Abstract: In a method for continuous, electrical monitoring of the electrodes of an electrical heart stimulator, having at least one stimulation electrode and an indifferent electrode, the inter-electrode voltage is kept constant by regulation of a very low compensating current, and the magnitude of this current is measured and monitored. A device for such electrode monitoring includes control electronics and an output stage for delivery to the stimulation electrode of stimulation pulses. The output stage is devised to supply the electrodes with a weak, continuous current, or a repeated, pulsed current, producing a net direct current, in addition to stimulation pulses. A monitoring unit senses the inter-electrode voltage and, on the basis thereof, deliver an output signal to the control electronics for the purpose of controlling the weak current so the inter-electrode voltage is kept constant at a given value.

Abstract: A myocardial lead is provided with at least one sensor for sensing at least one of heart rate, physiological demand, or arrhythmia. Preferably, the sensor is a piezoelectric crystal, and is designed to flex with the beating of the human heart. Other suitable sensors include accelerometers, hemo-reflectance sensors, and strain gauge sensors. Each sensor is provided on a separate conductive segment of the electrode assembly. The signals can be monitored by appropriate electronics to detect changes in heart rate or arrhythmias of the heart.

Abstract: A rate-response pacemaker includes a plurality of sensors that each sense a physiologic-related parameter suggestive of the physiological needs of a patient, and hence indicative of the pacing rate at which the rate-responsive pacemaker should provide pacing pulses on demand. The pacemaker includes appropriate selection circuitry for selecting which of the sensor parameters or weighted combinations thereof, should be used as the sensor indicated rate (SIR) signal to control the pacing rate of the pacemaker at any given time. In a preferred embodiment, a maximum sensor rate signal (MR.sub.i) is computed for each sensor, and a maximum sensor rate (MSR) signal is defined for the pacemaker, and the SIR signal is selected as the lesser of: (i) the MSR signal; (ii) the largest of the sensed sensor parameters; or (iii) the respective MR.sub.i signals.

Abstract: A programming system is provided that allows a physician or medical personnel to optimize the settings of various arrhythmia detection criteria and/or parameters related to hemodynamic performance to be programmed into the implanted cardiac stimulating device. The cardiac stimulating device may be a pacemaker or cardioverter/defibrillator that detects heart arrhythmias by using various arrhythmia detection criteria. The cardiac stimulating device is capable of recording the patient's cardiac signals and/or sensor data. The programming system may play back the recorded signals to test the detection criteria and hemodynamic performance and may simulate the response of the device to the cardiac signal. Alternatively, the programming system may play back an artificially created or previously stored cardiac signal for test purposes. As a result, the recorded signal may be played back repeatedly without unnecessarily stressing the patient's heart.

Abstract: A dual-chamber pacemaker provides DDI pacing with PVC-protected hysteresis and automatic AV interval adjustment. An extended hysteresis atrial escape interval (AEI.sub.H) is invoked in response to the occurrence of either an atrial paced event followed by a sensed R-wave (an AR event), or an atrial sensed event followed by a sensed R-wave (a PR event). The occurrence of a premature ventricular contraction (PVC) thus does not trigger AEI.sub.H. In one embodiment, AEI.sub.H is not invoked unless the sensed AR or PR interval exceeds a prescribed reference interval. In a further embodiment, the AV interval (AVI) associated with the DDI operation is automatically shortened following an atrial stimulation pulse (A-pulse) delivered upon the timing-out of the AEI.sub.H. The shortened AVI is maintained for a programmed number of cycles of DDI operation, after which a lengthened AVI is reestablished for one cycle.

Abstract: An autocapture system within an implantable pulse generator automatically maintains the energy of a stimulation pulse at a level just above that which is needed to effectuate capture. The electrical post-stimulus signal of the heart following delivery of a stimulation pulse is compared to a polarization template, determined during a capture verification test. A prescribed difference between the polarization template and the post-stimulus signal indicates capture has occurred. Otherwise, loss of capture is presumed, and a loss-of-capture routine is invoked that increases the energy a prescribed amount to obtain capture. Periodically, and/or at programmed intervals or events, the capture verification test is performed. During the capture verification test, the pulse generator determines a polarization template for a particular stimulation energy and for each of a plurality of sensitivity or threshold settings. A determination is also made as to which sensitivity settings yield capture.

