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: An implantable pacemaker system is provided with a conditional hysteresis feature, whereby a hysteresis value is added to the pacing escape interval only when the prior spontaneous rate corresponded to a rate below the top of a predetermined hysteresis band. This feature limits the lengthening of the escape interval when there are sudden drops in the natural rate thereby avoiding excessive changes in rate. In a preferred embodiment, the pacemaker defines a hysteresis band around a given pacing rate, e.g., lower rate limit, the band having an upper hysteresis limit and a lower hysteresis limit. No hysteresis lengthening of the escape interval is utilized for spontaneous heartbeats having rates above the upper hysteresis limit; for spontaneous heartbeats having rates between the lower rate limit and the upper hysteresis limit, an escape interval is set to have a value corresponding to a rate between the pacing limit and the lower rate limit of the hysteresis band which is, e.g.

Abstract: A dual chamber pacemaker system and method provide for safe tracking of PACs. The pacemaker obtains an indication of when the T-wave has occurred within the cycle when the PAC occurs, either by measuring the T wave during the cycle, or by getting a QT interval measure from one or more prior cycles. The pacemaker determines a safe V--V interval as the QT interval measure plus a safety factor, the safety factor being selected so as to insure that a pulse that tracks the PAC does not get delivered during the vulnerable period. A PAC is tracked if and only if the VA interval plus the AV delay is as great as the safe V--V interval.

Abstract: There is provided a pacemaker system with capture verification and threshold testing, in which the pacemaker waits after each change in delivered pace pulses for a stabilization interval, in order to minimize polarization and enhance capture verification. The threshold test utilizes a pace pulse pair, comprising a prior search pulse which is varied during the test, and the regular pacing pulse which is above threshold. When delivery of the pulse pairs is initiated, the search pulse is adjusted to optimize polarization, and the pacemaker waits for predetermined stabilization period of time in order to allow for minimum polarization and to optimize capture detection. The search pulse is increased incrementally in output value toward threshold, and following each such increase the pacemaker waits for a stabilization interval. The pacemaker detects when capture is achieved by the search pulse, thereby providing an indication of threshold.

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 is provided for adjusting AV delay to provide for an optimal AV setting for a selected pacing application. In the inventive system and method, the basis for determining the AV delay setting is to perform a ventricular fusion test, wherein variations in QT interval are monitored corresponding to variations in AV interval. Based upon the AV-QT data, the pacemaker can determine the ventricular fusion zone where the pacemaker AV interval is substantially the same as the intrinsic conduction interval, as well as the knee where AV intervals just shorter than the ventricular fusion zone result in full capture. The pacemaker selects a routine for adjusting AV interval depending upon a desired application, including the applications of adjusting AV interval for full capture and for treatment of a HOCM patient.

Abstract: A implantable cardiac pacemaker system which is battery powered, having an improved capability for monitoring patient threshold and adjusting pace pulse output to an optimized safety factor above patient threshold, thereby avoiding excessive energy expenditure in delivery of pace pulses and maximizing pacemaker lifetime. The improved threshold tracking system analyzes information from detected heart signals and correlates changes in such heart signal information to pulse output energy, enabling a determination of when the pulse output energy is near threshold without dropping below threshold. In a preferred embodiment, changes in the QT interval are monitored and correlated with changes in output pulse energy, enabling the pacemaker to obtain a measure of patient threshold without dropping pulse energy below threshold and suffering loss of capture.

Abstract: A programmable pacing system and method, the system having the capability for providing an indication of recommended replacement time (RRT) as well as a prior warning of six months to RRT. RRT is determined by storing a value in the pacemaker corresponding to battery impedance at RRT, continuously periodically measuring battery impedance, and comparing the measured value with the stored RRT value. Whenever the pacemaker is reprogrammed to different operating conditions which affect RRT, or there is a significant change in load lead resistance, a new value of RRT impedance is calculated based upon a selected formula corresponding to the reprogrammed set of operating conditions, and stored in the pacemaker. At the same time, an Aging value of impedance is re-calculated to provide a six month warning before RRT, and likewise stored in the pacemaker.

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 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 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 for providing ventricular pace pulses synchronized with atrial senses or paces, and having specific control for optimizing the AV escape interval and resultant AV delay for purposes of therapy for a patient with hypertrophic obstructive cardiomyopathy (HOCM). The pacemaker has an algorithm for varying the AV escape interval and detecting when the AV delay is lengthened to the point of evoking a fusion beat, thereby providing an accurate indication of a patient's underlying PR interval without significant loss of pacing capture. By monitoring T-wave detection and drop in amplitude of the evoked T-wave, an algorithm is enabled for optimizing the pacemaker AV delay within a range of values just less than the longest value for obtaining pre-excitation by the delivered pace pulse.

