Abstract: Methods, circuits and devices useful for maximizing the likelihood of successful defibrillation or cardioversion using an automatic implantable cardioverter/defibrillator ("AICD") system are provided which are capable of monitoring the impedance of AICDs for purposes of detecting lead malfunctions. After detection of a lead malfunction, the methods, circuits and devices are capable of connecting or disconnecting leads and electrodes to maximize the likelihood of effective cardioversion and defibrillation.

Abstract: A cardiac stimulator including a patient warning apparatus, having a real time-clock for delaying delivery of a warning stimulus until a preselected time of day. The time of day may be selected dynamically with respect to detected patterns of patient activity. The stimulator can adjust the time for delivery of patient warning based on the detected circadian rhythm of the patient. In one embodiment, the cardiac stimulator is an implantable pacemaker or defibrillator or combination which can also be programmed to automatically alter the peak voltage of its output stimulus, in particular, to increase the peak voltage of the output stimulus whenever a condition exists requiring patient notification or warning. A stimulus generator in the stimulator can delivers electrical current to the electrically conductive suture point or warning electrode at a preselected voltage level.

Abstract: An implantable endocardial lead with a retractable helix. A specialized stylet can be inserted into the lead at the proximal end and passed through the lead to the distal end. Located at the distal end of the lead is a piston supporting the helix. The piston is attached to a coiled trifilar conductor and has an electrode adjacent the helix. Immediately adjacent the piston proximally an additional first short coil of wire is interlocked between the wires of the trifilar conductor, providing a female thread within the conductor. The stylet has a second single strand short coil segment spot welded to the stylet adjacent a distal end thereof. The stylet is rotated to screw the second short coil segment on the stylet into the first short coil adjacent the piston.

Abstract: An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart as an indicator of cardiac stroke volume, wherein the baseline impedance is eliminated from the measurement of impedance. In one embodiment, an adaptively controlled, balanced bridge is utilized to eliminate the baseline. A Wein bridge is provided having a variable reactance whose impedance is controlled continuously. In another embodiment, an impedance measurement is modified by a signal conditioner providing an appropriate varying offset through the use of a sample and hold circuit and other signal modifying circuits prior to converting the impedance measurement to digital information. In a third embodiment, a sample and hold circuit may be used to provide digital information through an A to D converter to a microprocessor which directly controls a variable reactance. The end voltage of a pacing capacitor is used as an indication of a baseline impedance.

Abstract: A defibrillator has a signal generator implemented to deliver output shock waveforms and housed in a case adapted to be implanted in the left pectoral region of a cardiac patient. The case is implemented to interact with internal circuitry of the generator to maintain the case active as an electrode. An electrical transvenous lead has a proximal electrode for electrical connection to the internal circuitry of the signal generator and a distal end adapted to be positioned in the right ventricle (RV) of the patient's heart. The lead includes a sensing tip for contacting the RV to sense the patient's ECG signal and a shocking coil arranged to be located in the RV when the transvenous lead is implanted in the patient. The internal circuitry of the signal generator includes triggerable output circuit for developing an output shock waveform when triggered in response to detection of ventricular fibrillation of the patient's heart from the sensed ECG signal.

Abstract: An implantable medical device, such as a pacemaker, cardioverter or defibrillator, having a detachable power source, so that either the power source or the electronic circuitry can be replaced. The electronic circuitry is enclosed within a first container and the battery or power source is enclosed within a second container. The two containers are coupled by tracks slidingly connecting the containers along substantially planar sections thereof. In a first embodiment, the tracks comprise dovetail tongue and groove configurations. In a second embodiment, the tracks comprise a bayonet-type connection having male and female parts. The male part comprises two parallel arms. The female part comprises two parallel rails having a relatively inflexible section adjacent a distal end of the rail. Proximally on the rail, there is a relatively flexible section.

