Abstract: A special type of AV/PV hysteresis is provided in a dual-chamber pacemaker. A long AV delay is initially provided, thereby affording as much opportunity as possible for natural AV conduction to occur. Such long AV delay is automatically shortened should AV block occur. Periodic scanning for the return of AV conduction (absence of AV block) is performed so that the AV delay can be returned to its long value as soon as possible. In one embodiment, the pacemaker "learns" the natural conduction time (AR interval) of the patient and thereafter uses such learned natural conduction time as a reference against which subsequently measured AR intervals are compared to better distinguish conducted ventricular contractions from ectopic, pathologic, or other nonconducted ventricular contractions (e.g., PVC's).

Abstract: Preemptive tachyarrhythmia pacing is provided in an implantable cardiac-stimulation device, such as an implantable pacemaker or defibrillator, by modifying the operation of the implantable device in a way that minimizes the likelihood of occurrence of a tachyarrhythmia. The behavior modification is achieved through the use of an appropriate preemptive tachyarrhythmia pacing control routine stored within the memory of the device. Depending upon the needs of the patient, preemptive tachyarrhythmia pacing is invoked continuously or on demand. If invoked on demand, Preemptive tachyarrhythmia pacing is triggered only upon the sensing of one or more conditions suggest that the onset of a tachyarrhythmia is imminent. When thus invoked, preemptive tachyarrhythmia pacing remains invoked only for as long as the onset-of-a-tachyarrhythmia-is-imminent conditions persist.

Abstract: Methods and apparatus are provided for measuring the impedance of a patient's body. Pulse generating circuitry within a rate-responsive pacemaker is used to generate an impedance measurement signal that is applied to the body of the patient with conventional pacemaker leads. The impedance measurement signal contains a series of multiphasic impedance measurement waveforms, which have no net DC value and zero value after second integration. The impedance measurement signal allows the impedance of the body to be measured without interfering with external cardiac monitoring equipment such as electrocardiogram machines.

Abstract: A system and method for pulse modulating a cardiac pacing signal provides a way to have the pulse modulation characteristics be descriptive of critical information relating to the operational performance of an implanted pacemaker. The patient's ECG/EKG signal is modulated by varying the pulse-intervals of a prescribed plurality of ventricular stimulation pulses in a manner descriptive of important pacer/patient information, such as Pacemaker Battery Status, Pacemaker Sensor Function, Impedance of the Atrial Lead, Impedance of the Ventricular Lead, Existence of Specified Rhythmic Conditions, Indicated Extrsystoles Rates, and other related parameters. The resulting pulse-modulated signal is suitable for transtelephonic transmission to remote locations for subsequent demodulation and analysis. The preferred method comprises the steps of determining or measuring parametric information for selected pacemaker parameters of the implanted pacemaker, varying the pulse characteristics (i.e.

Abstract: A special type of AV/PV hysteresis is provided in a dual-chamber pacemaker. A long AV delay is initially provided, thereby affording as much opportunity as possible for natural AV conduction to occur. Such long AV delay is automatically shortened should AV block occur. Periodic scanning for the return of AV conduction (absence of AV block) is performed so that the AV delay can be returned to its long value as soon as possible. In one embodiment, the pacemaker "learns" the natural conduction time (AR interval) of the patient and thereafter uses such learned natural conduction time as a reference against which subsequently measured AR intervals are compared to better distinguish conducted ventricular contractions from ectopic, pathologic, or other nonconducted ventricular contractions (e.g., PVC's).

Abstract: An implantable device programmer includes a variety of features for allowing a clinician to perform an automated and customized follow-up examination of a patient having an implanted cardiac implantable device, the implantable device being of the type which captures and stores various types of diagnostic data for subsequent retrieval and evaluation. A custom protocol feature of the programmer allows the clinician pre-specify and then semi-automatically follow an ordered sequence of protocol steps, each protocol step involving the interrogation of the implantable device and the display by the programmer of associated implantable device data (such as a heart rate histogram, or the results of a ventricular capture test). When the clinician initiates a custom protocol, the programmer automatically retrieves all of the diagnostic data records of the protocol in the protocol order.

Abstract: A special type of AV/PV hysteresis is provided in a dual-chamber pacemaker. A long AV delay is initially provided, thereby affording as much opportunity as possible for natural AV conduction to occur. Such long AV delay is automatically shortened should AV block occur. Periodic scanning for the return of AV conduction (absence of AV block) is performed so that the AV delay can be returned to its long value as soon as possible. In one embodiment, the pacemaker "learns" the natural conduction time (AR interval) of the patient and thereafter uses such learned natural conduction time as a reference against which subsequently measured AR intervals are compared to better distinguish conducted ventricular contractions from ectopic, pathologic, or other nonconducted ventricular contractions (e.g., PVC's).

