Abstract: A pacemaker mediated tachycardia (PMT) is detected and suppressed in an implantable pacemaker operating in the VDD or VDDR modality. Such suppression is effectuated by extending the post ventricular atrial refractory period (PVARP) of the pacemaker to an extended PVARP that prevents retrograde P-waves from being tracked, thereby suppressing the PMT. The extended PVARP includes a retrograde window portion, following an absolute refractory portion. P-waves that occur during the retrograde window portion of the extended PVARP are deemed to be retrograde P-waves. The extended PVARP is returned to its original value whenever: (1) a P-wave is sensed following the extended PVARP, which P-wave is deemed to be a sinus P-wave, or (2) whenever a sufficient number of cardiac cycles elapse without the occurrence of a retrograde P-wave.

Abstract: An autocapture system within an implantable pulse generator automatically maintains the energy of a stimulation pulse at a level just above that which is needed to effectuate capture. The electrical post-stimulus signal of the heart following delivery of a stimulation pulse is compared to a polarization template, determined during a capture verification test. A prescribed difference between the polarization template and the post-stimulus signal indicates capture has occurred. Otherwise, loss of capture is presumed, and a loss-of-capture routine is invoked that increases the energy a prescribed amount to obtain capture. Periodically, and/or at programmed intervals or events, the capture verification test is performed. During the capture verification test, the pulse generator determines a polarization template for a particular stimulation energy and for each of a plurality of sensitivity or threshold settings. A determination is also made as to which sensitivity settings yield capture.

Abstract: An autocapture system within an implantable pulse generator automatically maintains the energy of a stimulation pulse at a level just above that which is needed to effectuate capture. The electrical post-stimulus signal of the heart following delivery of a stimulation pulse is compared to a polarization template, determined during a capture verification test. A prescribed difference between the polarization template and the post-stimulus signal indicates capture has occurred. Otherwise, loss of capture is presumed, and a loss-of-capture routine is invoked that increases the energy a prescribed amount to obtain capture. Periodically, and/or at programmed intervals or events, the capture verification test is performed. During the capture verification test, the pulse generator determines a polarization template for a particular stimulation energy and for each of a plurality of sensitivity or threshold settings. A determination is also made as to which sensitivity settings yield capture.

Abstract: An atrial tracking dual-chamber pacemaker and method of use thereof for terminating a pacemaker-mediated tachycardia (PMT). The pacemaker includes means for determining whether the present heart rate exceeds a tachycardia reference rate, and if so, whether a PMT-indicating sequence of a tracked P-wave, including a retrograde P-wave followed by a V-pulse, occurs repetitiously for at least a predetermined number of cardiac cycles. The pacemaker includes means for measuring the interval between a P-wave and a V-pulse (PVI) and sets the PVI to 250 milliseconds when the measured value is less than 250 milliseconds. The pacemaker issues a PMT-terminating timed atrial pulse which is timed from a retrograde P-wave by a time equal to the PVI, plus a delay of about 25-100 milliseconds. In the event the atrial pulse fails to terminate the PMT, the process is repeated after a fixed number of cardiac cycles has occurred.

Abstract: An implantable pacemaker having means for detecting and responding to a premature ventricular contraction (PVC), also includes circuit means for minimizing the likelihood of sensing a PVC when in fact a PVC has not occurred. The circuit means latches the occurrence of any atrial events sensed during the relative atrial refractory period of the pacemaker, whether such atrial events are noise or an early P-wave; and, in response to such latching, disables the PVC detection circuit until certain prescribed events occur, whereupon the PVC detection circuit is re-enabled. The prescribed events that re-enable the PVC detection circuit after it has been disabled include, e.g., the occurrence of a ventricular pulse or sensed R-wave. Further, in the event a PVC is detected and a desired PVC response is invoked, an additional circuit means automatically terminates the PVC response in the event the PVC response becomes stuck.

Abstract: A pacemaker mediated tachycardia (PMT) is detected by circuitry within an implantable pacemaker. The PMT is detected by first detecting a tachycardia condition that includes a prescribed number of consecutive cardiac cycles having a rate faster than a prescribed rate. Each cardiac cycle of the tachycardia condition includes a natural atrial event, i.e., a P-wave, and a paced ventricular event, i.e., a V-pulse generated by a pacemaker. After the prescribed number of such cardiac cycles, e.g., two to ten, a P-V delay in a single cardiac cycle is modified by a first prescribed amount, e.g., 50 milliseconds. The time interval of a V-P interval associated with at least one cardiac cycle preceding the modified P-V delay is then compared to a V-P interval immediately following the modified P-V delay. Only if the difference between the V-P intervals thus measured is less than a second prescribed amount, e.g., 25 milliseconds, is a PMT indicated. If a PMT is indicated, a PMT termination regimen, e.g.

Abstract: Programmable timing and logic circuitry is provided to detect crosstalk between paced chambers of the heart and to provide compensation in the event crosstalk is detected. Signals sensed during a prescribed time window early in the cardiac cycle following an atrial pulse are presumed to be crosstalk. If crosstalk occurs, a shortened AV delay is triggered. If crosstalk does not occur, a programmed AV delay is maintained. Absent the occurrence of a ventricular event after the prescribed time window up to the end of the AV delay, a ventricular stimulation pulse is provided. If a ventricular event is sensed during this time, the ventricular stimulation pulse is inhibited.

Abstract: An atrial tracking dual-chamber pacemaker and method of use for reducing the risk of initiating a pacer mediated tachycardia (PMT), and breaking such a PMT if once started. The pacemaker includes means for sensing a premature ventricular contraction (PVC). The pacemaker operates in a conventional manner unless a PVC is sensed. If a PVC is sensed, in accordance with one embodiment, an extended atrial refractory period is triggered in an attempt to block any retrograde atrial events resulting from the PVC. This is followed by an atrial alert time window. After a prescribed A-V delay subsequent to the timing out or other termination of the atrial alert time window, a ventricular stimulation pulse is generated, unless prior ventricular activity is sensed that inhibits such ventricular stimulation pulse.