Abstract: A method of verifying whether an atrium of the heart has been captured by an atrial cardiac stimulation pulse. An atrial signal is sensed via an electrode located in the atrium during a period of time from before delivery of the stimulation pulse to after delivery of the stimulation pulse. The sensed signal is analyzed by detecting whether a P-wave occurred prior to delivery of the cardiac stimulation pulse such that stimulation pulse would have been delivered within a refractory period. If a P-wave did not occur, the slope of the sensed waveform signal is determined within a selected interval of time beginning at a selected time after the time of delivery of the stimulation pulse. A capture status signal is generated that indicates non-capture, if a P-wave was detected, or capture, if a P-wave component was not detected and the determined slope of the sensed waveform signal surpasses a pre-selected slope threshold demarcating capture from non-capture.

Abstract: A transvenous implantable defibrillation lead includes a conductor and inner and outer coaxial cylindrical electrodes. The inner electrode is connected to the conductor, and the outer electrode is connected to a sheath overlying the conductor in rotatable relationship thereto. The sheath is fixed to the outer cylindrical electrode so that rotation of the sheath relative to the conductor results in rotation of the inner and outer cylindrical electrodes relative to each other. The inner electrode has a plurality of hooks extending generally transversely and tangentially thereto, with the hooks being biased such that the terminal ends of the hooks tend to spring outwardly from the inner electrode. The hooks are constrained against the inner cylindrical electrode by the outer cylindrical electrode, except that a window in the outer electrode permits the hooks to spring outwardly therethrough upon rotation of the outer electrode relative to the inner electrode.

Abstract: An implantable automatic cardioverter/defibrillator device for a cardiac patient has a primary control mode for a defibrillation therapy delivery system. The primary control mode is responsive to detection of fibrillation of the patient's heart for causing the delivery of a preselected electrical waveform therapy to the heart. The device also has a secondary control mode which is enabled by detecting a predetermined failure mechanism that causes malfunctioning of the primary mode. The enabled secondary control mode uses at least some of the functional part of the primary mode in responding to fibrillation of the patient's heart to initiate generation of defibrillation therapy for application to the patient's heart.

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 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. Our invention includes a specialized pin electrode with an orifice for a suture.

Abstract: An implantable automatic cardioverter/defibrillator device for a cardiac patient is automatically responsive to sensing of electrical cardiac activity of the heart of a patient in which the device is implanted for detection and treatment of fibrillation. A prescribed electrical shock waveform regimen is generated as electrical defibrillation therapy for application to the heart in response to detection of fibrillation of the heart. A timing function circuit responds to the detection by timing the delivery of the generated prescribed electrical waveform regimen to be applied at a point in time at which the fibrillation ECG has substantially its highest amplitude and lowest frequency, as a point of high susceptibility to reversion to sinus rhythm upon application of a shock, and with low defibfillation threshold, to enhance the probability of successful defibrillation, and to synchronize the shock delivery to this sensed intracardiac event.

Abstract: An implantable medical device having at least one lead connector. The lead connector has a collet-type mechanism. A bolt is securely affixed within the header of the implanted device. The bolt means has a central bore for receiving a pin of a lead, and fingers for contacting the end of the lead. Initial electrical contact is achieved by the bolt when the lead is inserted therein. A nut threadedly engages the bolt to compress the fingers against the lead. The nut is rotatably received within the header of the implanted device so that it can both tighten on the bolt and loosen therefrom. The nut is manipulated through a piercable septum.

Abstract: A method and apparatus is disclosed for an analog-to-digital converter (ADC) to minimize power consumption. The ADC of the present invention minimizes the number of clock cycles required to determine the correct digital code for a particular sample point on an electrogram signal, thus making it possible to turn off some or all of the ADC logic during idle periods. The ADC includes prediction logic that provides a starting point for subsequent digital code representations of the electrogram signal. The prediction logic receives recent code conversions values to predict a current digital code value. This predicted digital code is converted to an analog value and compared with the actual electrogram signal. Next, the ADC adds (or subtracts) a constant value (C) to (or from) the predicted code and compares the result to the electrogram signal.

