Abstract: Polarization signals, which represent voltages measured at a pacemaker electrode, are not constant and may drift. Polarization signal drift, which often precedes undesirable pace polarization artifacts, is more significant when the pacemaker is inhibited from providing an electrical stimulation to the patient's heart. The present invention provides an implantable system and methods for stabilization of a polarization signal. Electrical pulses may be applied to stabilize a polarization signal. In one implementation of the invention, polarization signal stabilization may be used as part of process to terminate tachycardia.

Abstract: An implantable medical device uses a method for dynamically managing physiological signal monitoring. A physiological signal is sensed for detecting physiological events in response a first threshold. A determination is made whether a second threshold has been met in response to detecting physiological events. If the second threshold has been met, detailed monitoring of the physiological events is enabled.

Abstract: An implantable medical device operates to promote intrinsic ventricular depolarization according to a pacing protocol. The medical device determines a course of action based upon the presence or absence of sensed ventricular activity. The device further determines whether that activity is properly conducted or the result of a PVC or nodal rhythm.

Abstract: Polarization signals, which represent voltages measured at a pacemaker electrode, are not constant and may drift. Polarization signal drift, which often precedes undesirable pace polarization artifacts, is more significant when the pacemaker is inhibited from providing an electrical stimulation to the patient's heart. The present invention provides an implantable system and methods for stabilization of a polarization signal. Electrical pulses may be applied to stabilize a polarization signal. In one implementation of the invention, polarization signal stabilization may be used as part of process to terminate tachycardia.

Abstract: A method and system nodal rhythm detection and treatment is provided. Detecting consecutive atrial events within a nodal activity window around ventricular events identifies nodal rhythm. Nodal rhythm is treated by calculating and applying a new atrial escape interval adjusted by the interval between the atrial and ventricular events.

Abstract: Systems and methods for distinguishing a valid sensed cardiac signal from an invalid signal, such as a myopotential. In one embodiment, sensing an electrical signal with one electrode causes a timing window to commence. When the electrical signal is sensed by another electrode in the timing window, the sense is deemed valid. When the electrical signal is not sensed by the other electrode in the timing window, the sense is deemed invalid. Therapy may be adjusted when an inordinate number of senses are invalid.

Abstract: A method and system for nodal rhythm detection and treatment is provided. Detecting consecutive atrial events within a nodal activity window around ventricular events identifies nodal rhythm. Nodal rhythm is treated by calculating and applying a new atrial escape interval adjusted by the interval between the atrial and ventricular events.

Abstract: There is provided a pacemaker system which includes intervention for overdriving the patient's natural heart rate in the event of a sensed incipient ventricular arrhythmia condition, and particularly torsades de pointes. The pacemaker continually acquires QT signals and analyzes them for respective properties, updating statistical information relating to the properties. In a preferred embodiment, the pacemaker analyzes QT interval, QT dispersion, time derivative of the QT interval, and/or T-wave amplitude and determines an intervention for pacing therapy based upon changes to these properties. The pacemaker also monitors premature ventricular beats and generates data representative of such occurrences, which data is used alone or in combination with QT data in determining whether intervention is indicated, for adjusting the intervention pacing rate.

Abstract: There is provided a system for regulating ventricular rate in the presence of abnormally high atrial rates, e.g., during episodes of atrial fibrillation. During such an episode, the system, preferably incorporated into an implantable pacemaker, applies subthreshold bursts of stimulus pulses to or proximate to the patient's AV node so as to inhibit conduction of electrical signals through to the ventricle during the bursts. The bursts are timed in relation to the last conducted ventricular signal, and in terms of burst length, to provide a rate of conducted signals through the AV node which results in a substantially regular and reduced ventricular rate. During the inhibition mode of operation, the system monitors to determine the efficacy of inhibition, by tracking the percentage of ventricular senses that occur during the burst periods.

