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: In a pacing system, the pacing controller induces the leads to deliver an impedance measurement pulse to the right ventricle of the heart at at least a 15 ms interval during a window of time following detection of the R-wave or the delivery of a pacing pulse. The window of time corresponds to a period of ventricular ejection. The two or three measured impedance values are then used to determine an impedance slope that has a strong biological correlation to the contractility of the heart. The impedance slope is then used by the controller of the pacing system to adjust the delivery of pacing pulses for purposes such as maximizing contractility for a given AV delay, PV delay and pacing rate of pacing pulses.

Abstract: An implantable pacemaker accurately senses the regular atrial rhythm even though some portions of the atrial rhythm, e.g., every other P-wave, may potentially be masked or hidden within the ventricular absolute refractory period. Such sensing includes unmasking or uncovering any hidden P-waves, thereby allowing an accurate atrial rate to be determined. The hidden P-waves are uncovered by: changing the PV delay, not tracking a sensed P-wave, or comparing the incoming morphology of the atrial channel signal to a prior stored baseline morphology signal. The accurate atrial rate, once determined, allows the presence of an atrial tachycardia to be reliably confirmed, thereby enabling appropriate atrial anti-tachycardia pacing (ATP) procedures to be invoked, or mode switching from an atrial synchronous mode of operation, e.g., DDD, to a non-atrial synchronous mode, e.g., VVIR.

Abstract: A single-pass atrio-ventricular (A-V) pacing lead includes an elongated main lead body having an atrial electrode at the distal end thereof, and includes a ventricular branch which departs from the main lead body just proximal to the tip of the atrial electrode. The ventricular branch has a ventricular electrode at its distal tip. The main lead body includes a preformed "J"-shaped portion which, following proper implantation, projects the atrial electrode against a wall of the atrial appendage. The ventricular branch includes a preformed bend which curves in the opposite direction of the J-shaped portion so as to maintain the ventricular branch generally away from the wall of the atrial appendage. The lead includes a single lumen which extends through both the main lead body and the ventricular branch, allowing the lead to be implanted using a single stylet.

Abstract: An implantable dual-chamber pacemaker programmed to operate primarily in an atrial tracking mode is provided, where the pacemaker maintains a consistent atrial rate of entry into, and exit from, a 2:1 block response mode by setting rate-responsive AV delay values in accordance with a continually monitored intrinsic atrial rate incorporating atrial events occurring during atrial refractory periods. The atrial rate of entry into, and exit from the 2:1 block response mode is determined by the length of a total atrial refractory period, which is the sum of the rate-responsive AV delay and a programmable refractory period.

Abstract: An implantable dual-chamber pacemaker programmed to operate primarily in an atrial tracking mode is provided, where the pacemaker includes an atrial rate smoothing filter for producing a filtered atrial rate from an intrinsic atrial rate, and where the pacemaker automatically switches its mode of operation from the atrial tracking mode to a non-atrial tracking mode in the event the filtered atrial rate exceeds a prescribed upper rate limit. The pacemaker switches from a primary set of operational parameter settings for the primary mode, to an alternate set of operational parameters for the alternate mode when the mode is switched from the primary mode to the alternate mode. The pacemaker also includes the capability of recording and storing mode switching events and data pertaining to the mode switching events.

Abstract: A rate-responsive pacemaker measures a patient's level of activity and stores the results in an activity level histogram. The patient's average level of activity is maintained as a running average. Based on a prescribed base pacing rate, a prescribed maximum pacing rate, the average level of activity, and the measured levels of activity stored in the activity level histogram, the rate-responsive pacemaker automatically calculates the slope of the pacemaker transfer function. An activity deviation histogram is also maintained. Analysis of the activity deviation histogram allows the pacemaker to determine if the patient was usually inactive for an extended period of time, and to inhibit an automatic slope calculation under such conditions. If a patient desires to reach a prescribed target heart rate during exercise, the slope may be calculated using the target heart rate and a prescribed fraction of time each week that the patient devotes to exercise.

Abstract: A system and method are provided for modulating the base rate of a transfer function for a rate-responsive cardiac pacemaker. Activity sensor measurements are used to derive activity variance measurements, which in turn are used to modulate the base pacing rate. In one embodiment, a histogram is used to store activity variance measurements collected over a period of about a week. The histogram is used to derive an activity variance threshold, which is compared to current activity variance measurements to determine if the patient is sleeping. If the patient is deemed to be sleeping, the pacing rate is set to a rate that comfortably meets the patient's low metabolic demands during sleep. In alternative embodiments, the activity variance measurements are applied to a base rate slope to modulate the base pacing rate.

Abstract: In a first embodiment, hysteresis is provided in a rate-responsive pacemaker to allow for natural AV synchrony when possible. In the absence of natural SA node signals, the heart is stimulated at a rate determined by the sensing of physiological need. When a natural heart signal is detected, the hysteresis is activated to extend the escape interval by a predetermined amount which is related to the sensed physiological need. The stimulating pulses are inhibited as long as normal heart activity is sensed. The extension of the escape interval under such conditions eliminates possible competition between normal activity and the paced stimulation. In a second embodiment automatic mode switching is provided in a dual chamber pacemaker to allow for more efficient operation at higher heart rates. When the heart rate (natural or paced) exceeds a prescribed level, such as 90 beats per minute, the pacemaker operates in a single chamber mode, such as VVI.

Abstract: A programmable cardiac stimulator capable of stimulation in the DDX modality having a first sensing system (46) for sensing electrical activity in the atrium, a second sensing system (48) for sensing electrical activity in the ventricle, a pulse generator (24) connected to the first (46) and second (48) sensing system and responsive to electrical activity sensed by these systems (46, 48) for determining the timing for supplying electrical pulses to the atrium and ventricle, for this depolarization and a circuit with the pulse generator (24) for changing the stimulation modality from DDD to DVI when premature ventricular activity is sensed by the second sensing system (46) prior to sensing electrical activity by the first sensing system (48) during the pacer cycle.