Abstract: An implantable device, such as a defibrillator which may include cardioversion and pacemaker capabilities, which automatically measures the impedance of the heart prior to the delivery of a cardioverting shock. The defibrillator adjusts the voltage level on output capacitors to deliver a selected energy to the patient's heart. Insulated gate bipolar transistors, or similar devices having an inherent capacitance such that when they are turned on a small voltage gradient will exist across the transistor, are used as switches to control the application of electrical energy to the heart for therapy. When the switches are turned on, a current flows through a connected circuit path, for example through the heart and associated leads. Measurement of the current gives a measure of the impedance of the heart. An initial measurement is performed at the time of implantation of the implantable device, when the initial energy level (and output voltage) is selected.

Abstract: An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart as an indicator of cardiac stroke volume, wherein common interfering signals such as the intracardiac electrogram, myoelectric signals, pacing artifacts and pacing after-potentials are eliminated from the measurement of impedance. The cardiac pacemaker senses varying impedance of the heart by discharging an active capacitor through an electrode implanted within the heart to a second electrode or to the case or can of the pacemaker. The active capacitor is discharged for a selected short period of time after which the voltage remaining on the capacitor is measured. To minimize error in the measurement of voltage discharged from the active capacitor, the selected short period of time for discharge can be varied dynamically by the cardiac pacemaker.

Abstract: An automatic defibrillator is arranged and adapted to be implanted in a cardiac patient. The defibrillator includes a stimulus generator for sensing fibrillation of the patient's heart and for responding by delivering defibrillation energy to the patient's heart via a defibrillation electrode positioned in the right ventricle of the heart. An electrically conductive case houses the stimulus generator, and a conforming biocompatible electrically non-conductive layer is coated over only a predetermined portion less than all of the case to produce a predetermined shape of electric field between the intracardiac defibrillation electrode and the case when the case is used as an electrode for defibrillation. The predetermined portion of the case coated with the non-conductive layer includes a side of the case to be implanted in a direction facing the heart of the patient, with the non-conductive layer being confined solely to the central portion of that side.

Abstract: A method and apparatus is disclosed for use in an implantable device that communicates with an external device through pulse position modulation. A timing generator is provided as part of said implantable device that determines the phase uncertainty between an external signal and an internal cock signal. The phase uncertainty then is added to the preset delay period to more precisely control the position of the response. The phase uncertainty is measured by a dual slope circuit that varies a state variable (which can be a digital timer, a capacitor voltage, or the like) at a fixed rate with either a positive or negative slope. When the external signal is detected, the state variable is reset and then decreased at a fixed rate until the next positive edge of the clock signal. The state variable then is increased at the same rate until the subsequent positive clock edge. The resulting variable value is proportional to the phase uncertainty.

Abstract: An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart as an indicator of cardiac stroke volume or minute volume, wherein common interfering signals such as the intracardiac electrogram, myoelectric signals, pacing artifacts and other pacing after potentials are reduced or eliminated from the measurement of the impedance by the use of a biphasic test signal. The cardiac pacemaker has a signal injector which produces biphasic test pulses of similar duration and magnitude and of constant current, though of opposite polarity. The pacemaker also has a detector which senses voltage resulting from the applied biphasic current pulses in each phase. Since the injector and detector are separate circuits, they can be used with a variety of electrode configurations.

Abstract: A connector terminal in a cardiac stimulator for receiving a connector pin of an associated lead includes a hollow box member having opposite end walls defining a first bore for receipt of the connector pin. A ring member movably disposed within the box member defines a second bore generally aligned with the first bore for also receiving the connector pin. A threaded neck connected to the ring member extends perpendicular to the second bore and is received within a through bore of the box member that is disposed perpendicular to the first bore. An internally threaded cap threadedly engages the threaded neck and bears in a thrust bearing relationship on the box portion. As the cap is rotated, the ring portion is drawn upwardly as the cap presses downwardly on the box portion, causing the second bore to be moved transversely out of alignment with the first bore. A connector pin received through both first and second bores is clamped therebetween and retained against axial withdrawal from the connector terminal.