Abstract: A method and apparatus for automatic determination of a pacemaker patient's pacing stimulation threshold. Circuitry is provided in a pacemaker for obtaining a signal reflecting cardiac impedance, which is known to reliably reflect certain aspects of cardiac function. Circuitry is also provided for monitoring the cardiac impedance waveform during a predetermined capture detect window following delivery of stimulating pulses. One or more values are derived which characterize the morphology of the impedance waveform during the capture detect window associated with each stimulation pulse delivered. These values are compared to predetermined control values in order to assess whether a stimulation pulse has achieved cardiac capture. The assessment of whether cardiac capture has been achieved is also based partly upon the conventional sensing of atrial and/or ventricular cardiac signals occurring during the capture detect window.

Abstract: Capture detection and stimulation threshold-measurement methods and apparatus for deriving atrial and ventricular pace pulse (A-pace and V-pace) stimulation energy strength-duration data. In a first atrial and ventricular threshold test regimen for use with patients having intact A-V conduction or first degree AV block, A-pace pulses are delivered at a test escape interval and A-V delay. Atrial loss of capture (ALOC) in response to an A-pace test stimulus is declared by the absence of a detected ventricular depolarization (V-event) in the latter portion of the paced A-V delay interval following the delivery of the A-pace test stimulus. In the ventricular threshold test regimen, a V-pace test stimulus is delivered after a shortened A-V delay. Ventricular loss of capture (VLOC) is declared by the detection of a V-event in the ventricular refractory period of the V-pace test stimulus.

Abstract: A method and apparatus for automatic determination of a pacemaker patient's pacing stimulation threshold. Circuitry is provided in a pacemaker for obtaining a signal reflecting cardiac impedance, which is known to reliably reflect certain aspects of cardiac function. Circuitry is also provided for monitoring the cardiac impedance waveform during a predetermined capture detect window following delivery of stimulating pulses. One or more values are derived which characterize the morphology of the impedance waveform during the capture detect window associated with each stimulation pulse delivered. These values are compared to predetermined control values in order to assess whether a stimulation pulse has achieved cardiac capture. The assessment of whether cardiac capture has been achieved is also based partly upon the conventional sensing of atrial and/or ventricular cardiac signals occurring during the capture detect window.

Abstract: A method and apparatus for variable rate cardiac stimulation, wherein sudden drops in the rate of delivery of stimulation pulses are avoided by means of rate smoothing and peak rate support functions. In one embodiment, circuitry in a cardiac pulse generator detects atrial events and maintains an updated value of the A-A time intervals between certain atrial events. If a preset ratio or total of these A-A intervals are found to have been shorter than the updated value by at a least a predetermined amount of time, a rate smoothing function is activated wherein the rate of delivery of stimulating pulses is prevented from changing, from cycle to cycle, by more than a predetermined maximum amount. A peak rate support function preferably employs the same updated value in the computation of "escape" intervals. Following the latest A-A interval, if that A-A interval is less than the updated value, then the updated value is used as the new escape interval.

Abstract: A method and apparatus for automatic determination of a pacemaker patient's pacing stimulation threshold. Circuitry is provided in a pacemaker for obtaining a signal reflecting cardiac impedance, which is known to reliably reflect certain aspects of cardiac function. Circuitry is also provided for monitoring the cardiac impedance waveform during a predetermined capture detect window following delivery of stimulating pulses. One or more values are derived which characterize the morphology of the impedance waveform during the capture detect window associated with each stimulation pulse delivered. These values are compared to predetermined control values in order to assess whether a stimulation pulse has achieved cardiac capture. The assessment of whether cardiac capture has been achieved is also based partly upon the conventional sensing of atrial and/or ventricular cardiac signals occurring during the capture detect window.

Abstract: A dual chamber, rate-responsive pacemaker for pacing a patient's heart novelly allows tracking of the patient's sinus rate when the sinus rate is slightly less than the sensor rate; i.e., within a predetermined "Sinus Preference Window Maximum Rate Drop." Pacing at the sensor rate occurs when the sensor rate exceeds the sinus rate by more than the Sinus Preference Window Maximum Rate Drop. In the preferred embodiment a Sinus Preference Window, which occurs at the end of the ventricle-to-atrium interval, is decremented with successive heart beats by a programmable delta to increase the pacing rate until the Sinus Preference Window reaches zero, in which case the pacemaker paces at the sensor rate. The Sinus Preference Window is reset to its maximum value upon either the detection of an atrial sensed event, or upon the expiration of a programmable Sinus Check Interval.

Abstract: Capture detection and stimulation threshold-measurement methods and apparatus for deriving atrial and ventricular pace pulse (A-pace and V-pace) stimulation energy strength-duration data. In a first atrial and ventricular threshold test regimen for use with patients having intact A-V conduction or first degree AV block, A-pace pulses are delivered at a test escape interval and A-V delay. Atrial loss of capture (ALOC) in response to an A-pace test stimulus is declared by the absence of a detected ventricular depolarization (V-event) in the latter portion of the paced A-V delay interval following the delivery of the A-pace test stimulus. In the ventricular threshold test regimen, a V-pace test stimulus is delivered after a shortened A-V delay. Ventricular loss of capture (VLOC) is declared by the detection of a V-event in the ventricular refractory period of the V-pace test stimulus.

Abstract: A dual chamber, rate-responsive pacemaker for pacing a patient's heart novelly allows tracking of the patient's sinus rate when the sinus rate is slightly less than the sensor rate; i.e., within a predetermined "Sinus Preference Window Maximum Rate Drop." Pacing at the sensor rate occurs when the sensor rate exceeds the sinus rate by more than the Sinus Preference Window Maximum Rate Drop. In the preferred embodiment a Sinus Preference Window, which occurs at the end of the ventricle-to-atrium interval, is decremented with successive heart beats by a programmable delta to increase the pacing rate until the Sinus Preference Window reaches zero, in which case the pacemaker paces at the sensor rate. The Sinus Preference Window is reset to its maximum value upon either the detection of an atrial sensed event, or upon the expiration of a programmable Sinus Check Interval.

Abstract: A cardiac pacemaker improves battery longevity by automatically providing optimized threshold amplitude and pulse width values. During capture verification and threshold searching, the pacemaker delivers a pacing pulse and a rapid, maximum amplitude backup pulse in case the pacing pulse fails to capture a patient's heart. Unlike the prior art, the backup pulse is delivered before a predefined Vulnerable Period (during which time pacing might lead to re-entrant tachycardia or fibrillation). This results in threshold searching which is quick, accurate and with smaller rate drops during loss of capture. In another aspect of the present invention, a diagnostic strength-duration curve is approximated by first setting the pulse width to a maximum value and determining the amplitude threshold (rheobase), and then by doubling the amplitude and determining the pulse width threshold (chronaxie).

Abstract: A dual chamber pacemaker is provided, preferably either DDDR or DDIR, having logic hardware and/or software for normally carrying out the DDIR or DDDR mode of operation, and further having means for carrying out a safe atrial pace method of operation in circumstances where normal atrial pacing could otherwise be competitive or result in loss of atrial capture. The pacemaker has means for detecting an atrial sense during PVARP, timing out a delay from the time of the early atrial sense, delivering a safe atrial pulse at the end of the delay, and controlling generation of a ventricular pace pulse in synchronous relation to the safe atrial pulse and with at least a minimum AV interval.