Abstract: A lead connector seal and locking assembly for an implantable pulse generator such as a pacemaker is detailed. The pulse generator includes a header portion and an enclosed metallic housing or can, wherein the header portion includes an orifice for receiving a lead connector. The lead connector is secured within the orifice by the use of a defeasible active seal and locking mechanism, which includes a sphincter seal and a beveled washer which is forced against the sphincter seal upon insertion of an actuator. The actuator may be a forked clip inserted into a slot formed within the epoxy header in such a manner that prongs of the forked clip force the beveled cam to be displaced axially within the orifice of the header portion, compressing the sphincter seal.

Abstract: An apparatus for treating arrhythmias of the human heart includes a defibrillator, and an arrangement for providing passive diode multiplexing between two patches for bidirectionally passing an electric current through a human heart. The arrangement is formed by connecting a cathode of a first diode to a first mesh electrode on a first conductor and connecting an anode of a second diode to a second mesh electrode on the first patch. An anode of the first diode and a cathode of the second diode are then connected to a lead. An identical diode arrangement is provided for the second patch.

Abstract: A programmable output connector of an implantable cardioverter-defibrillator (ICD), or similar implantable medical device, allows each of a multiplicity of output terminals to be selectively connected to either a positive or a negative output bus of the ICD. The positive and negative output buses of the ICD, in turn, are switched to an output capacitor, or equivalent output circuit, of the ICD. An electrical charge stored on the output capacitor, or otherwise generated by the output circuit, is presented to the multiplicity of output terminals in accordance with a programmed polarity. The programmed polarity causes a selected one or group of the multiplicity of output terminals to be connected to the positive output bus, and a selected other or group of the multiplicity of output terminals to be connected to the negative output bus. Respective electrodes designed for contacting cardiac tissue may then be electrically connected to each one of the multiplicity of output terminals.

Abstract: An improved cardiac pacemaker system of the kind that includes an oxygen sensor implantable into a patient's blood stream along with one or two electrical conductors for use in sensing heart beat activity and in selectively applying pacing pulses to the heart muscle. In an embodiment having just one implantable conductor, the oxygen sensor is integrated into the conductor, while in an embodiment having two implantable conductors, the oxygen sensor either is integrated into one of the conductors or is connected between the two conductors, in parallel with the heart muscle. In both cases, the oxygen sensor is selectively used without adversely affecting either heart beat sensing or pacing.

Abstract: A rate-response pacemaker includes a plurality of sensors that each sense a physiologic-related parameter suggestive of the physiological needs of a patient, and hence, indicative of the pacing rate at which the rate-responsive pacemaker should provide pacing pulses on demand. The pacemaker includes appropriate selection circuitry for selecting which of the sensor parameters, or weighted combinations thereof, should be used as the sensor indicated rate (SIR) signal to control the pacing rate of the pacemaker at any given time. The pacemaker also includes a memory circuit for selectively storing the sensor parameters from each of the plurality of sensors. The stored sensor parameters may thereafter be downloaded from the pacemaker memory and evaluated in non-real time with the various sensor parameters assuming different weighting (scaling) factors and different processing parameters (e.g.

Abstract: A myocardial lead having a tissue stimulating electrode attached via an insulated conductor to an epicardial pad the electrode embedded in the myocardial tissue of either the ventricles or the atria, for use as a pacing and/or sensing electrode. The myocardial electrode is configured to be pulled into position with a suture needle and thread. The myocardial electrode of the lead is designed to be highly reliable, to reduce exit block and fibrotic tissue growth, and to be utilized for extended periods even though designed to be implanted within the relatively thin myocardial muscle of a pediatric patient.

Abstract: A rate-responsive pacemaker (10) generates stimulation pulses on demand at a rate determined by a sensor indicated rate (SIR) signal. The pacemaker includes, in a preferred embodiment, an activity sensor (26) that generates a raw sensor signal (27) as a function of sensed body motion. The raw sensor signal is processed by two parallel signal processing channels with each channel emphasizing a different aspect of the raw sensor signal. A first sensor processing channel (28) produces a first processed sensor signal (S.sub.A) that is more sensitive to arm motion than to pedal impacts. A second sensor processing channel (30) produces a second processed sensor signal (S.sub.B) that is more sensitive to pedal impacts than to arm motion. The first and second processed sensor signals are each weighted by a programmable amount, and are then combined to form the SIR signal.

