical device. The parametric data may be measured and stored at predetermined time intervals, as indicated by a clock provided within the implantable medical device. In addition, the parametric data measurements may be synchronized with the occurrence of a cardiac event, such as the application of a stimulation pulse to the patient's heart. A plurality of measurements for each type of parametric data may be stored, so that when the parametric data are later retrieved and displayed on an external programmer/analyzer, trends in the data can be readily observed.

Abstract: Implantable leads incorporating accelerometer-based cardiac wall motion sensors, and a method of fabricating such leads, are provided. The cardiac wall motion sensors transduce accelerations of cardiac tissue to provide electrical signals indicative of cardiac wall motion to an implantable cardiac stimulating device. The implantable cardiac stimulating device may use the electrical signals indicative of cardiac wall motion to detect and discriminate among potentially malignant cardiac arrhythmias. In response to a detected abnormal cardiac rhythm, the cardiac stimulating device may deliver therapeutic electrical stimulation to selected regions of cardiac tissue.

Abstract: An implantable medical device including a piezoelectric accelerometer activity sensor. The activity sensor includes a thin film piezoelectric cell within a frame structure. A mass imposes a load based upon acceleration to apply lateral or transverse forces which cause the generation of an electrical potential within the piezoelectric cell, which can be used by a rate control algorithm within the device to control operation of the device.

Abstract: A fluid flow rate measuring apparatus having a thermistor exposed to a flow of fluid and a driver circuit operable in an initial constant-voltage mode, in which it applies a substantially constant voltage across the thermistor, and a subsequent constant-current mode, in which it applies a substantially constant current through the thermistor, such current corresponding to the current level at the end of the constant-voltage mode. A voltage sensor measures the resultant voltage drop across the thermistor, which is a direct measurement of the fluid flow rate and which is substantially insensitive to variations in ambient temperature.

Abstract: The present invention includes a body implantable lead having a multipolar proximal connector, at least a first conductor coupled to at least one stimulating electrode, a sensor for sensing at least one physiologic parameter of the body, and a second and a third conductor coupled to the sensor. The sensor is hermetically sealed in a D-shaped housing. Sensor components are mounted onto a microelectronic substrate which is advantageously placed on an inner flat portion of the D-shaped housing. End caps having sealing rings, either glass frit or metal, are used to seal the ends of the shell. A hermetic seal is easily achieved by heating the sealing material until they re-flow between the end caps and the shell. Advantageously, the sensor terminals are sized to fit snugly within a narrow bore of the end cap which is then circumferentially welded closed. The D-shaped sensor is placed on a carrier having at least two lumens.

Abstract: An active discharge circuit for use within an implantable medical device, such as a pacemaker, rapidly discharges a coupling capacitor connected between a therapy circuit and body tissue. The active discharge circuit has a switching device, a charge transfer capacitor, and a clock. The clock is coupled to a control input of the switching device and provides a clock signal thereto. In response to the clock signal, the switching device sequentially and repeatedly couples the charge transfer capacitor to a discharge voltage supply so that charge transfers therebetween, and then couples the charge transfer capacitor to the coupling capacitor so that charge transfers therebetween. As the switch oscillates in response to the clock signal, the coupling capacitor is actively discharged.

Abstract: The present invention is directed toward a pulse generator for detecting that a pulse generator and an implantable lead are properly implanted so that a plurality of automatic features can be automatically turned ON. The automatic features include: automatic sensitivity adjustment; automatic capture adjustment; automatic rate adjustment, and the automatic adjustment of associated rate-responsive parameters; automatic electrode configuration; and the automatic adjustment of other timing parameters. An impedance detector is used to detect that the electrodes are in contact with the body by determining if the lead impedance is within a prescribed range. Redundant sensors, such as a temperature sensor, a shorting plug, or a resistive load could be used to confirm that the electrodes are in contact with the body.

