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: 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.

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: 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: An implantable medical device for electrically stimulating the heart to beat including a pulse generator, a logic and control unit, and an atrial sense circuit. The atrial sense circuit processes signals from electrodes implanted in an atrial chamber of the heart. The atrial sense circuit provides an atrial sense signal to the logic and control unit when the magnitude of electrical activity in the atria exceeds a threshold. The medical device preferably paces the ventricles in response to detected electrical activity in the atria indicative of atrial contraction. Immediately following ventricular pacing, the medical device initiates an absolute atrial blanking period followed by an atrial sensing period and a programmable blanking period. During both the absolute atrial blanking period and the programmable blanking period, atrial sensing is disabled, while during the atrial sense period, atrial sensing is enabled.

Abstract: A cardiac stimulator lead and sleeve for anchoring the lead at its point of entry into a vein. More particularly, the present invention comprises a helical coil made of a resilient material that is capable of being uncoiled and wrapped around the lead and/or the vein such that it is biased to resume its fully coiled state and thereby frictionally engages the vein and or lead and functions as an anchoring device for the lead.

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: An implantable cardioverter/defibrillator device is implemented to be selectively non-invasively upgraded from time to time after implantation to enable the device to provide additional therapy for arrhythmia treatment as the patient's need for such treatment undergoes change. The device is adapted to provide a plurality of functions corresponding to different levels of therapy for treating arrhythmias, and to respond to each different type of arrhythmia that may be sensed, to supply a function which is designated as being appropriate to relieve that respective arrhythmia. Each function is not necessarily unique to treating a particular arrhythmia, and, in at least some instances, may be used to treat more than one of the plurality of different types of arrhythmias. At the time of its implant, the device is restricted from providing those of the plurality of functions which are deemed as being non-essential to the patient's needs at that time.

Abstract: An implantable medical device includes a giant magnetoresistance ratio (GMR) sensor is used to detect the presence of a magnet in order to command the device to enter a predetermined mode of operation. The GMR responds to a modulated magnetic field generated by the programming of a command transmitter apparatus for non-invasive programming or controlling of the implanted device. The implantable medical device also monitors for the presence of a steady magnetic field to place the implanted device in a known, safe mode.

Abstract: A method and apparatus for measuring impedance of heart tissue or the leads associated with a cardiac stimulation apparatus involves charging a capacitor, storing the value of the voltage across the capacitor when charged, discharging the capacitor into said lead/heart system and storing the voltage on said capacitor when discharged. The two voltages may then be used to determine the combined impedance of the lead and the heart tissue. This may be advantageously accomplished by using separate circuits to measure each of the voltages of the capacitor and storing those voltages. These voltages then may be applied to an analog-to-digital converter which converts the ratio of said voltages to digital form. This value can then be used to calculate the combined impedance of the heart tissue or the lead. If one of the two impedances is known the other can then be easily determined.

Abstract: A method and apparatus for determining the origin of a cardiac signal in the heart of a patient. A cardiac stimulator includes a multiple-chamber electrode arrangement having at least two electrodes positioned to sense and/or pace different chambers of the heart. The electrodes switch from a bipolar configuration to a unipolar configuration in order to verify the point of origin for the cardiac signal and in order to determine whether propagation of the cardiac signal occurs. The apparatus allows simultaneous and timed pacing of left and right chambers.

Abstract: An implantable cardiac stimulator for detecting capture or adjusting the strength or duration of pacing pulses by using an evoked response detector and periodically tuning the evoked response detector. When the electric evoked response detector is to be tuned, capture is verified by detecting the mechanical evoked response. As the magnitude of the stimulating pulse is adjusted to isolate the threshold as detected by the mechanical response detector. At the same time, the electrical evoked response is also monitored. The difference between the detected electrical signal following capture as detected by the mechanical response detector and the signal following non-capture is used to tune the electrical evoked response detection apparatus and algorithm. The energy of the pacing pulse can then be optimized by adjusting both strength and duration.

Abstract: A method and apparatus for detecting loss of cardiac pacing pulse amplitude includes a comparator for comparing the actual pulse voltage to a reference voltage. In one advantageous embodiment, the reference voltage is determined as a percentage of the programmed pulse amplitude. The comparison of the reference voltage and the actual voltage is latched at the time when a pulse is actually created to produce a signal indicative of whether the amplitude of the actual pulse exceeds the reference. When the amplitude falls below the reference, the system may take corrective action.

Abstract: A data communication system for control of transcutaneous energy transmission to an implantable medical device is disclosed having an implantable medical device with rechargeable batteries and a single coil that is employed both for energy transmission and data telemetry. Control circuitry in the implantable device senses battery voltage and current through the battery, encodes those values by use of a multiplexer, and transmits the sensed and encoded values through the coil to an external energy transmission device. The external device includes a coil that is electromagnetically coupled to the coil in the implantable device for receiving the encoded signals and for transmitting energy to the implantable device. The external device decodes the transmitted values and transmits those to a controller for controlling energy transmission.

Abstract: A method and apparatus for monitoring balanced biphasic current pulses used for measuring impedance in cardiac stimulators involves detecting imbalances between the pulses of opposite polarity. Such imbalances are potentially harmful to cardiac stimulator users. By converting the two different pulse phases into potentials, a determination can be made as to whether adequately balanced pulses are being generated. If an imbalance is detected, corrective action can be taken quickly enough to avoid harmful effects to the stimulator user.

Abstract: A method and apparatus for analyzing cardiac information involves recording both atrial and ventricular information related to a recognized event. This information can then be transmitted by telemetry to the physician and graphed on a common graph which plots both atrial and ventricular information over the time period of the event. This technique allows greater ability to discern the true nature of these events, including whether a given event is a sinus tachycardia due to exercise or a ventricular tachycardia which might necessitate treatment. Therefore, the present invention enables more accurate analysis of cardiac information and thereby makes possible the more appropriate application of treatment.