Abstract: A dual-chamber implantable pacemaker automatically sets its AV or PV interval to a value that is a function of the measured natural conduction time, or AR interval, of a user of the pacemaker. The AR interval is determined on a regular basis, thereby permitting the AV or PV interval set by the pacemaker to adaptively change with any changes in the AR interval. The AV or PV interval is set to a value that is a prescribed amount .DELTA. less than or greater than the measured AR interval. The measured AR interval is typically averaged, or otherwise determined or estimated, based on measurements of several cardiac cycles.

Abstract: A dual-chamber implantable pacemaker configured to operate in the DDD or DDDR mode automatically sets its AV (or PV) interval to an amount that is equal to the natural conduction time of a patient plus or minus a small prescribed amount, e.g., 1-100 msec. When set to a value that is less than the natural conduction time, preemptive ventricular pacing thus occurs at a time in the patient's cardiac cycle that is near when a natural ventricular contraction (an R-wave) would occur. Such ventricular pacing causes a mechanical contraction sequence of the patient's heart that differs from the natural contraction sequence following a natural depolarization, resulting in improved cardiac output. The pacemaker includes a pulse generator that generates ventricular stimulation pulses (V-pulses) at the conclusion of a pacemaker-defined AV (or PV) interval if no natural ventricular activity (an R-wave) is sensed during such AV (or PV) interval.

Abstract: A DDI pacemaker detects when a pacemaker mediated retrograde rhythm (PMRR) occurs, and automatically alters the DDI operation to terminate the PMRR. The PMRR is detected by measuring the P-to-V time interval in a DDI pacing cycle that terminates in the generation of a ventricular stimulation pulse (V-pulse). A PMRR is presumed to be present whenever the measured P-to-V interval exceeds a prescribed time interval, or whenever a programmed number of consecutive P-to-V time intervals, e.g., ten, are greater than the prescribed time interval. Once a PMRR is detected, the pacemaker automatically extends the post-ventricular atrial refractory period (PVARP) of the pacemaker to block any retrograde P-waves that may be occurring as part of the PMRR. As soon as the extended PVARP terminates, an alert time interval, T.sub.ALERT, begins that is selected to be of sufficient length to allow atrial tissue to repolarize and/or to detect a normal P-wave. If a P-wave is not sensed during the T.sub.

Abstract: A programming system is provided that allows a physician or medical personnel to optimize the settings of various arrhythmia detection criteria and/or parameters related to hemodynamic performance to be programmed into the implanted cardiac stimulating device. The cardiac stimulating device may be a pacemaker or cardioverter/defibrillator that detects heart arrhythmias by using various arrhythmia detection criteria. The cardiac stimulating device is capable of recording the patient's cardiac signals and/or sensor data. The programming system may play back the recorded signals to test the detection criteria and hemodynamic performance and may simulate the response of the device to the cardiac signal. Alternatively, the programming system may play back an artificially created or previously stored cardiac signal for test purposes. As a result, the recorded signal may be played back repeatedly without unnecessarily stressing the patient's heart.

Abstract: Capture is assessed in an implantable pacemaker by issuing a pair of stimulation pulses, separated by about 60-100 milliseconds. The second pulse of the stimulation pair is set to an energy level that assures capture, and remains at that level. The first pulse of the stimulation pair is initially set to an energy level that assures capture, and its energy level is thereafter systematically decreased, e.g., its amplitude is decreased, by a set amount each time the pair of stimulation pulses is issued. One of the stimulation pulses of the stimulation pair will always cause capture: the first pulse when its energy level is greater than the capture threshold (in which case the second pulse is issued into refractory cardiac tissue and has no effect); or the second pulse, when the energy of the first pulse drops below the capture threshold. In either event, a T-wave follows the capturing pulse, whether the first or the second, evidencing repolarization of the cardiac tissue.

Abstract: A cardiac arrhythmia is terminated by stimulating the heart during the narrow "region of susceptibility" or termination window of the arrhythmia cycle based upon a statistically significant starting value. The present invention will store a plurality of successful critically timed intervals and compute a central value (e.g., average, mean, median, etc.) and a measure of variability (sample range, standard deviation, etc.). The measure of variability is used to determine the termination window size. In one embodiment, the present invention then "scans" symmetrically-centrifugally about the statistically significant starting value. In an alternate embodiment, the present invention employs ranked scanning, that is, scanning according to the frequency of occurrence of previously successful starting values. The number and size of steps could be either programmable, or automatically computed by the pulse generator based upon the termination window size.

Abstract: A programming system is provided that allows a physician or medical personnel to optimize the settings of various arrhythmia detection criteria and/or parameters related to hemodynamic performance to be programmed into the implanted cardiac stimulating device. The cardiac stimulating device may be a pacemaker or cardioverter/defibrillator that detects heart arrhythmias by using various arrhythmia detection criteria. The cardiac stimulating device is capable of recording the patient's cardiac signals and/or sensor data. The programming system may play back the recorded signals to test the detection criteria and hemodynamic performance and may simulate the response of the device to the cardiac signal. Alternatively, the programming system may play back an artificially created or previously stored cardiac signal for test purposes. As a result, the recorded signal may be played back repeatedly without unnecessarily stressing the patient's heart.