Abstract: A body implantable lead is provided, suitably a pacing lead for delivering pacing stimulus pulses to a patient, the lead having a fixation element such as a helix at its distal tip. The lead is provided with a soluble covering over the helix, which covering presents a smooth surface during insertion of the lead transvenously and dissolves away after a predetermined time in the patient's body, thereby exposing the anchor element. The lead is further improved by combining a radiopaque or angiographic contrast material with the protective coating, so that the physician carrying out the implantation procedure can monitor and see exactly when the coating has dissolved, whereupon the fixation element can be directly attached to the patient's heart wall.

Abstract: A dual chamber pacemaker system having a dynamic tracking limit, as well as a dynamic pacing limit (flywheel rate), the two dynamic limits being normally coupled to a measure of the sensed atrial rate as long as such rate is physiological. When the atrial signal is lost, i.e., cannot be tracked, the pacemaker responds with asynchronous pacing and normally decrements both dynamic limits, taking the flywheel rate down toward a lower pacing limit. The pacemaker of this invention provides a freeze function whereby the dynamic pacing limit and dynamic tracking limit are maintained constant for a plurality of cycles following asynchronous operation, to improve the possibility of regaining tracking if an underlying physiological atrial signal reappears at about the rate prior to being lost. The freeze function may be timed out for a predetermined number of cycles, e.g., eight, or may have a reduced duration if a series of consecutive synchronous cycles is detected.

Abstract: A lead for use with a pacemaker in a pacing system, the lead having at least one electrode placed at its distal tip and a helical fixation member at the lead distal tip for screwing the lead into a patient's heart wall. The helical member is composed of shape-memory metal and until use is encapsulated in a shrunken state with a diameter less than the diameter of the lead casing. The encapsulation material is preferably mannitol or a like material which dissolves when placed in the human heart. The shape-memory helix when released from the encapsulation material assumes an expanded diameter, greater than electrode diameter and preferably greater, so that when it is screwed into the heart wall, the helical coils are displaced radially away from the outer edge of the tip electrode. By this design, the damage to the heart tissue caused by the helix does not affect the heart wall immediately proximate to the tip electrode.

Abstract: A pacemaker has logic incorporated for holding the pacemaker circuitry, or at least a portion of such circuitry, in a low current drain "standby" mode of operation from time of fabrication until time of implantation or preparation for implantation, in order to minimize battery depletion during shelf life. In one embodiment, the pacemaker detects when a lead has been connected to the pulse generator output so as to present an impedance below a predetermined threshold, and such detection is used to take the pacemaker out of the "standby" mode and place it in a fully operational mode. The pacemaker is further provided for sensing an externally generated signal in response to which the pacemaker is placed in an operational mode for a predetermined time duration, following which it reverts to the standby mode.

Abstract: A pacemaker system and method are provided with an improved way of detecting the presence of noise, and particularly intermittent noise. When a first signal is sensed by the pacemaker sense circuit, the pacemaker schedules and starts to time out a next escape interval while continuing to time out the escape interval which was previously set. The pacemaker sets up a predetermined noise interval and continues to monitor senses, for the purpose of determining whether the first sense is to be treated as a true cardiac signal, or as noise. In the preferred embodiment, if a second sense occurs within the noise interval, and before time out of a minimum pacing interval, the first sense is determined to be noise, and the pacemaker continues to time out the initial escape interval; however, if no additional sense occurs during the noise interval, the pacemaker proceeds to time out the previously set next escape interval.

Abstract: A dual chamber cardiac pacemaker system has logic for detecting high rate as well as normal atrial spontaneous signals, and for tracking atrial signals within a predetermined tracking rate range by delivering ventricular pace pulses at an AV interval following each atrial sense within said tracking range. The pacemaker also has detection circuitry for detecting a sequence of pacemaker cycles characterized by first degree AV block, wherein atrial sense signals occur too early to permit tracking, and ventricular spontaneous signals occur following an extended AV-delay such as is characterized by first degree block. The pacemaker restores tracking following detection of such a sequence by delivering ventricular pace pulses at an extended AV interval to override the spontaneous ventricle signals and gradually decreasing the AV-delay back to a normal value, thereby restoring tracking without pacing the ventricle at an excessive rate.

Abstract: A rate responsive pacemaker and method of pacing, having circuitry for controlling the rate of change of pacing rate in response to varying rate sensor signals. The pacemaker increments or decrements pacing rate each cycle, the change in rate being limited as a function of pacing rate, rate of change of sensor rate; the magnitude of the difference between sensor rate and pacing rate; whether prior cycles ended in sense or pace events; and/or a separate fast response sensor.

Abstract: A pacemaker is provided having an improved circuit for obtaining a measure of battery end-of-life. The EOL detector includes an input stage with a current mirror output providing a current which is proportional to the current being consumed by the pacemaker circuitry, and thus being expended by the battery. The proportional current is directed to charge a capacitor, which is periodically discharged at a constant current, following which the battery goes through repeated cycles of charging and discharging. A measuring circuit measures the time of capacitor discharge, thereby providing a measure of battery energy discharge during the interval that the capacitor was charging. The interval counts are accumulated to provide an overall count representative of battery expenditure, and thus of pacemaker EOL.