Abstract: An implantable defibrillator, which may include cardioversion and pacemaker capabilities, which has EMI filters which are not susceptible to defibrillation shocks and which reduce or eliminate the effects of charging noise on sensing circuits used for continuous confirmation. A first filter capacitor is provided between a sense electrode, which may include pacing capabilities, and a ground reference within a hermetically sealed can containing a pulse/shock generator. A second filter capacitor is provided between a sensing/pacing reference electrode, which may also be a high voltage or shock electrode, and the ground reference. In addition, there is a third filter capacitor between the ground reference and the can. Preferably, the connections of the first, second and third filter capacitors are physically as well as electrically adjacent to each other. The filter capacitors are housed in the can and in or adjacent to a feedthrough assembly which passes through the can.

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: An implantable medical device for electrically stimulating the heart to beat includes a sense circuit for detecting cardiac electrical activity. The sense circuit includes an amplifier with a dynamically adjustable gain to provide increased sensitivity to the electrogram during atrial fibrillation. Alternatively, sensitivity control is provided by dynamically adjusting threshold limits associated with a threshold detector included in the sense circuit. The sensitivity level of the medical device to the electrogram can be repeatedly adjusted after implantation and preferably is increased upon detection of the loss of normal sinus rhythm (NSR) in the heart's atria. The medical device is calibrated with the aid of a calibration device external to the body to determine appropriate sensitivity levels. A method for calibrating and operating an implanted medical device with dynamically adjustable sensitivity is also disclosed for improving the medical device's sensitivity to atrial fibrillation.

Abstract: Various endocardial lead assemblies are disclosed that may be particularly useful for placement within the coronary sinus. One lead assembly includes an open-ended electrode that may be implanted in a patient by passing it along a previously implanted stylet. Another disclosed embodiment combines an open-ended electrode with one or more flow passages that improve blood flow through the body vessel in the area of the implanted electrode. Yet another disclosed embodiment uses an electrode that has flow passages but no opening. This electrode provides improved blood flow in the area of the electrode but may be implanted using conventional methods.

Abstract: A programmable pacemaker and program therefor are disclosed, wherein the pacer is programmed to operate in a first pacing mode whenever the measured atrial rate is less than a certain threshold switching rate R.sub.T, and to operate in a second pacing mode whenever the measured atrial rate is greater than the threshold switching rate R.sub.T. The threshold switching rate R.sub.T is varied based on either a programmed algorithm or the measured value of one or more sensed parameters. In another embodiment, a hysteresis is introduced, so that the rate at which the pacer switches back to its low-activity mode is lower than the rate that triggers a switch to the high-activity mode.

Abstract: An implantable medical device, such as a pacemaker, for electrically stimulating the heart to beat includes two or more node logic units connected by communication paths over which signals between nodes are conducted. Each node can provide pacing energy to an electrode and amplify electrical signals from the electrode. In response to detecting an electrical event from the electrode or pacing an electrode, each node generates a sense signal or a pace signal. The sense and pace signals form each node can be transmitted to all other nodes with or without a time delay. The time delays between nodes are provided by delay modules controlled by a processor. As such, the implantable medical device can be configured to provide a variety of pacemaker therapies.

Abstract: An implantable cardiac stimulator delivers a first electrical shock via implantable stimulating electrodes at a time when there is substantially no flow of blood. At least one of the stimulating electrodes is disposed in a blood flow path of the cardiovascular system. The first shock is of insufficient energy level to cause defibrillation. An electrical potential is measured as a function of time between the blood-contacting electrode and a reference electrode following delivery of the first shock to obtain a first potential equilibration function under no-flow conditions. A second therapeutic electrical shock, of sufficient energy level to effect defibrillation, is delivered via the stimulating electrodes. A second potential equilibration function is measured following delivery of the second shock. The first and second potential equilibration functions are compared, and if the two functions are sufficiently different in morphology, it is determined that blood is flowing.

Abstract: An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart, wherein the cardiac pacing rate and maximum cardiac pacing rate, or either of them, are adjusted as a function of an interval between either the administration of a pacing pulse or the detection of the R-wave and the occurrence of a maximum detected impedance, called the intercept interval. Because an intercept point in derivative of the impedance curve is detected, the apparatus and method are insensitive to electrode characteristics, electrode movement, body posture or other factors which could affect the magnitude of the detected impedance. The information contained in the intercept interval can also be combined with other sensed or calculated information to set the desired rates.

Abstract: An implantable system is provided for subcutaneous surgical implantation. The implantable system includes a smoothly contoured casing and an implantable apparatus designed to perform a desired medical function, such as cardiac stimulation, diagnosis, or drug infusion. The casing includes a chamber for enclosing the implantable apparatus. The casing is provided with one end that is separated from a second, and opposing, end by a slit. The shape of the casing and the separated ends enables implantation via a shorter incision than is possible using a comparably sized conventional implantable device. Some examples of possible implantable apparatus include cardiac stimulators and sensors, or drug infusion pumps.

