Abstract: It has been determined that certain cardiac stimulators may operate in a manner in which the ventricular pace refractory period (VPRP) may be greater than the post-ventricular atrial refractory period (PVARP). Various exemplary techniques may be used to improve the ability of cardiac stimulators to lengthen the PVARP. In accordance with one technique, the VPRP is adjusted with the pacing rate so that as the pacing rate becomes slower the VPRP increases. The VPRP is compared with the PVARP. The PVARP remains constant until the VPRP becomes greater than the PVARP. Then, the PVARP is adjusted to make it greater than or equal to the VPRP. In accordance with another technique, the VPRP and the PVARP are adjusted with the pacing rate, with the PVARP remaining greater than or equal to the VPRP.

Abstract: An implantable medical device electrically stimulates the heart to beat and senses electrical activity in the heart. The medical device generally includes a processor, a plurality of electrodes, and a sense amplifier. The medical device is capable of performing a variety of diagnostic tests, such as a sensing test in which a suitable sensitivity setting is computed for the sense amplifier. An external programmer is also provided to initiate the diagnostic tests. The programmer transmits a start signal to the implantable medical device and the medical device's processor initiates the diagnostic test specified by the programmer via the start signal. The implantable device is capable of completing the diagnostic test without further communication from the programmer or may initiate communication with the programmer during a refractory period in which signals from the programmer will not interfere with the diagnostic test. In the latter case, the programmer responds before the refractory period ends.

Abstract: An implantable device for providing pacing and defibrillating stimuli to a heart, comprises: a power source, at least one electrode electrically connected to said power source, a sensor capable of providing data that can be used to determine a physiological pacing demand, and a control device. The control device controls the application of electrical stimuli to the heart. The control device calculates an adjusted pacing interval based on said demand, calculates an adjusted ventricular pace refractory period (VPRP.sub.current) that is a function of said pacing interval, and calculates a T-wave monitoring window. The end time, and optionally the start time also, of the T-wave window is a function of the pacing interval. The control device is also capable of adjusting the sensitivity of an amplifier based on signals received during the T-wave window.

Abstract: A pacemaker with a variable, asynchronous minimum heart rate and a second variable, synchronous heart rate. The second, variable heart rate has an absolute minimum, lower than the asynchronous minimum heart rate, which is preselected by the attending physician. The minimum heart rates can vary, conditioned upon sensed physiologic need. The cardiac pacemaker attempts to reestablish synchrony in every cycle, even if the intrinsic or natural atrial heart rate is below the asynchronous minimum heart rate in that cycle and can maintain cardiac synchrony at lower rates, thereby increasing cardiac efficiency and minimizing strain on the heart.

Abstract: A state machine for automatic gain control of sensing functions in an implantale cardiac stimulator. The state controls sensing levels based on present sensed conditions and on the prior state of the heart. Different rates of adjustment are selected under varying conditions so that the gain level for sense amplifiers can be adjusted without significant overshoot. The state machine comprises a set of four conditions or states together with interconnections or logical paths from one state to another. The rate of adjustment of sense amplifier gain is based on the path traversed in the state machine so that different effective time constants for the control function may be used for different conditions.

Abstract: A dual chamber pacemaker with variable V-A delay based on detection of multiple criteria before lengthening the V-A delay period. Before the V-A delay period can be extended, the pacemaker must be stimulating the ventricle at a maximum ventricular rate, and an atrial event must be sensed in a relative atrial refractory period. During this interval the pacemaker would not respond to an atrial event that was sensed, but the occurrence of the event would be detected. To optimize a ventricular blanking period, in each cardiac cycle, the energy level of the atrial output pulse and the sensitivity of the ventricular sense amplifier are sampled. Based on these dynamic parameters, the duration of the ventricle blanking period is adjusted for each cycle so that a minimum ventricular blanking period can be maintained without cross-talk.

Abstract: A series of test signals are generated by a microprocessor of a pacemaker to determine whether a bipolar or unipolar lead is attached to an implanted cardiac pacemaker restricting programming of said pacemaker to only an unipolar pacing mode unless the presence of an operational bipolar lead is detected. Detection is accomplished by generating a series of low frequency high impedance pulses, applying them to lead contacts and sensing a return signal. If a return signal is detected, then that indicates either a unipolar lead is connected to the pacemaker or that the ring conductor of a bipolar lead is open and bipolar pacing must be inhibited.