Abstract: There is provided a cardiac pacemaker system with a ventricular tachycardia prevention feature, whereby the pacemaker monitors ventricular activity during each patient awakening period to determine when VT is likely. In a preferred embodiment, QRS and T wave templates are generated cyclically during awakening, and compared to normal templates to obtain a measure of variability, indicative of refractory dispersion and thus of probable VT. Ventricular extra-systoles are also monitored and analyzed during the awakening period to see how closely they occur to the ventricular vulnerable period. When the monitored data indicates VT probability during awakening, the pacemaker responds by overdriving the heart with an intervention pacing rate which is continually adjusted as a function of the currently obtained data.

Abstract: There is provided a pacemaker system having the feature of delivering a ventricular safety pulse (VSP) following an early ventricular sense (VS), wherein the pacemaker automatically determines whether VSPs are to be delivered following early VSs, and if yes, with what timing. The pacemaker gathers data following delivered VSPs, which data contains information indicative of whether each early VS was indeed the result of a spontaneous R wave, or was due to crosstalk from a prior delivered atrial pace pulse. This data is processed and, when it presents a high statistical confidence, is used to make a determination of whether to respond with the assumption of a true R wave, or of crosstalk. If the data is not statistically significant, the pacemaker delivers VSPs in a normal fashion, e.g., at the end of a programmable VSP interval timed out following delivery of an atrial pace pulse.

Abstract: There is provided an implantable cardiac pacing system, having multiple sensing channels for sensing spontaneous cardiac signals which arise between respective different pairs of electrodes. In a preferred embodiment, the system utilizes a single pass VDD-type lead, having at least one atrial ring electrode for sensing atrial signals, and at least a distal tip electrode positioned in the right ventricle for sensing ventricular signals. Sensing channels concurrently process signals between the atrial ring and the pacemaker can (the indifferent electrode); the ventricular tip electrode and the pacemaker can; and the between the atrial ring and the ventricular tip. One or more additional electrode pairs can also be employed. Enable signals selectively enable the channels to be used for concurrent processing of the signals.

Abstract: There is provided an implanted pacemaker having a system and method for determining a measure of the circadian rhythm of a patient and adjusting the pacemaker nighttime setting of lower rate limit to correspond to the determined circadian rhythm. In a preferred embodiment, the circadian rhythm is determined by examining daily variations in QT interval. In a first QT embodiment of the invention, when QT interval becomes longer than a parameter QT.sub.-- sleep, which represents a value associated with patient nighttime, the LRL is dropped to a night value and maintained at such value for a predetermined duration. In another embodiment, the start of night LRL is determined as a function of when QT interval becomes longer than a sleep value for a predetermined elapsed time, and LRL is changed back to a day value when QT interval drops back down to a shorter value than the sleep value and stays there for an elapsed period of time.

Abstract: A dual chamber pacemaker and method for ventricular rate smoothing during high rate episodes such as atrial fibrillation are provided. The pacemaker determines when there is a pathologically high atrial rate episode, such as by determining when atrial senses correspond to a spontaneous atrial rate above a predetermined upper rate limit. When such an episode is determined, the pacemaker determines a ventricular pacing escape interval, corresponding to a flywheel rate, the flywheel rate being set at the beginning of the episode to substantially equal the atrial rate just before the high rate episode. As long as the episode continues, the flywheel rate is incremented upward whenever a ventricular sense occurs, thereby following the average ventricular rate; whenever the flywheel escape interval times out and a ventricular pace is delivered, the flywheel rate is decremented.

Abstract: There is provided a rate responsive pacemaker system and method employing an activity-type sensor for deriving signals for determining pacing rate, wherein the activity sensor threshold is automatically adjusted as a function of monitored sensor output. In a preferred embodiment, activity counts are categorized on a histogram basis, and the histogram data is stored over a selected period of time. The activity data in histogram form is then analyzed and compared to predetermined criteria to determine whether threshold seems to be proper, or whether threshold adjustment is indicated. The adjustment algorithm provides different degrees of adjustment depending upon the circumstances. Specifically, where the data suggests too many or too few counts within an expected range, the threshold is adjusted as a function of whether the analyzed outputs are only a little bit out of the expected range or quite a bit out of the expected range.

