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: 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 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 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 VDD-type pacing system which may have a floating atrial electrode analyzes P-wave events and absences of P-waves to determine data indicative of the likelihood of P-wave undersensing. The pacemaker logic chooses a reaction algorithm to respond to atrial events in accordance with whether an absence of a P-wave is more likely to have been an undersense or an incidence of bradycardia. Specific algorithms are presented which illustrate pacemaker reactions to probable undersense and brady occurrences. The pacemaker also incorporates a subsystem for detection of undersense events.

Abstract: There is disclosed a pacemaker, a dual chamber VDD(R) or DDD(R) pacemaker, having improved features for avoiding undesired sensor-sinus competition and providing blended sensor and sinus (atrial) control. The pacemaker employs atrial hysteresis which is used during sensing of natural atrial beats in order to enable tracking the sinus signals that occur at rates below the current pacing limit; and sensor hysteresis which prevents early takeover by sensor control and, in a DDDR pacer, controls when the sensor rate controls over a sensed sinus rate and also enables dropping the pacing rate during sensor control so as to enable finding and tracking of underlying lower rate sinus signals. The sensor hysteresis function is automatically adapted by obtaining and processing scattergram data representative of the sensor rate compared to the average of the natural sinus rate, and adjusting the sensor hysteresis function to optimally match the data.

Abstract: A pacing lead is disclosed having folded tine elements in a first normal state, the tine elements being adapted to be unfolded by insertion of a stylet. In the second unfolded state, the tine elements are stretched to conform closely to the outer diameter of the lead casing, providing a reduced cross-section that facilitates introduction of the lead, and repositioning of the lead tip. A telescoping arrangement of inner and outer tubing elements is used to enable the stretching of the tine elements.

Abstract: There is provided a pacemaker lead for use in a dual chamber pacemaker system, wherein the single lead provides for ventricular pacing and atrial sensing. The lead has at least two floating bipoles positioned for placement in the atrium. A first whole-ring bipole is positioned a distance from the distal end so as to be positioned in the lower atrium of an average patient when the distal end is in position for ventricular pacing, and a second split-ring bipole is placed on the lead proximal from the first bipole so as to be positioned in the upper atrium of the normal patient. The method thus comprises positioning a floating whole-ring bipole in the lower atrium, and/or positioning a floating split-ring bipole in the upper atrium. The pair of bipoles so placed provide for atrial sensing with a high degree of ventricular far-field rejection, enabling VDD pacing and also monitoring of P-wave direction and conduction duration.

Abstract: There is provided an endocardial pacing lead having a substantially cylindrical length and an electrode at about the distal end thereof, the lead having a conductor for conducting signals between the proximal and distal ends thereof and an outer tubing enclosing the conductor for substantially the length of the lead. A tined piece is provided which envelopes the lead tubing just proximal to the distal electrode, the tined piece having a plurality of tines, each such tine being formed with a substantially C-shaped cross-section having its inner or backward surface substantially complementary to the outer surface of the tubing. The tined piece also preferably provides riser elements interspaced between respective pairs of the tines for providing a raised lead surface adjacent the tine interangles, thereby increasing the effective tined inter-radius presented to heart wall structures.