Abstract: A miniature, hybrid-mountable, accelerometer-based, physical activity sensor for use with a rate-responsive implantable stimulation device is provided. The physical activity sensor is constructed as 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 pair of electrically conductive supports serve to anchor the physical activity sensor to a substrate and deliver the output signal provided by the sensor to circuitry within the rate-responsive implantable stimulation device. The physical activity sensor is adapted to be mounted directly to conductive traces on a suitable substrate, preferably an implantable stimulation device hybrid.

Abstract: A rate-responsive pacemaker includes programmable hysteresis means for automatically extending an escape interval, EI.sub.0, in the presence of sensed intrinsic cardiac activity, and returning the escape interval to its initial value in the presence of pacemaker-stimulated (paced) cardiac activity. The escape interval sets the rate at which stimulation pulses are generated on demand in the absence of sensed intrinsic cardiac activity. The initial value of the escape interval is selected to be the lessor of: (a) a programmed escape interval (determined from a minimum programmed rate), or (b) a sensor-indicated escape interval (determined from a physiological or metabolic sensor used as part of the rate-responsive pacemaker). In addition to the hysteresis mode, a scan mode is optionally provided wherein the escape interval, EI.sub.0, is gradually extended (lengthened) in small incremental steps if no intrinsic activity is sensed during the prior escape interval.

Abstract: A patch electrode including a generally oval-shaped metallic mesh affixed to a polymer insulation backing and an insulation frame, and further including a plurality of specially designed lattices which divide the metallic mesh into a plurality of windows or apertures. The windows effectively act as smaller electrodes distributing the higher current densities inward from each of their own individual edges.

Abstract: A method and apparatus for determining the actual capacitance of a capacitor in a cardiac stimulating device in order to determine the potential necessary to store a desired amount of energy on the capacitor, are provided. The discharge curve of the capacitor is measured during re-forming to determine the time constant of the capacitor and the dumping resistor, and hence the actual capacitance.

Abstract: An autocapture system within an implantable pulse generator automatically maintains the energy of a stimulation pulse at a level just above that which is needed to effectuate capture. The electrical post-stimulus signal of the heart following delivery of a stimulation pulse is compared to a polarization template, determined during a capture verification test. A prescribed difference between the polarization template and the post-stimulus signal indicates capture has occurred. Otherwise, loss of capture is presumed, and a loss-of-capture routine is invoked that increases the energy a prescribed amount to obtain capture. Periodically, and/or at programmed intervals or events, the capture verification test is performed. During the capture verification test, the pulse generator determines a polarization template for a particular stimulation energy and for each of a plurality of sensitivity or threshold settings. A determination is also made as to which sensitivity settings yield capture.

Abstract: An ICD/pacemaker device provides a shocking pulse whenever it senses cardiac activity indicative ventricular fibrillation by standard means and a unique algorithm to respond to low amplitude ventricular fibrillation that would not be expected to be recognized/sensed by standard means. The ICD/pacemaker device further provides stimulation pulses on demand to a patient's heart whenever cardiac activity is not sensed and determines whether a given stimulation pulse has caused capture. If capture has not occurred, the energy of the stimulation pulse is increased by a predetermined amount and capture is retested. If the energy of the stimulation pulses increases up to a maximum value without causing capture, the generation of further stimulation pulses is stopped, and the ICD/pacemaker device presumes that low amplitude ventricular fibrillation is present. When fibrillation is sensed or presumed to be present, a shocking pulse is generated.

Abstract: A system and method for preventing atrial competition during sensor-driven operation of a dual-chamber pacemaker includes means for sensing atrial activity during an atrial refractory period. Atrial competition is avoided by either: (1) generating an atrial competition prevention (ACP) interval upon the detection of any atrial activity during the relative refractory portion of an atrial refractory period, and preventing any atrial stimulation pulses from being generated for the duration of such ACP interval; or (2) shortening the atrial refractory period in the event that the sensor-driven rate of the pacemaker begins to approach a rate that might place atrial stimulation pulses near the end of the unshortened atrial refractory period.