Abstract: Capture is assessed in an implantable pacemaker by issuing a pair of stimulation pulses, separated by about 60-100 milliseconds. The second pulse of the stimulation pair is set to an energy level that assures capture, and remains at that level. The first pulse of the stimulation pair is initially set to an energy level that assures capture, and its energy level is thereafter systematically decreased, e.g., its amplitude is decreased, by a set amount each time the pair of stimulation pulses is issued. One of the stimulation pulses of the stimulation pair will always cause capture: the first pulse when its energy level is greater than the capture threshold (in which case the second pulse is issued into refractory cardiac tissue and has no effect); or the second pulse, when the energy of the first pulse drops below the capture threshold. In either event, a T-wave follows the capturing pulse, whether the first or the second, evidencing repolarization of the cardiac tissue.

Abstract: A movable self-locking suture sleeve which can be securely positioned on the lead body of a pacing lead. The self-locking suture sleeve includes first and second cooperative rigid elements interconnected by a flexible tubing element. The tubing element is constructed from a woven mesh designed to constrict when stretched. A resilient element or spring is interposed between the first and second cooperative rigid elements, tending to force the cooperative rigid elements axially apart. Once the suture sleeve is moved into position, a self-locking feature allows the suture sleeve to secure itself to the lead body.

Abstract: A system and method are provided for modulating the base rate of a transfer function for a rate-responsive cardiac pacemaker. Activity sensor measurements are used to derive activity variance measurements, which in turn are used to modulate the base pacing rate. In one embodiment, a histogram is used to store activity variance measurements collected over a period of about a week. The histogram is used to derive an activity variance threshold, which is compared to current activity variance measurements to determine if the patient is sleeping. If the patient is deemed to be sleeping, the pacing rate is set to a rate that comfortably meets the patient's low metabolic demands during sleep. In alternative embodiments, the activity variance measurements are applied to a base rate slope to modulate the base pacing rate.

Abstract: An improved digital frequency demodulator and method for demodulating a sampled asynchronous FM input signal that determines the time duration of each successive half cycle by counting the number of successive samples of the same polarity and by interpolating between the samples immediately before and immediately after the detected zero crossings at the beginning and the end of each half cycle.

Abstract: A defibrillator circuit that uses one or more self-switching switches to prevent the flow of leakage current through a patient's heart is provided. When the voltage across a self-switching switch is below a predetermined threshold the self-switching switch is open, which directs leakage current through a bypass resistor rather than the patient's heart. When a defibrillation pulse is generated the voltage across the self-switching switch rises above the predetermined threshold of the self-switching switch, which turns on the self-switching switch and allows the defibrillation pulse to be applied to the patient's heart. A monophasic defibrillator operates with one self-switching switch and one bypass resistor. Two sets of self-switching switches and bypass resistors are used in a biphasic defibrillator.

Abstract: An improved programmer apparatus for receiving digital data telemetered from an implantable device such as a heart pacemaker with substantially reduced hardware complexity and with convenient flexibility to adapt to data received in multiple modulation formats and data rates. The apparatus includes a conventional front-end receiver for receiving the data in both a reflected-impedance telemetry mode and an active telemetry mode, and it further includes a digital signal processor for efficiently processing data samples of the received telemetry data. Processing the received data in software allows for great processing flexibility, including a convenient reconfiguration to accommodate new modulation formats and data rates for implantable devices developed at a later time.

Abstract: A rotatable pin, screw-in type lead assembly includes a radiopaque element proximate the distal tip of the lead assembly for permitting direct, rapid fluoroscopic verification of the amount of extension of the helix electrode relative to the tip. The radiopaque element is preferably in the form of a metallic ring having a porous, tissue-engaging outer surface which promotes rapid tissue ingrowth and consequent lead stabilization. The lead assembly further includes a low friction seal assembly operatively associated with a shaft carrying the helix electrode. The seal assembly reduces the number of turns of the lead assembly connector pin required to effect lead fixation or removal.