Abstract: A dual-chamber pacemaker provides DDI pacing with PVC-protected hysteresis and automatic AV interval adjustment. An extended hysteresis atrial escape interval (AEI.sub.H) is invoked in response to the occurrence of either an atrial paced event followed by a sensed R-wave (an AR event), or an atrial sensed event followed by a sensed R-wave (a PR event). The occurrence of a premature ventricular contraction (PVC) thus does not trigger AEI.sub.H. In one embodiment, AEI.sub.H is not invoked unless the sensed AR or PR interval exceeds a prescribed reference interval. In a further embodiment, the AV interval (AVI) associated with the DDI operation is automatically shortened following an atrial stimulation pulse (A-pulse) delivered upon the timing-out of the AEI.sub.H. The shortened AVI is maintained for a programmed number of cycles of DDI operation, after which a lengthened AVI is reestablished for one cycle.

Abstract: A dual-chamber implantable pacemaker configured to operate in the DDD or DDDR mode automatically adjusts its AV (or PV) interval to an amount just less than the natural conduction time of a patient, thereby assuring that ventricular pacing occurs in a patient's cardiac cycle at a time near when a natural ventricular contraction (an R-wave) would occur. The pacemaker includes a pulse generator that generates ventricular stimulation pulses (V-pulses) at the conclusion of a pacemaker-defined AV (or PV) interval if no natural ventricular activity (an R-wave) is sensed during such AV (or PV) interval. The AV (or PV) intervals are automatically adjusted by the pacemaker to be just less than the natural conduction time sensed by the pacemaker, where the natural conduction time is the time between atrial activity (a sensed P-wave or a delivered A-pulse) and the subsequent natural ventricular activity (R-wave).

Abstract: A dual-chamber implantable pacemaker automatically adjusts its AV interval so that any ventricular stimulation pulses generated by the pacemaker at the conclusion of the pacemaker-defined AV interval occur at a time in the cardiac cycle that avoids fusion with the natural ventricular depolarization of a patient's heart. The AV interval is set using a search sequence that sets the AV interval value to be on one side or the other of the natural conduction time of the heart, and incrementally changes the AV interval value until it crosses over the natural conduction time interval. The cross-over point is manifest by the occurrence of an R-wave, where an R-wave had previously been absent, or the absence of an R-wave, where an R-wave had previously been present. A final AV interval value is then set as the AV interval value at the cross-over point, adjusted by appending an AV margin thereto.

Abstract: A cardiac pacing system includes circuitry for verification of capture having an indifferent electrode mounted on the pacemaker connector top. The cardiac pacing system may use one or two bipolar or unipolar leads. Capture is sensed between the indifferent electrode and one of the electrodes on the lead or leads. Either electrode on the lead or leads can be used as the other electrode forming a sensing pair with the indifferent electrode. The electrode is located in the plastic connector top portion of the implanted pacemaker, and may be disposed at a side of the pacemaker, when implanted, facing the interior of the patient, or facing the exterior of the patient.

Abstract: An implantable arrhythmia treatment system includes a sensor which generates an electrical signal corresponding to a physiological characteristic of a patient, the physiological characteristics and thus the electrical signal exhibit a change given the onset of an arrhythmia. The electrical signal is supplied to a fibrillation detector in an implantable housing, which initiates an appropriate treatment sequence upon the detection of the onset of the arrhythmia. Simultaneously with initiating the treatment sequence, the fibrillation detector causes, either by direct connection or by telemetry communication, the generation of an alarm signal which informs the patient that the sequence has been initiated, so that the patient knows that a treatment pulse is about to be released. The implantable unit includes circuitry responsive to a signal externally generated by the patient which prevents the release of the defibrillating pulse. If the patient feels no need for such a pulse, i.e.

Abstract: A pacemaker mediated tachycardia (PMT) is detected by circuitry within an implantable pacemaker. The PMT is detected by first detecting a tachycardia condition that includes a prescribed number of consecutive cardiac cycles having a rate faster than a prescribed rate. Each cardiac cycle of the tachycardia condition includes a natural atrial event, i.e., a P-wave, and a paced ventricular event, i.e., a V-pulse generated by a pacemaker. After the prescribed number of such cardiac cycles, e.g., two to ten, a P-V delay in a single cardiac cycle is modified by a first prescribed amount, e.g., 50 milliseconds. The time interval of a V-P interval associated with at least one cardiac cycle preceding the modified P-V delay is then compared to a V-P interval immediately following the modified P-V delay. Only if the difference between the V-P intervals thus measured is less than a second prescribed amount, e.g., 25 milliseconds, is a PMT indicated. If a PMT is indicated, a PMT termination regimen, e.g.