Abstract: A dual chamber pacemaker system and method are provided for placing the pacemaker in an asynchronous mode when retrograde conduction is present, having the capability of detecting the onset of retrograde conduction and also monitoring on a cycle-by-cycle basis to determine the end of retrograde conduction. The detection of end of retrograde conduction is accomplished by two operative algorithms, i.e., a first algorithm which is executed at the time of any atrial sense and a second algorithm which is executed at the time of each ventricular event. Following an atrial sense, the pacemaker checks to see whether the just concluded VA interval conforms to predetermined RC interval criteria, and if not, immediately switches the pacemaker out of the RC mode and into a synchronous tracking mode. Following each ventricular event while the pacemaker is in the RC mode, the pacemaker monitors a predetermined class of special events and determines end of RC upon detection of a pattern of such special events.

Abstract: A dual chamber pacemaker is provided with a dynamic PVARP which tracks the occurrence of high rate atrial senses within the normal PVARP range. The dynamic PVARP is a short window of about 50 ms which is moved toward the time of occurrence of any sense signal within the window range of about 50-200 ms following the ventricular event. Senses which occur within the dynamic window are rejected, or blanked, while senses occurring within the window range but outside of the window are recognized and evaluated. The dynamic window technique accordingly enables the pacemaker to recognize tachycardia senses which would otherwise be blanked by a fixed length PVARP, while providing efficient suppression of FFRS events. The pacemaker also provides a technique for determining whether rejected senses are tachy atrial senses or FFRS, by modulating the AV interval and thus shifting the dynamic window which is coupled to the ventricular pulse.

Abstract: A dual chamber pacemaker is provided with the capability of determining when there is retrograde conduction, and responding by switching into an asynchronous mode of ventricular pacing. The pacemaker's response to RC further includes delivering at least a first asynchronous ventricular pace pulse at a ventricular escape interval calculated to occur at an appropriate AV delay following the next expected spontaneous natural beat. Thus, the ventricular escape interval can be calculated as V.sub.esc =VA+AA.sub.avg +AV.sub.min, where VA is the retrograde time from the prior ventricular pulse to the retrograde atrial sense (or PAC), AA.sub.avg is a measure of the average natural atrial rate before retrograde conduction, and AV.sub.min is a predetermined value of AV delay. This optimum value of V.sub.esc is designed to regain synchronous tracking of the natural sinus after the first extended ventricular pulse. Alternatively, the response can aim to regain tracking in N cycles, where V.sub.esc =AA.sub.avg +.DELTA.

Abstract: A dual chamber pacemaker system is provided having an improved Wenckebach response for optimizing tracking of atrial signals having rates within a rate range above the normal tracking range, i.e., in a designated Wenckebach range. When an atrial sense occurs in the Wenckebach range, the AV delay is extended up to a predetermined maximum extension to enable delivery of a ventricular pulse at the ventricular upper rate limit (dynamic tracking limit). When the AV delay would have to be extended beyond the maximum extension in order to pace the ventricle at the dynamic tracking limit, the next ventricular stimulus is delivered asynchronously at an escape interval greater than the escape interval corresponding to the dynamic tracking limit, e.g., at a predetermined lower pacing limit.

Abstract: A dual chamber pacemaker is provided having incorporated therein a VA conduction test for concurrently testing for the conditions of retrograde conduction (RC) and far field R wave sensing (FFRS). The pacemaker changes the AV or VV interval to a predetermined interval over a number of pacemaker cycles, and determines whether the VA interval remains substantially unchanged, i.e., the VA intervals are substantially equal. When VA interval equality is determined, the pacemaker checks the measure of VA interval with stored RC and FFRS criteria to determine whether either can be verified. Respective corrective steps are taken if either RC or FFRS is verified.