Abstract: An implantable cardiac stimulator, which may include cardioversion and pacemaker capabilities, which has apparatus for detecting an externally applied shock, such as a defibrillation or cardioverting shock. In response to detection of such a shock, the cardiac stimulator has apparatus to adjust the parameters of applied therapy, or to select alternative therapy, including, but not limited to, adjusting the magnitude of stimulus pulses for a predetermined length of time. The risk of loss of capture, and consequent failure of cardiac function, following an externally applied shock is thereby reduced.

Abstract: An implantable medical device for electrically stimulating the heart to beat including a sense circuit for detecting cardiac electrical activity. The sense circuit includes a sense amplifier, band pass filter, and threshold detector. The threshold detector determines whether sensed cardiac electrical activity resulted from a normal heart beat or an ectopic beat such as a premature ventricular contraction. In a preferred embodiment, latches in the threshold detector are activated by output pulses from a pair of comparators. A positive comparator produces an output pulse upon detection of cardiac electrical activity exceeding a positive threshold voltage and a negative comparator produces an output pulse upon detection of cardiac electrical activity more negative than a negative threshold. Threshold logic produces output signals indicative of which comparator first produced an output pulse.

Abstract: A lead assembly includes a proximal end that has a connector for electrical connection to a cardiac stimulator, such as a pacemaker, a cardioverter/defibrillator, or a sensing instrument. The lead assembly includes an elongated proximal tubular portion that extends distally from the connector. The distal end of the proximal tubular portion is provided with a branch assembly that is joined distally to two elongated distal lead branches. The distal branches are provided, respectively, with lead tips that each function as electrodes for transferring electrical signals from and/or to the myocardium. The branch assembly includes structure for enabling a surgeon to selectively manipulate the distal branches using a single stylet passed through a single lumen in the proximal tubular portion.

Abstract: A pacemaker is disclosed that includes circuitry for monitoring the current and/or voltage delivered to the heart during a pacing pulse. A microprocessor connects to the monitoring circuitry and analyzes the current (and/or voltage) to determine when capture occurs. When capture occurs, the microprocessor terminates the pacing pulse to save energy. Conversely, if capture does not occur within a predetermined maximum time period, or if the pacing pulse amplitude falls below a predetermined threshold value, the processor immediately causes a safety pulse to fire to insure a regular beating of the heart. By monitoring the current and/or voltage delivered, and by permitting the pacing pulse width to be variable, the pacemaker of the present invention can closely track the pacing threshold of the patient with a minimum expenditure of energy.

Abstract: A lead assembly adapted for transvenous implantation into a human heart is provided. The lead assembly includes a connector for electrical connection to a cardiac stimulator. An elongated sheath assembly projects from the connector. The sheath assembly includes an inner elastic insulating sheath that includes a coextensive lumen for receipt of a stylet. An outer elastic insulating sheath is disposed around the inner sheath, thereby defining an elongated annular space. The outer sheath has an aperture that defines a gripping region. A biasing wire is disposed in the annular space. The biasing wire is connected to the connector proximally and is approximately coterminous at its distal end with the outer sheath. The biasing wire has a plurality of coils exposed by the aperture in the gripping region. By first stretching and then relaxing the lead assembly, the coils of the biasing wire pinch small portions of the myocardium to laterally fix the lead assembly at a given location in the heart.

Abstract: An implantable cardiac stimulation catheter includes a helical electrode segment disposed about a central core of electrically non-conductive material for delivering an electrical pulse to the heart of the patient. The catheter may include a tubular electrode segment disposed on the catheter and electrically connected with the helical electrode. The helical and tubular electrode segments may be defibrillation electrode segments. The catheter may also include a demand pacer electrode for delivering a demand pacing pulse to the heart and/or a fixation mechanism for securing the catheter within the patient's heart.

Abstract: An energy transmission system for transmitting energy non-invasively from an external unit to an implanted medical device to recharge a battery in the medical device. An alternating magnetic field is generated by the external charging unit and a piezoelectric device in the implanted medical device vibrates in response to the magnetic flux to generate a voltage. The voltage is rectified and regulated to provide charging current to a rechargeable battery in the medical device. A series of piezoelectric devices may be connected in series to produce a larger voltage than can be produced by any one piezoelectric device. Acoustic waves generated by the external charging unit alternatively can be used to vibrate the piezoelectric device instead of a changing magnetic flux. The acoustic waves are generated by an external source coupled to a piezoelectric transducer.

Abstract: A method and apparatus for evaluating heart rate variability of the heart of a person in order to forecast a cardiac event. A cardiac stimulator receives heart beat signals from the heart and determines a measurement of heart rate variability based on statistical data derived from the heart beat signals and sensing data derived from a sensor. This measurement of heart rate variability is compared with previously stored heart rate variability zones defining normal and abnormal heart rate variability. These zones are modifiable after the occurrence of a cardiac event. Once a cardiac event is detected, a pathway is computed which extends from a generally normal heart rate variability condition to an abnormal heart rate variability condition. Subsequent measurements of heart rate variability are compared with this pathway. Selective therapy regimes are initiated depending on the measurement of heart rate variability.

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: 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: 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.