Abstract: A lead assembly for fixation to a human heart via thoracoscopy is provided. The lead assembly includes a lead that has a connector for connection to a cardiac stimulator, such as a pacemaker, a cardioverter/defibrillator, or a sensing instrument. A fixation mechanism is coupled to the lead that includes a tubular housing and a proximally projecting hook that is adapted to engage heart tissue. The hook is pivotable between a retracted position and an extended position. The lead and the hook are manipulated by a stylet. The lead assembly also includes a tubular introducer that is passed through the chest wall of a patient and used to place the lead proximate the epicardium.

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, 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: 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 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: 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: 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 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 capture detection circuit for an implantable cardiac stimulator. A signal detected by an electrode in the heart following delivery of a stimulating pulse is amplified, bandpass and highpass filtered, rectified, integrated over a selected window of time starting at a selected delay after delivery of the stimulating pulse, and applied to two comparators having different reference values. If the integrated signal exceeds the first reference value, the first comparator output goes high. If the integrated signal exceeds the second reference value, the second comparator goes high. If both comparators remain low, non-capture is indicated. If the first comparator goes high and the second comparator remains low, capture is indicated. If the second comparator goes high, an intrinsic contraction is indicated. The window of integration can be extended to distinguish capture from intrinsic contraction.

Abstract: A method of verifying cardiac capture. A cardiac signal evoked in response to a cardiac stimulation pulse is sensed via an electrode. The sensed signal is lowpass filtered to remove noise and to pass frequencies characteristic of the evoked cardiac signal. The filtered signal is processed to render a waveform signal representing the second derivative of said filtered signal and the second derivative signal is further analyzed to detect a minimum and a maximum amplitude excursion during a selected window of time beginning at a selected time delay following delivery of the cardiac stimulation pulse. The amplitude difference between the minimum and the maximum is measured and compared to a first reference value. The amplitude of the second derivative is measured during a second selected window of time beginning at a selected time delay following delivery of said cardiac stimulation pulse, and compared to a second reference value.

Abstract: A cardiac pacemaker which automatically tests for changes in and adjusts output or other parameters in response to detected changes in environmental or physiologic conditions. One or more passive sensors detect environmental or physiologic conditions which may correlate to stimulation thresholds or other parameters. If a change in such conditions is detected, a test or search is initiated to achieve an energy efficient output, to optimize cardiac output, to improve sensing, etc.

Abstract: An apparatus for detecting an electrical potential in a human body to control the delivery of a therapy. The electrical potential comprises a principal signal and a baseline signal. The apparatus samples the potential through an electrode during a selected interval and stores the value of that potential at the end of the interval. The stored value of the potential will be restored as an initial condition on the electrode at the end of a second interval after delivery of the therapy. In a heart pacemaker, the baseline signal is useful for controlling the output pulses of the pacemaker. The apparatus permits sensing of the baseline signal despite stimulating pulses and charge canceling.

Abstract: A bipolar sensing lead for use with an implantable device, particularly a cardiac pacemaker, comprising a first sensing electrode located adjacent an outer surface of the lead and a second sensing electrode spaced away from that surface in at least two non-linear directions. In a preferred embodiment, the first sensing electrode is a ring electrode at the outer surface of the lead. The second sensing electrode comprises a conductive ring around the circumference of a collapsible, flexible disk.

Abstract: A lead system for a cardiac pacemaker comprising a lead having a proximal end and a distal end, the distal end having an electrode. A lumen passes through the lead from the proximal end to the distal end. A sensor-carrying flexible stylet is adapted to be inserted into the lumen of the lead. At the proximal end of the flexible stylet, there is an attachment means comprising a distal female connector and a proximal male connector adapted to connect to a pacemaker. The lead can also be provided with a distal aperture, which permits transport into the lead to the sensor of blood, gasses, heat, light, chemical or other phenomenon which are to be sensed.

Abstract: A system is provided for cardiac pacing, in which the output levels of the electrical stimulus pulses are responsive to the detection or non-detection of cardiac pacer evoked potentials. A pulse generator is provided for emitting electrical stimulus pulses at variable output levels. A pulse to pulse interval and an evoked response sensing period are provided. At the beginning of the pulse to pulse interval, an electrical stimulus having a first output level is emitted. If no evoked response is sensed during the sensing period, then an electrical stimulus at a selected maximum output level is emitted and, thereafter, the next electrical stimulus pulse is emitted at a second output level that is greater than the first output level.

Abstract: Automatic detection of cardiac pacer evoked potentials may be obtained through a cardiac pacer lead positioned in a heart chamber. An electrical stimulus is emitted in unipolar mode from a first electrode to stimulate muscular contraction. The cardiac electrical activity evoked by the stimulus is then detected in unipolar mode by a second electrode which is spaced from the first electrode and free of electrical connection thereto. Accordingly, signal interference caused by residual polarization of the first electrode is suppressed. The natural cardiac electrical activity is sensed in a bipolar mode, and the pulse is inhibited if a heartbeat is detected within an alert period.

Abstract: A method for cardiac pacing and sensing is disclosed. A cardiac pacing lead is inserted into a heart chamber. The lead carries a plurality of separate electrodes positioned at the distal tip of the lead and transversely spaced from and electrically isolated from each other. A separate electrical conductor is provided for each electrode. A plurality of the electrodes are combined via electrical conductors to provide a relatively large electrode area for sensing cardiac activity. One of the electrodes is used for providing pacing pulses to the heart chamber. The pacing electrode has a relatively smaller surface area than the relatively large surface area used for sensing.

Abstract: The apparatus for pacing a heart in accordance with the heart rate needed to produce a required cardiac output while the person is exercising, comprises a pacer adapted to be implanted in a human body and having a pulse generator and control circuitry (e.g. a microprocessor) therein, a pacing lead adapted to be implanted in a heart and having a distal electrode adapted to engage and supply pacing pulses to a right ventricle of a heart, and a pO.sub.2 sensor for sensing pO.sub.2 of the blood in the heart. An algorithm or routine utilizing same are stored in the control circuitry (microprocessor) and are adapted to relate pO.sub.2 and/or .DELTA.pO.sub.2 with the required heart rate or change in heart rate, .DELTA.R, needed to supply a desired cardiac output and to cause the pacer to pace the heart at the required heart rate when the heart is not naturally paced.