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 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 cardiac simulation system including a patient warning apparatus. The cardiac stimulator is an implantable pacemaker or defibrillator or combination which can be programmed to automatically alter the voltage of its output stimulus, in particular, to increase the voltage of the output stimulus whenever a condition exists requiring patient notification or warning. A specialized auxiliary lead with a shunt circuit can be connected to a standard socket of a cardiac stimulator header and a standard lead, such as a cardiac pacemaker lead, can then be connected to the auxiliary lead. The auxiliary lead allows a stimulation electrode to be implanted near excitable tissue in a secure fashion to assure stimulation of tissue. The auxiliary lead includes an apparatus for shunting electrical current from the standard stimulation electrode implanted in or near the patient's heart to the auxiliary electrode in the presence of a stimulation pulse with a voltage at or above a preselected level.

Abstract: Disclosed are apparatus and method for detecting electromagnetic interference (EMI), or noise, that may disrupt the proper operation of medical devices implantable in patients, such as cardiac stimulators. Circuitry of the detector of the invention is independent of other circuitry of the medical device. EMI is magnetically induced on an antenna that may be within the metal housing of the device in a receiver circuit, and the EMI signals are output to the noise detector. A variety of alert signals may be provided to the medical device circuitry to warn of the presence of EMI so that appropriate responses may be taken to insure the safety of the patient dependent on the device. The detector may share the telemetry antenna of the medical device, or utilize a separate, dedicated antenna to receive EMI. Alternative antennas external to the metal housing of the medical device include leads from the device to the heart of the patient, and a dedicated antenna in the non-metal header of the device.

Abstract: An implantable cardiac stimulation system having a patient warning system and an elongated electrode mounted near the can of the system for providing reliable stimulation for warning. The electrode has an extended length and a short width. The length is preferably at least double the width and more preferably at least four times the width. This extended length increases the probability that contact with the surrounding tissue will be achieved. The short width and rounded profile of the width, forming an "edge", on the other hand, increases the probability that a high enough current density will be achieved, causing stimulation to occur. The electrode may also be curved along its length, which tends to promote a "point" or small area contact between the electrode and the patient's tissue. The electrode may be mounted directly on the can or header of the cardiac stimulator or may be part of a separate pin electrode.

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. The pin electrode includes a hood which fits around a selected part of a header.

Abstract: A cardiac simulation system including a patient warning apparatus. The cardiac stimulator is an implantable pacemaker or defibrillator or combination which can be programmed to automatically alter the voltage of its output stimulus, in particular, to increase the voltage of the output stimulus whenever a condition exists requiring patient notification or warning. A specialized auxiliary lead with a shunt circuit can be connected to a standard socket of a cardiac stimulator header and a standard lead, such as a cardiac pacemaker lead, can then be connected to the auxiliary lead. The auxiliary lead allows a stimulation electrode to be implanted near excitable tissue in a secure fashion to assure stimulation of tissue. The auxiliary lead includes an apparatus for shunting electrical current from the standard stimulation electrode implanted in or near the patient's heart to the auxiliary electrode in the presence of a stimulation pulse with a voltage at or above a preselected level.

Abstract: A cardiac simulator including a patient warning apparatus, having a sensor for detecting patient reaction to a warning stimulus and means for adjusting the magnitude of said warning stimulus to obtain a preselected level of reaction. The cardiac stimulator is an implantable pacemaker or defibrillator or combination which can be programmed to produce a warning stimulus whenever a condition exists requiring patient notification or warning. A warning pulse stimulus generator directs electrical current to a warning electrode. Alternatively, a controlled switch may re-direct a stimulation pulse to the warning electrode. The sensor for detecting the reaction of the patient to the applied warning stimulus may be an accelerometer or motion/vibration transducer or other sensor capable of detecting a reaction to a warning stimulus. Means for adjusting the level of the stimulus directed to the patient's skeletal muscle regulate the stimulus until a pre-selected magnitude of reaction has been achieved.

Abstract: A cardiac simulator including a patient warning apparatus, having an electrically conductive suture point in electrical communication with the patient warning apparatus. An electrically conductive suture passed through the suture point connects said stimulator mechanically and electrically to excitable tissue such as skeletal tissue. Inside the suture point is a connection for assuring a reliable electrical contact between the suture point and the suture. The cardiac stimulator automatically alters the peak voltage of its output stimulus whenever a condition exists requiring patient notification or warning. A specialized shunt circuit mounted within the stimulator or in the header of the stimulator re-directs electrical current from the standard stimulation electrode to the electrically conductive suture point. A controlled switch may be mounted within a hermetically sealed can of the stimulator to re-direct a stimulation pulse to the suture point. The controlled switch could also be mounted in the header.

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 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.