Abstract: The present invention includes a body implantable lead having a multipolar proximal connector, at least a first conductor coupled to at least one stimulating electrode, a sensor for sensing at least one physiologic parameter of the body, and a second and a third conductor coupled to the sensor. The sensor is hermetically sealed in a D-shaped housing. Sensor components are mounted onto a microelectronic substrate which is advantageously placed on an inner flat portion of the D-shaped housing. End caps having sealing rings, either glass frit or metal, are used to seal the ends of the shell. A hermetic seal is easily achieved by heating the sealing material until they re-flow between the end caps and the shell. Advantageously, the sensor terminals are sized to fit snugly within a narrow bore of the end cap which is then circumferentially welded closed. The D-shaped sensor is placed on a carrier having at least two lumens.

Abstract: A cardiac arrhythmia is terminated by stimulating the heart during the narrow "region of susceptibility" or termination window of the arrhythmia cycle based upon a statistically significant starting value. The present invention will store a plurality of successful critically timed intervals and compute a central value (e.g., average, mean, median, etc.) and a measure of variability (sample range, standard deviation, etc.). The measure of variability is used to determine the termination window size. In one embodiment, the present invention then "scans" symmetrically-centrifugally about the statistically significant starting value. In an alternate embodiment, the present invention employs ranked scanning, that is, scanning according to the frequency of occurrence of previously successful starting values. The number and size of steps could be either programmable, or automatically computed by the pulse generator based upon the termination window size.

Abstract: An accelerometer-based, multi-axis physical activity sensor for use with a rate-responsive pacemaker, and a method for fabricating the sensor, are provided. The multi-axis physical activity sensor includes a cantilever beam having a film of a piezoelectric polymer adhered to each surface of an electrically conductive substrate. The piezoelectric films are highly resistant to fracturing during manufacture and in use, and they provide a strong output signal when stressed in response to bodily accelerations. A mass is mounted to a free end of the cantilever beam, and is substantially offset with respect to a planar surface of the beam so as to impart multi-axis sensitivity to the physical activity sensor. The accelerometer-based, multi-axis physical activity sensor provides an output signal that is communicated to pacemaker circuitry using a pair of electrical conductors.

Abstract: A rotatable pin, screw-in pacemaker lead assembly has a conductor coil enclosed within a silicone insulating tube. The conductor coil has a distal end secured to a helix electrode and a proximal end including a rotatable connector pin. The outer surface area of the conductor coil is coated with a super thin film of biocompatible Teflon. The Teflon coating substantially reduces the friction between the conductor coil and the inner wall of the insulating tube during lead fixation, thereby substantially reducing the number of turns of the connector pin required to effect fixation of the helix electrode.

Abstract: An external diagnostic/programming device is disclosed which includes means for both displaying intracardiac electrical signals sensed and telemetered from an implantable pacemaker in real-time, and for storing the intracardiac electrical signals for subsequent retrieval and analysis. The subsequent analysis selectively includes processing means for processing the signals off-line (i.e., not in real-time), using various signal processing strategies, such as digital filtering and frequency domain spectral analysis. The off-line signals may also be recursively processed in order to enhance the detection of a particular physiologic phenomena manifested by, but not readily discerned within, the unprocessed real-time signals.

Abstract: A programmable offset is added to an automatically generated baseline reference value to provide a Threshold value used by the rate-responsive sensor processing circuits of an implantable rate-responsive pacemaker to determine the significance of a sensor input signal. The rate-responsive pacemaker provides stimulation pulses on demand at a pacing rate determined by a sensed physiological parameter. The physiological parameter is sensed by a physiological sensor included within, or coupled to, the rate-responsive pacemaker. The physiological sensor generates a sensor input signal having a magnitude that varies as a function of the sensed physiological parameter. The invention provides a way for the rate-responsive pacemaker, when operating in an autothreshold mode, to automatically determine when the magnitude of the sensor input signal is sufficiently large to justify an increase in the pacing rate.